The 2014–16 Ebola virus (EBOV) outbreak in West Africa has attracted widespread concern. Rapid and sensitive detection methods are urgently needed for diagnosis and treatment of the disease. Here, we propose a novel method for EBOV detection based on efficient amplification of electroluminescent nanospheres (ENs) coupled with immunomagnetic separation. Uniform ENs are made by embedding abundant amounts of CdSe/ZnS quantum dots (QDs) into copolymer nanospheres through simple ultrasound. Compared to QDs, ENs can enhance electroluminescence (ECL) signals by approximately 85-fold, achieving a signal-to-background ratio high enough for EBOV detection. The introduction of magnetic nanobeads (MBs) can selectively separate targets from complex samples, simplifying the operation process and saving time. The presence of MBs can amplify ECL by approximately 3-fold, improving detection sensitivity. By integration of ENs with MBs, a sensitive electroluminescence biosensor is established for EBOV detection. The linear range is 0.02–30 ng/mL with a detection limit of 5.2 pg/mL. This method provides consistent reproducibility, specificity, and anti-interference ability and is highly promising in clinical diagnosis applications.

Rapid detection of highly contagious pathogens is the key to increasing the probability of survival and reducing infection rates. We developed a sensitive and quantitative lateral flow assay for detection of Ebola virus (EBOV) glycoprotein with a novel multifunctional nanosphere (RNs@Au) as a reporter. Each RNs@Au contains hundreds of quantum dots and dozens of Au nanoparticles and can achieve enhanced dual-signal readout (fluorescence signal for quantitative detection and colorimetric signal for visual detection). Antibody (Ab) and streptavidin (SA) were simultaneously modified onto the RNs@Au to label the target and act as signal enhancer. After the target was labeled by the Ab–RNs@Au–SA and captured on the test line, biotin-modified RNs@Au was used to amplify the dual signal by the reaction of SA with biotin. The assay enables naked-eye detection of 2 ng/mL glycoprotein within 20 min, and the quantitative detection limit is 0.18 ng/mL. Additionally, the assay has been successfully tested in field work for detecting EBOV in spiked urine, plasma, and tap water samples and is thus a promising candidate for early diagnosis of suspect infections in EBOV-stricken areas.

Virus-induced cell migration plays important roles in the direct and rapid spread of virus particles. As cell migration is also regulated by shear stress, it is necessary to explore the cell migration behavior influenced by multiple factors including a virus and shear stress. In this report, a three-layer microfluidic chip with symmetric channels was designed and fabricated to investigate vaccinia virus-induced cell migration in different shear stress environments. Regular “exclusion zones” without cell damage were formed by microvalves. The results showed that infected cells were more elongated and tended to migrate along the flow direction compared to the random cell migration under static conditions. Meanwhile, shear stress enhanced the natural directional persistence and accelerated the velocity of infected cell migration. Moreover, reduced peripheral lamellae and the axial lamella being confined to the flow direction were responsible for the increased directionality of cell migration under shear stress. Interestingly, in the presence of shear stress, the Golgi complex reoriented and relocated behind the nucleus and aligned to the flow direction in infected migratory cells accompanied by the rearrangement of the cytoskeleton. Our report reveals the cell migration behavior in the multi-environment of virus infection and shear stress based on the microfluidic cell migration assay platform. It helps us to deeply understand the interactions between the virus, host cells, and surrounding microenvironment.

As an ideal nanovector candidate, microvesicles (MVs) have been gradually utilized for packaging kinds of functional molecules for effective tumor diagnosis and therapy; however, the deficiency of their tumor targeting influenced their therapy efficacy. Through a facile phospholipid substitution strategy, MVs-based drug delivery system (DDS) was apparently endowed with high tumor targeting toward breast cancer thanks to the modified folate onto the membrane of MVs, simultaneously possessing a synergistic antitumor effect, and in vivo tumor imaging attributed to the SA-QDs labeling. Tumor killing effect could be improved up to 15 percentages with the help of the improved tumor targeting ability.Keywords: in vivo imaging; microvesicles; phospholipid substitution; synergistic therapy; tumor targeting;

