Gelatin electric double-layer side-gated FETs: Capacitive coupling mechanism for label-free detection of coptis alkaloids

Coptis chinensis (cc) was widely used in traditional Chinese medicine for the treatment of various diseases, and its quality evaluation directly influenced clinical efficacy and safety. Traditional analytical methods, such as chromatographic or mass spectrometric techniques, were limited by high equipment costs and complex operational procedures. Here, a gelatin (Gel) side-gated double-layer field-effect transistor (GGDL-FET) was designed for highly sensitive detection of cc. The electric double-layer (EDL) capacitance of GGDL-FET reached 12.2 μF with 2 wt. % Gel. The superposition effect of electric fields 1 and 2 (E1 and E2) enhanced the gate control capability, thus contributed to a significant increase in channel current (∼374.4%). Furthermore, berberine (BBR) as the main components of cc was first quantified, and the incorporation of BBR increased the ion concentration of Gel electrolyte as well as the EDL capacitance since the quaternary ammonium salt group in its structure produced more positive charges, which enhanced the gate controllability and led to an obvious increase in the channel current. Subsequently, cc samples with varying concentration gradients were introduced into Gel. The resulting changes of the channel current exhibited consistent behavior with BBR alone, demonstrating a concentration-dependent response. The device detected cc with concentrations of 1, 2, and 3 wt. %. Thus, the concentration of BBR in cc could be evaluated by analyzing the changing trend of channel current, which provided a reference for the quality assessment of cc.