Gold film over very small (107 nm) spheres as efficient substrate for sensitive and reproducible surface‐enhanced Raman scattering (SERS) detection of biologically important molecules

• Published in: Journal of Raman spectroscopy 2018-03, Vol.49 (3), p.499-505
• Main Authors: Štolcová, Lucie, Peksa, Vlastimil, Proška, Jan, Procházka, Marek
• Format: Article
• Language: English
• Subjects: Alkaloids; AuFON; biomolecules; Fabrication; Gold; Nanospheres; Nicotine; Polystyrene; Polystyrene resins; Protoporphyrin; Protoporphyrin IX; Raman spectra; Reproducibility; Sensitivity; SERS; Spectral sensitivity; Strychnine; Substrates
• ISSN: 0377-0486; 1097-4555
• DOI: 10.1002/jrs.5317

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 (107 nm in diameter) polystyrene spheres coated with 20 nm 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 100× 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 8.2 × 10−7 and 4.5 × 10−7 M (in order of 100 ng.ml−1) incubation concentration for strychnine and nicotine, respectively. Therefore, we conclude that the 20‐nm gold film deposited on polystyrene spheres of 107 nm 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. Au films over very small (107 nm) spheres (AuFON) were used for SERS spectroscopy of biologically important molecules. We demonstrated sensitive and reproducible SERS detection of thiolated‐polyA, protoporphyrin IX, and two alkaloids (nicotine and strychnine). Relative standard deviation of SERS signal was found to be less than 20%.