Ion Selective Amperometric Biosensors for Environmental Analysis of Nitrate, Nitrite and Sulfate

Inorganic ions that can be redox-transformed by living cells can be sensed by biosensors, where the redox transformation gives rise to a current in a measuring circuit. Such biosensors may be based on enzymes, or they may be based on application of whole cells. In this review focus will be on biosensors for the environmentally important ions NO3−, NO2−, and SO42−, and for comparison alternative sensor-based detection will also be mentioned. The developed biosensors are generally characterized by a high degree of specificity, but unfortunately also by relatively short lifetimes. There are several investigations where biosensor measurement of NO3− and NO2− have given new insight into the functioning of nitrogen transformations in man-made and natural environments such as sediments and biofilms, but the biosensors have not become routine tools. Future modifications resulting in better long-term stability may enable such general use

Electrochemical Assay for a Total Cellulase Activity with Improved Sensitivity

Electrochemical methods allow fast and inexpensive analysis of enzymatic activities. Here, we report a simple and yet efficient electrochemical assay for the total activity of cellulase, a hydrolytic enzyme widely used in food and textiles industries, and for production of bioethanol. The assay exploits the difference in electrochemical signals from a soluble redox indicator, ferricyanide, on nitrocellulose films treated by cellulases. Ferricyanide electrochemistry is totally inhibited on graphite electrodes modified with an insulating nitrocellulose film and is evoked after the cellulase treatment. Ferricyanide voltammetric responses correlate with the increased permeability of the films and electrochemically active surface area of electrodes becoming accessible to the ferricyanide reaction after nitrocellulose digestion by cellulase. Trichoderma and Aspergillus niger cellulases activities were determined in a 5 min assay with a sensitivity of 10^–8 U per assay, being 10³–10⁴-fold more sensitive than the standard commercially available optical assays. That makes the developed electrochemical approach the most prospective cost-effective alternative both for research and automated industrial applications

Origin of Low Detection Limit and High Selectivity of Roche Accu‐Chek Test Strips that Enables Measurement of Tear Glucose Levels

Tear glucose measurements have been suggested as a potential alternative to blood glucose monitoring for diabetic patients. While previous work has reported a correlation between blood and tear glucose levels in humans, this link has not been thoroughly established and additional clinical studies are needed. We recently reported that Roche’s electrochemical Accu‐Chek blood glucose test strips exhibit far superior analytical performance over other commercial brands, with the low detection limit and high selectivity required for quantitating tear glucose levels. Herein, we evaluate the origin of the high sensitivity and selectivity of the Roche test strips and show that the use of pyrroloquinoline quinone (PQQ)‐dependent glucose dehydrogenase (GDH) as an active enzyme reagent in combination with a nitrosoaniline derivative as an electron transfer mediator are primarily responsible for the low limit of quantification (LOQ) (ca. 9 µM) and enhanced selectivity achieved with these strips.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/110886/1/670_ftp.pd

Gated electron transfer reactions of truncated hemoglobin from Bacillus subtilis differently orientated on SAM-modified electrodes

Electron transfer (ET) reactions of truncated hemoglobin from Bacillus subtilis (trHb-Bs) are suggested to be implicated in biological redox signalling and actuating processes that may be used in artificial environment-sensing bioelectronic devices. Here, kinetics of ET in trHb-Bs covalently attached via its surface amino acid residues either to COOH- or NH2-terminated (CH2)(2-16) alkanethiol SAM assembled on gold are shown to depend on the alkanethiol length and functionalization, not being limited by electron tunnelling through the SAMs but gated by ET preceding reactions due to conformational changes in the heme active site/at the interface. ET gating was sensitive to the properties of SAMs that trHb-Bs interacted with. The ET rate constant k(s) for a 1e(-)/H+ reaction between the SAM-modified electrode and heme of trHb-Bs was 789 and 110 s(-1) after extrapolation to a zero length SAM, while the formal redox potential shifted 142 and 31 mV, for NH2- and COOH-terminated SAMs, respectively. Such domain-specific sensitivity and responsivity of redox reactions in trHb-Bs may be of immediate biological relevance and suggest the existence of bioelectronic regulative mechanisms of ET proceeding in vivo at the protein-protein charged interfaces that modulate the protein reactivity in biological redox signalling and actuating events