Understanding the competitive interactions in aptamer–gold nanoparticle based colorimetric assays using surface enhanced Raman spectroscopy (SERS)

Abstract

Aptamer–gold nanoparticle (AuNP) based colorimetric assays have become increasingly popular as viable rapid detection methods, but the molecular interactions governing the mechanism and successful interpretation of color changes have not been explored well. The objective of this study was to evaluate the competitive interactions that occur in this detection assay at the molecular level by employing surface enhanced Raman spectroscopy (SERS). The SERS signals of molecules in close proximity to AuNPs were exploited to give information on AuNP surface coverage as well as ssDNA aptamer conformational changes during target capture. Two antibiotics, ampicillin and kanamycin, and their respective aptamers were used in this study. The results indicate that the reason for the lack of AuNP aggregation with ampicillin could be due to a stronger binding affinity of AuNPs to ampicillin than to the aptamer. Kanamycin, on the other hand, induced AuNP aggregation to produce a color change and the SERS data indicate a stronger binding affinity of kanamycin to the aptamer than to the AuNPs as well as aptamer conformational changes. The use of SERS can be a potential tool to rapidly screen and validate the aptamer and target interaction for the application of aptamer–gold nanoparticle (AuNP) based colorimetric assays.