Chaogui Chen

Solid-State Probe Based Electrochemical Aptasensor for Cocaine: A Potentially Convenient, Sensitive, Repeatable, and Integrated Sensing Platform for Drugs

Aptamers, which are artificial oligonucleotides selected in vitro, have been employed to design novel biosensors (i.e., aptasensors). In this work, we first constructed a label-free electrochemical aptasensor introducing a probe immobilization technique by the use of a layer-by-layer (LBL) self-assembled multilayer with ferrocene-appended poly(ethyleneimine) (Fc-PEI) on an indium tin oxide (ITO) array electrode for detection of cocaine. The Fc-PEI and gold nanoparticles (AuNPs) were LBL assembled on the electrode surface via electrostatic interaction. Then, cocaine aptamer fragments, SH-C2, were covalently labeled onto the outermost AuNP layer. When the target cocaine and cocaine aptamer C1 were present simultaneously, the SH-C2 layer hybridized partly with C1 to bind the cocaine, which led to a decreased differential pulse voltammetry (DPV) signal of Fc-PEI. This DPV signal change could be used to sensitively detect cocaine with the lowest detectable concentration down to 0.1 microM and the detection range up to 38.8 microM, which falls in the the expected range for medical use of detecting drug abuse involving cocaine. Meanwhile, the sensor was specific to cocaine in complex biologic fluids such as human plasma, human saliva, etc. The sensing strategy had general applicability, and the detection of thrombin could also be realized, displayed a low detection limit, and exhibited worthiness to other analytes. The aptasensor based on the array electrode held promising potential for integration of the sensing ability in multianalysis for simultaneous detection.

Au NPs-enhanced surface plasmon resonance for sensitive detection of mercury(II) ions.

We reported a sensitive surface plasmon resonance (SPR) sensor for the detection of Hg(2+) in aqueous solution by using a thymine (T)-rich, mercury-specific oligonucleotide (MSO) probe and gold nanoparticles (Au NPs)-based signal amplification. The MSO probe was first immobilized on gold film through formation of Au-S bond between DNA and gold film. In the presence of Hg(2+), the MSO probe captured free Hg(2+) in aqueous media via the Hg(2+)-mediated coordination of T-Hg(2+)-T base pairs. This direct immobilization strategy led to a detection limit of 0.3 microM of Hg(2+). In order to improve the sensitivity, part complementary DNA (PCS)-modified Au NPs labels were employed to amplify SPR signals. We demonstrated that this Au NPs-based sensing strategy resulted in a detection limit down to 5 nM of Hg(2+), brings about an amplification factor of two orders of magnitude. This Au NPs-based Hg(2+) sensor also exhibited excellent selectivity over a spectrum of interference metal ions. Taking advantage of the high amplifying characteristic of Au NPs and the specificity of MSO to Hg(2+) recognition, we developed here a SPR sensor for specific Hg(2+) detection with high sensitivity.

Integrated self-powered microchip biosensor for endogenous biological cyanide.

In this work we developed a fully integrated biofuel cell on a microchip, which consisted of glucose dehydrogenase supported (carbon nanotubes/thionine/gold nanoparticles)(8) multilayer as the anode, and the (carbon nanotubes/polylysine/laccase)(15) multilayer as the cathode. The as-obtained biofuel cell produced open circuit potential 620 mV and power density 302 microW cm(-2), showing great potential as a small power resource of portable electronics. Most importantly, for the first time we demonstrated the feasibility of developing a self-powered biosensor based on the inhibitive effect on microchip enzyme biofuel cell. With cyanide employed as the model analyte, this method showed a linear range of 3.0 x 10(-7) to 5.0 x 10(-4) M and a detection limit with 1.0 x 10(-7) M under the optimal conditions. The detection limit was lower than the acceptable cyanide concentration in drinking water (1.9 x 10(-6) M) according to the World Health Organization (WHO). This self-powered sensor was successfully used to detect the cyanide concentration in a real sample, cassava, which is the main carbohydrate resource in South America and Africa. This presented biosensor combined with a resistor and a multimeter demonstrated the general applicability as a fast and simple detection method in the determination of endogenous biological cyanide.