•CTCs and WBCs were efficiently and specifically labeled with different IFNs tags.•Simultaneous capture and identification of CTCs were realized by coupled IMNs and IFNs.•One-step strategy shortened time consumption and improved efficiency of CTC detection.•The strategy was cell-friendly to detect viable CTCs for culture and functional study.Detecting viable circulating tumor cells (CTCs) without disruption to their functions for in vitro culture and functional study could unravel the biology of metastasis and promote the development of personalized anti-tumor therapies. However, existing CTC detection approaches commonly include CTC isolation and subsequent destructive identification, which damages CTC viability and functions and generates substantial CTC loss. To address the challenge of efficiently detecting viable CTCs for functional study, we develop a nanosphere-based cell-friendly one-step strategy. Immunonanospheres with prominent magnetic/fluorescence properties and extraordinary stability in complex matrices enable simultaneous efficient magnetic capture and specific fluorescence labeling of tumor cells directly in whole blood. The collected cells with fluorescent tags can be reliably identified, free of the tedious and destructive manipulations from conventional CTC identification. Hence, as few as 5 tumor cells in ca. 1 mL of whole blood can be efficiently detected via only 20 min incubation, and this strategy also shows good reproducibility with the relative standard deviation (RSD) of 8.7%. Moreover, due to the time-saving and gentle processing and the minimum disruption of immunonanospheres to cells, 93.8±0.1% of detected tumor cells retain cell viability and proliferation ability with negligible changes of cell functions, capacitating functional study on cell migration, invasion and glucose uptake. Additionally, this strategy exhibits successful CTC detection in 10/10 peripheral blood samples of cancer patients. Therefore, this nanosphere-based cell-friendly one-step strategy enables viable CTC detection and further functional analyses, which will help to unravel tumor metastasis and guide treatment selection.

The detection of circulating tumor cells (CTCs), a kind of “liquid biopsy”, represents a potential alternative to noninvasive detection, characterization and monitoring of carcinoma. Many previous studies have shown that the number of CTCs has a significant relationship with the stage of cancer. However, CTC enrichment and detection remain notoriously difficult because they are extremely rare in the bloodstream. Herein, aided by a microfluidic device, an immunomagnetic separation system was applied to efficiently capture and in situ identify circulating tumor cells. Magnetic nanospheres (MNs) were modified with an anti-epithelial-cell-adhesion-molecule (anti-EpCAM) antibody to fabricate immunomagnetic nanospheres (IMNs). IMNs were then loaded into the magnetic field controllable microfluidic chip to form uniform IMN patterns. The IMN patterns maintained good stability during the whole processes including enrichment, washing and identification. Apart from its simple manufacture process, the obtained microfluidic device was capable of capturing CTCs from the bloodstream with an efficiency higher than 94%. The captured cells could be directly visualized with an inverted fluorescence microscope in situ by immunocytochemistry (ICC) identification, which decreased cell loss effectively. Besides that, the CTCs could be recovered completely just by PBS washing after removal of the permanent magnets. It was observed that all the processes showed negligible influence on cell viability (viability up to 93%) and that the captured cells could be re-cultured for more than 5 passages after release without disassociating IMNs. In addition, the device was applied to clinical samples and almost all the samples from patients showed positive results, which suggests it could serve as a valuable tool for CTC enrichment and detection in the clinic.

Single molecule electrochemistry (SME) has gained much progress in fundamental studies, but it is difficult to use in practice due to its less reliability. We have solved the reliability of single molecule electrochemical detection by integration of digital analysis with efficient signal amplification of enzyme-induced metallization (EIM) together with high-throughput parallelism of microelectrode array (MA), establishing a digital single molecule electrochemical detection method (dSMED). Our dSMED has been successfully used for alkaline phosphatase (ALP) detection in the complex sample of liver cancer cells. Compared to direct measurement of the oxidation current of enzyme products, EIM can enhance signals by about 100 times, achieving signal-to-background ratio high enough for single molecule detection. The integration of digital analysis with SME can further decrease the detection limit of ALP to 1 aM relative to original 50 aM, enabling dSMED to be sensitively, specifically and reliably applied in liver cancer cells. The presented dSMED is enormously promising in exploring physical and chemical properties of single molecules, single biomolecular detection, or single-cell analysis.

