Development of a label-free, sensitive gold nanoparticles-poly(adenine) aptasensing platform for colorimetric...

In this work, a sensitive colorimetric bioassay method based on a poly(adenine) aptamer (polyA apt) and gold nanoparticles (AuNPs) was developed for the determination of aflatoxin B1 (AFB1). The polyA apt, adsorbed on the AuNPs, especially can bind to the analyte while deterring non-specific interactions. This nano aptasensor uses cationic polymer poly(diallyl dimethyl ammonium chloride) (PDDA), as an aggregating agent, to aggregate gold nanoparticles. PolyA apt-decorated gold nanoparticles (AuNPs/polyA apt) show resistance to PDDA-induced aggregation and maintains their dispersed state (red color) with the optical absorbance signal at λ = 520 nm. However, in the presence of AFB1 in the assay solution, the specific aptamer reacts with high affinity and folds into its three-dimensional form. Aggregation of AuNPs induced by PDDA caused their optical signal shift to λ = 620 nm (blue color). AFB1 concentration in the bioassay solution determines the amount of optical signal shift. Therefore, optical density ratio in two wavelengths (A_620/520) can be used as a sturdy colorimetric signal to detect the concentration of aflatoxin B1. AFB1 was linearly detected between 0.5 and 20 ng mL^-1, with a detection limit of 0.09 ng mL^-1 (S/N = 3). The fabricated aptasensor was applied to the detection of AFB1 in real corn samples.