Yong J. Yuan

Bond-rupture immunosensors—A review

It has long been the goal of researchers to develop fast and reliable point-of-care alternatives to existing lab-based tests. A viable point-of-care biosensor is fast, reliable, simple, cost-effective, and detects low concentrations of the target analyte. The target of biosensors is biological such as bacteria or virus and as such, the antibody-antigen bond derived from the real immune response is used. Biosensor applications include lab-based tests for the purposes of diagnostics, drug discovery, and research. Additional applications include environmental, food, and agricultural monitoring. The main merits of the bond-rupture method are quick, simple, and capable of discriminating between specific and non-specific interactions. The separation of specific and non-specific bonds is important for working in real-life complex serums such as blood. The bond-rupture technique can provide both qualitative results, the detection of a target, and quantitative results, the concentration of target. Bond-rupture achieves this by a label-free method requiring no pre-processing of the analyte. A piezoelectric transducer such as the quartz crystal microbalance (QCM) shakes the bound particles free from the surface. Other transducers such as Surface Acoustic Wave (SAW) are also considered. The rupture of the bonds is detected as electronic noise. This review article links diverse research areas to build a picture of a field still in development.

In-situ electrochemical studies on the redox properties of polypyrrole in aqueous solutions

Two electropolymerization techniques have been used in preliminary research on polypyrrole, such as potential cycling and galvanostatic modes. The cyclic voltammograms and chronopotentiograms can describe the proceeding of the growth of polypyrrole from various aqueous solutions. The cyclic voltammetry of a polypyrrole film in an electrolyte solution can further characterize the polypyrrole films electrochemically. Some evidence has been shown of doping with cations. Polypyrrole differs with respect to the extent of oxidation, doping anions, and also reduction, doping cations. Such properties can be switched dynamically between anion and cation coupling or hopping through electrochemical oxidation and reduction of the polypyrrole backbone.

Study on the formation of the Prussian blue films on the polypyrrole Surface as a potential mediator system for biosensing applications

Abstract The formation of a Prussian blue film under and above a polypyrrole film containing formate dehydrogenase and β-nicotinamide adenine dinucleotide has been investigated by electrochemical quartz crystal microbalance and cyclic voltammetry techniques. Two different deposition mechanisms of Prussian blue were identified and explained when the polypyrrole coated substrate electrode was used. Very stable current and frequency responses were obtained when the Prussian blue film was deposited under the polypyrrole film. This layered structure is potentially useful in solving the leakage problems of a biosensing system involves immobilised mediator. This advantage has been demonstrated using a formate biosensor fabricated with the enzyme, formate dehydrogenase, a co-factor, β-nicotinamide adenine dinucleotide and a Prussian blue mediator.

Natural Polymer-Based Sulfite Biosensor

As a natural product, chitosan has the inherent properties of being biodegradable, biocompatible and nontoxic. These properties render it an ideal matrix in enzyme immobilization for clinical analysis. In this work, the feasibility of electrochemical biosensor fabrication using chitosan has been demonstrated. As a test case, the enzyme, sulfite oxidase (SOD), was covalently immobilized onto the matrix of chitosan-poly(hydroxyethyl methacrylate) (chitosan-HEMA), a natural/synthetic polymer hybrid material obtainable via a UV curing process. An electron transfer mediator, p-benzoquinone was coupled onto the polymer network for the activation of chitosan-HEMA copolymer after the photo-induced polymerization reaction. The biological activity of the immobilized SOD and the electroactivity of the coupled p-benzoquinone were examined.

UV-cured natural polymer-based membrane for biosensor application

Chitosan, a natural product, is inherently biodegradable, biocompatible, and nontoxic. These properties make chitosan ideal for inclusion in matrices designed for use in enzyme immobilization for clinical analysis. This study demonstrates the feasibility of using chitosan in electrochemical biosensor fabrication. The enzyme sulfite oxidase (SOX) was covalently immobilized onto the matrix of chitosan–poly(hydroxyethyl methacrylate) (chitosan–pHEMA), a natural/synthetic polymer hybrid obtainable via UV curing. p-Benzoquinone, which served as an electron transfer mediator, was coupled onto the polymer network for activation of the chitosan–pHEMA copolymer, after completion of the photo-induced polymerization reaction. The biological activity of the immobilized SOX and the electroactivity of the coupled p-benzoquinone were investigated.

Chaining and dendrite formation of gold particles

Using the time-averaged dielectrophoretic force from an applied electric field, we have observed the assembly of gold colloid particles into nano/microwires, connections and dendrites according to location within different field regions of a lithographically patterned array of microelectrodes. The frequency of the fields has a marked effect on the structures. In situ inverse microscopy showed hydrodynamic flows, which probably arise from local heating and which play a significant part in shapes formed. Understanding and using the effects will allow the controlled fabrication and positioning of micro- and nanowires or connections at densities far above what is now achievable.

Determination of arsenic by hydride generation gas diffusion flow injection analysis with electrochemical detection

Abstract Hydride generation gas diffusion flow injection analysis with two different electrochemical detectors — conductometric or amperometric — has been investigated for the determination of arsenic. With amperometric detection, where a detection limit (signal-to-noise ratio = 3) of 0.01 mg 1 −1 As was achieved, the method was successfully applied to the determination of arsenic in contaminated soil samples. The technique is highly sensitive, accurate and precise, with low susceptibility to interferences, significant reagent and instrument economy, and affords the possibility of the development of a portable field instrument which could be used at a contaminated site.

Quartz Crystal Microbalance Induced Bond Rupture Sensing for Medical Diagnostics

Disease detection at the point of care could be performed using quartz crystal microbalance (QCM) induced rupture of antibody-antigen bonds. An integrated digital solution for smart sensing is proposed where the QCM is driven and its resonant frequency change is captured as an indication of bond rupture. After reviewing the principle of QCM induced bond rupture, a digital transceiver system is designed and fabricated that integrates transmitter, receiver, amplification, and impedance matching. The system communicates with a PC and its functionalities are implemented in digital signal processor (DSP) software. A benchmark test using biotin and streptavidin bond is conducted and the encouraging results are given

Effect of an intermediate on the amperometric response of a polypyrrole-based formate biosensing membrane

It was evidenced that an intermediate exists in the polypyrrole conjugation system, resulting in a negative response. This fact is a disadvantage with respect to the amperometric response, due to the changing background current that overlaps with the response of the biosensing system. The solution to this problem is to use an overoxidised polypyrrole film for stabilising the background.

Thin-Film Sensors for Detection of Formaldehyde: A Review

This paper reviewed the films used in formaldehyde gas sensing recently. They can be divided into three groups: 1) metal oxide semiconductor films; 2) polymer films; and 3) carbon nanotubes (CNTs) films. Detection limits of these three groups were 1 ppb, 1 ppm, and 20 ppb, respectively. In metal-oxide-semiconductor films, the sensitivity of ZnO conductimetric type sensor was down to 1 ppb with the detectable response of 7.4. Polyethyleneimine/TiO2 was the most sensitive film with quartz crystal microbalance sensor in polymer films, which could detect 1-ppm formaldehyde with the response (Δf ) of 0.8 Hz. Either multi-wall CNTs (MWCNTs) or single-walled CNTs, forming a CNTs film, had the higher sensitivity so far, and the MWCNTs-NH2 interdigital electrodes sensor exhibited 1.73% relative resistance change to 20 ppb of formaldehyde. The further research will be, however, needed to deal with the situation of real scenario influences, such as temperature, humidity, and interferents.