Co-reporter:George K. Tofaris;Qian Li
Analytical Chemistry March 7, 2017 Volume 89(Issue 5) pp:3184-3190
Publication Date(Web):January 27, 2017
DOI:10.1021/acs.analchem.6b05037
Exosomes are both active in mediating intracellular communication and potentially present a potent cargo of disease biomarkers to an assay. The robust evaluation of exosomal markers could lead to a paradigm shift in clinical analysis and associated care. To date, much of this has been hindered by issues of sample preparation and assay signal-to-noise. We introduce here the use of ultrasensitive electrochemical impedance spectroscopy to quantify both external (tetraspanin) and internal (syntenin) exosome-specific markers. Associated exosome detection limits are 1.9 × 105 particles mL–1 (equivalent to 320 aM or 9500 exosomes in 50 μL) for intact exosomes and 3–5 picomolar for internal exosomal syntenin levels with almost 5 decades of linear dynamic range. Sample preparation can be carried out by simple fine filtering of cell-conditioned medium prior to a non-NTA-determined (i.e., nanoparticle tracking analysis) exosome concentration analysis, lysing, and subsequent internal syntenin quantification. Such concentration-normalized dual-marker analysis can be used to define “analytical zones” in a manner which is then independent of absolute exosome concentration and sample preparation.
Co-reporter:Joshua Lehr;Justin R. Weeks;Adriano Santos;Gustavo T. Feliciano;Melany I. G. Nicholson;Paulo R. Bueno
Physical Chemistry Chemical Physics 2017 vol. 19(Issue 23) pp:15098-15109
Publication Date(Web):2017/06/14
DOI:10.1039/C7CP01500C
We have previously proposed, and experimentally resolved, an ionic charge relaxation model for redox inactive self-assembled monolayers (SAMs) on metallic electrodes in contact with a liquid electrolyte. Here we analyse, by capacitance spectroscopy, the resistance and capacitance terms presented by a range of thiolated molecular films. Molecular dynamics simulations support a SAM-specific energy barrier to solution-phase ions. Once surmounted, the entrapped ions support a film embedded ionic capacitance and non-faradaic relaxation, which can be assigned as a particular case of general electrochemical capacitance.
Co-reporter:Joshua Lehr, Manuel Tropiano, Paul D. Beer, Stephen Faulkner and Jason J. Davis
Chemical Communications 2015 vol. 51(Issue 88) pp:15944-15947
Publication Date(Web):08 Sep 2015
DOI:10.1039/C5CC05738H
Herein we describe the first example of a ratiometric lanthanide luminescent oxygen sensing interface. Immobilisation of terbium and europium cyclen complexes on glass substrates was achieved by a novel aryl nitrene photografting approach. The resulting interfaces demonstrated a ratiometric oxygen response between 0 and 0.2 atm partial oxygen pressure.
Co-reporter:Joshua Lehr, Manuel Tropiano, Paul D. Beer, Stephen Faulkner and Jason J. Davis
Chemical Communications 2015 vol. 51(Issue 30) pp:6515-6517
Publication Date(Web):06 Mar 2015
DOI:10.1039/C5CC01097G
Herein we demonstrate redox switchable emission from a sensitised, europium–ferrocene containing, molecular film assembled by a novel nitrene-based strategy. Electrochemical modulation of europium emission upon switching the ferrocene moiety's redox state is ascribed to the reversible generation of a quenching ferrocenium species.
Co-reporter:Gemma-Louise Davies, Asha Brown, Octavia Blackburn, Manuel Tropiano, Stephen Faulkner, Paul D. Beer and Jason J. Davis
Chemical Communications 2015 vol. 51(Issue 14) pp:2918-2920
Publication Date(Web):22 Dec 2014
DOI:10.1039/C4CC09952D
Strong bidentate ligation between a fluorinated isophthalate and binuclear lanthanide-DO3A species yields a new class of 19F NMR agent with very high nuclear relaxation rates at physiologically-relevant pH.
Co-reporter:Amol V. Patil, Flávio C. Bedatty Fernandes, Paulo R. Bueno, and Jason J. Davis
Analytical Chemistry 2015 Volume 87(Issue 2) pp:944
Publication Date(Web):December 9, 2014
DOI:10.1021/ac503156a
Impedance derived electroanalytical assays are inherently spectroscopic (frequency resolved) and potentially exceedingly sensitive indicators of interfacial change (such as target binding at an appropriate receptor). We introduce here the use of a portfolio of mathematically derived immittance functions and related components, capable, from the same raw data sets, of enabling increased assay sensitivity and markedly shorter assay times in comparison to traditional impedance analyses. The methodology, applied herein to faradaic (redox probe amplified) and non-faradaic assays, requires no equivalent circuit analysis or prior assumption of response. Its focus is to optimize analytical potency and to enable the user to select and apply the most frequency-optimized reporter of interfacial change and to, thereafter, run rapid (optimized) analyses at single frequencies.
Co-reporter:Flavio C. Bedatty Fernandes, Amol V. Patil, Paulo R. Bueno, and Jason J. Davis
Analytical Chemistry 2015 Volume 87(Issue 24) pp:12137
Publication Date(Web):November 19, 2015
DOI:10.1021/acs.analchem.5b02976
Among the numerous label free electronic biomarker assay methodologies now available, impedance based electrochemical capacitance spectroscopy (ECS), based upon mapping the perturbations in interfacial charging of redox elements incorporated into a biologically receptive interface, has recently been shown to be a convenient and highly sensitive mode of transduction and one which, additionally, requires no predoping of analytical solution. We present, herein, a data acquisition and analysis methodology based on frequency resolved immittance function analysis. Ultimately, this enables both a maximization of assay sensitivity and a reduction in assay acquisition time by an order of magnitude.
Co-reporter:Qiao Xu, Ho Cheng, Joshua Lehr, Amol V. Patil, and Jason J. Davis
Analytical Chemistry 2015 Volume 87(Issue 1) pp:346
Publication Date(Web):December 16, 2014
DOI:10.1021/ac503890e
A reliable quantification of protein markers will undoubtedly underpin profound developments in disease surveillance, diagnostics, and improved therapy. Although there potentially exist numerous means of achieving this, electrochemical impedimetric techniques offer scale of sensitivity, cost, convenience, and a flexibility with which few alternatives can compete. Though there have been marked developments in electroanalytical protein detection, the demands associated with accessing the inherent assay sensitivity in complex biological media largely remains. We report herein the use of cysteamine-graphene oxide modified gold microelectrode arrays in underpinning the ultrasensitive and entirely label free non-faradaic quantification of Parkinson’s-relevant autoantibodies in human serum.
Co-reporter:Wenting Wang, Xiaojian Fan, Shenghao Xu, Jason J. Davis, Xiliang Luo
Biosensors and Bioelectronics 2015 Volume 71() pp:51-56
Publication Date(Web):15 September 2015
DOI:10.1016/j.bios.2015.04.018
•A label-free electrochemical sensor for breast cancer biomarker was developed.•Low fouling PEG functional polymer was prepared and used for sensor construction.•The selective and sensitive BRCA1 biosensor could be used for serum sample assay.A label-free and low fouling biosensor based on functional polyethylene glycols selective for breast cancer susceptibility gene (BRCA1) is reported. Sensory interfaces were prepared through the modification of a glassy carbon electrode with highly cross-linked polyethylene glycol (PEG) film containing amine groups, followed by the self-assembly of gold nanoparticles and the immobilization of BRCA1 complementary single-strand 19-mer oligonucleotides. In the presence of a specific BRCA1 sequence capture and hybridization results in interfacial change sensitively monitored using electrochemical impedance spectroscopy. The combined utilization of a PEG polymer film and gold nanoparticle mixed interface enables very high levels of sensitivity and a highly effective assaying in patient samples. Assay linear range was from 50.0 fM to 1.0 nM, with a limit of detection of 1.72 fM. Furthermore, this label-free DNA sensor has been used for assaying BRCA1 in serum samples, showing its feasible potential for diagnostic applications in clinical analysis of breast cancer gene BRCA1. Foreseeable, this sensor made on this basis undoubtedly provide the most effective and sensitive detection for BRCA1.
