Abstract
Surface-enhanced Raman spectroscopy (SERS)-based biosensors have recently been extensively developed because of their high sensitivity and nondestructive nature. Conventional SERS substrates are unsuitable for detecting biomolecules directly from human skin. As a result, considerable effort is being devoted on developing a gel-based SERS sensor capable of segregating and detecting biomolecules because of differences in molecular transport phenomena within the gel. However, no comprehensive studies on the transport processes of molecules in gels have been published for gel-type SERS sensors. This paper reports the differences in the transport phenomena of different molecules based on the time change of SERS spectrum intensity. The Au nanorod array substrate was coated with HEC gel to prepare a sample cell to study diffusion. The SERS spectra of aqueous solutions of 9 types of molecules were measured using the prepared sample cells. The rate at which each molecule diffuses into the gel differs depending on the molecule. The time variation of the characteristic SERS peak of each molecule was investigated on the basis of a one-dimensional diffusion model, and the diffusion coefficient D was calculated for each molecule. The diffusion coefficient was compared with the molecular weight and size, and it was discovered that the larger the molecular weight and size, the slower the diffusion, which is consistent with molecular motion theory and the inhibitory effect of the gel substance.
Highlights
The molecular weight, molecular formula, van der Waals volume, and solventexposed surface area (SEA) of the nine types of Raman probes used in this study are shown in Table 1, and the molecular structure is shown in Figure S1 (Supplementary Information)
In conclusion, we investigated the differences in transport processes of molecules of varying molecular weight as a function of SERS intensity when dispersed across HEC gel
We investigated a model function that can characterize this temporal change and derived the diffusion coefficient D for each molecule that matches the experimental observations
Summary
Surface-enhanced Raman spectroscopy (SERS) is a vibrational spectroscopic technique that has emerged as a promising method for the non-destructive study of materials down to the single-molecule level.(Schlucker 2013) SERS has proven to be a powerful analysis tool for molecular structure analysis, cell imaging, and biomolecule detection, among other things.(Kumar et al 2015; El-Zahry and Lendl 2018; Yu et al 2020; Hickey and He 2021) SERS has found its application in the fields of physics, chemistry, and biology, and in engineering, pharmacy, and medicine.(McNay et al 2011; Sharma et al 2012; Bochenkov et al 2015; Singh et al 2019; Segawa et al 2019a; Kumar et al 2020c, d) Surfaceenhanced Raman scattering is the phenomenon of enormous enhancement in the Raman scattering cross-section of molecules adsorbed in the vicinity of plasmonic nanoparticles.(Le Ru and Etchegoin 2009) Recently, SERS-based biosensors have been proposed for the detection of trace levels of biomolecules and diagnostics.(Kumar et al 2015; Premasiri et al 2018; Joseph et al 2018) A SERS substrate is any nanostructure that supports SERS enhancement. Yu and White have reported paper-based SERS devices for chromatographic separation and detection of target analytes in complex samples.(Yu and White 2013) because of differences in the transport processes of biomolecules that permeate through the gel, gelbased SERS sensors may differentiate and detect biomolecules. If this technology is developed, it may serve as a biosensor and a new means of analyzing biomolecules.
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