Microfluidic Electrochemical Aptameric Assay Integrated On-Chip: A Potentially Convenient Sensing Platform for the Amplified and Multiplex Analysis of Small Molecules

Aptamers are artificial oligonucleotides that have been widely employed to design biosensors (i.e., aptasensors). In this work, we report a microfluidic electrochemical aptamer-based sensor (MECAS) by constructing Au-Ag dual-metal array three-electrode on-chip for multiplex detection of small molecules. In combination with the microfluidic channels covering on the glass chip, different targets are transported to the Au electrodes integrated on different positions of the chip. These electrodes are premodified by different kinds of aptamers, respectively, to fabricate different sensing interfaces which can selectively capture the corresponding target. It is an address-dependent sensing platform; thus, with the use of only one electrochemical probe, multitargets can be recognized and detected according to the readout on a corresponding aptamer-modified electrode. In the sensing strategy, the electrochemical probe, [Ru(NH(3))(6)](3+) (RuHex), which can quantitatively bind to surface-confined DNA via electrostatic interaction, was used to produce chronocoulometric signal; Au nanoparticles (AuNPs) were used to improve the sensitivity of the sensor by amplifying the detection signals. Moreover, the sensing interface fabrication, sample incubation, and electrochemical detection were all performed in microfluidic channels. By using this detection chip, we achieved the multianalysis of two model small molecules, ATP, and cocaine, in mixed samples within 40 min. The detection limit of ATP was 3 × 10(-10) M, whereas the detection limit of cocaine was 7 × 10(-8) M. This Au-Ag dual metal electrochemical chip detector integrated MECAS was simple, sensitive, and selective. Also it is similar to a dosimeter which accumulates signal upon exposure. It held promising potential for designing electrochemical devices with high throughput, high automation, and high integration in multianalysis.

New Insight into a Microfluidic-Based Bipolar System for an Electrochemiluminescence Sensing Platform

In this work, a novel style of a microfluidic-based bipolar system with two-direction driving electrodes and dual-channel configuration was described for the first time, which could reach 100% current efficiency in theory. More importantly, the background signal from the integrated driving electrodes was completely eliminated, when this unique design was used to construct an electrochemiluminescence (ECL) sensing platform. First, universal pH indicator was employed to study the mechanism and demonstrate that this new bipolar system possessed 100% current efficiency theoretically. Then, the Ru(bpy)₃²⁺/TPrA ECL system was introduced to construct the dual-channel bipolar ECL sensing platform, and the results of visual ECL experiments proved that the background signals from the driving electrodes were completely dispelled with our design. To illustrate the promising applications of this dual-channel device, TPrA, dopamine (DA), H₂O₂, and K₃Fe(CN)₆ were detected as model targets under different principles.

Layer-by-layer electrochemical biosensor with aptamer-appended active polyelectrolyte multilayer for sensitive protein determination

Herein, we report two simple label-free electrochemical aptasensors for protein detection using layer-by-layer (LBL) self-assembled multilayers with ferrocene-appended poly(ethyleneimine) (Fc-PEI), carbon nanotubes (CNTs) and aptamer. In one sensing strategy, the Fc-PEI, CNTs and DNA aptamer are LBL assembled on the electrode surface via electrostatic interaction. In the presence of target, the aptamer on the outermost layer of the LBL self-assembled multilayer would catch the target on the electrode interface, which makes a barrier for electrons and inhibits the electro-transfer, resulting in the decreased DPV signals of Fc-PEI. Using this strategy, a wide detection range (0.3-165 ng ml(-1)) for model target thrombin is obtained, with a low detection limit of 0.14 ng ml(-1). In the similar sensing strategy for detection of lysozyme, a wide detection range (0.2 ng ml(-1) to 1.66 microg ml(-1)) and a low detection limit (0.17 ng ml(-1)) are obtained. These results prove that the LBL sensing strategies developed possess sensitivity, selectivity, stability and generality.