Co-reporter:Joshua Lehr, Paul D. Beer, Stephen Faulkner and Jason J. Davis
Chemical Communications 2014 vol. 50(Issue 43) pp:5678-5687
Publication Date(Web):13 Mar 2014
DOI:10.1039/C4CC01138D
Lanthanide ions, due to their unique photo-physical characteristics, have attracted considerable attention in recent years. Their long lifetimes, sharp, well-defined emission bands, and designable environmental sensitivity make them ideal for integration into switchable supramolecular assemblies where emission can report on local conformation and/or coupled energy levels (redox state). The immobilisation of lanthanide containing constructs on interfaces facilitates device integration, the fabrication of advanced sensory and molecular electronic platforms and presents a means by which conformational dynamics within molecular assemblies can be analysed. In this feature article we discuss the current and potential applications for lanthanide luminescence in supramolecular, switchable and surface bound architectures.
Co-reporter:Paulo R. Bueno and Jason J. Davis
Analytical Chemistry 2014 Volume 86(Issue 3) pp:1337
Publication Date(Web):January 9, 2014
DOI:10.1021/ac403135b
The Fermi level or electrochemical signature of a molecular film containing accessible orbital states is ultimately governed by two measurable series energetic components, an energy loss term related to the charging of appropriately addressable molecular orbitals (resonant or charge transfer resistance), and an energy storage or electrochemical capacitance component. The latter conservative term is further divisible into two series contributions, one being a classic electrostatic term and the other arising from the involvement and charging of quantized molecular orbital states. These can be tuned in and out of resonance with underlying electrode states with an efficiency that governs electron transfer kinetics and an energetic spread dependent on solution dielectric. These features are experimentally resolved by an impedance derived capacitance analysis, a methodology which ultimately enables a convenient spectroscopic mapping of electron transfer efficacy, and of density of states within molecular films.
Co-reporter:Paulo R. Bueno and Jason J. Davis
Analytical Chemistry 2014 Volume 86(Issue 4) pp:1997
Publication Date(Web):January 6, 2014
DOI:10.1021/ac4031708
The electron exchange between a redox-active molecular film and its underlying electrode can be cleanly tracked, in a frequency-resolved manner, through associated capacitive charging. If acquired data is treated with a classical (non quantum) model, mathematically equivalent to a Nernst distribution for one redox energy level, redox site coverage is both underestimated and environmentally variable. This physically unrealistic model fails to account for the energetic dispersion intrinsically related to the quantized characteristics of coupled redox and electrode states. If one maps this redox capacitive charging as a function of electrode potential one not only reproduces observations made by standard electroanalytical methods but additionally and directly resolves the spread of redox state energies the electrode is communicating with. In treating a population of surface-confined redox states as constituting a density of states, these analyses further resolve the effects of electrolyte dielectric on energetic spread in accordance with the electron-transfer models proposed by Marcus and others. These observations additionally underpin a directly (spectrally) resolved dispersion in electron-transfer kinetics.
Co-reporter:Joshua Lehr, Flávio C. Bedatty Fernandes, Paulo R. Bueno, and Jason J. Davis
Analytical Chemistry 2014 Volume 86(Issue 5) pp:2559
Publication Date(Web):February 3, 2014
DOI:10.1021/ac403727h
An electrode surface confined redox group contributes to a substantial potential-dependent interfacial charging that can be sensitively probed and frequency-resolved by impedance-derived capacitance spectroscopy. In utilizing the sensitivity of this charging fingerprint to redox group environment, one can seek to generate derived sensory configurations. Exemplified here through the generation of mixed molecular films comprising ferrocene and antibody receptors to two clinically important targets, the label-free methodology is able to report on human prostatic acid phosphatase (PAP), a tumor marker, with a limit of detection of 11 pM and C-reactive protein with a limit of detection of 28 pM. Both assays exhibit linear ranges encompassing those of clinical value.
Co-reporter:Xiliang Luo, Qiao Xu, Tim James, and Jason J. Davis
Analytical Chemistry 2014 Volume 86(Issue 11) pp:5553
Publication Date(Web):May 9, 2014
DOI:10.1021/ac5010037
A substantial outstanding challenge in diagnostics and disease monitoring is an ability to rapidly and conveniently assay for protein biomarkers within complex biological media. Label-free electroanalytical methods present, arguably, the most promising and scalable means of achieving this but, as with all label-free assays, can struggle with response selectivity issues that arise from nonspecific surface interactions. Impedimetric methods are ultrasensitive and have been applied to the quantification of a wide range of proteins but have not previously been utilized in a multiplexed format capable of operation in complex analytical fluid. Herein, we present the use of thermally cross-linked poly(ethylene glycol) (PEG) polymer sensory array interfaces in the ultrasensitive quantification of two protein markers, insulin and C-reactive protein (CRP). This was achieved with detection limits of 171 ± 19 fM and 150 ± 10 pM, respectively. Significantly, the arrays not only enable the simultaneous, fast, nonamplified, and label-free detection of both markers without reagent addition but do so with little cross talk, even in human serum. A blind analysis of 17 real patient samples generated results in excellent agreement with those obtained through a clinically approved chemiluminescence assay.
Co-reporter:Qiao Xu, Samuel Evetts, Michele Hu, Kevin Talbot, Richard Wade-Martins and Jason J. Davis
RSC Advances 2014 vol. 4(Issue 102) pp:58773-58777
Publication Date(Web):30 Oct 2014
DOI:10.1039/C4RA10100F
α-Synuclein (α-Syn), a protein synthesized by neurons, as the major protein component of Lewy body inclusions, undoubtedly has a prominent role in the pathogenesis of Parkinson's Disease (PD). In an attempt to enable pre-symptomatic and definitive diagnosis, numerous attempts have been made to align assayed total α-Syn levels in serum (where there is a native presence) to PD disease status. Results have been conflicting. The status of circulating and potentially neuroprotective α-Syn autoantibodies in PD subjects is also unclear. In previous work we demonstrated that electrochemically assayed autoantibody levels were higher in PD patients compared to controls and, significantly, noted that this differentiation was most marked early in disease. Herein we report a robust (coefficient of variation 3.0%) single step and label free analysis of 90 subjects, including 60 PD patients, with a mean disease duration of 1.4 years and 29 control subjects. In this cross sectional cohort we observe a statistically significant (p < 0.05; Mann–Whitney U test) difference in autoantibody levels in PD patients versus controls, although there was no resolved scaling with symptomatic disease stage (p > 0.05; Kruskal–Wallis test).
Co-reporter:Xiliang Luo and Jason J. Davis
Chemical Society Reviews 2013 vol. 42(Issue 13) pp:5944-5962
Publication Date(Web):24 Apr 2013
DOI:10.1039/C3CS60077G
Electrical detection methodologies are likely to underpin the progressive drive towards miniaturised, sensitive and portable biomarker detection protocols. In being easily integrated within standard electronic microfabrication formats, and developing capability in microfluidics, the facile multiplexed detection of a range of proteins in a small analytical volume becomes entirely feasible with something costing just a few thousand pounds and benchtop or handheld in scale. In this review, we focus on recent important advances in label free assays of protein using a number of electrical methods, including those based on electrochemical impedance spectroscopy (EIS), amperometry/voltammetry, potentiometry, conductometry and field-effect methods. We introduce their mechanistic features and examples of application and sensitivity. The current state of the art, real world applications and challenges are outlined.
Co-reporter:Wen-Yen Huang, Gemma-Louise Davies and Jason J. Davis
Chemical Communications 2013 vol. 49(Issue 1) pp:60-62
Publication Date(Web):08 Nov 2012
DOI:10.1039/C2CC37545A
Internally Gd doped mesoporous nanoparticles have been prepared and exhibit unprecedented relaxivities that are retained on external biomodification. In tuning diffusive water access, image contrast can be reversibly switched in the presence of a specific protein target.
Co-reporter:Gemma-Louise Davies, Iris Kramberger and Jason J. Davis
Chemical Communications 2013 vol. 49(Issue 84) pp:9704-9721
Publication Date(Web):10 Sep 2013
DOI:10.1039/C3CC44268C
Biomedical imaging techniques can provide a vast amount of anatomical information, enabling diagnosis and the monitoring of disease and treatment profile. MRI uniquely offers convenient, non-invasive, high resolution tomographic imaging. A considerable amount of effort has been invested, across several decades, in the design of non toxic paramagnetic contrast agents capable of enhancing positive MRI signal contrast. Recently, focus has shifted towards the development of agents capable of specifically reporting on their local biochemical environment, where a switch in image contrast is triggered by a specific stimulus/biochemical variable. Such an ability would not only strengthen diagnosis but also provide unique disease-specific biochemical insight. This feature article focuses on recent progress in the development of MRI contrast switching with molecular, macromolecular and nanoparticle-based agents.
