Giant “molecular capacitor” arrays - portable sensors to determine ionizable compounds

Abstract

Portable sensors have been developed for the determination of ionizable compounds based on molecularly imprinted polymers (MIPs). These polymers are charged due to the utilization of ionizable monomers such as diallylamine and sodium vinyl sulfonate (SVS). Mediated by the charged templates, imprinted sites with specific shapes and charge distributions were build in the MIPs. At the time of molecular recognition, the imprinted sites were reoccupied by the templates, making the polymer charges neutralized. This procedure led to significant permittivity changing and contributed much to device sensitivity. The capacitive signal drop of 1 million molecules (~1.66 × 10−18 mol) adds up to >10−12 f, which is detectable to a current portable multimeter. At the same time interferent components were expediently washed off because of poor affinities to an MIP. Consequently a handheld LCR (Inductance Capacitance Resistance) meter was used to successfully monitor the molecular recognition signals. High sensitive and selective analysis has been achieved for three exemplified compounds, i.e. aspirin, propranolol hydrochloride, and glyphosate, with linear ranges as 5.50 × 10−13–10−9 mol·L−1, 3.39 × 10−13–10−6 mol·L−1 and 5.89 × 10−16–10−6 mol·L−1. Meanwhile the related detection limits are 1.68 × 10−13 mol·L−1, 3.02 × 10−13 mol·L−1 and 1.94 × 10−16 mol·L−1. The more charges the template possesses, the more sensitive the sensor is.