Sensitive electrochemical detection of enrofloxacin in eggs based on carboxylated multi-walled carbon nanotubes-reduced graphene oxide nanocomposites: Molecularlyimprintedrecognition versus direct electrocatalytic oxidation.

A sensitive electrochemical method for detecting enrofloxacin was proposed using carboxylated multi-walled carbon nanotubes-reduced graphene oxide (MWCNT-COOH-RGO) nanocomposites. The MWCNT-COOH-RGO nanocomposites were firstly electrodeposited on a bare electrode, followed by electropolymerization of molecularly imprinted polymers. Enrofloxacin was determined by the mechanisms of direct electrocatalytic oxidation and molecularly imprinted recognition, respectively. Under the optimized conditions, a response range of 5.0×10-7 M to 5.5×10-5 M and limit of detection (LOD) of 2.3×10-7 M were obtained by direct electrocatalytic oxidation of enrofloxacin using chronoamperometry. By contrast, the response range of 1.0×10-10 M to 5.0×10-5 M and LOD of 2.5×10-11 M were achieved by molecularly imprinted recognition of enrofloxacin using square-wave voltammetry. Moreover, the proposed method exhibited good repeatability, stability and selectivity, and could be used for enrofloxacin detection in egg samples with satisfactory results.

Highly sensitive detection of fluoride based on poly(3-aminophenylboronic acid)-reduced graphene oxide multilayer modified electrode.

A novel electrochemical method for detecting fluoride was developed based on gold electrode modified by layer-by-layer (LBL) assembly of poly(3-aminophenylboronic acid)-reduced graphene oxide (PAPBA-RGO) multilayers. The PAPBA-RGO multilayer-modified gold electrode was constructed by using alternating LBL assembly of RGO and PAPBA on a bare gold electrode by one-step electrodeposition. Fluoride was electrochemically determined based on the proposed modified electrode by evaluating the changes in peak current for potassium ferricyanide reduction caused by the conjunction of fluoride and boronic acid groups of PAPBA. The results indicated that the peak current for potassium ferricyanide reduction obviously decreased with the increasing fluoride concentration. The response range of our method for fluoride was 1 × 10-8 to 1 × 10-1 M with a detection limit of 6 × 10-10 M and high sensitivity and selectivity. This method was applied to detect fluoride in tap water, rice, apple, and edible fungi samples.

A novel biosensor array with a wheel-like pattern for glucose, lactate and choline based on electrochemiluminescence imaging.

Electrochemiluminescence (ECL) imaging provides a superior approach to achieve array detection because of its ability for ultrasensitive multiplex analysis. In this paper, we reported a novel ECL imaging biosensor array modified with an enzyme/carbon nanotubes/chitosan composite film for the determination of glucose, choline and lactate. The biosensor array was constructed by integrating a patterned indium tin oxide (ITO) glass plate with six perforated poly(dimethylsiloxane) (PDMS) covers. ECL is generated by the electrochemical reaction between luminol and hydrogen peroxide that is produced by the enzyme catalysed oxidation of different substrates with molecular oxygen, and ECL images were captured by a charge-coupled device (CCD) camera. The separated electrochemical micro-cells enabled simultaneous assay of six samples at different concentrations. From the established calibration curves, the detection limits were 14 µM for glucose, 40 µM for lactate and 97 µM for choline, respectively. Moreover, multicomponent assays and cross reactivity were also studied, both of which were satisfied for the analysis. This biosensing platform based on ECL imaging shows many distinct advantages, including miniaturization, low cost, and multi-functionalization. We believe that this novel ECL imaging biosensor platform will have potential applications in clinical diagnostics, medicine and food inspection.

Integrating bipolar electrochemistry and electrochemiluminescence imaging with microdroplets for chemical analysis.

Here we develop a microdroplet sensor based on bipolar electrochemistry and electrochemiluminescence (ECL) imaging. The sensor was constructed with a closed bipolar cell on a hybrid poly(dimethylsioxane) (PDMS)-indium tin oxide (ITO) glass microchip. The ITO microband functions as the bipolar electrode and its two poles are placed in two spatially separate micro-reservoirs predrilled on the PDMS cover. After loading microliter-sized liquid droplets of tris(2,2'-bipyridyl) ruthenium (II)/2-(dibutylamino) ethanol (Ru(bpy)3(2+)/DBAE) and the analyte to the micro-reservoirs, an appropriate external voltage imposed on the driving electrodes could induce the oxidation of Ru(bpy)3(2+)/DBAE and simultaneous reduction of the analyte at the anodic and cathodic poles, respectively. ECL images generated by Ru(bpy)3(2+)/DBAE oxidation at the anodic pole and the electrical current flowing through the bipolar electrode can be recorded for quantitative analyte detection. Several types of quinones were selected as model analytes to demonstrate the sensor performance. Furthermore, the cathodic pole of bipolar electrode can be modified with (3-aminopropyl)triethoxysilane-gold nanoparticles-horseradish peroxidase composites for hydrogen peroxide detection. This microdroplet sensor with a closed bipolar cell can avoid the interference and cross-contamination between analyte solutions and ECL reporting reagents. It is also well adapted for chemical analysis in the incompatible system, e.g., detection of organic compounds insoluble in water by aqueous ECL generation. Moreover, this microdroplet sensor has advantages of simple structure, high sensitivity, fast response and wide dynamic response, providing great promise for chemical and biological analysis.

Proton-coupled O2 reduction reaction catalysed by cobalt phthalocyanine at liquid/liquid interfaces.

Pushed over the edge: Proton-transfer coupled O(2) reduction catalysed by cobalt phthalocyanine ([CoPc]) was studied at the water/1,2-dichloroethane (DCE) interface (see figure). This system represents a new model of molecular electrocatalysis with the proton transfer controlled by the Galvani potential difference and the electron transfer by the molecular properties of the catalyst and electron donor.

Microfluidic droplet-based liquid/liquid extraction modulated by the interfacial Galvani potential difference.

With a microfluidic droplet-based liquid/liquid extraction setup, we demonstrate that the extraction of an ionic analyte from complex matrices can be modulated by the interfacial Galvani potential difference and the extraction equilibrium follows the classical Nernst equation.

Mode-filtered light methane gas sensor based on cryptophane A.

A mode-filtered light sensor has been developed for methane (CH(4)) gas determination at ambient conditions. The proposed chemosensor consisted of an annular column which was constructed by inserting an optical fiber coated with a thin silicone cladding of cryptophane A into a fused-silica capillary. When CH(4) was introduced to the sensor, selective inclusion of CH(4) into the silicone layer would cause a change in the local refractive index of the cladding, resulting in the change of mode-filtered light that emanated from the fiber. Three detection windows were set alongside the capillary to propagate the light to a charge-coupled device (CCD). The changes of mode-filtered light on exposure to various concentrations of CH(4) were thus simultaneously monitored. The mode-filtered light intensity decreased with the increase in concentration of CH(4). The dynamic concentration range of the sensor for CH(4) was 0.0-16.0% v/v with a detection limit of 0.15% v/v. The highest sensitivity was found at the channel furthest away from the excitation light source. The response time (t(95%)) was about 5min. The reproducibility was good with a relative standard deviation (RSD) of less than 7% from evaluating six cryptophane A-coated fibers. Oxygen, hydrogen and carbon dioxide showed very little interference on detection but interferences from dichloromethane and carbon tetrachloride were observed. The proposed mode-filtered light sensor has been successfully applied to determine CH(4) samples and the accuracy was good. Our work offers a promising approach for CH(4) detection.