A smartphone-based dual-modal lateral flow immunochromatographic assay for multiplex detection of illegal stimulant laxatives in slimming foods

Stimulant laxatives (especially bisacodyl and sodium picosulfate) are frequently found to be adulterated into slimming foods, causing health-threatening effects to consumers. Sensitive, accurate, easy-to-operate and portable multiplex analytical techniques are still desired for the rapid screening of stimulant laxatives in slimming foods. In this work, a highly sensitive dual-modal colorimetric/photothermal lateral flow immunochromatographic assay (LFIA) was established based on facilely prepared concentrated gold nanoparticles (cAuNPs). Due to the enhanced local surface plasmon resonance and absorption intensity of our unique cAuNPs, this LFIA can simultaneously detect bisacodyl, bis-(p-hydroxyphenyl)-pyridyl-2-methane and sodium picosulfate in slimming food as low as 0.014-0.308 ng/mL by a smartphone-based photothermal device or 1.4-10 ng/mL by naked eyes. Compared with traditional AuNPs-LFIA, it demonstrated 8.48-10.27 times higher sensitivity in photo- thermal mode. Moreover, in the recovery test and blind sample analysis, this dual-modal LFIA exhibited reasonable recoveries (85.04 %-119.18 %) and high correlation with authorized LC-MS/MS method, suggesting high accuracy and applicability. This work offers a highly sensitive, accurate and convenient way for the on-site determination of stimulant laxatives, which can also be employed to detect other food hazards, environmental pollutants, or clinical analytes within a few minutes.