Biosensors & Bioelectronics

In this work we describe a new urea biosensor, based on the immobilization of bacteria, Proteus mirabilis on gold electrode. To improve the stability of the bio-system, additional materials were used such as functionalized Fe3O4 nanoparticles (NPs), cationic (PAH), anionic (PSS) polyelectrolytes, Bovine Serum Albumin (BSA) and glutaraldehyde as a cross-linking agent. The electrochemical performances of the developed bacteria biosensor was evaluated using the electrochemical impedance spectroscopy (EIS) and cyclic voltammetry measurements. The adhesion of the bacteria cell on gold electrode was evaluated using contact angle measurements. The morphology of bacteria and its interaction with Fe3O4 nanoparticles were evaluated with the atomic force microscopy (AFM). As a result, a sensitive, stable and reproducible urea biosensor was developed.

In this work, we report for the first time on the successful selection and identification of peptide motives that exhibit a specific affinity to anodic alumina surfaces when multivalently displayed on a filamentous phage. It was also demonstrated that, for a selected phage clone, a chemical functionalisation (biotinylation) of the bacteriophage does not deteriorate its specific affinity to anodic alumina. Moreover, such biotinylated bacteriophages, after being immobilised onto an anodic alumina surface, have been shown to allow for the quantitative detection of streptavidine using an ELISA protocol. These results are believed to pave the way for shifting the surface design of integrated biosensing devices from traditional, chemically modified synthetic surfaces, like silane-based self-assembled monolayers, towards molecular linkers based on genetically engineered polypeptides.

Acoustic wave chemical sensors have several features such as high resolution and sensitivity, fast responserecovery time, superb overall stability and high dynamic range, which determine their appropriateness for gas analyte detection. The usability of acoustic sensors requires specific knowledge relating to the sensing mechanism, the properties of different acoustic wave modes and the criteria for selection of sensitive layers, involved in a wide range of gas-phase applications. This paper reports the most commonly used metal oxide film coated acoustic wave sensors, as well as their operation principle and practical application. Several advantages and disadvantages of each particular acoustic wave device are identified and the selectivity of the sensors is presented and discussed.

A voltammetric sensor using differential pulse voltammetry (DPV) was developed for the detection of Vitamin C (ascorbic acid). The sensing platform was ZnO-decorated reduced graphene oxide on glassy carbon electrode (ZnO-RGO-GCE). Graphene oxide, synthesized by an improved Hummers method, was reduced with zinc powder under ultrasonication, followed by washing with HCl. X-ray diffraction and scanning electron microscopy showed ZnO nanoparticles decorating the reduced graphene oxide sheets. ZnO-RGO-GCE showed reversible behaviour with ferricyanide system, had about 3.5 times more surface area than GCE, and exhibited higher currents for ascorbic acid oxidation compared to bare GCE. Ascorbic acid was sensed over a wide range of 1 μM to 5000 μM (R2=0.9899) with a sensitivity of 0.178 μA/μM-cm2 and detection limit of 0.01 μM, with good reproducibility (RSD=2.02%; n=5). The recovery of Vitamin C from pharmaceutical formulations, lemon juice, and gooseberry (amla) extract was also studied and compared against results from colorimetric methods. These results indicate that the developed ZnO-RGO-GCE platform could be used for voltammetric determination of Vitamin C in food samples