Conductive Hydrogel-Based Electrochemical Sensor: A Soft Platform for Capturing Analyte

Electrode modifications for electrochemical sensors attract a lot of attention every year. Among them, hydrogels are a relatively special class of electrode modifier. Since hydrogels often contain polymers, even though they are conductive polymers, they are not ideal electrode modifiers because of their poor conductivity. However, the micro-aqueous environment and the three-dimensional structure of hydrogels are an excellent platform for immobilizing bioactive molecules and maintaining their activity. This gives the hydrogel-modified electrochemical sensor the potential to perform specific recognition. At the same time, the rapid development of nanomaterials also makes the composite hydrogel have good electrical conductivity. This has led many scientists to become interested in hydrogel-based electrochemical sensors. In this review, we summarize the development process of hydrogel-based electrochemical sensors, starting from 2000. Hydrogel-based electrochemical sensors were initially used only as a carrier for biomolecules, mostly for loading enzymes and for specific recognition. With the widespread use of noble metal nanoparticles and carbon materials, hydrogels can now be used to prepare enzyme-free sensors. Although there are some sporadic studies on the use of hydrogels for practical applications, the vast majority of reports are still limited to the detection of common model molecules, such as glucose and H2O2. In the review, we classify hydrogels according to their different conducting strategies, and present the current status of the application of different hydrogels in electrochemical sensors. We also summarize the advantages and shortcomings of hydrogel-based electrochemical sensors. In addition, future prospects regarding hydrogel for electrochemical sensor use have been provided at the end

Preparation of β-cyclodextrin functionalized reduced graphene oxide: application for electrochemical determination of paracetamol

β-Cyclodextrin functionalized reduced graphene oxide (β-CD/RGO) was successfully prepared using a simple wet chemical method. The β-CD/RGO nanohybrid was characterized by UV-vis spectroscopy, FTIR, Raman spectroscopy, TEM and SEM. The results confirmed that β-CD had effectively covered the RGO surface. The β-CD/RGO nanohybrid modified glassy carbon electrode was employed for the sensitive electrochemical determination of paracetamol. Cyclic voltammetry measurements indicated that β-CD/RGO could significantly enhance the electrochemical response of paracetamol due to the outstanding electronic properties of RGO sheets and the high supramolecular recognition and enrichment capability of β-CD. The experimental factors were investigated and optimized. Under optimized conditions, the amperometric oxidation currents of paracetamol were linearly proportional to the concentration in the range of 0.01 to 0.8 mM with a detection limit of 2.3 μM (S/N = 3). Furthermore, the proposed sensor exhibited an excellent anti-interference property and acceptable reproducibility

Preparation and electrocatalytic properties of polydopamine functionalized reduced graphene oxide-silver nanocomposites

Polydopamine functionalized reduced graphene oxide-silver nanoparticle (PDA-RGO/Ag NP) nanocomposites were successfully prepared by a simple and mild procedure. Graphene oxide (GO) sheets were firstly coated with PDA via a self-polymerization process which provided an excellent interface for in-situ growing silver nanoparticles. Fourier transform infrared spectroscopy (FTIR) confirmed the successful coating of PDA and informed the reduction of the surface functional groups of GO. The formation of reduced GO and silver NPs was further evidenced by UV-Vis and X-ray diffraction spectroscopy. The as-prepared PDA-RGO/Ag nanocomposites could greatly enhance the electrochemical reduction of hydrogen peroxide (H2O2). This excellent performance was attributed to the increased effective electrode surface area due to the deposition of nano-sized Ag particles and graphene. The PDA-RGO/Ag-based electrochemical sensor displayed a rapid amperometric response for H2O2 measurement with a wide linear range from 0.5 μM to 8 mM and a low detection limit of 2.07 μM

Ultrasensitive Immunoassay based on amplified inhibition of the Electrochemical Stripping Signal of Silver Nanocomposite by Silica Nanoprobe

A silver nanocomposite was one - step synthesized in chitosan solution and used to prepare an immunosensor with the aid of gold nanoparticles (Au NPs) assembly. The Ag NPs at the immunosensor exhibited sensitive electrochemical stripping signal in KCl solution. After a sandwich immunoreaction, the current response of the immunosensor decreased due to the formation of antibody - antigen immunocomplex on its surface, which was greatly amplified by the captured silica nanoprobes and thus enabled an ultrasensitive electrochemical immunoassay method. This method showed excellent analytical performance for human IgG measurement including wide linear range, low detection limit, cheap cost, satisfactory reproducibility and stability

Amplified inhibition of the electrochemical signal of ferrocene by enzyme-functionalized graphene oxide nanoprobe for ultrasensitive immunoassay

A nanoprobe-induced signal inhibition mechanism was designed for ultrasensitive electrochemical immunoassay at a chitosan-ferrocene (CS-Fc) based immunosensor. The nanoprobe was prepared by covalently loading signal antibody and high-content horseradish peroxidase (HRP) on the graphene oxide (GO) nanocarrier. The immunosensor was prepared through the stepwise assembly of gold nanoparticles (Au NPs) and capture antibody at a CS-Fc modified electrode. After sandwich immunoreaction, the GO-HRP nanoprobes were quantitatively captured onto the immunosensor surface and thus induced the production of a layer of insoluble film through the enzymatically catalytic reaction of the HRP labels. Both the dielectric immunocomplex formed on the immunosensor surface and the enzymatic precipitate with low electroconductivity led to the electrochemical signal decease of the Fc indicator, which was greatly amplified by the multi-enzyme signal amplification of the nanoprobe. Based on this amplified signal inhibition mechanism, a new ultrasensitive electrochemical immunoassay method was developed. Using carcinoembryonic antigen as a model analyte, this method showed a wide linear range over 5 orders of magnitude with a detection limit down to 0.54 pg/mL. Besides, the immunosensor showed good specificity, acceptable reproducibility and stability as well as satisfactory reliability for the serum sample analysis

