Development of Digital Nanoplasmonmetry Method for Label-Free Detections of Small Biomolecules

We present a local surface plasmon resonance (LSPR)-based digital nanoplasmonmetry (DiNM) method for sensitively detecting biomolecules without labeling. This method simultaneously compares scattering images of gold nanoparticles (AuNPs) in the left band (L) and right band (R) of the LSPR peak. The LSPR redshift due to biomolecular absorption results in a decrease of the L band and an increase of the R band. The changes of (R-L)/(R+L) of each AuNP are counted and analyzed using a digital analysis approach. The DiNM method has a detection limit down to 1 pg/mL, which is three orders of magnitude smaller than conventional LSPR immunoassays. The DiNM can further be applied for small molecule detections, e.g., pesticides. The blind tests for pesticides show a high consistency with the standard method, and the rate of true positives was 83% and 87.5% for green and black teas, respectively.