Current trends in biosensor research and development

Rapid prototyping of electrochemical lateral flow devices: stencilled electrodes

A straightforward and very cost effective method is proposed to prototype electrodes using pressure sensitive adhesives and a simple cutting technique. The prototyping approach presented here is highly suitable for the development of novel electroanalytical tools.

Evidence for Conformational Mechanism on the Binding of TgMIC4 with β-Galactose-Containing Carbohydrate Ligand

A deeper understanding of the role of sialic/desialylated groups during TgMIC4-glycoproteins interactions has importance to better clarify the odd process of host cell invasion by members of the apicomplexan phylum. Within this context, we evaluated the interaction established by recombinant TgMIC4 (the whole molecule) with sialylated (bovine fetuin) and desialylated (asialofetuin) glycoproteins by using functionalized quartz crystal microbalance with dissipation monitoring (QCM-D). A suitable receptive surface containing recombinant TgMIC4 for monitoring β-galactose-containing carbohydrate ligand (limit of quantification ∼ 40 μM) was designed and used as biomolecular recognition platform to study the binding and conformational mechanisms of TgMIC4 during the interaction with glycoprotein containing (fetuin), or not, terminal sialic group (asialofetuin). It was inferred that the binding/interaction monitoring depends on the presence/absence of sialic groups in target protein and is possible to be differentiated through a slower binding kinetic step using QCM-D approach (which we are inferring to be thus associated with β-galactose ligand). This slower binding/interaction step is likely supposed (from mechanical energetic analysis obtained in QCM-D measurements) to be involved with Toxoplasma gondii (the causative agent of toxoplasmosis) parasitic invasion accompanied by ligand (galactose) induced binding conformational change (i.e., cell internalization process can be additionally dependent on structural conformational changes, controlled by the absence of sialic groups and to the specific binding with galactose), in addition to TgMIC4-glycoprotein solely recognition binding process.

Controlling interferometric properties of nanoporous anodic aluminium oxide

A study of reflective interference spectroscopy [RIfS] properties of nanoporous anodic aluminium oxide [AAO] with the aim to develop a reliable substrate for label-free optical biosensing is presented. The influence of structural parameters of AAO including pore diameters, inter-pore distance, pore length, and surface modification by deposition of Au, Ag, Cr, Pt, Ni, and TiO2 on the RIfS signal (Fabry-Perot fringe) was explored. AAO with controlled pore dimensions was prepared by electrochemical anodization of aluminium using 0.3 M oxalic acid at different voltages (30 to 70 V) and anodization times (10 to 60 min). Results show the strong influence of pore structures and surface modifications on the interference signal and indicate the importance of optimisation of AAO pore structures for RIfS sensing. The pore length/pore diameter aspect ratio of AAO was identified as a suitable parameter to tune interferometric properties of AAO. Finally, the application of AAO with optimised pore structures for sensing of a surface binding reaction of alkanethiols (mercaptoundecanoic acid) on gold surface is demonstrated.

Production of biosensors with exchangeable enzyme-containing threads

We introduce a simple method for the construction of biosensors, based on coiling an enzyme-containing, thread-shaped material around a cylindrical signal transducer in the form of winding stairs with a variable length of step and so forming a variable biocatalytic membrane on the sensor surface, which can be easily modified for particular purposes. In the model system, we immobilized glucose oxidase (GO) on a nylon thread, formatted from a sheaf of numerous minor filaments and used as a biorecognition element integrated with a Clark-type oxygen sensor. The immobilized enzyme was evenly distributed throughout the thread, and the activity of the enzyme could be measured in units of length. Appropriate pieces of the enzyme-containing thread with a certain amount of GO could be cut for a definite biosensor or bioreactor. The enzyme amount and substrate diffusion parameters, which together control the sensor's working range and sensitivity, could be changed simultaneously with the change of the length of the thread. Besides glucose oxidase, experiments with other enzymes have confirmed the applicability of the proposed technological solution. Thus, the thread-type matrixes enable one to construct sensors with a required range of work, sensitivity, and selectivity, which can be easily customized within seconds.

Detection of 2,4,6-trinitrotoluene in seawater using a reversed-displacement immunosensor

Reported in this study are the experimental design and results of an immunosensor for the detection of the explosive, 2,4,6-trinitrotoluene (TNT) in seawater using a reversed-displacement format. This reversed-displacement immunosensor methodology has successfully measured TNT in seawater by direct injection, eliminating the need for preconcentration or pretreatment of samples. A microcolumn containing an Affi-Gel resin derivatized with a 2,4,6-trinitrobenzene (TNB) moiety and a fluorophore-labeled anti-TNT antibody composed the immunoassay reactive chamber. Fluorophore-labeled anti-TNT antibody was incubated with the modified Affi-Gel resin until binding equilibrium was reached. Under a constant flow, samples containing TNT were introduced into the flow stream displacing the fluorophore-labeled TNT antibody. Limits of detection were 2.5ng/mL or part-per-billion (ppb) for TNT in saline buffer and 25ppb in seawater with an analysis time of 10 min. Two anti-TNT antibodies with differing binding affinities were compared in the reversed-displacement assay format, and a correlation between affinity and detection limits was observed. Furthermore, we have demonstrated that the reversed-displacement format can be used to screen seawater samples containing TNT, remains effective after dozens of cycles, and provides significant fluorescence response before regeneration is required.

A piezoelectric immunosensor for the detection of cortisol

A piezoelectric crystal immunosensor has been developed for the detection and determination of cortisol. Cortisol antibody was layered onto the gold electrodes of a 10 MHz piezoelectric crystal which was pre-coated with either protein A or gluteraldehyde. Crystals pre-coated with protein A showed the best results with respect to stability and sensitivity. The sensor was successfully used for the determination of cortisol in standard solutions from 36-3628 micrograms/L (part per billion). The advantages of the proposed sensor include simplicity, short analysis time, cost effectiveness and selectivity. The results demonstrate the feasibility of cortisol assay in clinical testing and in drug monitoring.

Biosensors for environmental monitoring

Increasing environmental legislation which controls the release and the levels of certain chemicals in the environment has created a need for reliable monitoring of these substances in air, soil and especially water. Conventional analytical techniques, although highly precise, suffer from the disadvantages of high cost, the need for trained personnel and the fact that they are mostly laboratory bound. Biosensors because of their specificity, fast response times, low cost, portability, ease of use and a continuous real time signal, can present distinct advantages in certain cases. Their biological base makes them ideal for toxicological measurements which are suited for health and safety applications. Over the last 3-4 years there has been an increase in the number of publications concerning biosensors for environmental monitoring, especially in the field of pesticide measurements. This paper reviews some of the more important developments over the past 3-4 years.

Immobilized enzymes as tools in food analysis

A lot of publications described the possibilities of using selective enzymatic reactions in analysis, but not much authors described applications for the analysis of real samples. In this paper important publications, which described different applications in food analysis, are reviewed. In the first section the use of biosensors for food analysis, in the second section the combination of immobilized enzymes and flow injection analysis and in the last section the use of immobilized enzymes in combination with HPLC are described. Most of the applications described used enzymes for the determination of sugars mainly glucose, but also methods for the determination of inhibitors in foods are described.