Co-reporter:Xiliang Luo, Mengyun Xu, Charlotte Freeman, Tim James, and Jason J. Davis
Analytical Chemistry 2013 Volume 85(Issue 8) pp:4129
Publication Date(Web):March 6, 2013
DOI:10.1021/ac4002657
Electrical assays potentially offer a highly sensitive, cheap, portable, automated, and multiplexed means of protein biomarker detection, characteristics with an ability to underpin both disease stratification and the development of point of care diagnostics. Most conveniently applied in a reagent free manner, all sensitive assays such as these suffer, however, from profound problems when applied in complex fluids such as blood serum. We report herein, the development, and clinical application, of a highly sensitive and selective electrical insulin biosensor based on a chemisorbed zwittorionic polymer support and a novel reagentless sensing technique based on phase monitoring electrochemical impedance spectroscopy. The polymer adlayer is exceptionally effective in both reducing background response and maintaining receptive antibody binding efficacy, while the non-Faradaic analysis avoids potential interference from background electro-active molecules. Applied to the detection of even a low molecular weight protein (here, insulin), a linear range from 0.1 to 200 pM and an unprecedented femtomolar detection limit are possible in undiluted blood serum.
Co-reporter:Paulo R. Bueno, Francisco Fabregat-Santiago, and Jason J. Davis
Analytical Chemistry 2013 Volume 85(Issue 1) pp:411
Publication Date(Web):November 29, 2012
DOI:10.1021/ac303018d
Electrochemical analyses on confined electroactive molecular layers, herein exemplified with electroactive self-assembled monolayers, sample current contributions that are significantly influenced by additional nonfaradaic and uncompensated resistance effects that, though unresolved, can strongly distort redox analysis. Prior work has shown that impedance-derived capacitance spectroscopy approaches can cleanly resolve all contributions generated at such films, including those which are related to the layer dipolar/electrostatic relaxation characteristics. We show herein that, in isolating the faradaic and nonfaradaic contributions present within an improved equivalent circuit description of such interfaces, it is possible to accurately simulate subsequently observed cyclic voltammograms (that is, generated current versus potential patterns map accurately onto frequency domain measurements). Not only does this enable a frequency-resolved quantification of all components present, and in so doing, a full validation of the equivalent circuit model utilized, but also facilitates the generation of background subtracted cyclic voltammograms remarkably free from all but faradaic contributions.
Co-reporter:Paulo R. Bueno, Tiago Azevedo Benites, Márcio Sousa Góes, and Jason J. Davis
Analytical Chemistry 2013 Volume 85(Issue 22) pp:10920
Publication Date(Web):October 14, 2013
DOI:10.1021/ac402378n
This work introduces a simple, single-step, impedance-derived capacitance spectroscopic approach as a convenient and direct way of reporting the heterogeneous rate of electron-transfer between an electrode and solution-phase redox species. The proposed methodology requires no equivalent circuit analysis or data fitting and is equally applicable to the strong coupling (diffusion-mediated) or weak coupling electron-transfer regimes.
Co-reporter:Dr. Joshua Lehr;Dr. Thomas Lang;Dr. Octavia A. Blackburn;Timothy A. Barendt; Stephen Faulkner;Dr. Jason J. Davis; Paul D. Beer
Chemistry - A European Journal 2013 Volume 19( Issue 47) pp:15898-15906
Publication Date(Web):
DOI:10.1002/chem.201302886
Abstract
We report the preparation of [2]rotaxanes containing an electrochemically and optically active osmium(II) bipyridyl macrocyclic component mechanically bonded with cationic pyridinium axles. Such interlocked host systems are demonstrated to recognise and sense anionic guest species as shown by 1H NMR, luminescence and electrochemical studies. The rotaxanes can be surface assembled on to gold electrodes through anion templation under click copper(I)-catalysed Huisgen cycloaddition conditions to form rotaxane molecular films, which, after template removal, respond electrochemically and selectively to chloride.
Co-reporter:Dr. Wen-Yen Huang;Dr. Gemma-Louise Davies ;Dr. Jason J. Davis
Chemistry - A European Journal 2013 Volume 19( Issue 52) pp:17891-17898
Publication Date(Web):
DOI:10.1002/chem.201303239
Abstract
A low native membrane permeability and ineffective access to the cellular cytosol, together with aggressive proteolytic degradation, often severely hampers the practical application of any therapeutic protein or antibody. Through engineering the charging profile of mesoporous silica nanoparticles, cellular uptake and subsequent subcellular distribution can be controlled. We show herein that programmed cell death can subsequently be induced across a population of cancer cells with remarkable efficacy on conjugating a specific caspase-cascade-activating cytochrome to such cytosol-accessing particles.
Co-reporter:Joshua Lehr, Jamie Bennett, Manuel Tropiano, Thomas J. Sørensen, Stephen Faulkner, Paul D. Beer, and Jason J. Davis
Langmuir 2013 Volume 29(Issue 5) pp:1475-1482
Publication Date(Web):January 15, 2013
DOI:10.1021/la3046725
The recruitment of DO3A-derived lanthanide complexes by ligation to isophthalic acid and catechol-modified gold surfaces, and their resulting sensitization, is reported herein. Predictably pH-dependent surface recruitment is associated with the expected fingerprint europium and terbium emission characteristics. The intensity of the lanthanide luminescence scales exponentially with spacer length, indicating a strong quenching interaction between the lanthanide and the gold surface. The switchable catechol oxidation state provides a means of electrochemically triggering the release of prior ligated complexes.
Co-reporter:Thomas Bryan, Xiliang Luo, Paulo R. Bueno, Jason J. Davis
Biosensors and Bioelectronics 2013 Volume 39(Issue 1) pp:94-98
Publication Date(Web):15 January 2013
DOI:10.1016/j.bios.2012.06.051
C-reactive protein (CRP) is an acute phase protein whose levels are increased in many disorders. There exists, in particular, a great deal of interest in the correlation between blood serum levels and the severity of risk for cardiovascular disease. A sensitive, label-free, non-amplified and reusable electrochemical impedimetric biosensor for the detection of CRP in blood serum was developed herein based on controlled and coverage optimised antibody immobilization on standard polycrystalline gold electrodes. Charge transfer resistance changes were highly target specific, linear with log CRP concentration across a 0.5–50 nM range and associated with a limit of detection of 176 pM. Significantly, the detection limits are better than those of current CRP clinical methods and the assays are potentially cheap, relatively automated, reusable, multiplexed and highly portable. The generated interfaces were capable not only of comfortably quantifying CRP across a clinically relevant range of concentrations but also of doing this in whole blood serum with interfaces that were, subsequently, reusable. The importance of optimising receptor layer resistance in maximising assay sensitivity is also detailed.Highlights► An antibody based CRP immunoassay can be generated and operated in whole blood. ► Assay sensitivity can be tuned through initial receptive layer resistance. ► Receptive layers can be regenerated and reused with good fidelity. ► Whole blood assays span entire clinically relevant range.
Co-reporter:Mengyun Xu, Xiliang Luo, Jason J. Davis
Biosensors and Bioelectronics 2013 Volume 39(Issue 1) pp:21-25
Publication Date(Web):15 January 2013
DOI:10.1016/j.bios.2012.06.014
Insulin, a polypeptide hormone secreted by pancreatic cells, is a key regulator in glucose homeostasis. Its deficiency leads to insulin-dependent (type I) diabetes whereas resistance to insulin is common in type II diabetes, obesity and a range of endocrine disorders. Its determination is of considerable value, particularly in the clinical diagnosis of diabetes mellitus and the doping control of athletes. It has, additionally, been noted as a potential breast cancer marker (serum insulin levels being found to be raised in comparison to control patients). Electrochemical assays are potentially very cheap, highly sensitive, and very readily transposed to a point of care. Though there exist numerous examples of label free impedimetric or capacitative assaying of biomolecules, these are rarely demonstrated to be effective in complex biological mixtures or to be applicable to low molecular weight targets (since they operate through the interfacial displacement of water/ions and/or the steric blocking of a redox probe). We report herein an ultrasensitive electrochemical and label-free biosensor for insulin in blood serum with a clinically relevant linear range and detection limit of 1.2 pM. The transducing surfaces, based on readily prepared, antibody modified, polyethylene glycol monolayer modified polycrystalline gold surfaces, respond in a highly specific and re-useable manner to the target in up to 50% blood serum.Highlights► The low molecular weight, clinically important polypeptide, insulin, can be reliably and selectively assayed in blood by a label free facile impedance immunoassay. ► Assays span entire clinically relevant range with low pM limits of detection. ► There is no precedent for the label free impedance assaying this protein and very little precedent for the label free detection of targets of this molecular weight in complex media. ► The receptive surfaces are readily generated and reuseable.
