Dual Colorimetric/Electrochemical Detection of Salmonella typhimurium Using a Laser-Induced Graphene Integrated Lateral Flow Immunoassay Strip

Foodborne illnesses caused by the ingestion of contaminated foods or beverages are a serious concern due to the millions of reported cases per year. It is essential to develop sensitive and rapid detection methods of foodborne pathogens to ensure food safety for producers and consumers. Unfortunately, current detection techniques still suffer from time-consuming operations and the need for highly skilled personnel. Here, we introduce a highly sensitive dual colorimetric/electrochemical detection approach for Salmonella enterica serovar typhimurium (S. typhimurium) based on a laser-induced graphene-integrated lateral flow immunoassay (LIG-LFIA) strip. The LIG electrode was fabricated by laser engraving on a polyimide tape containing a pseudo silver/silver chloride reference electrode from silver sintering and chlorination. Using double-sided tape inserted into the strip, automatic sequential reagent delivery was enabled for the dual-mode signal readout by single-sample loading. A gold-deposited gold nanoparticle strategy was first employed to simultaneously obtain a colorimetric signal for early screening and a signal turn-on electrochemical response for high-sensitivity and -quantitative analysis. A superior performance of the strip was established, characterized by a short analysis time (12 min assay +15 min sample preparation), a broad working concentration range (1 cfu/10 mL to 10(8) cfu/mL), and the lowest limit of detection (1 +/- 0.5 cfu/10 mL; mean +/- standard deviation, n = 3) among reported multimode S. typhimurium detection schemes. The strip was successfully applied in the analysis of various food products without any bacterial enrichment or amplification required, and the results were comparable to those of the standard culture method.

Automated summary

Foodborne illnesses caused by contaminated foods are a serious concern, and there is a need for sensitive and rapid detection methods of foodborne pathogens. In this study, a highly sensitive dual colorimetric/electrochemical detection approach using a laser-induced graphene-integrated lateral flow immunoassay strip was developed for Salmonella enterica serovar typhimurium (S. typhimurium). The strip showed superior performance with a short analysis time, a broad working concentration range, and the lowest detection limit compared to reported S. typhimurium detection schemes. The strip was successfully used for analysis of various food products without the need for bacterial enrichment or amplification.