Paper-based readout to improve the measuring accuracy of gold nanoparticle aggregation-based colorimetric biosensors

The dynamic process of nanoparticle aggregation, especially the salt-induced aggregation that has a high aggregation rate in 300 seconds, is an obstacle to accurate signal capture in a predetermined time and well-repeatable result acquisition for biosensing purposes. In this study, chromatography paper was used to inhibit the aggregating process of gold nanoparticles (AuNPs) in a label-free ssDNA and unmodified AuNP system. To verify the inhibition ability of the chromatography paper towards AuNP aggregation, the aggregation behavior of AuNPs in solution state and on the chromatography paper was studied through monitoring the surface plasmon resonance (SPR) absorbance of 13 nm AuNPs at 520 and 650 nm (A650/A520). To avoid the effect of environmental light during data acquisition, a UV-vis diffuse reflectance spectrometer was employed for paper samples instead of a smartphone as a signal recorder. Then, the paper-based biosensor was applied to our pH alarm system and the biosensing of ochratoxin A, and the results showed that the paper-based assay provided accurate sensing results with stable signals as compared to the solution assay.