Co-reporter:Olivia Berthoumieu, Amol V. Patil, Wang Xi, Lubica Aslimovska, Jason J. Davis, and Anthony Watts
Nano Letters 2012 Volume 12(Issue 2) pp:899-903
Publication Date(Web):December 9, 2011
DOI:10.1021/nl203965w
Bacteriorhodopsin (BR) is a robust light-driven proton pump embedded in the purple membrane of the extremophilic archae Halobacterium salinarium. Its photoactivity remains in the dry state, making BR of significant interest for nanotechnological use. Here, in a novel configuration, BR was depleted from most of its endogenous lipids and covalently and asymmetrically anchored onto a gold electrode through a strategically located and highly responsive cysteine mutation; BR has no indigenous cysteines. Chemisorption on gold was characterized by surface plasmon resonance, reductive striping voltammetry, ellipsometry, and atomic force microscopy (AFM). For the first time, the conductance of isolated protein trimers, intimately probed by conducting AFM, was reproducibly and reversibly switched under wavelength-specific conditions (mean resistance of 39 ± 12 MΩ under illumination, 137 ± 18 MΩ in the dark), demonstrating a surface stability that is relevant to potential nanodevice applications.
Co-reporter:Nicholas H. Evans, Habibur Rahman, Alexandre V. Leontiev, Neil D. Greenham, Grzegorz A. Orlowski, Qiang Zeng, Robert M. J. Jacobs, Christopher J. Serpell, Nathan L. Kilah, Jason J. Davis and Paul D. Beer
Chemical Science 2012 vol. 3(Issue 4) pp:1080-1089
Publication Date(Web):06 Jan 2012
DOI:10.1039/C2SC00909A
The first examples of ferrocene containing catenanes, in solution and assembled on a surface are described. Chloride anion templation is exploited to synthesize redox-active [2]- and [3]-catenanes via Grubbs' ring closing metathesis, utilizing a novel ferrocene-appended isophthalamide macrocycle. X-ray crystal structures of both catenanes were determined. The ability of the [2]catenane to selectively bind and characteristically sense its chloride anion template is demonstrated by use of 1H NMR and electrochemical voltammetric techniques. Self-assembled monolayers of analogous surface-confined catenanes have been prepared on gold. In addition to being characterized by cyclic voltammetry and ellipsometry, detailed information regarding the structure of the catenane monolayers has been provided by use of angle integrated high resolution X-ray photoelectron spectroscopy.
Co-reporter:Thomas Bryan, Xiliang Luo, Lars Forsgren, Ludmilla A. Morozova-Roche and Jason J. Davis
Chemical Science 2012 vol. 3(Issue 12) pp:3468-3473
Publication Date(Web):11 Sep 2012
DOI:10.1039/C2SC21221H
Protein aggregation, leading to amyloid deposition in the brain, is implicated in the pathology of a number of increasingly prevalent neurodegeneration states such as Parkinson's disease (PD), Alzheimer's disease and prion diseases. The body's protective response to the formation of such deposits is to generate specific autoimmune antibodies. Alpha-synuclein, a natively unfolded protein relatively abundant in the brain, is the main constituent of Lewy body amyloid dispositions in PD. Previous assays determining content of alpha-synuclein in bodily fluids have proven to be largely inconclusive. Here we have taken a novel approach in utilising alpha-synuclein modified electrodes to sample the autoantibodies generated as the body responds to changes in its homeostasis. We show that these electroanalytical assays not only robustly distinguish between disease state and control individuals but also map out disease progression with unprecedented sensitivity and clarity. The impedimetric electrode surfaces are highly specific, reusable, exhibit a linear range from 0.5 to 10 nM and a detection limit of 55 ± 3 pM. We believe electroanalyses such as these, possible with less than 10 microlitres of fluid and a total assay time of only a few minutes, to be of value for early diagnosis of PD and possibly other alpha-synucleinopathies, and for monitoring disease progression and effects of possible disease modifying interventions.
Co-reporter:Jason J. Davis, Wen-Yen Huang and Gemma-Louise Davies
Journal of Materials Chemistry A 2012 vol. 22(Issue 43) pp:22848-22850
Publication Date(Web):25 Sep 2012
DOI:10.1039/C2JM35116A
In tuning the sub-particle localisation of Gd(III) binding macrocycles within a mesoporous scaffold, nanoparticle contrast agents of unprecedented relaxivity and low Gd(III) loadings can be realised.
Co-reporter:Anthony Johnson, Qifeng Song, Paul Ko Ferrigno, Paulo R. Bueno, and Jason J. Davis
Analytical Chemistry 2012 Volume 84(Issue 15) pp:6553
Publication Date(Web):July 10, 2012
DOI:10.1021/ac300835b
C-reactive protein (CRP) is an acute phase protein whose levels are increased in many disorders. Levels greater than 3 μg/mL serum have hitherto been considered to indicate pathology, but there is increasing interest in assessments between 0.1 and 10 μg/mL, which have been found to correlate with severity of risk for cardiovascular disease. We report herein the generation of both antibody and Affimer based impedance immunoassays for CRP that are substantially more sensitive than clinically utilized immunonephelometry and immunoturbidity assessments. Significant in this study is not only the use of a constrained peptide to detect a clinically important target but also that derived electrochemical impedance assays can be highly sensitive even with probes whose relatively weak (μM) affinities are not amenable to target detection by surface plasmon resonance (SPR). Key to this finding is acknowledging that receptive surfaces of comparatively low initial steric bulk and charge transfer resistance are especially primed to be highly responsive to target binding in electroanalytical assays of this type.
Co-reporter:Paulo R. Bueno, Giulia Mizzon, and Jason J. Davis
The Journal of Physical Chemistry B 2012 Volume 116(Issue 30) pp:8822-8829
Publication Date(Web):June 11, 2012
DOI:10.1021/jp303700f
Redox active self-assembled monolayers inherently possess both electrochemically addressable and polarizable components. The latter will contribute, with additional parasitic terms, to the iR drop effects within any form of electronic analysis, potentially distorting results. A capacitive analysis of such interfaces (Electroactive Monolayer Capacitance Spectroscopy), presented here, enables a clean mapping of both the thermodynamic and kinetic faradaic characteristics in a single experimental run, with parasitic nonfaradaic contributions (polarization and resistance terms) both spectrally resolved and cleanly removed. The methodology enables a rapid and undistorted quantification of accessible redox site density of states (reported directly by redox capacitance), molecular surface coverage, electron transfer kinetics, and reorganization energies with comparatively little experimental effort. Exemplified here with electroactive copper protein and ferrocene films the approach is equally applicable to any redox active interface.
Co-reporter:Amol V. Patil, Thenhuan Premaruban, Olivia Berthoumieu, Anthony Watts, and Jason J. Davis
The Journal of Physical Chemistry B 2012 Volume 116(Issue 1) pp:683-689
Publication Date(Web):December 8, 2011
DOI:10.1021/jp210520k
The integration of the transmembrane protein bacteriorhodopsin (BR) with man-made electrode surfaces has attracted a great deal of interest for some two decades or more and holds significant promise from the perspective of derived photoresponse or energy capture interfaces. Here we demonstrate that a novel and strategically engineered cysteine site (M163C) can be used to intimately and effectively couple delipidated BR to supporting metallic electrode surfaces. By virtue of the combined effects of the greater surface molecular density afforded by delipidation, and the vicinity of the electrostatic changes associated with proton pumping to the transducing metallic continuum, the resulting films generate a considerably greater photocurrent density on wavelength-selective illumination than previously achievable with monolayers of BR. Given the uniquely photoresponsive, wavelength-selective, and photostable characteristics of this protein, the work has implications for utilization in solar energy capture and photodetector devices.
