Reliable and cheap SERS active substrates

Abstract

Raman spectroscopy is a label-free technique for the detection and structural analysis of molecular materials. Unfortunately, Raman signals are inherently weak, so a very low number of scattered photons are available for detection.Surface Enhanced Raman Spectroscopy (SERS) is a useful method to amplify weak Raman signals by an increment of the apparent Raman cross-section of the analyte though the local amplification of the electromagnetic field in the close proximity of metal nanostructures caused by the excitation of localized surface plasmon resonances. Laser excitation resonantly drives the metal surface charges, creating highly localized plasmonic light fields at these photonic structures, which are known as hot-spots. Since the Raman signal is proportional to the intensity of the field, when a molecule is bonded, adsorbed or lies close to the enhanced field of a hot-spot, a huge increase in the Raman signal can be observedusually of several orders of magnitude, consequently boosting the sensibility of the technique to concentrations as low as 10 À18 M or even down to single molecule detection [1,2].A key parameter to take into account in SERS experiments is the choice of the enhancing substrate. SERS substrates can be roughly classified into three main classes: 1. Metallic electrodes: These played an important role in the development of SERS. However, their importance has decreased substantially due to development of substrates with higher amplification power. 2. Metal nanoparticles in solution: Colloids have been and still are very important in the development of the technique. The liquid media is a useful aid to drive target molecules to the plasmonic surfaces, but sometimes the analyte is insoluble or incompatible with the liquid media, representing a problem for its easy and general application. 3. Nanostructured substrates: These may be obtained by two main methods: (a) deposition of metal nanoparticles from colloidal solutions by drying or evaporation of solvent onto appropriate substrates, or (b) fabrication of nanostructured metal surfaces, taking advantage of micro and nano-fabrication techniques.The main obstacle limiting the use of SERS as an everyday and routine lab technique is the lack of suitable substrates. Despite the high number of publications and patents where new active materials are proposed, commercial substrates are still scarce and often expensive and quite unstable, e.g. requiring storage in controlled atmospheres and careful handling to maintain their enhancement properties.The image featured on this issue's cover was taken with a field emission scanning electron microscope (FE-SEM Zeiss Ultra-Plus, at 1.5 kV with an in-lens secondary electron detector) and depicts a nanostructured substrate obtained by drying a colloidal solution of gold nanoparticles on a silicon wafer. These substrates are attractive because of the beauty and variety of morphologies, but also due to the simple synthesis of the nanoparticles and the ease of the fabrication process; however, they are often hinder...

Simple, Flexible, and Ultrastable Surface Enhanced Raman Scattering Substrate Based on Plasmonic Nanopaper Decorated with Graphene Oxide

“…Surface enhanced Raman spectroscopy (SERS) is a viable method to achieve the aforementioned amplification phenomenon, which is able to reach the single‐molecule detection level . Typically, SERS involves a sharp rise in the Raman scattering via the local amplification of the electromagnetic field occurring near noble metal nanomaterials, which is triggered by the excitation of localized surface plasmon resonances (LSPR) . However, it should be considered that SERS also involves other enhancement factors including chemical mechanisms and density of photon states and their theoretical models are well established in the literature .…”

“…Moreover, conventional SERS substrates may suffer from loss of signal reproducibility, low throughput, scarce stability, and limited shelf life. On top of that, SERS substrates built with silver nanostructures are prone to be air sensitive and generally require a controlled environment and a very delicate handling to preserve their desired properties . Consequently, SERS substrates applications are often hindered by these bottlenecks.…”

Graphene Oxide as an Optical Biosensing Platform: A Progress Report

“…[94][95][96] Recently, Chung et al, reported the SPR enhancement at pristine graphene/metal (Au) interface. [105] In addition, composite materials based on noble metal nanoparticles and graphene derivatives have been reported to provide advantageous SERS substrates, see Figure 5C. [97] Moreover, spectroscopic ellipsometry revealed that GO-coated SPR substrates displayed much lower optical absorption in the visible range than its counterpart coated with pristine graphene.…”

Influence of the long-range ordering of gold-coated Si nanowires on SERS

“…These two requirements are mainly influenced by the peculiar method for the deposition of the NSs. To fulfil this task, several deposition techniques have been explored so far, including floating 27 , micropropulsive injection 28 , spin coating 29 or Roll-to-Roll Langmuir-Blodgett 30 . Among all these possible techniques, spin coating is one of the most convenient because of its applicability to wafer-scale processes and simple utilisation.…”