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.