Co-reporter:Márcio S. Góes, Habibur Rahman, Joshua Ryall, Jason J. Davis, and Paulo R. Bueno
Langmuir 2012 Volume 28(Issue 25) pp:9689-9699
Publication Date(Web):May 18, 2012
DOI:10.1021/la301281y
The presence of self-assembled monolayers at an electrode introduces capacitance and resistance contributions that can profoundly affect subsequently observed electronic characteristics. Despite the impact of this on any voltammetry, these contributions are not directly resolvable with any clarity by standard electrochemical means. A capacitive analysis of such interfaces (by capacitance spectroscopy), introduced here, enables a clean mapping of these features and additionally presents a means of studying layer polarizability and Cole–Cole relaxation effects. The resolved resistive term contributes directly to an intrinsic monolayer uncompensated resistance that has a linear dependence on the layer thickness. The dielectric model proposed is fully aligned with the classic Helmholtz plate capacitor model and additionally explains the inherently associated resistive features of molecular films.
Co-reporter:Dr. Amol V. Patil;Thenuhan Premaraban;Olivia Berthoumieu; Anthony Watts;Dr. Jason J. Davis
Chemistry - A European Journal 2012 Volume 18( Issue 18) pp:5632-5636
Publication Date(Web):
DOI:10.1002/chem.201103597
Abstract
Bacteriorhodopsin, BR, is a natural, photoresponsive, biomolecule that has potential application in data storage, imaging and sensing. Being membrane-bound, however, it is coupled with metallic electronic surfaces only with some difficulty. We report herein a facile method to generate uniformly orientated, anchored and active monolayers of BR on metallic electrodes. In the present study, the cytoplasmic side of the BR is equipped with an engineered cysteine to achieve largely lipid-free, orientation-specific, highly stable, covalent immobilization on gold surfaces. By using non-invasive Kelvin probe force microscopy, it is possible to measure the light-induced proton accumulation at the extracellular protein surface at truly molecular scales. The intimate probe–BR interaction possible on lipid removal facilitates the detection of photoinduced surface potential switching substantially larger ((20.4±7.5) mV) with functional single delipidated mutant BR trimers than for the wild-type protein. The proton pumping detected is also notably highly unidirectional with the orientated protein.
Co-reporter:Nicholas H. Evans;Habibur Rahman
Analytical and Bioanalytical Chemistry 2012 Volume 402( Issue 5) pp:1739-1748
Publication Date(Web):2012 February
DOI:10.1007/s00216-011-5403-7
The development of surface-attached sensors for cationic and anionic guests is of intense current research interest. In addition to the environmental flexibility, robustness and reusability of such devices, surface-confined sensors typically exhibit an amplified response to target analytes owing to preorganization of the receptor. Whereas redox-active cations may be sensed by studying the cyclic voltammetry of host–guest systems containing ion-selective receptors attached to an appropriate electrode, redox-inactive ionic species require the use of electrochemical impedance spectroscopy, with appropriately functionalized electrodes and redox probes. Alternatively, receptors may be constructed that incorporate an electrochemical or optical reporter group within their structure to provide a macroscopic response to the presence of an ionic guest. This critical review seeks to present an up-to-date, although necessarily selective, account of the progress in the field, and provides insights into possible future developments, including the utilization of receptor–nanoparticle conjugates and mechanically interlocked receptors.
Co-reporter:A.V. Patil, J.J. Davis
Coordination Chemistry Reviews 2011 Volume 255(17–18) pp:1970-1980
Publication Date(Web):September 2011
DOI:10.1016/j.ccr.2011.02.002
Our ability to interface with biological macromolecules continues to advance at a significant pace and brings with it potential applications that are as broad as they are powerful. Running alongside this evolution has been the refinement of methods by which interfaces can be probed at scales approaching (or being at) the molecular. Through combinations of experimental design, proximal probe technology and high sensitivity optical imaging, one can truly probe the bioelectronic interface at levels that are both startling and associated with unprecedented levels of detail.
Co-reporter:Jy D. Chartres, Michael Busby, Mark J. Riley, Jason J. Davis, and Paul V. Bernhardt
Inorganic Chemistry 2011 Volume 50(Issue 18) pp:9178-9183
Publication Date(Web):August 3, 2011
DOI:10.1021/ic201495r
In the treatment of chronic iron overload disorders, ligands capable of complexing so-called “labile” (nonprotein bound) Fe are required to enter iron-loaded cells, sequester excess Fe, and then exit the cell (and the body) as an intact Fe complex. Despite the emergence of several ligand families that show high activity in mobilizing intracellular Fe, the mechanism and the locations of these subcellular labile Fe pools are still poorly understood. Our previous studies have unearthed a class of heterocyclic hydrazine-based chelators (e.g., benzoyl picolinoyl hydrazine, H2BPH) that show excellent activity at mobilizing Fe from Fe-loaded cells. Herein, we have grafted a fluorescent tag (rhodamine B) onto H2BPH to generate a ligand (L1) that is nonfluorescent in its uncomplexed form but becomes strongly fluorescent in complex with FeIII. The free ligand and its 1:2 Fe complex [FeIII(L1)2]3+ have both been fully characterized spectroscopically and with X-ray crystallography. Confocal fluorescent microscopy of HeLa cells incubated with [FeIII(L1)2]3+ shows that the complex rapidly enters HeLa cells and localizes within endosomes/lysosomes.
Co-reporter:Amol Virendra Patil ;Jason John Davis
Journal of the American Chemical Society 2010 Volume 132(Issue 47) pp:16938-16944
Publication Date(Web):November 10, 2010
DOI:10.1021/ja1065448
In coupling the redox state of an adsorbed molecule to its spectral characteristics redox profiles can be directly imaged by means of far-field fluorescence. At suitable levels of dilution, on optically transparent electrode surfaces, reversible interfacial electron transfer processes can be followed pixel by pixel down to scales which approach the molecular. In mapping out switching potentials across a surface population, thermodynamic dispersion, related to variance in the orientation, electronic coupling, protein fold, electric field drop, and general surface order, can be quantified. The self-assembled monolayer buffering the protein from the underlying metallic electrode surface not only acts to tune electronic coupling between the two but also potentially provides a variable more easily segmented from other contributions to molecular dispersion. We have, specifically, considered the possibility that the supporting monolayer crystallinity is a significant contributor to the subsequently observed spread in half-wave potentials. We report here that this is indeed the case and that this spread diminishes from 17 to 12 mV for the blue copper protein azurin as the supporting alkanethiol layer crystallinity increases. The work herein, then, presents not only a direct determination of submonolayer scale variance in redox character but also a means of tuning this through gross surface and entirely standard chemical means.
Co-reporter:Jason J. Davis, Grzegorz A. Orlowski, Habibur Rahman and Paul D. Beer
Chemical Communications 2010 vol. 46(Issue 1) pp:54-63
Publication Date(Web):22 Oct 2009
DOI:10.1039/B915122B
Mechanically interlocked molecules are of considerable interest from data storage, molecular scale or sensory device perspectives. Though the solution phase characterisation of these compounds has been extensively explored, progress towards real world application will, in many cases, necessitate a detailed understanding of their interfacing with supportive, optically transparent or electroactive surfaces. This feature article summarises the developments made in surface assembly and characterisation including recent progress in exploiting templating methods to interlock molecular systems on surfaces.
Co-reporter:David P. Cormode, Andrew J. Evans, Jason J. Davis and Paul D. Beer
Dalton Transactions 2010 vol. 39(Issue 28) pp:6532-6541
Publication Date(Web):15 Jun 2010
DOI:10.1039/C0DT00217H
A disulfide functionalized bis-ferrocene urea acyclic receptor and disulfide functionalized mono- and bis-ferrocene amide and urea appended upper rim calix[4]arene receptors were prepared for the fabrication of SAM redox-active anion sensors. 1H NMR and diffusive voltammetric anion recognition investigations revealed each receptor to be capable of complexing and electrochemically sensing anions via cathodic perturbations of the respective receptor's ferrocene/ferrocenium redox couple. SAMs of a ferrocene urea receptor 3 and ferrocene urea calixarene receptor 17 exhibited significant enhanced magnitudes of cathodic response upon anion addition as compared to observed diffusive perturbations. SAMs of 17 were demonstrated to sense the perrhenate anion in aqueous solutions.
