Development of a novel, efficient and fast method for colorimetric detection of multiple Salmonella serovars based on aptamer-nanoparticle biosensor

In this research, the stability, specificity, and sensibility of a colorimetric detection method based on gold nanoparticles conjugated with aptamers for detection of Salmonella enterica serovar Typhimurium was investigated. The synthesis of gold nanoparticles by citrate reduction and conjugation with aptamers were studied to obtain high stability over time and to hinder inaccurate results. The reaction conducted at initial pH 5.0 and molar ratio 3.5:1 Na3Ct to HAuACl₄ produced stable, monodisperse and spherical particles, with a mean particle diameter of 18 nm. Gold nanoparticles showed stability upon salt exposure limited to 120 mmol/L, which was enhanced with aptamer conjugation to 700 mmol/L. Experiments with different microorganisms confirmed the biosensor specificity to Salmonella, with a detection limit of 10³ CFU/mL for S. Typhimurium, as well as 10⁴ CFU/mL for S. minnesota, S. heidelberg, and Salmonella spp. The assays carried out with artificially contaminated samples and environmental samples resulted in a detection time and detection limit identical to those obtained with pure samples. Results confirm that the biosensor synthesized is a great alternative for detection methods, making it possible to improve time and efficiency detection in the routine inspections as well as reduce costs.