Amplifying the invisible: Liquid crystal-hydrogel microcavities decode trace Hg ions and aflatoxin B1

Chinese herbal medicines (CHMs) have been applied to the prevention and treatment of numerous diseases. Ensuring the safety and pharmacological efficacy of CHMs demands precise detection of trace heavy metal ions and toxins, especially Hg and aflatoxin B1 (AFB1). However, due to subtle chemical signals, current technologies still make it challenging to monitor these quality parameters in a highly sensitive manner. Herein, we introduced a liquid crystal whispering gallery mode microresonator formed by encapsulating liquid crystal droplets in a hydrogel microcavity for monitoring analyte interactions. By employing an aptamer-target assay within the hydrogel, interfacial liquid crystal molecule reorientations and strong light-matter interactions in an optical microresonator can amplify signals. The tuning of resonance wavelength can be converted to improve monitoring of interaction processes. With narrow resonance linewidth, the limit of detection can reach 3.58 nM (Hg²⁺) and 101 fg/ml (aflatoxin B1). This method has been applied to detect the targets in real herbs (relative errors ranging from -2.931-5.572% compared with gold-standard methods) and demonstrated batch-to-batch heterogeneity in herbal analyte content. Further applications in various Chinese herbs evaluation demonstrated the applicability of this method supporting its potential for herbal safety assessment.