Charles R. Martin

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Name: Martin, Charles R.

Organization: University of Florida , USA

Department: Department of Chemistry and Center for Research at the Bio/Nano Interface

Title: Professor(PhD)

Chemicals
References

An Alternating Current Electroosmotic Pump Based on Conical Nanopore Membranes

Co-reporter:Xiaojian Wu, Pradeep Ramiah Rajasekaran, and Charles R. Martin

ACS Nano 2016 Volume 10(Issue 4) pp:4637

Publication Date(Web):April 5, 2016

DOI:10.1021/acsnano.6b00939

Electroosmotic flow (EOF) is used to pump solutions through microfluidic devices and capillary electrophoresis columns. We describe here an EOF pump based on membrane EOF rectification, an electrokinetic phenomenon we recently described. EOF rectification requires membranes with asymmetrically shaped pores, and conical pores in a polymeric membrane were used here. We show here that solution flow through the membrane can be achieved by applying a symmetrical sinusoidal voltage waveform across the membrane. This is possible because the alternating current (AC) carried by ions through the pore is rectified, and we previously showed that rectified currents yield EOF rectification. We have investigated the effect of both the magnitude and frequency of the voltage waveform on flow rate through the membrane, and we have measured the maximum operating pressure. Finally, we show that operating in AC mode offers potential advantages relative to conventional DC-mode EOF pumps.Keywords: AC electroosmotic pump; conical nanopore; electroosmotic flow rectification; high pressure; ion-current rectification; nanofluidic diode

Low-Voltage Flow-Through Electroporation in Gold-Microtube Membranes

Co-reporter:Juliette Experton, Aaron G. Wilson, and Charles R. Martin

Analytical Chemistry 2016 Volume 88(Issue 24) pp:

Publication Date(Web):November 17, 2016

DOI:10.1021/acs.analchem.6b03820

Electroporation is used to create pores within the membrane of living cells in order to deliver a substance, for example, a gene, into the cytoplasm. To achieve the high electric field gradients required to porate the membrane, current electroporation devices deliver voltage pulses in the kV range to the cell medium. We describe a new device based on gold-microtube membranes that can accomplish electroporation with voltage pulses that are orders of magnitude smaller, ≤5 V. This is possible because the voltage pulses are applied to the gold microtubes resulting in large electric field gradients down the length of the tubes. We used COMSOL simulations to calculate the electric field gradients, and these theoretical results were compared with known experimental values required to electroporate Escherichia coli. We developed two fluorescence-based methods to demonstrate successful electroporation of E. coli. The percentages of electroporated bacteria were found to be more than an order of magnitude higher than obtained with a commercial electroporator, although the voltage employed was 500 times lower. Furthermore, this microtube membrane device is flow through and is therefore capable of continuous, as opposed to batch-wise, electroporation and cell analysis. Cell throughput of >30 million cells per min, higher than any previously reported device, were obtained.

Electroosmotic Flow Rectification in Membranes with Asymmetrically Shaped Pores: Effects of Current and Pore Density

Co-reporter:Gregory W. Bishop

The Journal of Physical Chemistry C 2015 Volume 119(Issue 29) pp:16633-16638

Publication Date(Web):June 2, 2015

DOI:10.1021/acs.jpcc.5b03510

We have recently demonstrated a new electrokinetic phenomenon—electroosmotic flow rectification in membranes with asymmetrically shaped pores. Flow rectification means that at constant driving force the flow rate in one direction through the membrane is faster than the flow rate in the opposite direction. EOF rectification could be of practical use in microfluidic devices incorporating porous membranes, but additional research is required. We explore here the effects of two key experimental variables—current density used to drive flow through the membrane and membrane pore density—on EOF rectification. We have found that the extent of EOF rectification, as quantified by the rectification ratio, increases with increasing current density. In contrast, the rectification ratio decreases with increasing membrane pore density. We propose explanations for these results based on simple EOF and membrane-transport theories.

