We will present surface enhanced Raman spectroscopy (SERS) detection of molecules using plasmonic nanoparticles that are embedded in agarose gel and in filter paper-integrated microfluidic channels, respectively. It has been known that, when SERS detection is performed in complex fluids such as cell culture media, a method to reduce interferences from a variety of molecules in the fluids on the detection results is very important. If continuous monitoring of molecules in cell culture media is needed, there should be a method to prevent large molecules such as proteins from reaching SERS substrates when sample solutions flow over the substrates. Since both agarose gel and filter paper can be used to separate molecules by size, in this study we have integrated them with plasmonic nanoparticles for SERS detection in complex fluids. We will report how to use filter paper-integrated microfluidic channels to detect melamine and sodium thiocyanate (NaSCN) in milk using SERS. In addition, we will demonstrate how to use plasmonic agarose gels to detect illegal drug in urine.
Surface enhancement Raman spectroscopy (SERS) has drawn much attention in recent years because its ability to greatly enhance Raman signals to allow for the detection of molecules at low concentration. When using metallic nanoparticles as SERS substrates, many studies have shown that the size of the interparticle gap significantly affects the enhancement of the Raman signals. Given that the optimal interparticle gap is as small as a few nanometers, fabricating sensitive, uniform, and reproducible SERS substrates remains challenging. Here we report a three-dimensional SERS substrate created through the assembly of core-shell nanoparticles using DNA. By using DNA of appropriate sequence and length, DNA-functionalized nanoparticles were assembled into ordered and highly packed nanostructures. The interparticle distance was precisely controlled by adjusting the design of the DNA and the thickness of the silver shell coated on the gold nanoparticles. Compared with randomly aggregated nanoparticles, the interparticle distance in the synthesized nanostructures can be more uniform and better controlled. In addition, the DNA-guided assembly process allows us to create precise nanostructures without using complex and expensive fabrication methods. The study demonstrates that the synthesized nanostructures can be used as effective SERS substrates to successfully measure the Raman signals of malachite green, a toxic compound that is sometimes illegally used on fish, as well as Fluorescein isothiocyanate (FITC) at low concentrations.
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