With the combination of the two parts, the sample can be purified before detection and the detection can be conducted on chip, so the device possesses stronger anti-interference ability and the detection results are more reliable.By controlling the flow rate of sample and buffer, the magnetophoretic separation unit can separate and enrich the target pathogens.The capture of target pathogens was conducted in the tube, we can remove the particulates in food samples before injected into the chip, avoiding the clog of channel.The on chip detection can save regents and reduce costs, and the continuous washing steps can greatly reduce the clean-up time and sample loss.Foodborne illnesses have always been a serious problem that threats public health, so it is necessary to develop a method that can detect the pathogens rapidly and sensitively. In this study, we designed a magnetic controlled microfluidic device which integrated the dynamic magnetophoretic separation and stationary magnetic trap together for sensitive and selective detection of Salmonella typhimurium (S. typhimurium). Coupled with immunomagnetic nanospheres (IMNs), this device could separate and enrich the target pathogens and realize the sensitive detection of target pathogens on chip. Based on the principle of sandwich immunoassays, the trapped target pathogens identified by streptavidin modified QDs (SA-QDs) were detected under an inverted fluorescence microscopy. A linear range was exhibited at the concentration from 1.0×104 to 1.0×106 colony-forming units/mL (CFU/mL), the limit of detection (LOD) was as low as 5.4×103 CFU/mL in milk (considering the sample volume, the absolute detection limit corresponded to 540 CFU). Compared with the device with stationary magnetic trap alone, the integrated device enhanced anti-interference ability and increased detection sensitivity through dynamic magnetophoretic separation, and made the detection in complex samples more accurate. In addition, it had excellent specificity and good reproducibility. The developed system provides a rapid, sensitive and accurate approach to detect pathogens in practice samples.

•A kind of bifunctional magnetic nanobeads were fabricated.•Enzyme-induced metallization was integrated to construct animmunosensor.•The proposed immunosensor could be applied directly in complex samples.Bifunctional magnetic nanobeads (bi-MBs) were fabricated by co-immobilizing target recognition molecules and signal molecules on a magnetic nanobead surface, which were used as both separation and enrichment carriers and signal carriers. The bi-MBs could capture and separate avian influenza A (H7N9) virus (H7N9 AIV) from complex samples efficiently based on the specific reaction between antigen–antibody and their good magnetic response, which simplified sample pretreatment and saved the detection time. Taking advantages of their high surface to volume ratio and rich surface functional groups, multiple alkaline phosphatase (ALP) signal molecules were tethered on the surface of bi-MBs which greatly amplified the detection signal. As an efficient signal amplification strategy, enzyme-induced metallization had been integrated with bi-MBs and anodic stripping voltammetry to construct an ultrasensitive electrochemical immunosensor for H7N9 AIV detection. Under the optimal conditions, the introduction of bi-MBs could amplify the detection signal in about four times compared with the same immunoassay without MBs, and the method showed a wide linear range of 0.01–20 ng/mL with a detection limit of 6.8 pg/mL. The electrochemical immunosensor provides a simple and reliable platform with high sensitivity and selectivity which shows great potential in early diagnosis of diseases.

A novel colorimetric assay method based on enzyme-induced metallization has been proposed for detection of alkaline phosphatase (ALP), and it was further applied to highly sensitive detection of avian influenza virus particles coupled with immunomagnetic separation. The enzyme-induced metallization-based color change strategy combined the amplification of the enzymatic reaction with the unique optical properties of metal nanoparticles (NPs), which could lead to a great enhancement in optical signal. The detection limit for ALP detection was 0.6 amol/50 μL which was 4–6 orders of magnitude more sensitive than other metal NP-based colorimetric methods. Moreover, this technique was successfully employed to a colorimetric viral immunosensor, which could be applied to complex samples without complicated sample pretreatment and sophisticated instruments, and a detection limit as low as 17.5 pg mL–1 was achieved. This work not only provides a simple and sensitive sensing approach for ALP and virus detection but also offers an effective signal enhancement strategy for development of a highly sensitive nonaggregation metal NP-based colorimetric assay method.

