Signal on-off ratiometric electrochemical sensor based on semi-complementary aptamer couple for sensitive cadmium detection in mussel

Abstract

Abstract The synergy of semi-complementary aptamer couple and signal on-off ratiometric strategy is applied with multi-purpose screen-printed electrode (SPE). The homemade SPE simultaneously accommodates capacities for primary ratiometric sensing and supplementary on-chip pH monitoring. Cd2+ aptamer performs as a molecular recognizer, in the sensing system, to provide target signal of Cd2+ (ICd2+). Polythionine-Au (PTh-Au) is bound to a single-strand DNA (ssDNA), semi-complementary to Cd2+ aptamer. The ssDNA@PTh-Au, self-assembled with Cd2+ aptamer by hybridization, can be competitively replaced by Cd2+, causing a loss in IPTh-Au. Thus, the target signal (ICd2+) and the reference signal (IPTh-Au) well compose a ratiometric sensing system. Modifications and sensing behaviors are comprehensively validated with laboratorial methods from morphology, spectroscopy and electrochemistry. The proposed aptasensor presents considerable advances in analytical performances. During interference study and stability examination, the ratiometric signal, ICd2+/IPTh-Au, is proven a more reliable indicator than solo-signal readout. Following a log-linear relationship, this sensor provides wide dynamic range, as 2 × 10−3∼8 × 10−1 mg L−1, to target Cd2+. Limit of detection is well found as 7 × 10−4 mg L−1 based on experimental criterion. The proposed sensor is consequently applied for Cd2+ determination in real mussel samples. Recommend results meet well with those from ICP-MS and recovery test.