Abstract:Plasmonics is an emerging field that examines the interaction between light and metallic nanostructures at the metal-dielectric interface. Surface-enhanced Raman scattering (SERS) is a powerful analytical technique that uses plasmonics to obtain detailed chemical information of molecules or molecular assemblies adsorbed or attached to nanostructured metallic surfaces. For bioanalytical applications, these surfaces are engineered to optimize for high enhancement factors and molecular specificity. In this review we focus on the fabrication of SERS substrates and their use for bioanalytical applications. We review the fundamental mechanisms of SERS and parameters governing SERS enhancement. We also discuss developments in the field of novel SERS substrates. This includes the use of different materials, sizes, shapes, and architectures to achieve high sensitivity and specificity as well as tunability or flexibility. Different fundamental approaches are discussed, such as label-free and functional assays. In addition, we highlight recent relevant advances for bioanalytical SERS applied to small molecules, proteins, DNA, and biologically relevant nanoparticles. Subsequently, we discuss the importance of data analysis and signal detection schemes to achieve smaller instruments with low cost for SERS-based point-of-care technology developments. Finally, we review the main advantages and challenges of SERS-based biosensing and provide a brief outlook.

We demonstrate a simple method to prepare porous biosilica plasmonic composites on an inexpensive flexible substrate. The method does not require any chemical modification of the materials, and it allows the deposition of the nanocomposite on regular office-grade adhesive tape. This material was further characterized via scanning electron microscopy and optical microscopy, revealing unique properties such as pore size, plasmon resonance, and Raman enhancement factors suitable for biosensing applications. To demonstrate the usability of these strips in SERSbased sensing applications, we performed measurements on several proteins and bacteria of interest. Because of the porous nature of the nanocomposite, smaller proteins and nanostructures disperse within the material and present a reduced particle density for optical detection, which limits the ability to measure low concentrations of the analyte. On the other hand, particles that are larger than ∼100 nm concentrate at the top surface of the material and will be easier to detect via focused optical beams. We demonstrate that SERS can help detect and identify bacteria on this nanocomposite and believe that other applications are possible as well, in particular for the chemical characterization of biological particles of nano-to micrometer sizes.

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