A new multi-identification system based on a poly(l-cysteine) sensor for simultaneous detection of multiple steroid hormones in serum

In this study, poly-l-cysteine (P(l-Cys)), used as the multi-identification unit to sensitively sense multiple steroid hormones, was proposed. The mechanisms of the electropolymerization and electrochemical behavior of P(l-Cys) were revealed. Based on the experimental data and Faraday's law, the P(l-Cys) obtained by electropolymerization possessed abundant sulfonic acid groups. As steroid hormones (STHs) can bind to sulfuric acid for metabolism, the proposed P(l-Cys) system was used as synthetic receptors to detect STHs in serum. The results showed that the reduction peaks obtained from the STHs with different parent nucleus were different and did not interfere with each other when detected simultaneously. The interactions between P(l-Cys) and STHs as well as the reduction mechanisms of hormones were explored by using density functional theory and Faraday's law. To verify the generalizability of this method, thirty-eight different substances (including 30 steroid hormones and 8 nonsteroid hormones) were studied, and it was verified that this method could directly detect three classes of steroid hormones: progestogens, corticosteroids and androgens. The recognition site of this sensor for STHs was the Δ4-3-ketone in the parent nucleus. The P(l-Cys)/GCE sensor allows for the rapid detection of all three types of hormones simultaneously in less than 1 min. The limit of detection for progesterone, dexamethasone and hydrocortisone were 0.0008 μMb, 0.0055 μM and 0.011 μM, respectively. In addition to the applications presented in this study, P(l-Cys)/GCE is a low-cost method that can be applied to detect STHs in other samples, such as environmental and food products.