Making good use of interactions between analyte molecules and the metal nanoparticles is key to impact the detection limit in a surface-enhanced Raman scattering (SERS) based detections. SERS was applied to the analysis of catechin and it was found that the relative abundance of catechin in the sample to citrate-capped AgNPs and the aggregation agent NaCl plays a critical role in the quality of detection. At a component volume ratio of 6:2:1 (catechin:AgNPs:NaCl), catechin can be detected at µM levels. When the ratio is 12:2:1, Raman signals are discernible even at the attomolar concentration level (10−18 M). Under these conditions, the SERS mechanisms and the force of laser tweezers function best. The extent of signal enhancement enabled an ultrasensitive and reproducible Raman spectroscopic determination of catechin.
