Detection of Fish Hormones by Electrochemical Impedance Spectroscopy and Quartz Crystal Microbalance

Detection of three fish hormones, cortisol, insulin-like growth factor 1 (IGF-1), and vitellogenin is reported using both electrochemical impedance spectroscopy (EIS) and quartz crystal microbalance (QCM). For cortisol, IGF-1, and vitellogenin, the EIS (QCM) detection limits are 7.9 (0.50) μM, 3.0 (2.4) nM, and 43 (13) pM, respectively, in PBS buffer. Thus the two detection methods, EIS and QCM, have similar sensitivity, but QCM is ~4× more sensitive, which is consistent with the published literature. The molecular weights of cortisol, IGF-1, and vitellogenin are 362.5 Da, 7.3 kDa, and 440.5 kDa, respectively. For both EIS and QCM, the sensitivity and detection limit improve dramatically with increasing molecular weight, reflecting the larger change in polymer-protein film thickness at the Au electrode upon recognition and binding of larger analytes. This is the first time that such a trend has been reported for EIS biosensing, since the published literature does not show any clear trend with molecular weight. Potential applications to understanding of fish physiology are discussed, including hormone detection in fish blood plasma, and ambient water

Amperometric Bioelectronic Tongue for glucose determination

An amperometric Bioelectronic Tongue is reported for glucose determination that contains eight sensor electrodes constructed using different metal electrodes (Pt, Au), oxidoreductase enzymes (glucose oxidase, ascorbate oxidase, uricase), and membrane coatings (Nafion, chitosan). The response to varying concentrations of glucose, ascorbic acid, uric acid, and acetaminophen was tested for two models, concentration determination by current density measurements at individual electrodes and concentration determination by a linear regression model for the entire electrode array. The reduced chi-squared for the full array model was found to be about one order of magnitude lower than that for the individual-electrode model. Discrimination of glucose from chemical interference by the other three species is accomplished through a combination of enzyme catalysis, metal electrocatalysis, and membrane surface charge. The benefit of incorporating enzyme electrodes into the sensor array is illustrated by the lower correlation coefficients between different enzyme electrodes relative to non-enzyme coated electrodes. This approach can be more generally applied to detection of other substrates of oxidoreductase enzymes