Development of Gold Nanoparticle-Based SERS Substrates on TiO2-Coating to Reduce the Coffee Ring Effect

Hydrophilic surface-enhanced Raman spectroscopy (SERS) substrates were prepared by a combination of TiO₂-coatings of aluminium plates through a direct titanium tetraisopropoxide (TTIP) coating and drop coated by synthesised gold nanoparticles (AuNPs). Differences between the wettability of the untreated substrates, the slowly dried Ti(OH)₄ substrates and calcinated as well as plasma treated TiO₂ substrates were analysed by water contact angle (WCA) measurements. The hydrophilic behaviour of the developed substrates helped to improve the distribution of the AuNPs, which reflects in overall higher lateral SERS enhancement. Surface enhancement of the substrates was tested with target molecule rhodamine 6G (R6G) and a fibre-coupled 638 nm Raman spectrometer. Additionally, the morphology of the substrates was characterised using scanning electron microscopy (SEM) and Raman microscopy. The studies showed a reduced influence of the coffee ring effect on the particle distribution, resulting in a more broadly distributed edge region, which increased the spatial reproducibility of the measured SERS signal in the surface-enhanced Raman mapping measurements on mm scale.

Fast High-Resolution Screening Method for Reactive Surfaces by Combining Atomic Force Microscopy and Surface-Enhanced Raman Scattering

A fast high-resolution screening method for reactive surfaces is presented. Atomic force microscopy (AFM) and surface-enhanced Raman spectroscopy (SERS) are combined in one method in order to be able to obtain both morphological and chemical information about processes at a surface. In order to accurately align the AFM and SERS images, an alignment pattern on the substrate material is exploited. Subsequent SERS scans with sub-micron resolution are recorded in 30 min per scan for an area of 100 × 100 µm² and are accompanied by morphological information, supplied by a fast AFM, of the same area. Hence, a complete reactivity overview is obtained within several hours with only a monolayer of reactant. To demonstrate the working principle of this method, a SERS substrate containing the alignment pattern and silver nanoparticle aggregates as catalytic sites is prepared to study the photo-catalytic reduction of p-nitrothiophenol ( p-NTP).

A primary SERS-active interconnected Si-nanocore network for biomolecule detection with plasmonic nanosatellites as a secondary boosting mechanism

We report in this study, the development of a polymorphic biosensitive Si nanocore superstructure as a SERS biosensing platform.

New post-processing method of preparing nanofibrous SERS substrates with a high density of silver nanoparticles

The protocol to control density of AgNP on surfaces of nanofibers, and thus electromagnetic hotspots by variation of Tollens' reagent is established. Nanofiber films enable SERS either of solutes or macromolecular structures such as bacterial cells.

A nanoaggregate-on-mirror platform for molecular and biomolecular detection by surface-enhanced Raman spectroscopy

A nanoaggregate-on-mirror (NAOM) structure has been developed for molecular and biomolecular detection using surface-enhanced Raman spectroscopy (SERS). The smooth surface of the gold mirror allows for simple and homogeneous functionalization, while the introduction of the nanoaggregates enhances the Raman signal of the molecule(s) in the vicinity of the aggregate-mirror junction. This is evidenced by functionalizing the gold mirror with 4-nitrothiophenol, and the further addition of gold nanoaggregates promotes local SERS activity only in the areas with the nanoaggregates. The application of the NAOM platform for biomolecular detection is highlighted using glucose and H2O2 as molecules of interest. In both cases, the gold mirror is functionalized with 4-mercaptophenylboronic acid (4-MPBA). Upon exposure to glucose, the boronic acid moiety of 4-MPBA forms a cyclic boronate ester. Once the nanoaggregates are added to the surface, detection of glucose is possible without the use of an enzyme. This method of indirect detection provides a limit of detection of 0.05 mM, along with a linear range of detection from 0.1 to 15 mM for glucose, encompassing the physiological range of blood glucose concentration. The detection of H2O2 is achieved with optical inspection and SERS. The H2O2 interferes with the coating of the gold mirror, enabling qualitative detection by visual inspection. Simultaneously, the H2O2 reacts with the boronic acid to form a phenol, a change that is detected by SERS.