Insights of adsorption mechanisms of Trp-peptides on plasmonic surfaces by SERS

Tracking chemical interactions of caspofungin on silver nanoparticles through SERS spectroscopy for antifungal applications

Silver nanoparticles (AgNP) act as efficient drug delivery carriers due to particular surface chemistry and high surface area, and even though such may present toxicity in function of the size distribution and molecular ion coverage, have been receiving special attention for their inhibitory potential against bacteria and fungi. This study explored the use of AgNP to deliver the antifungal caspofungin (CFG) for in vitro combating Candida albicans. CFG molecules were coadsorbed with low-weight chitosan (LWC) on AgNP surfaces, in the presence and absence of 2-mercaptoethanol (ME) surface modifier. Surface-enhanced Raman scattering (SERS) spectroscopy was used both to monitor the adsorption process and to assess the synergistic interaction between the components in actions against fungal cultures, observed by checkerboard assays. Results showed significant lowering of minimum inhibitory concentration (MIC) values for the CFG-LWC-AgNP ternary mixture in comparison with CFG alone. Transmission Electron Microscopy (TEM) images provided insights about the mechanism of action of components of the ternary mixture. Spectral analysis of CFG by using FT-Raman, FTIR, and SERS spectroscopies identified distinct spectral patterns, indicating effective chemical interactions of CFG on AgNP surfaces. The vibrational assignment of such spectra was done based on Density Functional Theory (DFT) calculations. Such findings suggest that AgNP could be a promising platform for enhancing the efficacy of CFG drug against fungal infections.

Synthesis and characterization of Au@Ag nanoparticles for multiwavelength SERS biosensing

Gold-core silver-shell (Au@Ag) nanoparticles are promising substrates for surface-enhanced Raman spectroscopy (SERS) due to their tunable plasmonic properties and enhanced stability. In this study, we synthesized Au@Ag nanoparticles with varying core sizes (13 nm and 23 nm) and silver shell thicknesses, controlled via silver nitrate concentration during a seed-mediated growth process. The nanoparticles were characterized using TEM, UV-vis, DLS, and zeta potential measurements. A significant shift from 528 nm to 405 nm in surface plasmon resonance maxima is observed in forming the Ag shell layer on the Au core. The SERS performance of the nanoparticles was systematically evaluated using 4-mercaptobenzoic acid (4-MBA) across multiple excitation wavelengths (442-830 nm). The results demonstrated that thicker silver shells significantly enhanced SERS signals, achieving an enhancement factor up to 9.4 × 108 at 633 nm excitation. Additionally, biologically relevant ergothioneine was detected in fetal bovine serum with a limit of detection of 0.5 µM, corresponding to physiological concentrations. Spectral shifts observed at varying ergothioneine concentrations suggested adsorption-dependent molecular orientation changes. Stability tests confirmed that thin silver shells provided improved resistance to oxidation and aggregation, while thicker shells offered enhanced SERS activity at the expense of long-term colloidal stability. Overall, these systematically optimized Au@Ag core-shell nanoparticles show substantial potential for sensitive, stable, and versatile SERS-based biosensing and diagnostic applications.

Sustainable Formation of Gold Nanoparticle-Decorated Amyloid Fibrils for the Development of Functional Hybrid Materials

Amyloid fibrils have recently emerged as promising building blocks for functional materials due to their exceptional physicochemical stability and adaptable properties. These protein-based structures can be functionalized to create hybrid materials with a diverse range of applications. Here we report a simple eco-friendly protocol for generating amyloid fibrils from hen egg white lysozyme decorated with gold nanoparticles that can self-assemble in a hydrogel. Reactive oligomeric species act as reducing agents, enabling the efficient and simple formation of small gold nanoparticles without the need of harsh reagents. Furthermore, the protein molecules template the formation of gold nanoparticles, which are stabilized at regular intervals along the fibril axis, preserving gold nanoparticle properties at a macroscopic scale. As an illustration of potential application, we show that the gold nanoparticle functionalized hydrogel can be employed to sense and quantify creatinine using fluorescence detection. These findings reinforce the growing interest in utilizing proteins as foundational elements for functional biomaterials due to their high biocompatibility, availability, and the ability to finely tune supramolecular assemblies.

