Functional silver nanostructured surfaces applied in SERS and SIMS

Remarkable differences in the voltammetric response towards hydrogen peroxide, oxygen and Ru(NH3)63+ of electrode interfaces modified with HF or LiF-HCl etched Ti3C2Tx MXene

An electrochemical study was performed on the behavior of Ti₃C₂T_x MXenes prepared by using either HF (MXene1) or LiF/HCl as etchants (MXene2). The use of two redox probes indicates the presence of a higher negative charge density on MXene2 in comparison to MXene1. The characterization of two nanomaterials shows that titanium and fluoride are present higher by one order of magnitude at the interface of MXene2, compared to MXene1. The high Ti and F content is accompanied by a 82-fold larger (249 μA·cm^-2 vs. 5.64 μA·cm^-2) anodic peak at the peak potential near 0.4 V (vs. Ag/AgCl). Similarly, the peak current on MXene2 is 317-fold higher for the oxygen reduction at pH 7.0 (at a voltage of -0.84 V) and 215-fold higher for the reduction of H₂O₂ at -0.89 V, when compared to MXene1. Graphical abstractDifference in electrochemical behavior of MXene prepared by HF (MXene1) and LiF/HCl (MXene2) as etchants.

SERS active self-assembled diphenylalanine micro/nanostructures: A combined experimental and theoretical investigation

Enhancing Raman signatures of molecules by self-assembled metal nanoparticles, nanolithography patterning, or by designing plasmonic nanostructures is widely used for detection of low abundance biological systems. Self-assembled peptide nanostructures provide a natural template for tethering Au and Ag nanoparticles due to its fractal surface. Here, we show the use of L,L-diphenylalanine micro-nanostructures (FF-MNSs) for the organization of Ag and Au nanoparticles (Nps) and its potential as surface-enhanced Raman scattering (SERS)-active substrates. The FF-MNSs undergo an irreversible phase transition from hexagonally packed (hex) micro-nanotubes to an orthorhombic (ort) structure at ∼150 °C. The metal Nps form chains on hex FF-MNSs as inferred from transmission electron microscopy images and a uniform non-aggregated distribution in the ort phase. The high luminescence from the ort FF-MNS phase precludes SERS measurements with AgNps. The calculated Raman spectra using density-functional theory shows a higher intensity from rhodamine 6G (R6G) molecule in the presence of an Ag atom bound to ort FF compared with hex FF. The SERS spectra obtained from R6G bound to FF-MNSs with AuNps clearly show a higher enhancement for the ort phase compared with hex FF, corroborating our theoretical calculations. Our results indicate that FF-MNSs both in the hex and ort phases can be used as substrates for the SERS analysis with different metal nanoparticles, opening up a novel class of optically active bio-based substrates.

Electrochemical performance of Ti3C2Tx MXene in aqueous media: towards ultrasensitive H2O2 sensing

An extensive characterization of pristine and oxidized Ti₃C₂T_x (T: =O, -OH, -F) MXene showed that exposure of MXene to an anodic potential in the aqueous solution oxidizes the nanomaterial forming TiO₂ layer or TiO₂ domains with subsequent TiO₂ dissolution by F^- ions, making the resulting nanomaterial less electrochemically active compared to the pristine Ti₃C₂T_x. The Ti₃C₂T_x could be thus applied for electrochemical reactions in a cathodic potential window i.e. for ultrasensitive detection of H₂O₂ down to nM level with a response time of approx. 10 s. The manuscript also shows electrochemical behavior of Ti₃C₂T_x modified electrode towards oxidation of NADH and towards oxygen reduction reactions.

Nanocrystalline Ag microflowers as a versatile SERS platform

In this paper, the synthesis of Ag microflowers for use as manipulable and reusable substrates in surface enhanced Raman spectroscopy (SERS) is demonstrated, working with ultra-low volumes of the analyte. Flower-like AgBr crystallites with a growth direction of 〈110〉 were first obtained by thermolysing a complex obtained by the stabilization of (AgCl2)(-) anions with tetraoctylammonium bromide. NaBH4 reduction leads to the formation of porous Ag microflowers (50-100 μm) with interconnected nanoparticles. The coupling of the nanoparticles in the microflower results in broadband extinction from visible to IR wavelengths, facilitating SERS using both red and green wavelengths. Using thiophenol as test analyte, uniform SERS enhancement factors in the range of 10(6)-10(8) have been achieved from different parts of the microflower. The microflowers have been used for labeled and non-labeled detection of both single- and double-stranded DNA and using simple manipulation techniques, SERS data have been collected from ultra-low volumes of the analyte solution (∼0.34 nL). The reusability of the substrate for SERS over multiple cycles involving a rapid and efficient wet chemical cleaning procedure is also demonstrated. Finally, by placing the microflower in a microfluidic device, chemical reactions have been examined in situ.

Novel Ag/Au/Pt trimetallic nanocages used with surface-enhanced Raman scattering for trace fluorescent dye detection

Trimetallic nanocages possess inter-metallic synergies among elements and are able to generate significant SERS signal enhancement due to “hot spot” formation.