Co-reporter:Michael Busby, Lukas Kurt Josef Stadler, Paul Ko Ferrigno, Jason J. Davis
Biophysical Chemistry 2010 Volume 152(1–3) pp:170-177
Publication Date(Web):November 2010
DOI:10.1016/j.bpc.2010.09.005
The Strep tag is a peptide sequence that is able to mimic biotin's ability to bind to streptavidin. Sequences of Strep tags from 0 to 5 have been appended to the N-terminus of a model protein, the Stefin A Quadruple Mutant (SQM) peptide aptamer scaffold, and the recombinant fusion proteins expressed. The affinities of the proteins for streptavidin have been assessed as a function of the number of tags inserted using a variety of labelled and label-free bioanalytical and surface based methods (Western blots, microarray assays and surface plasmon resonance spectroscopy). The binding affinity increases with the number of tags across all assays, reaching nanomolar levels with 5 inserts, an observation assigned to a progressive increase in the probability of a binding interaction occurring. In addition a novel interfacial FRET based assay has been developed for generic Strep tag interactions, which utilises a conventional microarray scanner and bypasses the requirement for expensive lifetime imaging equipment. By labelling both the tagged StrepX-SQM2 and streptavidin targets, the conjugate is primed for label-free FRET based displacement assays.Research Highlights►Multi-Strep tag aptamers show enhanced affinity to streptavidin binding. ►Multi-Strep tags show similar binding properties across a variety of bioanalytical platforms. ►Multi-Strep tags have established the basis for an assay compatible with a future FRET based label-free biosensors.
Co-reporter:JanteM. Salverda Dr.;AmolV. Patil Dr.;Giulia Mizzon;Sofya Kuznetsova Dr.;Gerhild Zauner Dr.;Namik Akkilic;GerardW. Canters Dr.;JasonJ. Davis Dr.;HendrikA. Heering Dr.;ThijsJ. Aartsma Dr.
Angewandte Chemie 2010 Volume 122( Issue 33) pp:5912-5915
Publication Date(Web):
DOI:10.1002/ange.201001298
Co-reporter:JanteM. Salverda Dr.;AmolV. Patil Dr.;Giulia Mizzon;Sofya Kuznetsova Dr.;Gerhild Zauner Dr.;Namik Akkilic;GerardW. Canters Dr.;JasonJ. Davis Dr.;HendrikA. Heering Dr.;ThijsJ. Aartsma Dr.
Angewandte Chemie International Edition 2010 Volume 49( Issue 33) pp:5776-5779
Publication Date(Web):
DOI:10.1002/anie.201001298
Co-reporter:Jason J. Davis, Ben Peters, Wang Xi, Jeroen Appel, Alexander Kros, Thijs J. Aartsma, Razvan Stan and Gerard W. Canters
The Journal of Physical Chemistry Letters 2010 Volume 1(Issue 10) pp:1541-1546
Publication Date(Web):April 28, 2010
DOI:10.1021/jz100375m
Further developments in the field of molecular electronics will require an understanding of the key relationships between chemical composition and subsequently observed electron transport characteristics. Although the relationship between redox activity and conductance gating has emerged in recent years, our ability to chemically engineer these characteristics (such as “on−off” switching magnitudes) is only now emerging. The report herein describes, to our knowledge, the first example of gated conductance in a single wired redox molecule in which a 3 orders of magnitude “on/off” switching ratio is observed. This switching magnitude significantly exceeds that observed with molecules weakly coupled to the supporting electrode and correlates directly with both electrochemical switching and an in situ determined heterogeneous electron transfer rate constant.Keywords (KEYWORDS): conductance gating; electrochemical STM; electrochemistry; ferrocene wire; molecular conductance;
Co-reporter:Liyun Zhao, Kathleen M. Mullen, Michał J. Chmielewski, Asha Brown, Nick Bampos, Paul D. Beer and Jason J. Davis
New Journal of Chemistry 2009 vol. 33(Issue 4) pp:760-768
Publication Date(Web):14 Jan 2009
DOI:10.1039/B818854H
The surface covalent attachment of fluorescent axles of indolocarbazole enables anion templation to be exploited in the formation of pseudorotaxane assembliesvia the threading of neutral isophthalamide macrocycles. In utilising the surface of polystyrene beads this threading process can be followed by both magnetic resonance methods and changes in the axle fluorescent emission spectrum. The analogous surface assembly and anion templated threading can be achieved, with fluoride and sulfate, on silica nanoparticles where anion recognition and macrocycle threading are associated with equivalent and specific optical change.
Co-reporter:Liyun Zhao, Jason J. Davis, Kathleen M. Mullen, Michał J. Chmielewski, Robert M. J. Jacobs, Asha Brown and Paul D. Beer
Langmuir 2009 Volume 25(Issue 5) pp:2935-2940
Publication Date(Web):February 10, 2009
DOI:10.1021/la803960z
The surface covalent attachment of indolocarbazole axles enables anion templation to be exploited in the formation of pseudorotaxane assemblies via the threading of neutral isophthalamide macrocycles from solution. The anion selectivity of this templating process can be monitored by a number of surface spectroscopic methods and shows subtle differences compared to the same process in solution. Though the fluxional and disordered nature of ethylene glycol extended axle adlayers prohibits detectable threading on the surface, rotaxane monolayers can be generated by a preassociation of the components and templating anion in solution. The threaded macrocycles therein can subsequently be released and detected by mass spectrometry by reductive stripping of the axle.
Co-reporter:Michał J. Chmielewski, Liyun Zhao, Asha Brown, David Curiel, Mark R. Sambrook, Amber L. Thompson, Sergio M. Santos, Vitor Felix, Jason J. Davis and Paul D. Beer
Chemical Communications 2008 (Issue 27) pp:3154-3156
Publication Date(Web):09 May 2008
DOI:10.1039/B804941F
The first example of anion templated pseudorotaxane formation between two neutral components in solution and in surface assembled monolayers is described.
Co-reporter:Simon R. Bayly, Thomas M. Gray, Michał J. Chmielewski, Jason J. Davis and Paul D. Beer
Chemical Communications 2007 (Issue 22) pp:2234-2236
Publication Date(Web):08 May 2007
DOI:10.1039/B701796K
Anion templation is used to assemble novel redox-active bis-ferrocene functionalised rotaxane self-assembled monolayers (SAMs) on to gold electrode surfaces; after template removal, the unique SAM rotaxane binding domain is capable of selectively sensing chloride ions electrochemically.
Co-reporter:J. J. Davis, D. A. Morgan, C. L. Wrathmell, D. N. Axford, J. Zhao and N. Wang
Journal of Materials Chemistry A 2005 vol. 15(Issue 22) pp:2160-2174
Publication Date(Web):11 Apr 2005
DOI:10.1039/B417712F
Recent work by a number of groups has highlighted the emerging potential associated with the marriage of nanoscale electronics and biological structure. Many biological macromolecules have evolved into structures typically primed for highly-specific surface recognition, analyte binding and, in some cases, facile and directional electron tunnelling. The redox-active centres of metalloproteins, for example, play a central role in photosynthesis and respiration and much progress has been made in constructively interfacing these moieties to man-made surfaces. Specifically, a variety of methodologies can be applied that not only facilitate controllable electronic coupling to underlying metallic electrode surfaces but also a highly spatially-resolved analysis of the (potentially switchable) tunnel transport characteristics. Developments in our understanding and manipulation of these entities at a molecular level has further led us to the point where nanobiotechnological advances can be realistically proposed. Strategies to exploit combined advanced lithography and molecular manipulation methods are described. Recent protein tunnel transport experiments in proximal probe junctions are discussed. In a CP-AFM metal–protein–metal tunnel junction experimental data in the low voltage regime is well-described by a non-resonant charge transfer process in which the protein matrix is modelled as a uniform tunnel barrier, the absolute magnitude of which can be controllably modulated by compressional force. Comparative analysis within STM-based junctions of metal substituted metalloproteins are additionally supportive of transport being dominantly non-resonant. Recent progress in interfacing the unique properties of nanoscale electrical junctions to biological structure, more generally, is reviewed herein.