Voltage Charging Enhances Ionic Conductivity in Gold Nanotube Membranes

Co-reporter:Peng Gao and Charles R. Martin

ACS Nano 2014 Volume 8(Issue 8) pp:8266

Publication Date(Web):July 25, 2014

DOI:10.1021/nn502642m

Ionically conductive membranes are used in many electrochemical processes and devices, including batteries, fuel cells, and electrolyzers. In all such applications, it is advantageous to use membranes with high ionic conductivity because membrane resistance causes a voltage loss suffered by the cell. We describe here a method for enhancing ionic conductivity in membranes containing small diameter (4 nm) gold nanotubes. This entails making the gold nanotube membrane the working electrode in an electrochemical cell and applying a voltage to the membrane. We show here that voltage charging in this way can increase membrane ionic conductivity by over an order of magnitude. When expressed in terms of the ionic conductivity of the electrolyte, κ, within an individual voltage-charged tube, the most negative applied voltage yielded a κ comparable to that of 1 M aqueous KCl, over 2 orders of magnitude higher than κ of the 0.01 M KCl solution contacting the membrane.Keywords: electrochemical energy; electrochemistry; electrolyte resistance; gold nanotubes; ionic conductivity; membrane resistance; nanotube membranes; voltage charging

Drug-Delivery Strategies by Using Template-Synthesized Nanotubes

Co-reporter:Jillian L. Perry;Jon D. Stewart

Chemistry - A European Journal 2011 Volume 17( Issue 23) pp:6296-6302

Publication Date(Web):

DOI:10.1002/chem.201002835

Abstract

Encapsulating drugs within hollow nanotubes offers several advantages, including protection from degradation, the possibility of targeting desired locations, and drug release only under specific conditions. Template synthesis utilizes porous membranes prepared from alumina, polycarbonate, or other materials that can be dissolved under specific conditions. The method allows for great control over the lengths and diameters of nanotubes; moreover, tubes can be constructed from a wide variety of tube materials including proteins, DNA, silica, carbon, and chitosan. A number of capping strategies have been developed to seal payloads within nanotubes. Combining these advances with the ability to target and internalize nanotubes into living cells will allow these assemblies to move into the next phase of development, in vivo experiments.

An Adsorption-Based Model for Pulse Duration in Resistive-Pulse Protein Sensing

Co-reporter:Lindsay T. Sexton ; Hitomi Mukaibo ; Parag Katira ; Henry Hess ; Stefanie A. Sherrill ; Lloyd P. Horne

Journal of the American Chemical Society 2010 Volume 132(Issue 19) pp:6755-6763

Publication Date(Web):April 22, 2010

DOI:10.1021/ja100693x

We have been investigating an electrochemical single-molecule counting experiment called nanopore resistive-pulse sensing. The sensor element is a conically shaped gold nanotube embedded in a thin polymeric membrane. We have been especially interested in counting protein molecules using these nanotube sensors. This is accomplished by placing the nanotube membrane between two electrolyte solutions, applying a transmembrane potential difference, and measuring the resulting ionic current flowing through the nanopore. In simplest terms, when a protein molecule enters and translocates the nanopore, it transiently blocks the ion current, resulting in a downward current pulse. We have found that the duration of such current-pulses are many orders of magnitude longer than the electrophoretic transport time of the protein through the nanotube detection zone. We develop here a simple model that accounts for this key, and previously explained, observation. This model assumes that the protein molecule engages in repeated adsorption/desorption events to/from the nanotube walls as it translocates through the detection zone. This model not only accounts for the long pulse duration but also for the triangular shape of the current pulse and the increase in the standard deviation of the pulse duration with increasing protein size. Furthermore, the results of our analyses are in general agreement with results obtained from other investigations of protein adsorption to surfaces. This includes the observations that smaller proteins stick more readily to the surface but remain adsorbed for shorter times than larger proteins. In addition, the sticking probabilities calculated from our data are in general agreement with results obtained from other methods.

Electroosmotic Flow Rectification in Pyramidal-Pore Mica Membranes

Co-reporter:Pu Jin ; Hitomi Mukaibo ; Lloyd P. Horne ; Gregory W. Bishop

Journal of the American Chemical Society 2010 Volume 132(Issue 7) pp:2118-2119

Publication Date(Web):February 1, 2010

DOI:10.1021/ja909335r

We demonstrate here a new electrokinetic phenomenon, Electroosmotic flow (EOF) rectification, in synthetic membranes containing asymmetric pores. Mica membranes with pyramidally shaped pores prepared by the track-etch method were used. EOF was driven through these membranes by using an electrode in solutions on either side to pass a constant ionic current through the pores. The velocity of EOF depends on the polarity of the current. A high EOF velocity is obtained when the polarity is such that EOF is driven from the larger base opening to the smaller tip opening of the pore. A smaller EOF velocity is obtained when the polarity is reversed such that EOF goes from tip to base. We show that this rectified EOF phenomenon is the result of ion current-rectification observed in such asymmetric-pore membranes.

