Improving Sensitivity and Reproducibility of SERS Sensing in Microenvironments Using Individual, Optically Trapped Surface-Enhanced Raman Spectroscopy(SERS) Probes

Abstract

Surface-enhanced Raman spectroscopy (SERS) sensors offer many advantages for chemical analyses, including the ability to provide chemical specific information and multiplexed detection capability at specific locations. However, to have operative SERS sensors for probing microenvironments, probes with high signal enhancement and reproducibility are necessary. To this end, dynamic enhancement of SERS (i.e., in-situ amplification of signal-to-noise and signal-to-background ratios) from individual probes has been explored. In this paper, we characterize the use of optical tweezers to amplify SERS signals as well as suppress background signals via trapping of individual SERS active probes. This amplification is achieved through a steady presence of a single "hot" particle in the focus of the excitation laser. In addition to increases in signal and concomitant decreases in non-SERS backgrounds, optical trapping results in an eightfold increase in the stability of the signal as well. This enhancement strategy was demonstrated using both single and multilayered SERS sub-micron probes, producing combined signal enhancements of 24-fold (beyond the native 10 SERS enhancement) for a three-layered geometry. The ability to dynamically control the enhancement offers the possibility to develop SERS-based sensors and probes with tailored sensitivities. In addition, since this trapping enhancement can be used to observe individual probes with low laser fluences, it could offer particular interest in probing the composition of microenvironments not amenable to tip-enhanced Raman spectroscopy or other scanning probe methods (e.g., intracellular analyses, etc.).

Microsphere-supported gold nanoparticles for SERS detection of malachite green

“…7,41 The use of optical tweezers also allows background signals to be reduced due to trapping of individual SERS active probes. 43 Malachite green was chosen as a model probe due to its well characterized Raman activity and…”

“…7,41 The use of optical tweezers also allows background signals to be reduced due to trapping of individual SERS active probes. 43 Malachite green was chosen as a model probe due to its well characterized Raman activity and prevalence as a contaminant in fish stocks. 46,62 Malachite green isothiocyanate has a strong visible absorption at 619 nm, which is far removed from the laser excitation and is therefore not expected to result in significant background fluorescence in the Raman spectrum (Fig.…”

“…7 Metal composites that can be optically trapped have also been prepared as potential SERS probes of cellular membranes. 43 In the final part of this study we demonstrate the SERS activity of individual composite particles to detect malachite green ( MG ). MG is a carcinogenic, teratogenic and mutagenic fungicide used in fish farming that has been restricted or banned in many countries and is not approved by the US Food and Drug Administration.…”

Universal and simple MoO3 substrate for identification of SERS enhancement mechanism

“…The selection of appropriate probe molecules is also required to explore the SERS mechanism. [14] Therefore, filling this knowledge gap is important not only for deepening understanding of SERS but also for developing mechanisms based on Raman analysis techniques.…”

Nanotrap-Enhanced Raman Spectroscopy: An Efficient Technique for Trace Detection of Bioanalytes

“…For example, one such approach focused on developing various fabrication techniques for structural optimization of SERS substrates that can optimize the signal enhancement factor. − However, it still remains challenging to develop a cost-effective and time-saving method that can offer high sensitivity and reproducibility. The other recent approach is to shorten the gap between the pointed structures either by plasmonic trapping of spherical nanoparticles in combination with lithographic patterns − or by evaporation on a slippery surface resulting in the formation of three-dimensional aggregates of nanoparticle and analytes .…”