Simple sequence repeat (SSR) markers are widely used for genome mapping, genetic diversity characterization and medical diagnosis. The fast isolation by AFLP of sequence containing repeats (FIASCO) is a powerful method for SSR marker isolation, but it is laborious, costly, and time consuming and requires multiple rounds of washing. Here, we report a superparamagnetic bead (SPMB)-based FIASCO method in a magnetic field controllable microfluidic chip (MFCM-Chip). This method dramatically reduces the assay time by 4.25-fold and reduces the quantity of magnetic beads and probes by 10-fold through the magnetic capture of (AG)n-containing fragments from Herba Leonuri, followed by washing and eluting on a microchip. The feasibility of this method was further evaluated by PCR and sequencing, and the results showed that the proportion of fragments containing SSRs was 89%, confirming that this platform is a fast and efficient method for SSR marker isolation. This cost-effective platform will make the powerful FIASCO technique more accessible for routine use with a wide variety of materials.

A simple and robust approach to control the magnetic field distribution by nickel powder@PDMS pillars was established. The nickel powder@PDMS pillars were fabricated in several simple steps, using a simple and robust method, and no training in techniques or expensive equipment is necessary compared to other methods. The localized magnetic field distributions in microchannels can be tailored by the nickel powder@PDMS pillars with automatic generation of high magnetic field gradients around them due to the high relative magnetic permeability of the nickel powder@PDMS. The numerical simulation and red fluorescent magnetic nanoparticle capture experiment results convinced us that our approach could effectively control the localized magnetic field distribution in the microchannels. Two kinds of tailoring events were studied at the powder@PDMS pillars in the microchannels underneath two different external magnetic fields. To the best of our knowledge, this is the first time different localized magnetic field distributions have been obtained in microchannels by nickel powder@PDMS pillars due to different external magnetic fields. This approach was used to capture fluorescent magnetic nanoparticles and magnetic bead–yeast cell complexes. We believe that this approach has great potential applications in chemistry, biology, biomedicine and tissue engineering.

Picoliter droplets were developed as microreactors for ultrafast and continuous synthesis of multi-color, water-soluble CdTe quantum dots (QDs). Through a slight change in the local controllable reaction temperature of 1–2 °C, we could obtain a series of different colored fluorescent QDs in about 1 min.

Labeling of viruses can be used to reveal viral infection pathways and screen potential anti-viral drugs. Complex procedures, including virus cultivation, purification and labeling are involved in traditional virus labeling methods. And the manipulation of living virus brings risk to researcher health. In this work, we report a general method for site-specific labeling of the envelope virus in an integrated microfluidic device with simple procedures and high security. Site-specific labeling of virus was achieved by fusing the biotin acceptor peptide (AP-tag) and the biotin ligase enzyme (BirA enzyme) with the envelope protein GP64 of baculovirus. The AP-tag could be modified by BirA enzyme to introduce the biotin moiety onto the viral envelope. Western blots and fluorescence colocalization analysis proved that the baculoviruses were biotinylated and labeled with high efficiency. The integrated device incorporated several operation steps including cell seeding, cell culture, cell transfection, virus culture and virus labeling. Since virus biotinylation was achieved during the process of virus cultivation, the complex procedures of virus labeling were simplified in our device. Furthermore the whole process could be completed in the integrated microfluidic device, and direct contact between viruses and researchers could be eliminated in our method, which could greatly reduce the risk to researcher health during living virus labeling.

In this work, we reported a simple rapid and point-of-care magnetic immunofluorescence assay for avian influenza virus (AIV) and developed a portable experimental setup equipped with an optical fiber spectrometer and a microfluidic device. We achieved the integration of immunomagnetic target capture, concentration, and fluorescence detection in the microfluidic chip. By optimizing flow rate and incubation time, we could get a limit of detection low up to 3.7 × 104 copy/μL with a sample consumption of 2 μL and a total assay time of less than 55 min. This approach had proved to possess high portability, fast analysis, high specificity, high precision, and reproducibility with an intra-assay variability of 2.87% and an interassay variability of 4.36%. As a whole, this microfluidic system may provide a powerful platform for the rapid detection of AIV and may be extended for detection of other viral pathogens; in addition, this portable experimental setup enables the development of point-of-care diagnostic systems while retaining adequate sensitivity.