Biosensing with conically shaped nanopores and nanotubes

Co-reporter:Youngseon Choi, Lane A. Baker, Heather Hillebrenner and Charles R. Martin

Physical Chemistry Chemical Physics 2006 vol. 8(Issue 43) pp:4976-4988

Publication Date(Web):07 Aug 2006

DOI:10.1039/B607360C

In this review we consider recent results from our group that are directed towards developing “smart” synthetic nanopores that can mimic the functions of biological nanopores (transmembrane proteins). We first discuss the preparation and characterization of conical nanopores synthesized using the track-etch process. We then consider the design and function of conical nanopores that can rectify the ionic current that flows through these pores under an applied transmembrane potential. Finally, two types of sensors that we have developed with these conical nanopores are described. The first sensor makes use of molecular recognition elements that are bound to the nanopore mouth to selectively block the nanopore tip, thus detecting the presence of the analyte. The second sensor makes use of conical nanopores in a resistive-pulse type experiment, detecting the analyte via transient blockages in ionic current.

Nanostructured Electrodes and the Low-Temperature Performance of Li-Ion Batteries

Co-reporter:C. R. Sides;C. R. Martin

Advanced Materials 2005 Volume 17(Issue 1) pp:

Publication Date(Web):13 JAN 2005

DOI:10.1002/adma.200400517

Template-synthesized V₂O₅ nanostructured electrodes (see Figure and cover) are used as tools for fundamental investigations into the poor low-temperature performance of Li-ion batteries. The electrodes consisted of nanofibers of V₂O₅, and by controlling the dimensions of the nanofibers it has been determined that the rate-limiting factor at low temperatures is the concentration polarization of the Li ion in the electrode material.

Cover Picture: Nanostructured Electrodes and the Low-Temperature Performance of Li-Ion Batteries (Adv. Mater. 1/2005)

Co-reporter:C. R. Sides;C. R. Martin

Advanced Materials 2005 Volume 17(Issue 1) pp:

Publication Date(Web):18 JAN 2005

DOI:10.1002/adma.200590003

The cover image shows a scanning electron micrograph of a commercially available track-etch polycarbonate filter. This porous membrane serves as the host for the template-synthesis of V₂O₅ nanowires of various diameters. Nanowires that are 70 nm in diameter are shown in the inset. Because V₂O₅ reversibly intercalates Li-ions, it has potential for use as a cathode material in Li-ion batteries. On p. 125, Sides and Martin report the use of these V₂O₅ nanowires as tools to investigate the poor low-temperature performance of Li-ion batteries.

Molecular filters: Pores within pores

Co-reporter:

Nature Materials 2004 3(5) pp:

Publication Date(Web):

DOI:10.1038/nmat1124

A composite membrane in which the nanoscopic pores of a material are aligned within the larger pores of a matrix brings us a step closer to the realization of molecular filters.

DNA-Functionalized Nanotube Membranes with Single-Base Mismatch Selectivity

Co-reporter:Punit Kohli;C. Chad Harrell;Zehui Cao;Rahela Gasparac;Weihong Tan

Science 2004 Vol 305(5686) pp:984-986

Publication Date(Web):13 Aug 2004

DOI:10.1126/science.1100024

Abstract

We describe synthetic membranes in which the molecular recognition chemistry used to accomplish selective permeation is DNA hybridization. These membranes contain template-synthesized gold nanotubes with inside diameters of 12 nanometers, and a “transporter” DNA-hairpin molecule is attached to the inside walls of these nanotubes. These DNA-functionalized nanotube membranes selectively recognize and transport the DNA strand that is complementary to the transporter strand, relative to DNA strands that are not complementary to the transporter. Under optimal conditions, single-base mismatch transport selectivity can be obtained.

The emerging field of nanotube biotechnology

Co-reporter:Charles R. Martin & Punit Kohli

Nature Reviews Drug Discovery 2003 2(1) pp:29

Publication Date(Web):

DOI:10.1038/nrd988

Nanoparticles are being developed for a host of biomedical and biotechnological applications, including drug delivery, enzyme immobilization and DNA transfection. Spherical nanoparticles are typically used for such applications, which reflects the fact that spheres are easier to make than other shapes. Micro- and nanotubes — structures that resemble tiny drinking straws — are alternatives that might offer advantages over spherical nanoparticles for some applications. This article discusses four approaches for making micro- and nanotubes, and reviews the current status of efforts to develop biomedical and biotechnological applications of these tubular structures.

