A facile solvent mediated self-assembly silver nanoparticle mirror substrate for quantitatively improved surface enhanced Raman scattering

Abstract

Herein, a facile solvent mediated silver nanoparticle (AgNP) mirror was introduced as a reproducible and sensitive surface-enhanced Raman scattering (SERS) substrate. The AgNP mirror was fabricated based on commercially available citrate coated AgNPs via a facile and unique water–solvent interface assembly method without using any electrical equipment. By adding 0.2 mg ml⁻¹ citrate coated AgNPs dropwise into a mediating solvent, self-assembled AgNP mirrors were formed instantly and gradually settled down at the bottom. The mediating solvent is the key for this fabrication, which should contain a mixture of a non-polar (e.g. hexane, cyclohexane, and iso-octane) and a polar (e.g., acetonitrile, acetone, methanol, and ethanol) organic solvents that have a lower density than water. The fabricated AgNP mirror showed a uniform monolayer arrangement which produced highly reproducible and sensitive signals. The coefficient of variance (i.e., percentage relative standard deviation) for AgNP mirrors was 7.3% compared to 33.0% for AgNP aggregates. A lower limit of detection (0.008 ppm) and a higher coefficient of determination (0.9981) for the detection of the fonofos pesticide were also obtained from the AgNP mirror compared to that from the AgNP aggregates. The practical application of this nanoscale AgNP mirror sensing substrate was also confirmed by its accurate quantification of 0.5 ppm fonofos in apple juice and green tea (i.e., 105.06% and 106.16% recovery value, respectively).