•This immunosensor is based on immunomagnetic separation and bienzymatic system.•HRP modified electrode was fabricated by LBL technique with excellent properties.•The electrode could be regenerated with a simple washing procedure.•The detection could be finished in a short time with high sensitivity.•The proposed immunosensor could be applied to complex samples.A novel electrochemical immunosensor based on the integration of immunomagnetic separation and bienzymatic amplification for sensitive detection of virus particles was fabricated in this work. The bienzymatic strategy was realized by using the first enzyme as tracer tagged on immunomagnetic beads which could be accumulated on the magneto controlled home-made Au electrode (m-AuE) and the second enzyme immobilized on the m-AuE by layer-by-layer (LBL) assembly technique. The proposed immunosensor not only provides a rapid, simple, cost-effective and on-site platform with high sensitivity, selectivity, and reproducibility for early diagnosis but also presents a new approach for sensitive magneto immunoassay.

A sandwich immunoassay method for rapid detection of dual cancer biomarkers in serum on a magnetic field controllable microfluidic chip (MFCM-Chip) was established. A nickel pattern was used to generate high magnetic field gradients to increase the magnetic force on the superparamagnetic beads (SPMBs), which enabled the rapid generation of controllable SPMB patterns in microfluidic channels. The SPMB patterns could keep stable during the fast continuous washing process even at a flow rate of 50 μL/min. This approach demonstrated excellent specificity because the fast continuous washing could remove non-specifically adsorptive contaminants more efficiently than fixed volume batch washing. This approach was used to simultaneously detect carcinoma embryonic antigen (CEA) and α-fetoprotein (AFP) directly in serums. The whole on-chip detection was finished within 40 min, which was much faster than conventional enzyme-linked immunosorbent assay (ELISA) method. High luminescent streptavidin modified QDs (SA-QDs) were used as fluorescence indicators, and the detection limits were 3.5 ng/mL and 3.9 ng/mL for CEA and AFP, respectively. The linear ranges were from 10.0 ng/mL to 800.0 ng/mL. With the high sensitivity, high selectivity and short assay time, this approach could be used for rapid, high throughput detection of cancer biomarkers in clinical trials.Highlights► An approach for on-chip dual detection of cancer biomarkers was developed. ► Serum samples could be directly analyzed with this method. ► This approach is time-saving and low reagent consumption.

Microarray technology has been proved to be greatly helpful for biomedical and biological diagnosis. And the evaluation of its biological applications lies in the detection sensitivity, which requires high intensity and stability of the signal. Recently, several nanomaterials, especially semiconductor nanomaterials, due to their excellent fluorescence properties, have been widely used to construct microarrays for biosensors. Here, we presented an approach for constructing CdSe/ZnS quantum dot (QD) microarray in microfluidic channels on a glass slide by photolithography. The conditions for immobilizing stable and uniform QD microarray on the glass slide were optimized. Several types of QD microarrays with different emission wavelengths and modified groups were constructed using silanization and lithography technology. Based on the fluorescence quenching effect of Cu2+ on QDs, the microfluidic chip with QD microarray was applied for the determination of Cu2+. 1 nmol/L Cu2+ could be detected by this method.

As is well known, controlling the local magnetic field distribution on the micrometer scale in a microfluidic chip is significant and has many applications in bioanalysis based on magnetic beads. However, it is a challenge to tailor the magnetic field introduced by external permanent magnets or electromagnets on the micrometer scale. Here, we demonstrated a simple approach to controlling the local magnetic field distribution on the micrometer scale in a microfluidic chip by nickel patterns encapsulated in a thin poly(dimethylsiloxane) (PDMS) film under the fluid channel. With the precisely controlled magnetic field, magnetic bead patterns were convenient to generate. Moreover, two kinds of fluorescent magnetic beads were patterned in the microfluidic channel, which demonstrated that it was possible to generate different functional magnetic bead patterns in situ, and could be used for the detection of multiple targets. In addition, this method was applied to generate cancer cell patterns.

