Polypyrrole–polydimethylsiloxane sponge-based compressible capacitance sensor with molecular recognition for point-of-care immunoassay

A highly compressible and all-solid-state polydimethylsiloxane (PDMS) sponge-based flexible capacitance sensor modified with polypyrrole (PPy) was designed as the signal readout for sensitive immunoassay of prostate-specific antigen (PSA). This system mainly consisted of a compressible capacitance sensor, immunoreaction protocol and gas delivery channel. The capacitance sensor connected to a single microplate by the syringe, whereas the immunoreaction was carried out in the microplate. The conjugated catalase with detection antibody via biotin-streptavidin interaction could trigger the gas generation to cause the pressure change, thus resulting in the increasing capacitance of PPy-PDMS sponge on an LCR-6100 digital bridge capacitance meter. By coupling with the capacitance sensor, the capacitance change could be monitored in real-time to achieve the portable detection of PSA. Under optimum conditions, compressible supercapacitor PPy-PDMS sponge performed great electrochemical performance and maintained stably under compressive strains. The capacitance increased with the increasing target PSA concentration within a dynamic working range of 0.1–50 ng mL-1 at a detection limit of 57 pg mL-1. Moreover, acceptable reproducibility, precision and high specificity were acquired for PSA analysis, and good accordance with the commercial PSA ELISA kit.