Template-Fabricated Gold Nanowires and Nanotubes

Co-reporter:M. Wirtz;C.R. Martin

Advanced Materials 2003 Volume 15(Issue 5) pp:

Publication Date(Web):7 MAR 2003

DOI:10.1002/adma.200390106

Gold nanowires and nanotubes are prepared via electroless deposition of Au onto the pore walls of a porous polymeric membrane. The pores in the support membrane act as a template for the nanostructures. The support is a commercially available nanoporous polycarbonate filter with cylindrical nanoscopic pores. We have shown that by controlling the Au deposition time, Au nanotubes (short deposition times) or nanowires (longer deposition times) can be prepared. The gold nanowires and nanotube membranes can be utilized for nanoelectrode ensembles, molecular filters and as chemical switches.

Template synthesized gold nanotube membranes for chemical separations and sensing

Co-reporter:Marc Wirtz, Shufang Yu and Charles R. Martin

Analyst 2002 vol. 127(Issue 7) pp:871-879

Publication Date(Web):14 May 2002

DOI:10.1039/B201939F

We have developed a new class of synthetic membranes that consist of a porous polymeric support that contains an ensemble of gold nanotubes that span the thickness of the support membrane. The support is a commercially-available microporous polycarbonate filter with cylindrical nanoscopic pores. The gold nanotubes are prepared via electroless deposition of Au onto the pore walls; i.e., the pores acts as templates for the nanotubes. We have shown that by controlling the Au deposition time, Au nanotubes that have effective inside diameters of molecular dimensions (<1 nm) can be prepared. These membranes are a new class of molecular sieves and can be used to separate both small molecules and proteins on the basis of molecular size. In addition, the use of these membranes in new approaches to electrochemical sensing is reviewed here. In this case, a current is forced through the nanotubes, and analyte molecules present in a contacting solution phase modulate the value of this transmembrane current.

Molecular Sieving and Sensing with Gold Nanotube Membranes

Co-reporter:Marc Wirtz;Matthew Parker;Yoshio Kobayashi

The Chemical Record 2002 Volume 2(Issue 4) pp:

Publication Date(Web):19 JUL 2002

DOI:10.1002/tcr.10027

We have developed a new class of synthetic membranes that consist of a porous polymeric support that contains an ensemble of gold nanotubes that span the thickness of the support membrane. The support is a commercially available microporous polycarbonate filter with cylindrical nanoscopic pores. The gold nanotubes are prepared via electroless deposition of Au onto the pore walls; i.e., the pores act as templates for the nanotubes. We have shown that by controlling the Au deposition time, Au nanotubes that have effective inside diameters of molecular dimensions (<1 nm) can be prepared. These nanotube membranes can be used to cleanly separate small molecules on the basis of molecular size. Furthermore, use of these membranes as a novel electrochemical sensor is also discussed. This new sensing scheme involves applying a constant potential across the Au nanotube membrane and measuring the drop in the transmembrane current upon the addition of the analyte. This paper reviews our recent progress on size-based transport selectivity and sensor applications in this new class of membranes. © 2002 The Japan Chemical Journal Forum and Wiley Periodicals, Inc. Chem Rec 2:259–267, 2002: Published online in Wiley InterScience (www.interscience.wiley.com) DOI 10.1002/tcr.10027

Template-Synthesized Nanotubes for Chemical Separations and Analysis

Co-reporter:Marc Wirtz Dr.;Matthew Parker;Yoshio Kobayashi

Chemistry - A European Journal 2002 Volume 8(Issue 16) pp:

Publication Date(Web):29 JUL 2002

DOI:10.1002/1521-3765(20020816)8:16<3572::AID-CHEM3572>3.0.CO;2-9

We have developed a new class of synthetic membranes that consist of a porous polymeric support that contains an ensemble of gold nanotubes that span the thickness of the support membrane. The support is a commercially-available microporous polycarbonate filter with cylindrical nanoscopic pores. The gold nanotubes are prepared by electroless deposition of Au onto the pore walls, that is, the pores acts as templates for the nanotubes. We have shown that by controlling the Au deposition time, Au nanotubes that have effective inside diameters of molecular dimensions (<1 nm) can be prepared. These nanotube membranes can be used to cleanly separate small molecules on the basis of molecular size. Furthermore, use of these membranes as a novel electrochemical sensor is also discussed. This new sensing scheme involves applying a constant potential across the Au nanotube membrane and measuring the drop in the transmembrane current upon the addition of the analyte. This paper reviews our recent progress on size-based based transport selectivity and sensor applications in this new class of membranes.