Droplet-based microfluidic chips have shown great advantages in fields of chemical and biological researches. Based on the different wettabilities of water, IL (ionic liquid, 1-butyl-3-methylimidazolium hexafluorophosphate) and soybean oil in hydrophobic channels, three kinds of droplet pairs (including an alternating water–IL droplet chain, connected water–IL droplet pairs and separated water–IL droplet pairs) were generated for the first time in soybean oil on microfluidic chips containing double flow-focusing regions. The influences of fluid flow rate and channel geometry on droplet pair formation were carefully studied.

Quantum dots (QDs) have been used as a new class of bioprobes in medical imaging in recent years. The study of interaction between QDs and biomacromolecules is important for interpreting biological data. In this work, Rayleigh light scattering (RLS) was employed to investigate the nonspecific interaction between mercaptoacetic acid modified CdSe/ZnS quantum dots (MAA–QDs) and human immunoglobulin G (IgG). The conjugation processes between QDs and IgG in different conditions including addition sequence, pH were carefully studied. The addition of IgG to QDs solution was found to form a fixed size of QDs–IgG conjugate, with the QDs-to-IgG ratio of ∼13, while the addition of QDs to IgG solution resulted in a gradually increased conjugate size, with variable QDs-to-IgG ratio till the binding saturation was reached.

The performance of electrochemical sensor is related to the surface structure of electrode. Electrochemical treatment was often used to improve the performance of glassy carbon electrodes (GCEs) for the simplicity of operation. The densely compact oxide film formed on the surface of the electro-oxidized glassy carbon electrodes (GCEs-ox) could be changed to be porous by following electro-reduction of the GCEs-ox obtaining the totally reduced GCEs-ox (GCEs-re). The GCEs-re with a porous film exhibited high sensitivity in detecting epinephrine (EP) accompanying with poor stability and incapability of anti-interference from negatively charged ascorbic acid (AA) because both of AA and EP could permeate the porous film. Compared to the GCEs-re, the GCEs-ox with a densely compact film displayed relatively lower sensitivity but higher stability. To combine the advantages of both porous and densely compact oxide films, a partially reduced GCE-ox (GCE-ox-re) with an oxide film porous outer and densely compact inner was designed by controlling the electro-reduction time and potential, which will provide a new strategy for improving the performance of GCEs. The GCEs-ox-re exhibited high sensitivity, excellent stability and high selectivity in the detection of EP. In the presence of 0.1 mM AA, the anodic peak current of EP was directly proportional to its concentration in the range of 8.0 × 10−9–2.0 × 10−7 M and EP as low as 2.0 × 10−9 M could be detected.

Ionic liquids (ILs) as a kind of novel green solvent are being widely used in various researches related to the life sciences and chemistry, which demands the knowledge of interaction between ILs and biomacromolecules. However, the almost completely inert optical, electric, thermal properties of ILs make it difficult to directly obtain information about the interactions. Herein, by using a hydrophilic ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate ([bmim]BF4) as a model, the electrostatic interaction between ILs and calf thymus DNA (ctDNA) was investigated by a surface electrochemical micromethod. A convenient and simple method was established to obtain the thermodynamic and kinetic information about the DNA-IL interaction only with microscale sample consumption. The quantitative thermodynamic and kinetic parameters about the interaction of [bmim]BF4 and ctDNA, such as the binding constant (K), the Gibbs energy of surface binding (ΔGb), and the dissociation rate constant (k), were obtained for the first time.

