SERS and DFT study of indigo adsorbed on silver nanostructured surface

Applied surface enhanced Raman Spectroscopy in plant hormones detection, annexation of advanced technologies: A review

Plant hormones are the molecules that control the vigorous development of plants and help to cope with the stress conditions efficiently due to vital and mechanized physiochemical regulations. Biologists and analytical chemists, both endorsed the extreme problems to quantify plant hormones due to their low level existence in plants and the technological support is devastatingly required to established reliable and efficient detection methods of plant hormones. Surface Enhanced Raman Spectroscopy (SERS) technology is becoming vigorously favored and can be used to accurately and specifically identify biological and chemical molecules. Subsistence molecular properties with varying excitation wavelength require the pertinent substrate to detect SERS signals from plant hormones. Three typical mechanisms of Raman signal enhancement have been discovered, electromagnetic, chemical and Tip-enhanced Raman spectroscopy (TERS). Though, complex detection samples hinder in consistent and reproducible results of SERS-based technology. However, different algorithmic models applied on preprocessed data enhanced the prediction performances of Raman spectra by many folds and decreased the fluorescence value. By incorporating SERS measurements into the microfluidic platform, further highly repeatable SERS results can be obtained. This review paper tends to study the fundamental working principles, methods, applications of SERS systems and their execution in experiments of rapid determination of plant hormones as well as several ways of integrated SERS substrates. The challenges to develop an SERS-microfluidic framework with reproducible and accurate results for plant hormone detection are discussed comprehensively and highlighted the key areas for future investigation briefly.

Surface enhanced Raman spectroscopic (SERS) behavior of phenylpyruvates used in heterogeneous catalytic asymmetric cascade reaction

The strength and geometry of adsorption of substituted phenylpyruvates on silver surface was studied by means of surface enhanced Raman spectroscopy (SERS) using silver sol. 2'-nitrophenylpyruvates were used as starting materials in a newly developed heterogeneous catalytic asymmetric cascade reaction to produce substituted quinoline derivatives. Substituents on the aromatic ring of the starting materials had significant influence on the yield of the desired quinoline derivatives. Product selectivity of the transformation of nitrophenylpyruvates were enhanced by the acid added. The geometry and the strength of the adsorption are assumed to play an important role in the outcome of this reaction, so we have tried to find correlation between the structure of adsorbed phenylpyruvates and their catalytic performance. Based on the results of our spectroscopic measurements, the enol form is predominant in the series of phenylpyruvates in solid form and methanol solutions. Stronger adsorption of phenylpyruvates in acidic media through oxygen atoms was indicated by the increased enhancement in the SERS spectrum. The nitro group of 2'-nitrophenylpyruvates has no direct role in the adsorption on Ag surface. This observation has explained why the hydrogenation of the keto group (presumably via the enol form) occurs preferentially and why the formation of the undesired indole derivatives requiring reduction of the nitro group is suppressed. The SERS behavior has helped to get a closer look on the first step of adsorption of starting materials contributing to a better understanding of the cascade reaction studied, thus providing a better flexibility in catalyst design.

SERS and DFT studies of 2-(trichloroacetyl)pyrrole chemisorbed on the surface of silver and gold coated thin films: In perspective of biosensor applications

The adsorption and orientations of 2-(trichloroacetyl)pyrrole (TCAP) adsorbed on a fabricated silver-coated thin film (SCF), and gold-coated thin film (GCF) were investigated using surface-enhanced Raman scattering (SERS) studies and compared with the normal Raman scattering (nRs) spectrum of TCAP. The observed nRs and SERS spectra of TCAP were validated theoretically using DFT quantum chemical calculations. Initially, the molecular structure of TCAP, TCAP-Ag₃ , and TCAP-Au₄ molecular systems were optimized and analyzed. The fabricated SCF and GCF are characterized using FESEM analysis, which confirms that the silver and gold nanoparticles of the corresponding films are spherical in shape. The obtained significant red-shift in UV-visible spectra of TCAP added on SCF and GCF surfaces reveal that the TCAP strongly adsorbed on SCF and GCF surfaces. The frontier molecular orbitals analysis authenticates the charge-transfer interaction from Ag₃ and Au₄ metal clusters to the TCAP molecule, leading to the adsorption of TCAP molecule on Ag₃ and Au₄ metal clusters, which validates the UV-vis results. SERS spectral analysis confirms that the TCAP chemisorbed on SCF and GCF surfaces with tilted orientation and the corresponding results were validated theoretically. The calculated SERS enhancement factor values illustrate that the GCF surface exhibits a higher SERS signal enhancement than the SCF surface. Therefore, the present investigation will be useful for the development of active SERS substrates and pyrrole-related biosensors.