Controlling Ion-Transport Selectivity in Gold Nanotubule Membranes

Co-reporter:C. R. Martin;M. Nishizawa;K. Jirage;M. Kang;S. B. Lee

Advanced Materials 2001 Volume 13(Issue 18) pp:

Publication Date(Web):5 SEP 2001

DOI:10.1002/1521-4095(200109)13:18<1351::AID-ADMA1351>3.0.CO;2-W

We have developed a new class of synthetic membranes that consist of a porous polymeric support. This support contains an ensemble of gold nanotubules that span the complete thickness of the support membrane. The support is a commercially available microporous polycarbonate filter with cylindrical nanoscopic pores. The gold nanotubules are prepared via electroless deposition of Au onto the pore walls, and tubules that have inside diameters of molecular dimensions (<1 nm) can be prepared. Hence, these membranes are a new class of molecular sieves. We review in this paper the ion-transport properties of these Au nanotubule membranes. We will show that these membranes can be cation-permselective or anion-permselective, and that the permselectivity can be reversibly switched between these two states. Ion permselectivity can be introduced by two different routes. The first entails chemisorption of an ionizable thiol, e.g., a carboxylated or ammonium-containing thiol to the Au tubule walls. If the thiol contains both of these functionalities (e.g., the amino acid cysteine), the permselectivity can be reversibly switched by varying the pH of the contacting solution phase. Ion permselectivity can also be introduced by potentiostatically charging the membrane in an electrolyte solution. By applying excess negative charge, cation permselective membranes are obtained, and excess positive charge yields anion permselective membranes. In this case the permselectivity can be reversibly switched by changing the potential applied to the membrane.

Nanomaterial-based Li-ion battery electrodes

Co-reporter:Naichao Li, Charles R. Martin, Bruno Scrosati

Journal of Power Sources 2001 Volumes 97–98() pp:240-243

Publication Date(Web):July 2001

DOI:10.1016/S0378-7753(01)00760-1

We have been exploring the use of the template method to prepare nanostructured Li-ion battery electrodes. These nanostructured electrodes show improved rate capabilities relative to thin-film control electrodes prepared from the same material. In this paper we discuss nanostructured Sn-based anodes. Li-ion battery anodes derived from oxides of tin have been of considerable recent interest because they can, in principle, store over twice as much Li+ as graphite. However, large volume changes occur when Li+ is inserted and removed from these Sn-based materials, and this causes internal damage to the electrode resulting in loss of capacity and rechargability. We describe here a new nanostructured SnO2-based electrode that has extraordinary rate capabilities, can deliver very high capacities (e.g. >700 mAh g−1 at 8°C), and still retain the ability to be discharged and recharged through as many as 800 cycles. These electrodes, prepared via the template method, consist of monodisperse 110 nm-diameter SnO2 nanofibers protruding from a current-collector surface like the bristles of a brush. The dramatically-improved rate and cycling performance is related to the small size of the nanofibers that make up the electrode and the small domain size of the Sn grains within the nanofibers.

Electrochemistry of phenothiazine and methylviologen biosensor electron-transfer mediators at nanoelectrode ensembles

Co-reporter:Barbara Brunetti, Paolo Ugo, Ligia M Moretto, Charles R Martin

Journal of Electroanalytical Chemistry 2000 Volume 491(1–2) pp:166-174

Publication Date(Web):8 September 2000

DOI:10.1016/S0022-0728(00)00169-8

Gold nanoelectrode ensembles (NEEs) have been prepared by using an electroless plating method to deposit disk-shaped Au electrode elements (diameter=38 nm) within the pores of a microporous polycarbonate template membrane. The electrochemistry of three electron-transfer mediators used for biosensors based on reductase enzymes — two phenothiazines (Azure A and B) and methylviologen — were investigated at these NEEs. As has been observed previously, detection limits obtained at the NEE are lower than corresponding detection limits for a Au disk electrode of conventional dimensions (diameter=3.2 mm, called a macro electrode here). However, the enhancement in the detection limit at the NEE depends on the E1/2 value of the mediator used. All three of these mediators have more negative E1/2 values than the redox couples investigated previously at such NEEs. As such, their voltammetric waves are close to the negative limit for Au in the pH 7.4 buffer used as the electrolyte. The effects of background currents, associated with proton reduction, on the detection limits were investigated. At the macro electrode, the voltammograms for the phenothiazines are distorted by adsorption of the reduced forms to the electrode surface. This adsorption process is concentration dependent. The lower detection limits obtained at the NEE allow for the use of lower mediator concentrations, and this unwanted adsorption process can be eliminated at the NEE. Finally, we report here the first use of the NEEs for the determination of standard heterogeneous rates constants.