The effects of Li+ and polyethylene glycol (PEG) on the genetic transformation of Saccharomyces cerevisiae were investigated by using fluorescence microscopy (FM) to visualize the binding of plasmid DNA labeled with YOYO-1 to the surface of yeast cells, scanning electron microscopy (SEM) and atomic force microscopy (AFM) to image the change in surface topography of yeast cells, coupled with transformation frequency experiments. The results showed that under the same conditions, the transformation frequencies of yeast protoplasts were much higher than those of intact yeast cells. PEG was absolutely required for the binding of DNA to the surface of intact yeast cells or yeast protoplasts, and had no effect on the surface topography of intact yeast cells or yeast protoplasts. In the presence of PEG, Li+ could greatly enhance the binding of plasmid DNA to the surface of intact yeast cells, increase their transformation frequency, and affect their surface topography. On the other hand, no effect on the DNA binding to the surface of protoplasts and no increase in the number of transformants and no surface topography changes were found upon the treatment with Li+ to protoplasts. In the present work, the effects of Li+ and PEG on yeast genetic transformation were directly visualized, rather than those deduced from the results of transformation frequencies. These results indicate that cell wall might be a barrier for the uptake of plasmid DNA. Li+ could increase the permeability of yeast cell wall, then increase the exposed sites of DNA binding on intact yeast cells. The main role of PEG was to induce DNA binding to cell surface.

As is known to us all, quantum dots (QDs), the fluorescent semiconductor nanocrystals, have many excellent optical properties which make them attractive fluorescent tags in single-molecule tracking in live cells. Because the intracellular environment is so complex, this paper aimed at simulating the intracellular solution environment in vitro and investigated the influence of the solution environment on the diffusion of water-soluble core/shell CdSe/ZnS QDs. Single-particle tracking (SPT) was applied to measure the diffusion coefficients of two water-soluble core/shell QDs, CTAB-modified CdSe/ZnS QDs (CTAB-QDs) and octylamine-modified poly(acrylic acid)-modified CdSe/ZnS QDs (OPA-QDs). The exposure time was optimized to be 29.95 ms. Then the paper was focused on the effects of pH value, salt concentration, and solution viscosity on the diffusion coefficients of the two water-soluble QDs. The results demonstrated that the pH value had a great influence on the diffusion coefficient of CTAB-QDs but little on that of OPA-QDs. The difference should be mainly due to the distinguishment of the charge and structure of surface ligands on the two water-soluble QDs. The diffusion coefficient of either CTAB-QDs or OPA-QDs was hardly affected by the salt concentration of the solution. Furthermore, for both CTAB-QDs and OPA-QDs, the diffusion coefficients decreased as the solution viscosity increased, which obeyed the Stokes−Einstein relation. In summary, OPA-QDs have more promising applications in single-molecule tracking in live cells, as compared with CTAB-QDs. The obtained results would benefit the further applications of QDs in single-molecule tracking in live cells. This system could also serve as a model system for studying the diffusion behavior of nanoparticles.

A glassy carbon electrode (GCE) modified with multi-wall carbon nanotubes (MCNTs) was achieved by electrodeposition process directly from the MCNT suspension, and the modified electrode was used to examine the phenylephrine (PHE) oxidation in phosphate solutions. Experimental results showed that the oxidation of PHE at the modified electrode was a one-electron/one-proton process controlled by diffusion and the modified electrode exhibited excellent behavior for PHE determination, clearly outperforming GCE. In a range 1 × 10−7–7 × 10−6 mol L−1 the peak current varied linearly with the concentration of PHE, and the detection limit reached 3 × 10−8 mol L−1, which could be used as a basis for determining PHE.

Carboxylic multi-wall carbon nanotubes (MWCNT) were directly cast onto the glassy carbon electrode to fabricate the MWCNT modified electrode, which showed good stability and reproducibility. The modified electrode exhibited good promotion to the electrochemical reaction of theophylline (TP) and greatly enhanced the peak currents. The possible mechanism of the catalytic oxidation of TP was investigated by means of cyclic voltammetry and UV–Vis spectroscopy. Under optimal conditions there was a good linear relationship between anodic peak current and TP concentration in the range from 3 × 10−7 to 1 × 10−5 mol L−1, and a detection limit of 5 × 10−8 mol L−1 (S/N = 3) was achieved after 2 min of open-circuit accumulation. The MWCNT modified electrode can be applied to determination of TP in drug.

Picoliter droplets were developed as microreactors for ultrafast and continuous synthesis of multi-color, water-soluble CdTe quantum dots (QDs). Through a slight change in the local controllable reaction temperature of 1–2 °C, we could obtain a series of different colored fluorescent QDs in about 1 min.