A novel label-free colorimetric polyA aptasensing approach based on cationic polymer and silver nanoparticles for detection of tobramycin in milk.

In this study, a novel colorimetric bioassay method was developed for the sensitive determination of tobramycin (TOB). To detect TOB, silver nanoparticles (AgNPs) were decorated with TOB-specific aptamers (apt), and positively charged poly diallyl dimethyl ammonium chloride (PDDA) was used. As long as tobramycin is not present in the assay system, PDDA can coalesce with the aptamer, and AgNPs would remain stable (λmax = 400 nm) in the dispersed system against PDDA-induced aggregation. When TOB is added, aptamer can bind to the compound, which leads to release of PDDA and subsequent aggregation of AgNPs (λmax = 540 nm). This remarkable change, as a colorimetric analytics signal, can be used for quantitative analysis of TOB. TOB can be detected by this highly sensitive colorimetric aptasensor with a limit of detection (LOD) of 70 pM. Furthermore, TOB can be detected with the naked eye at concentrations above 1 nM.