Dynamic and Reversible Accumulation of Plasmonic Core‐Satellite Nanostructures in a Light‐Induced Temperature Gradient for In Situ SERS Detection

Abstract

A surface‐enhanced Raman spectroscopy (SERS) detection method that allows dynamic on‐demand generation of SERS substrates at locations of interest for in situ molecular sensing is demonstrated. Thermal convection and thermophoresis, which are both generated in a laser‐induced temperature gradient, are used to accumulate suspended plasmonic nanostructures to form 3D SERS substrate. Raman signals of melamine, which is used as a model analyte, increase to ≈117‐fold within 2 min of laser irradiation because of the accumulation. In addition, it is demonstrated that the accumulation of the nanostructures is reversible, and that reproducible SERS effects can be obtained during a repeated heating and cooling process. Because of the capability of on‐demand generation of a high density of SERS hot spots at different locations in solution, this particle manipulation and SERS detection method is applicable to monitor temporal and spatial variations of the concentrations of molecules. The complexity of the detection system remains the same when using this method since all the measurements are performed with a conventional Raman system and simple fluid channels. The required temperature gradient is generated by the laser used to excite Raman signals, and no nanofabricated substrates and complicated microfluidic or optical components are needed.

Opto-Thermophoretic Manipulation

“…One of the interesting aspects is the possible relevance of thermophoresis to the origin of life, where the replication and accumulation of nucleotides under the non-equilibrium thermal condition on the early earth led to molecular assembly and evolution. 13−15 In recent decades, thermophoresis has been extensively exploited as a facile and contact-free technique for manipulation of colloidal particles and biomolecules, 16,17 throughs in colloidal assembly, 18,19 microfluidics, 20,21 sensing, 22,23 and biology. 24−27 Thermophoretic manipulation is a two-step process, that is, the design and acquisition of the temperature gradient field and the directed migration under the temperature gradient.…”

“…This general phenomenon provides a potential strategy to manipulate target objects in fluidic environments. One of the interesting aspects is the possible relevance of thermophoresis to the origin of life, where the replication and accumulation of nucleotides under the non-equilibrium thermal condition on the early earth led to molecular assembly and evolution. − In recent decades, thermophoresis has been extensively exploited as a facile and contact-free technique for manipulation of colloidal particles and biomolecules, , which contributes to tremendous breakthroughs in colloidal assembly, , microfluidics, , sensing, , and biology. − …”

Reversible assembly of nanoparticles: theory, strategies and computational simulations

“…Among all stimulus to control the assembly process of nanoparticles, light is one of the most attractive because it is noninvasive and can be applied remotely and easily modulated, as also recently highlighted by Klajn and coworkers. 205 Although optical trapping 206 and thermophoresis 207,208 have been exploited to control the assembly of NPs, this strategy is mainly based on the functionalization of NPs with ligands containing photoresponsive groups that can be reversibly photoi- somerized, between a conformation that favors assembly and one that favors the disassembly of nanoparticles (Fig. 15a and b), or photodimerized (Fig.…”

Recent progress of microfluidics in surface‐enhanced Raman spectroscopic analysis

“…High-density hot spots can be achieved through microfluidic particle preconcentration techniques in external injection microfluidic SERS detection system, with the help of variously assisted fields including force [85][86][87][88][89][90], electric [91][92][93], magnetic [94], acoustic [95], and thermal [96] fields. Figure 4 summarizes typical microfluidic particle preconcentration techniques.…”

“…A controllable AgNPs aggregation occurred by placing microdroplet of sample and AgNPs on their microchip device, which enables SERS analysis of intracellular oxidative damage. Recently, light-induced thermal field was applied by Kang et al [96] for SERS-active particle preconcentration. According to the phenomena of nanoparticle migrations in temperature gradient, a laser irradiation takes place on the SERS detection point of their microchannel.…”