Comparative Study of SERS-Spectra of NQ21 Peptide on Silver Particles and in Gold-Coated "Nanovoids"

The NQ21 peptide has relatively recently attracted attention in the biomedical sphere due to its prospects for facilitating the engineering of the HIV1 vaccine and ELISA test. Today, there is still a need for a reliable and fast methodology that reveals the secondary structure of this analyte at the low concentrations conventionally used in vaccines and immunological assays. The present research determined the differences between the surface-enhanced Raman scattering (SERS) spectra of NQ21 peptide molecules adsorbed on solid SERS-active substrates depending on their geometry and composition. The ultimate goal of our research was to propose an algorithm and SERS-active material for structural analysis of peptides. Phosphate buffer solutions of the 30 µg/mL NQ21 peptide at different pH levels were used for the SERS measurements, with silver particles on mesoporous silicon and gold-coated "nanovoids" in macroporous silicon. The SERS analysis of the NQ21 peptide was carried out by collecting the SERS spectra maps. The map assessment with an originally developed algorithm resulted in defining the effect of the substrate on the secondary structure of the analyte molecules. Silver particles are recommended for peptide detection if it is not urgent to precisely reveal all the characteristic bands, because they provide greater enhancement but are accompanied by analyte destruction. If the goal is to carefully study the secondary structure and composition of the peptide, it is better to use SERS-active gold-coated "nanovoids". Objective results can be obtained by collecting at least three 15 × 15 maps of the SERS spectra of a given peptide on substrates from different batches.

Emerging Trends of Computational Chemistry and Molecular Modeling in Froth Flotation: A Review

Froth flotation is the most versatile process in mineral beneficiation, extensively used to concentrate a wide range of minerals. This process comprises mixtures of more or less liberated minerals, water, air, and various chemical reagents, involving a series of intermingled multiphase physical and chemical phenomena in the aqueous environment. Today's main challenge facing the froth flotation process is to gain atomic-level insights into the properties of its inherent phenomena governing the process performance. While it is often challenging to determine these phenomena via trial-and-error experimentations, molecular modeling approaches not only elicit a deeper understanding of froth flotation but can also assist experimental studies in saving time and budget. Thanks to the rapid development of computer science and advances in high-performance computing (HPC) infrastructures, theoretical/computational chemistry has now matured enough to successfully and gainfully apply to tackle the challenges of complex systems. In mineral processing, however, advanced applications of computational chemistry are increasingly gaining ground and demonstrating merit in addressing these challenges. Accordingly, this contribution aims to encourage mineral scientists, especially those interested in rational reagent design, to become familiarized with the necessary concepts of molecular modeling and to apply similar strategies when studying and tailoring properties at the molecular level. This review also strives to deliver the state-of-the-art integration and application of molecular modeling in froth flotation studies to assist either active researchers in this field to disclose new directions for future research or newcomers to the field to initiate innovative works.

Spectroscopic Investigations of 316L Stainless Steel under Simulated Inflammatory Conditions for Implant Applications: The Effect of Tryptophan as Corrosion Inhibitor/Hydrophobicity Marker

In this paper, the conformational changes of tryptophan (Trp) on the corroded 316 L stainless steel (SS) surface obtained under controlled simulated inflammatory conditions have been studied by Raman (RS) and Fourier-transform infrared (FT-IR) spectroscopy methods. The corrosion behavior and protective efficiency of the investigated samples were performed using the potentiodynamic polarization (PDP) technique in phosphate-buffered saline (PBS) solution acidified to pH 3.0 at 37 °C in the presence and absence of 10−2 M Trp, with different immersion times (2 h and 24 h). The amino acid is adsorbed onto the corroded SS surface mainly through the lone electron pair of the nitrogen atom of the indole ring, which adopts a more/less tilted orientation, and the protonated amine group. The visible differences in the intensity of the Fermi doublet upon adsorption of Trp onto the corroded SS surface, which is a sensitive marker of the local environment, suggested that a stronger hydrophobic environment is observed. This may result in an improvement of the corrosion resistance, after 2 h than 24 h of exposure time. The electrochemical results confirm this statement—the inhibition efficiency of Trp, acting as a mixed-type inhibitor, is made drastically higher after a short period of immersion.