Enzymatic deposition of gold nanoparticles at vertically aligned carbon nanotubes for electrochemical stripping analysis and ultrasensitive immunosensing of carcinoembryonic antigen

Herein we combine the sandwich immunoreaction at a vertically aligned single-walled carbon nanotube (SWCNT)-based immunosensor and the enzymatically catalytic deposition of gold nanoparticles (Au NPs) by a gold nanoprobe to develop a novel electrochemical immunosensing method. The vertically arranged nanostructure was prepared through the covalent linking of terminally carboxylated SWCNTs at an aryldiazonium-modified electrode. It not only provides an excellent platform for the high density immobilization of antibodies to obtain the immunosensor but also serves as useful molecular wires to accelerate electron transfer during the electrochemical immunosensing process. Meanwhile, the enzymatic reaction of the nanoprobe prepared by surface functionalization of the nanocarrier of Au NPs by high-content glucoamylases can catalyze the deposition of a large number of Au NPs at the immunosensor. The electrochemical stripping analysis of these nanoparticles enabled the convenient signal transduction of the method. Due to the sensitive gold stripping analysis at the vertically aligned SWCNTs and the multi-enzyme signal amplification of the nanoprobe, the electrochemical signal response was greatly enhanced. Thus, the method can be used for the ultrasensitive detection of the tumor biomarker of carcinoembryonic antigen in a wide linear range of 5 orders of magnitude with a low detection limit of 0.48 pg mL(-1). Considering its obvious performance superiorities, this immunosensing method exhibits an extensive prospect for practical applications

Development of Ag dendrites-reduced graphene oxide composite catalysts via galvanic replacement reaction

Silver dendrites/reduced graphene oxide (AgD/RGO) composites were synthesized via a facile galvanic replacement method. The successful formation of Ag dendrites and the graphene oxide reduction were proved by a series of characterization techniques. The possible formation mechanism of Ag dendrites during the galvanic replacement reaction was discussed. The catalytic activity of the as-synthesized AgD/RGO composite was evaluated by its performance on the chemical reduction of an organic dye methylene blue. The AgD/RGO composite showed a much higher catalytic performance and stability than that of Ag dendrites

Enzymatically catalytic deposition of gold nanoparticles by glucose oxidase-functionalized gold nanoprobe for ultrasensitive

A novel ultrasensitive immunoassay method was developed by combination of the enzymatically catalytic gold deposition with the prepared gold nanoprobe and the gold stripping analysis at an electrochemical chip based immunosensor. The immunosensor was constructed through covalently immobilizing capture antibody at a carbon nanotube (CNT) modified screen-printed carbon electrode. The gold nanoprobe was prepared by loading signal antibody and high-content glucose oxidase (GOD) on the nanocarrier of gold nanorod (Au NR). After sandwich immunoreaction, the GOD-Au NR nanoprobe could be quantitatively captured onto the immunosensor surface and then induce the deposition of gold nanoparticles (Au NPs) via the enzymatically catalytic reaction. Based on the electrochemical stripping analysis of the Au NR nanocarriers and the enzymatically produced Au NPs, sensitive electrochemical signal was obtained for the immunoassay. Both the GOD-induced deposition of Au NPs by the nanoprobe and the sensitive electrochemical stripping analysis on the CNTs based sensing surface greatly amplified the signal response, leading to the ultrahigh sensitivity of this method. Using carcinoembryonic antigen as a model analyte, excellent analytical performance including a wide linear range from 0.01 to 100ng/mL and a detection limit down to 4.2pg/mL was obtained. In addition, this immunosensor showed high specificity and satisfactory reproducibility, stability and reliability. The relatively positive detection potential excluded the conventional interference from dissolved oxygen. Thus this electrochemical chip based immunosensing method provided great potentials for practical applications

Nanocomposite coating of multilayered carbon nanotube-titania

In this paper, we report a multiwalled carbon nanotube (MWCNT)/TiO 2 composite film fabricated via a solution-based layer-by-layer self-assembly technique. The thin film deposition procedure was recorded by a UV/Vis spectrometer, which showed a linear increasing of absorbance with the bilayer number. X-ray diffraction analysis confirmed the formation of anatase titania after heat treatment. The enhanced photocatalytic property of the composite thin film was evaluated by its capacity to degrade rhodamine B under the UV radiation. Compared with TiO2 thin film, the MWCNT/TiO 2 composite film showed a much higher photocatalytic performance. A 30 bilayer composite thin film (ca. 0.24 mg catalyst) was capable of completely degrading 10 mL of 2 mg/L Rh B solution within 5 h. The results also indicated that the hybrid catalyst could be reused for several cycles

One-pot preparation of graphene/gold nanocomposites for ultrasensitive nonenzymatic electrochemical immunoassay

A graphene/gold nanoparticles (Au NPs) composite was one-pot synthesized to design a new gold nanoprobe for electrochemical immunoassay. After sandwich immunoreaction at a carbon nanotubes (CNTs)-based immunosensor, the nanoprobes were quantitatively captured on the immunosensor surface and produced sensitive signal response through the electrochemical stripping analysis of Au NP labels. Both the multi-label signal amplification of nanoprobe and the electrode modification of CNTs greatly improved the signal response resulting in the development of an ultrasensitive immunoassay method for human IgG measurement. Additionally, this method also showed wide linear range, high specificity as well as satisfactory reproducibility, stability and reliability