Co-reporter:Yann Astier Dr.;Gerard W. Canters Dr. Dr.;H. Allen O. Hill Dr.;Martin P. Verbeet Dr.;Hein J. Wijma
ChemPhysChem 2005 Volume 6(Issue 6) pp:
Publication Date(Web):18 MAY 2005
DOI:10.1002/cphc.200400384
Nitrite is converted to nitric oxide by haem or copper-containing enzymes in denitrifying bacteria during the process of denitrification. In designing an efficient biosensor, this enzymic turnover must be quantitatively assessed. The enzyme nitrite reductase from Alcaligenes faecalis contains a redox-active blue copper centre and a nonblue enzyme-active copper centre. It can be covalently tethered to modified gold-electrode surfaces in configurations in which direct electron transfer is possible. A surface cysteine mutant of the enzyme can be similarly immobilised on bare electroactive gold substrates. Under such circumstances, however, electron transfer cannot be effectively coupled with substrate catalytic turnover. In using either the natural redox partner, pseudoazurin, or ruthenium hexammine as an “electron-shuttle” or “conduit” between enzyme and a peptide-modified electrode surface, the coupling of electron transfer to catalysis can be utilised in the development of an amperometric nitrite sensor.
Co-reporter:Paul D. Beer, David P. Cormode and Jason J. Davis
Chemical Communications 2004 (Issue 4) pp:414-415
Publication Date(Web):20 Jan 2004
DOI:10.1039/B313658B
Disulfide-functionalised zinc metalloporphyrins self-assembled on gold nanoparticles exhibit remarkable, surface-enhanced, anion binding affinities as compared to the free metalloporphyrin.
Co-reporter:C. L. Wrathmell;J. Fletcher;J. Zhao;J. J. Davis
Journal of Molecular Recognition 2004 Volume 17(Issue 3) pp:167-173
Publication Date(Web):27 APR 2004
DOI:10.1002/jmr.677
Metalloproteins can be self-assembled in molecularly ordered, electrochemically addressable arrays. We report here on a study of the transport characteristics of the blue copper protein, azurin, from Pseudomonas aeruginosa, by a combination of electrochemical and scanning probe techniques (scanning tunnelling microscopy and conducting atomic force microscopy). Redox-switchable chemisorbed molecular arrays can be formed from both wild-type and mutant proteins using the strong affinity of cysteine residue thiolates for pristine gold surfaces. The molecular transconductance of single protein molecules within these arrays has been studied under controllable conditions where it has been additionally possible to resolve the effects of protein mechanical perturbation. Although tunnelling appears to be non-resonant and adequately explained through the use of a square barrier model, under some conditions the contribution of the redox-active copper centre to conductance is resolvable. Copyright © 2004 John Wiley & Sons, Ltd.
Co-reporter:Jason J. Davis, Delphine Bruce, Gerard W. Canters, John Crozier and H. Allen O. Hill
Chemical Communications 2003 (Issue 5) pp:576-577
Publication Date(Web):11 Feb 2003
DOI:10.1039/B211246A
Engineered metalloproteins and enzymes can be self assembled on pristine gold electrodes in robust, electrochemically-addressable, arrays.
Co-reporter:Jason J. Davis Dr.;Karl S. Coleman Dr.;Bobak R. Azamian;Claire B. Bagshaw;Malcolm L. H. Green
Chemistry - A European Journal 2003 Volume 9(Issue 16) pp:
Publication Date(Web):22 JUL 2003
DOI:10.1002/chem.200304872
The nano dimensions, graphitic surface chemistry and electronic properties of single walled carbon nanotubes make such a material an ideal candidate for chemical or biochemical sensing. Carbon nanotubes can be nondestructively oxidized along their sidewalls or ends and subsequently covalently functionalized with colloidal particles or polyamine dendrimers via carboxylate chemistry. Proteins adsorb individually, strongly and noncovalently along nanotube lengths. These nanotube–protein conjugates are readily characterized at the molecular level by atomic force microscopy. Several metalloproteins and enzymes have been bound on both the sidewalls and termini of single walled carbon nanotubes. Though coupling can be controlled, to a degree, through variation of tube oxidative pre-activation chemistry, careful control experiments and observations made by atomic force microscopy suggest that immobilization is strong, physical and does not require covalent bonding. Importantly, in terms of possible device applications, protein attachment appears to occur with retention of native biological structure. Nanotube electrodes exhibit useful voltammetric properties with direct electrical communication possible between a redox-active biomolecule and the delocalized π system of its carbon nanotube support.
Co-reporter:Bobak R. Azamian, Karl S. Coleman, Jason J. Davis, Neal Hanson and Malcolm L. H. Green
Chemical Communications 2002 (Issue 4) pp:366-367
Publication Date(Web):05 Feb 2002
DOI:10.1039/B110690B
Carboxylate chemistry is used to covalently couple metal nanoparticles to defect sites in controllably oxidized single-walled carbon nanotube termini and side-walls, and this process monitored by atomic force microscopy.
Co-reporter:Gemma-Louise Davies, Iris Kramberger and Jason J. Davis
Chemical Communications 2013 - vol. 49(Issue 84) pp:NaN9721-9721
Publication Date(Web):2013/09/10
DOI:10.1039/C3CC44268C
Biomedical imaging techniques can provide a vast amount of anatomical information, enabling diagnosis and the monitoring of disease and treatment profile. MRI uniquely offers convenient, non-invasive, high resolution tomographic imaging. A considerable amount of effort has been invested, across several decades, in the design of non toxic paramagnetic contrast agents capable of enhancing positive MRI signal contrast. Recently, focus has shifted towards the development of agents capable of specifically reporting on their local biochemical environment, where a switch in image contrast is triggered by a specific stimulus/biochemical variable. Such an ability would not only strengthen diagnosis but also provide unique disease-specific biochemical insight. This feature article focuses on recent progress in the development of MRI contrast switching with molecular, macromolecular and nanoparticle-based agents.
Co-reporter:David P. Cormode, Andrew J. Evans, Jason J. Davis and Paul D. Beer
Dalton Transactions 2010 - vol. 39(Issue 28) pp:NaN6541-6541
Publication Date(Web):2010/06/15
DOI:10.1039/C0DT00217H
A disulfide functionalized bis-ferrocene urea acyclic receptor and disulfide functionalized mono- and bis-ferrocene amide and urea appended upper rim calix[4]arene receptors were prepared for the fabrication of SAM redox-active anion sensors. 1H NMR and diffusive voltammetric anion recognition investigations revealed each receptor to be capable of complexing and electrochemically sensing anions via cathodic perturbations of the respective receptor's ferrocene/ferrocenium redox couple. SAMs of a ferrocene urea receptor 3 and ferrocene urea calixarene receptor 17 exhibited significant enhanced magnitudes of cathodic response upon anion addition as compared to observed diffusive perturbations. SAMs of 17 were demonstrated to sense the perrhenate anion in aqueous solutions.
Co-reporter:Xiliang Luo and Jason J. Davis
Chemical Society Reviews 2013 - vol. 42(Issue 13) pp:NaN5962-5962
Publication Date(Web):2013/04/24
DOI:10.1039/C3CS60077G
Electrical detection methodologies are likely to underpin the progressive drive towards miniaturised, sensitive and portable biomarker detection protocols. In being easily integrated within standard electronic microfabrication formats, and developing capability in microfluidics, the facile multiplexed detection of a range of proteins in a small analytical volume becomes entirely feasible with something costing just a few thousand pounds and benchtop or handheld in scale. In this review, we focus on recent important advances in label free assays of protein using a number of electrical methods, including those based on electrochemical impedance spectroscopy (EIS), amperometry/voltammetry, potentiometry, conductometry and field-effect methods. We introduce their mechanistic features and examples of application and sensitivity. The current state of the art, real world applications and challenges are outlined.
Co-reporter:Joshua Lehr, Manuel Tropiano, Paul D. Beer, Stephen Faulkner and Jason J. Davis
Chemical Communications 2015 - vol. 51(Issue 30) pp:NaN6517-6517
Publication Date(Web):2015/03/06
DOI:10.1039/C5CC01097G
Herein we demonstrate redox switchable emission from a sensitised, europium–ferrocene containing, molecular film assembled by a novel nitrene-based strategy. Electrochemical modulation of europium emission upon switching the ferrocene moiety's redox state is ascribed to the reversible generation of a quenching ferrocenium species.
