A SERS platform based on diatomite modified by gold nanoparticles using a combination of layer-by-layer assembly and a freezing-induced loading method.

Siliceous diatom frustules represent an up-and-coming platform for a range of bio-assisted nanofabrication processes able to overcome the complexity and high cost of current engineering technology solutions in terms of negligibly small power consumption and environmentally friendly processing combined with unique highly porous structures and properties. Herein, the modification of diatomite - a soft, loose, and fine-grained siliceous sedimentary rock composed of the remains of fossilized diatoms - with gold nanoparticles using layer-by-layer technology in combination with a freezing-induced loading approach is demonstrated. The obtained composite structures are characterized by dynamic light scattering, extinction spectroscopy, scanning (SEM) and transmission electron microscopy (TEM), and photoacoustic imaging techniques, and tested as a platform for surface-enhanced Raman scattering (SERS) using Rhodamine 6G. SEM, TEM, and energy dispersive X-ray spectroscopy (EDX) confirmed a dense coating of gold nanoparticles with an average size of 19 nm on the surface of the diatomite and within the pores. The photoacoustic signal excited at a wavelength of 532 nm increases with increasing loading cycles of up to three polyelectrolyte-gold nanoparticle bilayers. The hybrid materials based on diatomite modified with gold nanoparticles can be used as SERS substrates, but also as biosensors, catalysts, and platforms for advanced bioimaging.

SERS Platform Based on Hollow-Core Microstructured Optical Fiber: Technology of UV-Mediated Gold Nanoparticle Growth.

Surface-enhanced Raman spectroscopy (SERS) is a powerful technique for biosensing. However, SERS analysis has several concerns: the signal is limited by a number of molecules and the area of the plasmonic substrate in the laser hotspot, and quantitative analysis in a low-volume droplet is confusing due to the change of concentration during quick drying. The usage of hollow-core microstructured optical fibers (HC-MOFs) is thought to be an effective way to improve SERS sensitivity and limit of detection through the effective irradiation of a small sample volume filling the fiber capillaries. In this paper, we used layer-by-layer assembly as a simple method for the functionalization of fiber capillaries by gold nanoparticles (seeds) with a mean diameter of 8 nm followed by UV-induced chloroauric acid reduction. We also demonstrated a simple and quick technique used for the analysis of the SERS platform formation at every stage through the detection of spectral shifts in the optical transmission of HC-MOFs. The enhancement of the Raman signal of a model analyte Rhodamine 6G was obtained using such type of SERS platform. Thus, a combination of nanostructured gold coating as a SERS-active surface and a hollow-core fiber as a microfluidic channel and a waveguide is perspective for point-of-care medical diagnosis based on liquid biopsy and exhaled air analysis.