Microfabricated on-chip integrated Au–Ag–Au three-electrode system for in situ mercury ion determination

In this paper, a new two-step photolithography fabrication method is used for the fabrication of an on-chip integrated two-metal electrode system, with a Ag reference electrode and two gold electrodes used as working and counter electrodes, respectively. Combined with a microfluidic channel, the total detector has the advantages of ease of use, low analyte consumption, fast sensing time and is suited for in situ target metal ion determination. Herein, the three-electrode system was used for Hg(2+) ion measurement, and both the capabilities of Au working and Ag reference electrodes were characterized by using electrochemical techniques. The results show that the as-prepared on-chip integrated electrochemical detector performed with high sensitivity and good reproducibility in Hg(2+) determination. The detection range extends from 10 to 1000 ppb with a good linear correlation, and the detection limit is low to 3 ppb (S/N = 3). Our method provides a rapid and effective, miniaturized electrochemical analysis platform in Hg(2+) measurement and demonstrates great potential for the application of in situ or on-line mercuric pollutant analysis.

Fabrication of a sensor chip containing Au and Ag electrodes and its application for sensitive Hg(II) determination using chronocoulometry

In this work, we explored a novel fabrication method to construct Au and Ag electrodes on chip, utilizing the different solubility of gold and silver in different etching solutions. KI-I(2) etching solution and 50% HNO(3) were chosen to dissolve the metal layers alternatively. Planar electrodes with gold and silver could be simultaneously and accurately patterned on chip using photolithographic technique. The as-prepared electrode could be directly served as integrated three-electrode system for electrochemical measurement. Based on it, a sensing strategy has been carried out using home-made electrochemical sensing (ECS) chip, which depended on the competition of double strand DNA and Hg(II)-mediated T-T base pairs (T-Hg(II)-T). Actually, a mercury specific oligonucleotide (MSO) was immobilized onto the thus-fabricated gold working electrode and employed as the sensing element. Chronocoulometry (CC) was chosen to monitor the differences of surface charge volume and quantify the concentrations of Hg(II) ions with a low detection limit down to 1nM. Therefore, a facile method to fabricate Au and Ag electrodes has been demonstrated to simplify the production of ECS chip. The ECS chip was finally used for constructing an effective sensing platform for sensitive Hg(II) determination, which held promising potential for designing ECS chip in lab-on-a-chip device or point-of-care diagnosis.

Portable and Visual Electrochemical Sensor Based on the Bipolar Light Emitting Diode Electrode

Here we report a novel sensing strategy based on the closed bipolar system, in which we utilize a light emitting diode (LED) to connect a split bipolar electrode (BPE) and generate the luminescent signal in the presence of the target. With this design, we have constructed a BPE array for the quick and high-throughput determination of various electroactive substances with naked eyes. Due to the ultrahigh current efficiency of the closed bipolar system, the sample concentration can be reported by the luminous intensity of the inserted LED without the expensive luminescent agent and instruments. Besides, the stability of the signal is improved because of the electroluminescent property of the LED. To demonstrate the promising applications of the bipolar LED electrode (BP-LED-E), the rapid quantification of four model targets (H2O2, ascorbic acid (AA), glucose, and blood sugar) has been achieved based on different principles.

Multiplexed bioactive paper based on GO@SiO2@CeO2 nanosheets for a low-cost diagnostics platform

In this paper, Graphene oxide@SiO2@CeO2 hybrid nanosheets (GSCs) have been successfully synthesized by the wet-chemical strategy. TEM, FITR and XPS were applied to characterize the morphology and composition of the nanosheets. The colorimetric assay of these nanosheets indicated that they possessed high intrinsic peroxidase activity, which should be ascribed to the combination of graphene oxide and CeO2. A fully integrated reagentless bioactive paper based on GSCs was fabricated, which were able to simultaneously detect glucose, lactate, uric acid and cholesterol. The results demonstrated that GSCs have great potential as an alternative to the commonly employed peroxidase in daily nursing and general physical examination.