Co-reporter:Joshua Lehr, Manuel Tropiano, Paul D. Beer, Stephen Faulkner and Jason J. Davis
Chemical Communications 2015 - vol. 51(Issue 88) pp:NaN15947-15947
Publication Date(Web):2015/09/08
DOI:10.1039/C5CC05738H
Herein we describe the first example of a ratiometric lanthanide luminescent oxygen sensing interface. Immobilisation of terbium and europium cyclen complexes on glass substrates was achieved by a novel aryl nitrene photografting approach. The resulting interfaces demonstrated a ratiometric oxygen response between 0 and 0.2 atm partial oxygen pressure.
Co-reporter:Wen-Yen Huang, Gemma-Louise Davies and Jason J. Davis
Chemical Communications 2013 - vol. 49(Issue 1) pp:NaN62-62
Publication Date(Web):2012/11/08
DOI:10.1039/C2CC37545A
Internally Gd doped mesoporous nanoparticles have been prepared and exhibit unprecedented relaxivities that are retained on external biomodification. In tuning diffusive water access, image contrast can be reversibly switched in the presence of a specific protein target.
Co-reporter:Jason J. Davis, Grzegorz A. Orlowski, Habibur Rahman and Paul D. Beer
Chemical Communications 2010 - vol. 46(Issue 1) pp:NaN63-63
Publication Date(Web):2009/10/22
DOI:10.1039/B915122B
Mechanically interlocked molecules are of considerable interest from data storage, molecular scale or sensory device perspectives. Though the solution phase characterisation of these compounds has been extensively explored, progress towards real world application will, in many cases, necessitate a detailed understanding of their interfacing with supportive, optically transparent or electroactive surfaces. This feature article summarises the developments made in surface assembly and characterisation including recent progress in exploiting templating methods to interlock molecular systems on surfaces.
Co-reporter:Thomas Bryan, Xiliang Luo, Lars Forsgren, Ludmilla A. Morozova-Roche and Jason J. Davis
Chemical Science (2010-Present) 2012 - vol. 3(Issue 12) pp:NaN3473-3473
Publication Date(Web):2012/09/11
DOI:10.1039/C2SC21221H
Protein aggregation, leading to amyloid deposition in the brain, is implicated in the pathology of a number of increasingly prevalent neurodegeneration states such as Parkinson's disease (PD), Alzheimer's disease and prion diseases. The body's protective response to the formation of such deposits is to generate specific autoimmune antibodies. Alpha-synuclein, a natively unfolded protein relatively abundant in the brain, is the main constituent of Lewy body amyloid dispositions in PD. Previous assays determining content of alpha-synuclein in bodily fluids have proven to be largely inconclusive. Here we have taken a novel approach in utilising alpha-synuclein modified electrodes to sample the autoantibodies generated as the body responds to changes in its homeostasis. We show that these electroanalytical assays not only robustly distinguish between disease state and control individuals but also map out disease progression with unprecedented sensitivity and clarity. The impedimetric electrode surfaces are highly specific, reusable, exhibit a linear range from 0.5 to 10 nM and a detection limit of 55 ± 3 pM. We believe electroanalyses such as these, possible with less than 10 microlitres of fluid and a total assay time of only a few minutes, to be of value for early diagnosis of PD and possibly other alpha-synucleinopathies, and for monitoring disease progression and effects of possible disease modifying interventions.
Co-reporter:Nicholas H. Evans, Habibur Rahman, Alexandre V. Leontiev, Neil D. Greenham, Grzegorz A. Orlowski, Qiang Zeng, Robert M. J. Jacobs, Christopher J. Serpell, Nathan L. Kilah, Jason J. Davis and Paul D. Beer
Chemical Science (2010-Present) 2012 - vol. 3(Issue 4) pp:NaN1089-1089
Publication Date(Web):2012/01/06
DOI:10.1039/C2SC00909A
The first examples of ferrocene containing catenanes, in solution and assembled on a surface are described. Chloride anion templation is exploited to synthesize redox-active [2]- and [3]-catenanes via Grubbs' ring closing metathesis, utilizing a novel ferrocene-appended isophthalamide macrocycle. X-ray crystal structures of both catenanes were determined. The ability of the [2]catenane to selectively bind and characteristically sense its chloride anion template is demonstrated by use of 1H NMR and electrochemical voltammetric techniques. Self-assembled monolayers of analogous surface-confined catenanes have been prepared on gold. In addition to being characterized by cyclic voltammetry and ellipsometry, detailed information regarding the structure of the catenane monolayers has been provided by use of angle integrated high resolution X-ray photoelectron spectroscopy.
Co-reporter:Simon R. Bayly, Thomas M. Gray, Michał J. Chmielewski, Jason J. Davis and Paul D. Beer
Chemical Communications 2007(Issue 22) pp:NaN2236-2236
Publication Date(Web):2007/05/08
DOI:10.1039/B701796K
Anion templation is used to assemble novel redox-active bis-ferrocene functionalised rotaxane self-assembled monolayers (SAMs) on to gold electrode surfaces; after template removal, the unique SAM rotaxane binding domain is capable of selectively sensing chloride ions electrochemically.
Co-reporter:Michał J. Chmielewski, Liyun Zhao, Asha Brown, David Curiel, Mark R. Sambrook, Amber L. Thompson, Sergio M. Santos, Vitor Felix, Jason J. Davis and Paul D. Beer
Chemical Communications 2008(Issue 27) pp:NaN3156-3156
Publication Date(Web):2008/05/09
DOI:10.1039/B804941F
The first example of anion templated pseudorotaxane formation between two neutral components in solution and in surface assembled monolayers is described.
Co-reporter:Joshua Lehr, Justin R. Weeks, Adriano Santos, Gustavo T. Feliciano, Melany I. G. Nicholson, Jason J. Davis and Paulo R. Bueno
Physical Chemistry Chemical Physics 2017 - vol. 19(Issue 23) pp:NaN15109-15109
Publication Date(Web):2017/05/12
DOI:10.1039/C7CP01500C
We have previously proposed, and experimentally resolved, an ionic charge relaxation model for redox inactive self-assembled monolayers (SAMs) on metallic electrodes in contact with a liquid electrolyte. Here we analyse, by capacitance spectroscopy, the resistance and capacitance terms presented by a range of thiolated molecular films. Molecular dynamics simulations support a SAM-specific energy barrier to solution-phase ions. Once surmounted, the entrapped ions support a film embedded ionic capacitance and non-faradaic relaxation, which can be assigned as a particular case of general electrochemical capacitance.
Co-reporter:Joshua Lehr, Paul D. Beer, Stephen Faulkner and Jason J. Davis
Chemical Communications 2014 - vol. 50(Issue 43) pp:NaN5687-5687
Publication Date(Web):2014/03/13
DOI:10.1039/C4CC01138D
Lanthanide ions, due to their unique photo-physical characteristics, have attracted considerable attention in recent years. Their long lifetimes, sharp, well-defined emission bands, and designable environmental sensitivity make them ideal for integration into switchable supramolecular assemblies where emission can report on local conformation and/or coupled energy levels (redox state). The immobilisation of lanthanide containing constructs on interfaces facilitates device integration, the fabrication of advanced sensory and molecular electronic platforms and presents a means by which conformational dynamics within molecular assemblies can be analysed. In this feature article we discuss the current and potential applications for lanthanide luminescence in supramolecular, switchable and surface bound architectures.
Co-reporter:Jason J. Davis, Wen-Yen Huang and Gemma-Louise Davies
Journal of Materials Chemistry A 2012 - vol. 22(Issue 43) pp:NaN22850-22850
Publication Date(Web):2012/09/25
DOI:10.1039/C2JM35116A
In tuning the sub-particle localisation of Gd(III) binding macrocycles within a mesoporous scaffold, nanoparticle contrast agents of unprecedented relaxivity and low Gd(III) loadings can be realised.
Co-reporter:Gemma-Louise Davies, Asha Brown, Octavia Blackburn, Manuel Tropiano, Stephen Faulkner, Paul D. Beer and Jason J. Davis
Chemical Communications 2015 - vol. 51(Issue 14) pp:NaN2920-2920
Publication Date(Web):2014/12/22
DOI:10.1039/C4CC09952D
Strong bidentate ligation between a fluorinated isophthalate and binuclear lanthanide-DO3A species yields a new class of 19F NMR agent with very high nuclear relaxation rates at physiologically-relevant pH.
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