Development of a label-free immunosensor system for detecting plasma cortisol levels in fish

Abstract

Fishes display a wide variation in their physiological responses to stress, which is clearly evident in the plasma corticosteroid changes, chiefly cortisol levels in fish. In the present study, we describe a novel label-free immunosensor for detecting plasma cortisol levels. The method is based on immunologic reactions and amperometric measurement using cyclic voltammetry. For the immobilization of the antibody on the surface of sensing electrode, we used a self-assembled monolayer of thiol-containing compounds. Using this electrode, we detect the CV signal change caused by the generation of antigen-antibody complex. The immunosensor showed a response to cortisol levels, and the anodic peak value linearly decreased with a correlation coefficient of 0.990 in diluted plasma. The specificity of the label-free immunosensor system was investigated using other steroid hormones, such as 17α, 20β-dihydroxy-4-pregnen-3-one, progesterone, estriol, estradiol, and testosterone. The specific detection of cortisol was suggested by a minimal change from -0.32 to 0.51 μA in the anodic peak value of the other steroid hormones. The sensor system was used to determine the plasma cortisol levels in Nile tilapia (Oreochromis niloticus), and the results were compared with those of the same samples determined using the conventional method (ELISA). A good correlation was obtained between values determined using both methods (correlation coefficient 0.993). These findings suggest that the proposed label-free immunosensor could be useful for rapid and convenient analysis of cortisol levels in fish plasma samples.

Measuring cortisol, the major stress hormone in fishes

“…Electrochemical immunosensing measures the change in the electrochemical properties of a conductive material in response to the association of the antigen to the antibody coated on the surface (Figure ). Both, electrochemical impedance spectroscopy and cyclic voltammetry have been used to characterise electrochemical properties of the immunosensors during detection of cortisol in fishes (Pali et al, ; Wu et al, , ). The conductive material is commonly a gold electrode transformed to fix the antibody (Figure a).…”

“…The electrode can then be used directly in the liquid sample, for direct and multiple measurements. This technique was able to measure very low concentrations of cortisol, down to 6.6 pg ml −1 (Wu et al, ).…”

Biosensors for the assessment of fish health: a review

“…Pottinger and Carrick (2001) described the plasma cortisol profiles and physiological effects in response to various stressors in fish. Electrochemical immunoassays are highly sensitive, inexpensive methods for evaluating biochemistry, and we developed these types of biosensor systems to rapidly and easily measure fish cortisol levels (Muramatsu et al 2011;Wu et al 2015aWu et al , 2016Wu et al , 2017a.…”