Gold film over very small (107nm) spheres as efficient substrate for sensitive and reproducible surface-enhanced Raman scattering (SERS) detection of biologically important molecules
Abstract
Gold plasmonic nanostructures with high sensitivity and spectral reproducibility are key components of molecular sensors based on surface-enhanced Raman scattering (SERS). In this paper, we report a bottom-up fabrication of gold film over nanosphere (FON) substrates for SERS sensing on the basis of very small (107nm in diameter) polystyrene spheres coated with 20nm of gold.
To obtain close-packed spheres in a large scale area, the self-assembly at the water-air interface was found to be very efficient. Sensitivity and reproducibility of the AuFON substrates were tested using various molecular probes: 5,10,15,20-tetrakis(1-methyl-4-pyridyl)porphyrin, p-aminothiophenol, and benzocaine.
Relative standard deviation of SERS signal was found to be less than 20% confirming good spectral reproducibility especially using a 100x objective. Then, we demonstrated sensitive SERS detection of other biologically important molecules adsorbed on our AuFON substrates: thiolated-polyA, protoporphyrin IX, and two alkaloids (nicotine and strychnine).
Estimated limits of detection were 8.2x10(-7) and 4.5x10(-7)M (in order of 100ng.ml(-1)) incubation concentration for strychnine and nicotine, respectively. Therefore, we conclude that the 20-nm gold film deposited on polystyrene spheres of 107nm in diameter provided both good spectral reproducibility and sensitivity.
Their implementation into the SERS-active system will enable to bring about new quantitative and analytical SERS applications.