Impedance Biosensors: Applications to Sustainability and Remaining Technical Challenges

Due to their all-electrical nature, impedance biosensors have significant potential for use as simple and portable sensors for environmental studies and environmental monitoring. Detection of two endocrine-disrupting chemicals (EDC), norfluoxetine and BDE-47, is reported here by impedance biosensing, with a detection limit of 8.5 and 1.3 ng/mL for norfluoxetine and BDE-47, respectively. Although impedance biosensors have been widely studied in the academic literature, commercial applications have been hindered by several technical limitations, including possible limitations to small analytes, the complexity of impedance detection, susceptibility to nonspecific adsorption, and stability of biomolecule immobilization. Recent research into methods to overcome these obstacles is briefly reviewed. New results demonstrating antibody regeneration atop degenerate (highly doped) Si are also reported. Using 0.2 M KSCN and 10 mM HF for antibody regeneration, peanut protein Ara h 1 is detected daily during a 30 day trial.

Control of protein immobilization: coupling immobilization and site-directed mutagenesis to improve biocatalyst or biosensor performance

Mutagenesis and immobilization are usually considered to be unrelated techniques with potential applications to improve protein properties. However, there are several reports showing that the use of site-directed mutagenesis to improve enzyme properties directly, but also how enzymes are immobilized on a support, can be a powerful tool to improve the properties of immobilized biomolecules for use as biosensors or biocatalysts. Standard immobilizations are not fully random processes, but the protein orientation may be difficult to alter. Initially, most efforts using this idea were addressed towards controlling the orientation of the enzyme on the immobilization support, in many cases to facilitate electron transfer from the support to the enzyme in redox biosensors. Usually, Cys residues are used to directly immobilize the protein on a support that contains disulfide groups or that is made from gold. There are also some examples using His in the target areas of the protein and using supports modified with immobilized metal chelates and other tags (e.g., using immobilized antibodies). Furthermore, site-directed mutagenesis to control immobilization is useful for improving the activity, the stability and even the selectivity of the immobilized protein, for example, via site-directed rigidification of selected areas of the protein. Initially, only Cys and disulfide supports were employed, but other supports with higher potential to give multipoint covalent attachment are being employed (e.g., glyoxyl or epoxy-disulfide supports). The advances in support design and the deeper knowledge of the mechanisms of enzyme-support interactions have permitted exploration of the possibilities of the coupled use of site-directed mutagenesis and immobilization in a new way. This paper intends to review some of the advances and possibilities that these coupled strategies permit.