Biosensors & Bioelectronics

This research was aiming at developing liquid biochip which was coded by impedance microsphere of different diameter and providing research foundation for its detecting device. Adopting the method of loading constant current source between both ends of micropore in ruby, it were tested that three sorts of microspheres’ impedance with particle sizes of 2μm, 5μm, 10μm. It was resultantly found that microsphere diameter is in direct proportion to impedance and voltage between both ends of micropore. In other words, microsphere of different size could be distinguished from each other by their impedance. Our research drew the indication that impedance of microspheres in different sizes could be theoretically calculated as well as measured and automatically distinguished, offering experimental and theoretical foundation for liquid biochip development.

A novel route has been introduced to fabricate the composite of polyaniline (PANI) and cadmium sulphide quantum dots (CdS-QD) using electrochemical polymerization technique for mediator free biosensing. The synthesis process involves in situ formation of CdS quantum dots that provide template for eletro-polymerization of aniline resulting in nanostructured PANI-(CdS-QD) film deposition on the indium-tin-oxide (ITO) coated glass plate. Transmission electron microscopy and scanning electron microscopy have been used to reveal the formation of CdS-QD and morphological changes involved during incorporation of CdS in PANI matrix and while immobilization of cholesterol oxidase (ChOx). The UV–visible and FT-IR investigations show the formation of PANI-(CdS-QD) composite at the molecular level. This matrix has been utilized for the covalent immobilization of cholesterol oxidase to explore its application for cholesterol sensing. The results of the CV and EIS studies indicate enhanced electrochemical and charge transfer behaviour of the composite. The response studies, carried out using CV technique, reveal this ChOx/ PANI-(CdS-QD)/ITO bioelectrode to detect cholesterol in the concentration range of 50 to 500 mgdL -1 with good detection limit (47.8 mgdL -1 ) and low app m K value (0.82 mM).

A phage-based magnetoelastic (ME) biosensor method was compared with a TaqMan-based quantitative real- time PCR (Q-PCR) method for the detection of Salmonella typhimurium on tomato surfaces. This ME biosensor method utilizes magnetoelastic resonators coated with E2 filamentous phage to bind with and measure the concentration of S. typhimurium . In this study, standard curves, correlations, and limits of detection (LOD) for the ME biosensor and Q-PCR methods were determined by inoculating tomato surfaces with S. typhimurium suspensions in concentrations ranging from 1 to 8 log CFU/tomato. The LOD for the ME biosensor method and Q-PCR were 3 and 2 log CFU/tomato, respectively. In a direct comparison of the detection methods, S. typhimurium suspensions (3 log CFU/tomato) were inoculated on 65 tomato surfaces, then incubated at 37°C and 100% RH for 24 h. After 24 h, S. typhimurium was positively detected by both methods and the quantified concentrations were nearly the same, (6.35 ± 2.03) and (6.34 ± 0.17) log CFU/tomato respectively for the ME biosensor method and the Q-PCR method, which were significantly greater than the concentration determined by the BGS-plate count method (5.33 ± 0.21). Scanning electron microscopy (SEM) was used to confirm the growth of S. typhimurium on the tomato surfaces and the binding of S. typhimurium on the measurement sensors. This study demonstrated that the ME biosensor method was robust and competitive with Q-PCR for S. typhimurium detection on fresh produce.

We demonstrate a novel, highly efficient glucose sensor based on functionalized graphene. Glucose oxidase (GOD) immobilization has been apprehendedbythe direct interaction between carboxyl acid groups of the reduced graphene oxide (RGO) and amines of GOD together with the electrostatic interactions existing between the positively charged polymeric ionic liquid (PIL) and GOD. This combined system can provide a favorable microenvironment for the GOD to retain its good bioactivity. The enzyme-coated graphene biosensor exhibited glucose-dependent electrochemical measurements against an Ag/AgCl reference electrode. The resulting sensor show broad range detection, up to 100 mM glucose concentration, with a sensitivity of 5.59 μA/ decade. It was found that glucose biosensor based on functionalized graphene can be seen as an effective candidate for the detection of sugar concentration in clinical diagnoses.

Currently available TNT sensors are characterized by high sensitivity, but low specificity, which limits the detection of TNT in dirty environments. We report here a TNT sensor designed to measure the displacement of a TNT-specific antibody by quartz crystal microbalance (QCM). This sensor combines high sensitivity of detection (0.1 ng/mL) with the ability to distinguish TNT from molecules with similar chemical properties. Particularly, the reliability of this method for the detection of TNT in dirty environments was investigated by using fertilizer solution and artificial seawater. Instead of measuring actual binding of TNT, the method described is based on the displacement of an anti-TNT antibody, which allows quantifying the concentration of TNT in solution with higher sensitivity. In addition, by utilizing the rate of antibody displacement, the detection time is significantly decreased from hours, which would be necessary to measure the frequency change at equilibrium, to minutes. A Langmuir kinetic model was used to describe the molecular interactions on the surface of the sensor and to establish a standard curve to estimate on-site TNT detection. In summary, QCM detection of anti-TNT antibody displacement provides a method for rapid detection of TNT with high sensitivity and specificity.

A simple technique is described for constructing a glucose sensor so that enzymes, glucose oxidase (GOD) was immobilized by cross-linking via glutaraldehyde 0.1% at 0.1 M phosphate buffer with 7.0 pH in a polyaniline and poly(aniline-co-2anilinoethanol) thin films, which were electrochemically deposited on a platinum plate in phosphate and acetate buffer. The results of EIS and SEM indicated the successful immobilization for enzymes in the polymers film. The maximum current response was observed for the electrodes at pH 7 and potential 0.65 V (versus Ag/ AgCl). The poly (aniline-co-2anilinoethanol)/GOD electrode gives high stability and fast response as compared to polyaniline/GOD electrode in amperometric measurements so results show that the poly (aniline-co 2anilinoethanol) electrode is more suitable for biological systems.

A general type of molecular level metabolic control that is common to all living organisms is the feedback inhibition, wherein an increase in the product of a metabolic pathway regulates an enzyme upstream in the cascade by binding to it and decreasing enzyme activity. The de novo pyrimidine biosynthetic pathway provides a specific example for the feedback inhibition. Aspartate transcarbamoylase (ATCase) catalyzes the first step in the biosynthesis of pyrimidines and one of the best understood allosteric enzymes. The structure of ATCase is roughly triangular in shape, similar to the symbol of an op-amp IC. Since most of the enzymatic properties were analogous to the properties of IC, this inspired us to mimic the enzyme (EC 2.1.3.2) with an IC (PIN μ A741CN) in our circuit design. The Michaelis-Menten model, Lineweaver-Burk equation and the equation for the non-inverting amplifier were theoretically related and used for our model. As a result, an electronic feedback circuit was designed and tested. The biomolecular mimic circuit will develop a new level of understanding of the metabolic complexity in the cell.