Surface-Enhanced Raman scattering of methylene blue on titanium nitride nanoparticles synthesized by laser ablation in organic solvents

Laser polarization as a critical factor in the SERS-based molecular sensing performance of nano-gapped Au nanowires

Nowadays, Au dimer-based nanostructures are exhaustively studied due to their outstanding potential as plasmonic nanoantennas for future applications in high-sensitivity molecular sensing by Surface-Enhanced Raman Spectroscopy (SERS). In this work, we analyze nano-gapped Au nanowires (NWs) or Au-NW dimers for designing efficient nanoantennas, reporting an exhaustive study about dimer length and laser polarization orientation effects on their SERS-based molecular sensing performance. Arrays of nanoantennas with gaps of about 22 ± 4 nm, nominal square cross-sections of 60 nm × 60 nm, and different segment lengths from 300 nm up to 1200 nm were fabricated by Au evaporation and subsequent e-beam lithography. The SERS performance was studied by confocal Raman microscopy using a linearly-polarized 633 nm laser. A critical impact of the polarization alignment on the spectral resolution of the studied Raman marker imprint was observed. The results show that the Raman signal is maximized by aligning the polarization orientation with the nanowire long axis, it is reduced by increasing the relative angle, and it is abruptly minimized when both are perpendicular. These observations were consistent with numerical simulations carried out by the FDTD method, which predicts a similar dependence between the orientation of linearly-polarized light and electric-near field amplification in the nano-gap zone. Our results provide an interesting paradigm and relevant insights in determining the role of laser polarization in the Raman signal enhancement in nano-gapped Au nanowires, showing the key role of this measurement condition on the SERS-based molecular sensing efficiency of this kind of nanostructure.

Colloidal Titanium Nitride Nanoparticles by Laser Ablation in Solvents for Plasmonic Applications

Titanium nitride (TiN) is a candidate material for several plasmonic applications, and pulsed laser ablation in liquids (PLAL) represents a rapid, scalable, and environmentally friendly approach for the large-scale production of nanomaterials with customized properties. In this work, the nanosecond PLAL process is developed, and we provide a concise understanding of the process parameters, such as the solvent and the laser fluence and pulse wavelength, to the size and structure of the produced TiN nanoparticles (NPs). TiN films of a 0.6 μm thickness developed by direct-current (DC) magnetron sputtering were used as the ablation targets. All laser process parameters lead to the fabrication of spherical NPs, while the laser pulse fluence was used to control the NPs' size. High laser pulse fluence values result in larger TiN NPs (diameter around 42 nm for 5 mJ and 25 nm for 1 mJ), as measured from scanning electron microscopy (SEM). On the other hand, the wavelength of the laser pulse does not affect the mean size of the TiN NPs (24, 26, and 25 nm for 355, 532, and 1064 nm wavelengths, respectively). However, the wavelength plays a vital role in the quality of the produced TiN NPs. Shorter wavelengths result in NPs with fewer defects, as indicated by Raman spectra and XPS analysis. The solvent type also significantly affects the size of the NPs. In aqueous solutions, strong oxidation of the NPs is evident, while organic solvents such as acetone, carbides, and oxides cover the TiN NPs.

Application of sensitive SERS plasmonic biosensor for high detection of metabolic disorders

Due to the importance of early detection of metabolic diseases in newborns, it is essential to measure organoacids; L-Tryptophan, Sebacic acid, and Glutaric acid in very low concentrations. Therefore, the necessity of the construction of a powerful nondestructive biosensor just like the surface-enhanced Raman scattering (SERS) sensor is demonstrated. Through the growth of silver dendritic nanostructures on different substrates like aluminum (Al), copper (Cu), indium tin oxide (ITO), and silicon (Si), a new SERS-based biosensor was developed. Because the Raman signal of molecules adsorbed on dendritic nanostructures is significantly increased, SERS biosensors based on these nanostructures can be used to detect very low concentrations of materials. In this study, first, the organoacid L-Lysine was detected up to a concentration of 10^-12 M, by using a biosensor based on Al, Cu, ITO, and Si substrates. Then, by comparing the results obtained from different substrates, the silicon substrate as the most successful substrate with the best results was used in the SERS biosensor to detect the organoacids, L-Tryptophan, Sebacic acid, and Glutaric acid up to a concentration of 10^-12 M. SEM imaging was used to characterize silver dendritic nanostructures on solid substrates. The successful performance of the SERS biosensor based on silver dendrites in this study promises to be effective in diagnostic applications such as cancer diagnosis (the limit of single molecular detection).

Design of high SERS sensitive substrates based on branched Ti nanorods

This paper reports a rational design of branched titanium (Ti) nanorods formed by glancing angle physical vapor deposition and their applications as substrates for surface-enhanced Raman scattering (SERS). Ti nanorods with branches have larger surface areas than non-branched nanorods. However, Ti surface oxidizes easily resulting in very little SERS effect. The SERS sensitivity of the branched titanium nanorod is improved by annealing Ti nanorods in nitrogen in an effort to reduce oxidation. Additionally, the plasmonic resonance of the branched titanium nanorod is further improved by coating the top of the nanorods and branches with silver (Ag). The sensitivity of the SERS substrates is about 3700% that of as-deposited branched Ti nanorods with a native oxide layer. Our investigation provides a mechanism to fabricate sensitive SERS sensors of Ti nanorods that are known to be thermally and chemically stable and compatible with silicon-based electronics.

Nitrogen-Doped Ti3C2Tx MXene Induced by Plasma Treatment with Enhanced Microwave Absorption Properties

Ti₃C₂T_x has microwave absorption (MA) properties due to its dielectric loss, but the absence of magnetic loss capability of pure Ti₃C₂T_x causes unmatched impedance and unsatisfied MA performance. Modification of Ti₃C₂T_x with magnetic particles is an effective way to introduce the magnetic loss mechanism. However, these modified Ti₃C₂T_x particles have higher density and require complicated fabrication processes, restricting the industrial production and functional applications. Here, a low-temperature and simple method of radio-frequency N₂ plasma treatment was adopted to modify Ti₃C₂T_x with N. More interestingly, the N-doped Ti₃C₂T_x flakes demonstrated magnetic properties and thus exhibited drastically enhanced MA properties. The minimum reflection loss (RL_min) of -59.20 dB at 10.56 GHz was achieved in N-doped Ti₃C₂T_x products after only 3 min of plasma treatment, remarkably higher than RL_min of -11.07 dB at 7.92 GHz for the pristine Ti₃C₂T_x. The main mechanism is due to the combination of dielectric loss, magnetic loss, and the good impedance matching in the N-doped Ti₃C₂T_x. Further prolonging the nitriding time induces much desorption of -F and the formation of TiO₂, thus deteriorating the impedance matching and the MA properties.