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

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 (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.

Recent advances in linear and nonlinear Raman spectroscopy. Part XIII

“…They report that measured relative standard deviation values of AgNPs grown with optimum successive ionic layer adsorption and reduction parameters suggest an excellent homogeneity and reproducibility of the SERS signal . Stolcova and co‐workers described gold films over very small (107 nm) spheres as an efficient substrate for sensitive and reproducible SERS detection of biologically important molecules . Wu et al reported both solution and solid substrates with built‐in calibration for quantitative SERS applications.…”

“…[20] Stolcova and co-workers described gold films over very small (107 nm) spheres as an efficient substrate for sensitive and reproducible SERS detection of biologically important molecules. [21] Wu et al reported both solution and solid substrates with built-in calibration for quantitative SERS applications. The internal and external enhancement factor calculation of the two types of SERS substrates indicates a promising method to further improve the reliability of the SERS analysis.…”

Surface‐enhanced Raman scattering studies of gold‐coated ripple‐like nanostructures on iron substrate achieved by femtosecond laser irradiation in water

“…Giant enhancements in SERS signals can be observed when the analyte molecule is in between two adjacent NPs/NSs (separated by few nm distances), generally referred to as hotspots. During the past few years, intense efforts have been directed towards fabricating efficient SERS substrates with high sensitivity, high reproducibility, long‐term stability, and low cost but several efforts are on to achieve all these qualities in a single substrate . In this regard, several micro/nanofabrication techniques were investigated for the preparation of SERS substrates such as nanolithography, chemical deposition, self‐assembly, and ultrafast laser ablation in liquids (ULAL) techniques .…”

“…During the past few years, intense efforts have been directed towards fabricating efficient SERS substrates with high sensitivity, high reproducibility, long‐term stability, and low cost but several efforts are on to achieve all these qualities in a single substrate . In this regard, several micro/nanofabrication techniques were investigated for the preparation of SERS substrates such as nanolithography, chemical deposition, self‐assembly, and ultrafast laser ablation in liquids (ULAL) techniques . Among these, ULAL is a viable and straightforward approach to fabricate novel NPs/NSs with diverse morphologies in a single step, and it has several advantages over the conventional techniques, especially regarding controllability and repeatability .…”

“…[12][13][14][15] In this regard, several micro/nanofabrication techniques were investigated for the preparation of SERS substrates such as nanolithography, chemical deposition, self-assembly, and ultrafast laser ablation in liquids (ULAL) techniques. [15][16][17][18] Among these, ULAL is a viable and straightforward approach to fabricate novel NPs/NSs with diverse morphologies in a single step, and it has several advantages over the conventional techniques, especially regarding controllability and repeatability. [17] Notably, the NPs/NSs morphology can be altered by tuning the various laser parameters such as pulse width, laser power, scan rate, and the surrounding media.…”