Silver-Nanoparticle-Decorated Gold Nanorod Arrays via Bioinspired Polydopamine Coating as Surface-Enhanced Raman Spectroscopy (SERS) Platforms

Mehmet Yilmaz

doi:10.3390/coatings9030198

Abstract

The controlled deposition of nanoparticles onto 3-D nanostructured films is still facing challenges due to the uncontrolled aggregation of colloidal nanoparticles. In the context of this study, a simple yet effective approach is demonstrated to decorate the silver nanoparticles (AgNP) onto the 3-D and anisotropic gold nanorod arrays (GNAs) through a bioinspired polydopamine (PDOP) coating to fabricate surface-enhanced Raman spectroscopy (SERS) platforms. Since the Raman reporter molecules (methylene blue, MB, 10 µM) were not adsorbed directly on the surface of the plasmonic material, a remarkable decrease in SERS signals was detected for the PDOP-coated GNAs (GNA@PDOP) platforms. However, after uniform and well-controlled AgNP decoration on the GNA@PDOP (GNA@PDOP@AgNP), huge enhancement was observed in SERS signals from the resultant platform due to the synergistic action which originated from the interaction of GNAs and AgNPs. I also detected that PDOP deposition time (i.e., PDOP film thickness) is the dominant parameter that determines the SERS activity of the final system and 30 min of PDOP deposition time (i.e., 3 nm of PDOP thickness) is the optimum value to obtain the highest SERS signal. To test the reproducibility of GNA@PDOP@AgNP platforms, relative standard deviation (RSD) values for the characteristic peaks of MB were found to be less than 0.17, demonstrating the acceptable reproducibility all over the proposed platform. This report suggests that GNA@PDOP@AgNP system may be used as a robust platform for practical SERS applications.

Highlights

Surface-enhanced Raman spectroscopy (SERS) has attracted remarkable attention as a highly sensitive and powerful approach for the detection of chemical and biological substances in trace amount, since its discovery in 1974 [1,2,3,4,5]
The gold nanorod arrays (GNAs) were fabricated via a physical vapor deposition (PVD) system (NANOVAK HV, Ankara, Turkey)
We showed that directional GNAs having tilt angles could be created on solid substrates via the oblique angle deposition (OAD) technique and the surface densities of the resultant films can be controlled by manipulating the deposition angle (α) [25]

Summary

Introduction

Surface-enhanced Raman spectroscopy (SERS) has attracted remarkable attention as a highly sensitive and powerful approach for the detection of chemical and biological substances in trace amount, since its discovery in 1974 [1,2,3,4,5]. Some recent studies depicted the employment of inorganic [6,7,8,9] and organic semiconductors [10,11,12] as SERS platforms, nanostructures of noble metals are still major systems in SERS applications. The increase in Raman signals basically is originated to the enhancement in electromagnetic field due to the close vicinity (in nm scale) of plasmonic nanostructures [4]. To obtain the fingerprint SERS spectra of analyte molecules at ultralow concentrations, various approaches have been demonstrated to fabricate a sensitive, selective, and reliable SERS platforms [3,13]. 2-D/3-D plasmonic nanostructures are the main strategies to fabricate SERS platforms.

Methods

Results

Conclusion