Contactless gas-sensitive photoelectrochemical biosensor for determination of Salmonella typhimurium based on SnO2/CeO2 heterojunction.

BACKGROUND

Salmonella typhimurium (S. typhimurium) is a prevalent foodborne pathogen that causes severe gastrointestinal symptoms and even systemic infections in humans following the ingestion of contaminated food, posing a persistent threat to public health. Conventional detection methods often suffer from limitations including moderate sensitivity, cumbersome procedures, and time-consuming processes, which hinder their applicability for rapid on-site food monitoring. This study developed a novel contactless photoelectrochemical biosensor based on a SnO2/CeO2 heterojunction with abundant oxygen vacancies, which operates via a gas-sensing mechanism in which H2S-producing Salmonella bacteria trigger in-situ H2S generation to enable highly sensitive and reliable detection.

RESULTS

A SnO2/CeO2 heterojunction rich in oxygen vacancies was successfully synthesized via a hydrothermal method. Density functional theory calculations confirmed its strong capability to accept electrons from adsorbed H2S molecules. In the presence of S. typhimurium, intracellular thiosulfate reductase catalyzed the reduction of sodium thiosulfate to produce H2S. This gaseous product diffused from the culture medium to the sensor, where it donated electrons, dramatically amplifying the photocurrent response of the SnO2/CeO2-modified photoelectrode. Under optimized conditions, the biosensor achieved an exceptionally wide linear detection range, for S. typhimurium used as a representative model strain, from 1.7 × 10-1 to 1.7 × 108 CFU/mL, with a limit of detection as low as 0.11 CFU/mL. Furthermore, the proposed biosensor showed rapid response, high stability, excellent selectivity, as well as acceptable accuracy on real samples (chicken and milk), suggesting its potential as an effective tool for food safety analysis.

SIGNIFICANCE AND NOVELTY: This study demonstrated a significant advancement in PEC biosensing through the integration of a gas-sensitive mechanism with a heterojunction material. It overcomes common limitations of traditional methods, notably material detachment and solution-phase interference. The contactless gas-sensitive photoelectrochemical biosensor holds great promise as a tool for on-site monitoring of food safety and pathogen detection.