Biomimetic quartz crystal sensors for caffeine based on conducting polymers

A biomimetic caffeine sensor based on conducting polymers was fabricated by integrating the molecularly imprinted polymer (MIP) with a piezoelectric quartz crystal. This was achieved through galvanostatic electrodeposition of the MIP directly onto one electrode of the quartz crystal in the presence of a template caffeine molecule. Electropolymerization parameters for poly(o-phenelynediamine) (PoPD) and polypyrrole (PPy) were optimized. The sensors exhibited a linear relationship between the frequency shift and the logarithm of the caffeine concentration from 0.1 to 10 mg/mL. Correlation coefficients observed for the sensors based on PoPD and PPy were 0.9923 and 0.9888 respectively. The steady state response (∼10 min) achieved was similar for both sensors. The sensitivity of PoPD-based sensor (130 Hz/ ln conc. (mg/mL) was about half of that for the sensor based on PPy (255 Hz/ln conc. (mg/mL). A good repeatability (rsd = 9 %) was obtained for both sensors using 0.5 mg/mL caffeine solution.