Surface-enhanced Raman spectroscopy (SERS) is a sensitive and nondestructive technique used for the detection of molecules, traditionally applied on noble-metal or semiconductor substrates. Point defect introduction has been applied to increase the enhancement of semiconductor templates due to more efficient charge transfer; however, they are still limited by low detection sensitivity and inferior SERS enhancement. Here we propose a universal approach of oxygen incorporation into metal oxide nanowire/metal nanoparticle templates that allows for greater SERS enhancement due to localized surface plasmon resonance excitation, point defect-induced optical gap shrinking, and wettability change of the substrate. We report up to 5-fold Raman relative peak intensity enhancement after annealing-induced oxygen introduction. This approach is applied to defect formation in metal oxide semiconductor nanowires such as ZnO, WO 3 , TiO 2 , and NiO and is applicable for a wide variety of probe molecules, making the method suitable for medical, security, and environmental applications.
Piezoelectric quasi-1D peptide nanotubes and plasmonic metal nanoparticles are combined to create a flexible and self-energized surface-enhanced Raman spectroscopy (SERS) substrate that strengthens SERS signal intensities by over an order of magnitude compared to an unflexed substrate. The platform is used to sense bovine serum albumin, lysozyme, glucose, and adenine. Finite-element electromagnetic modelling indicates that the signal enhancement results from piezoelectric-induced charge, which is mechanically-activated via substrate bending. The results presented here open the possibility of using peptide nanotubes on conformal substrates for in situ SERS detection.
Using surface plasmons as a catalyst for surface reactions has been of great interest in recent years. Local surface plasmon resonance excitation has been shown to accelerate the rate of chemical reactions due to the excitation of hot carriers and local temperature increase. Nanocomposites containing both metal and semiconductor have also been used in the field in order to control the charge states in the metal and to allow catalytic activity and selectivity tuning. However, the specific mechanisms responsible for plasmon-driven photocatalysis are still not entirely understood, and the precise control of the catalytic reactions using external stimuli remains challenging. Here we report that the use of thermally annealed tungsten oxide WO 3+x yields an effective substrate for driving catalytic redox reactions when decorated with silver nanoparticles. We show that the rate of the oxidation reaction of p-aminothiophenol (PATP) can be controlled by introducing defects into the semiconductor structure via heat treatment. We suggest that defect introduction allows for more efficient charge generation and transfer and may be used for catalysis of redox reaction for industrial processes.
Molecular
dynamics simulations based on an atomistic empirical
force field have been carried out to investigate structural, thermodynamic,
and dynamical properties of adlayers made of porphyrin-type molecules
physisorbed on surfaces of cellulose Iβ nanocrystals. The results
show that low-index surfaces provide a thermally stable, weakly perturbing
support for the deposition of non-hydrogen-bonded organic molecules.
At submonolayer coverage, the discoidal porphyrin molecules lay flat
on the surface, forming compact 2D clusters with clear elements of
ordering. The adlayer grows layer-by-layer for the smallest porphyrin
species on compact cellulose surfaces, while forming 3D clusters on
a first relatively ordered adlayer (Stranski–Krastanov growth)
in all other cases. The adsorption energy exceeds ∼1 eV per
molecule, underlying the thermal stability of the adsorbate. Entropy
plays a non-negligible role, destabilizing to some extent the adlayer.
The in-plane dynamics of the smallest porphyrin species, i.e., porphine,
on compact surfaces shows signs of superlubricity, due to the low
energy and momentum exchange between the flat admolecule and the equally
flat cellulose surface.
The detection of analytes using spectroscopy methods, such as surface-enhanced Raman spectroscopy (SERS), is crucial in the fields of medical diagnostics, forensics, security, and environmental monitoring. In recent years, a lot of focus has been directed toward organic polymer material-based SERS platforms due to their lower cost, controllable synthesis and fabrication, structural versatility, as well as biocompatibility and biodegradability. Here, we report that cellulose nanofiber-based substrates can be used as a metal-free SERS platform for the detection of porphyrin-type molecules. We report SERS signal enhancement for five different porphyrin molecules with exceptional 2 orders of magnitude peak intensity enhancement observed resulting in a detection limit of 10 −5 M. We show that the cellulose-based platform is more suitable for porphyrin molecule detection than traditionally used semiconductor materials like graphene oxide. The observed enhancement is attributed to the disturbed growth of self-assembled structures on the cellulose nanofibers and the generation of disordered 3D clusters of porphyrin molecules.
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