Unveiling the interaction of protein fibrils with gold nanoparticles by plasmon enhanced nano-spectroscopy

The development of various degenerative diseases is suggested to be triggered by the uncontrolled organisation and aggregation of proteins into amyloid fibrils. For this reason, there are ongoing efforts to develop novel agents and approaches, including metal nanoparticle-based colloids, that dissolve amyloid structures and prevent pathogenic protein aggregation. In this contribution, the role of gold nanoparticles (AuNPs) in degrading amyloid fibrils of the model protein lysozyme is investigated. The amino acid composition of fibril surfaces before and after the incubation with AuNPs is determined at the single fibril level by exploiting the high spatial resolution and sensitivity provided by tip-enhanced and surface-enhanced Raman spectroscopies. This combined spectroscopic approach allows to reveal the molecular mechanisms driving the interaction between fibrils and AuNPs. Our results provide an important input for the understanding of amyloid fibrils and could have a potential translational impact on the development of strategies for the prevention and treatment of amyloid-related diseases.

Adsorption of dipeptide L-alanyl-L-tryptophan on gold colloidal nanoparticles studied by surface-enhanced Raman spectroscopy

Surface adsorption of a dipeptide L-alanyl-L-tryptophan (Ala-Trp) on gold nanoparticles reduced by citrate (CT) and borohydride (BH) ions was investigated by a surface-enhanced Raman scattering (SERS) technique. Two distinct SERS spectra of Ala-Trp depending on the types of gold nanoparticles were observed, and the vibrational assignments were based on the density functional theory simulations and the previous SERS results of Trp. Ala-Trp mainly adsorbs through the amine group on CT gold nanoparticles with a perpendicular orientation of the indole ring to the surface. In contrast, the adsorption occurs via the π electrons of the indole ring on the BH gold surfaces while maintaining a flat geometry of the indole ring to the surface. The amide I band of Ala-Trp was observed only with the CT gold colloids in acidic and neutral conditions where partial surface adsorption via the amide group is expected.

Raman spectroscopy and neuroscience: from fundamental understanding to disease diagnostics and imaging

Neuroscience would directly benefit from more effective detection techniques, leading to earlier diagnosis of disease. The specificity of Raman spectroscopy is unparalleled, given that a molecular fingerprint is attained for each species. It also allows for label-free detection with relatively inexpensive instrumentation, minimal sample preparation, and rapid sample analysis. This review summarizes Raman spectroscopy-based techniques that have been used to advance the field of neuroscience in recent years.

Near-Infrared Surface-Enhanced Raman Scattering on Silver-Coated Porous Silicon Photonic Crystals

Surface-enhanced Raman scattering (SERS) with near-infrared (NIR) excitation offers a safe way for the detection and study of fragile biomolecules. In this work, we present the possibility of using silver-coated porous silicon photonic crystals as SERS substrates for near-infrared (1064 nm) excitation. Due to the deep penetration of NIR light inside silicon, the fabrication of photonic crystals was necessary to quench the band gap photoluminescence of silicon crystal, which acts as mechanical support for the porous layer. Optimal parameters of the immersion plating process that gave maximum enhancement were found and the activity of SERS substrates was tested using rhodamine 6G and crystal violet dye molecules, yielding significant SERS enhancement for off-resonant conditions. To our knowledge, this is the first time that the 1064 nm NIR laser excitation is used for obtaining the SERS effect on porous silicon as a substrate.

Tracking pereirine and flavopereirine in pau-pereira using Raman and SERS spectroscopies

Raman and SERS spectroscopies have been used to identify the bioactive compounds pereirine and flavopereirine from stem bark, ethanolic crude extracts and infusions.

In Vitro and In Vivo SERS Biosensing for Disease Diagnosis

For many disease states, positive outcomes are directly linked to early diagnosis, where therapeutic intervention would be most effective. Recently, trends in disease diagnosis have focused on the development of label-free sensing techniques that are sensitive to low analyte concentrations found in the physiological environment. Surface-enhanced Raman spectroscopy (SERS) is a powerful vibrational spectroscopy that allows for label-free, highly sensitive, and selective detection of analytes through the amplification of localized electric fields on the surface of a plasmonic material when excited with monochromatic light. This results in enhancement of the Raman scattering signal, which allows for the detection of low concentration analytes, giving rise to the use of SERS as a diagnostic tool for disease. Here, we present a review of recent developments in the field of in vivo and in vitro SERS biosensing for a range of disease states including neurological disease, diabetes, cardiovascular disease, cancer, and viral disease.