Role of pH on Nanostructured SERS Active Substrates for Detection of Organic Dyes

Surface Enhanced Raman Spectroscopy is commonly used as analytical improvement to conventional Raman spectroscopy, able to respond to qualitative diagnostic enquiries, which involve low-concentrated molecular species in complex matrix. In this paper, we described fabrication, characterization and testing of a type of SERS-active substrates realized specifically to detect pigments in work of art. In particular, we detailed the SERS activity of nanostructured noble metal films deposited by pulsed laser ablation onto glass and polishing sheets substrates. The SERS response of the substrates was tested against the presence of some organic dyes in aqueous solutions. Measurements were performed at different pH values, in acidic or basic range, in order to investigate its role in the adsorption mechanism, thus fostering the SERS amplification. In addition, we checked the possible deterioration of the structural properties of the substrates that could occur in presence of alkaline or acidic environment. SERS activity of the substrates was tested against a commonly dye used as a SERS standard (Blue Methylene). Thereafter, substrates have been tested on two organic dyes (Alizarine red-S and Brazilwood), which had proven to be Raman active but present also either a weak Raman scattering cross section and/or a high fluorescence emission. The substrates have proven effective in amplifying Raman scattering of all dyes, quenching troubling fluorescence effects. Furthermore, they have proven to be stable in the pH range between 3 and 11. Furthermore, we carry out of vibrational DFT-calculation of dyes that provide a complete description of the observed SERS spectra.

Spectroscopic insights into the effect of pH, temperature, and stabilizer on erlotinib adsorption behavior onto Ag nanosurface

In this study, surface - enhanced Raman spectroscopy (SERS) was applied at the first time for estimation of how pH, temperature, and nanoparticle (NP) stabilizer affect an adsorption behavior of erlotinib (drug approved in a non-small cell lung cancer therapy) onto citrate-stabilized silver nanoparticles (AgNPs). Novel approach to improve cancer therapy assumes application of NPs as an efficient drug delivery system. This strategy requires designing stable drug/nanocarrier conjugates that can effectively interact in the target site. It is also important to perform deeply characterization of a drug orientation on the potential carrier surface and estimation how stable the appeared interaction is. Performed analysis, indicates that pH, temperature, presence of NP stabilizers, and time of incubation have an influence on the occurring adsorption geometry of the drug. However, the observed erlotinib/AgNP interaction remains stable regardless of the applied conditions. These considerations were supported by insightful physicochemical characteristics of the AgNPs and the erlotinib/AgNP conjugates by conducting transmission electron microscopy (TEM) imaging, determination of colloid stability conducted with the use of dynamic light scattering technique (DLS) and measurements of electrophoretic mobility. Such complex approach allows a better understanding of the stability of the erlotinib/AgNP conjugates and provides information how the investigated interaction is affected by the induced perturbations.

Durable Antimicrobial Behaviour from Silver-Graphene Coated Medical Textile Composites

Silver nanoparticle (AgNP) and AgNP/reduced graphene oxide (rGO) nanocomposite impregnated medical grade polyviscose textile pads were formed using a facile, surface-mediated wet chemical solution-dipping process, without further annealing. Surfaces were sequentially treated in situ with a sodium borohydride (NaBH4) reducing agent, prior to formation, deposition, and fixation of Ag nanostructures and/or rGO nanosheets throughout porous non-woven (i.e., randomly interwoven) fibrous scaffolds. There was no need for stabilising agent use. The surface morphology of the treated fabrics and the reaction mechanism were characterised by Fourier transform infrared (FTIR) spectra, ultraviolet-visible (UV-Vis) absorption spectra, X-ray diffraction (XRD), Raman spectroscopy, dynamic light scattering (DLS) energy-dispersive X-ray analysis (EDS), and scanning electron microscopic (SEM). XRD and EDS confirmed the presence of pure-phase metallic silver. Variation of reducing agent concentration allowed control over characteristic plasmon absorption of AgNP while SEM imaging, EDS, and DLS confirmed the presence of and dispersion of Ag particles, with smaller agglomerates existing with concurrent rGO use, which also coincided with enhanced AgNP loading. The composites demonstrated potent antimicrobial activity against the clinically relevant gram-negative Escherichia coli (a key causative bacterial agent of healthcare-associated infections; HAIs). The best antibacterial rate achieved for treated substrates was 100% with only a slight decrease (to 90.1%) after 12 equivalent laundering cycles of standard washing. Investigation of silver ion release behaviours through inductively coupled plasmon optical emission spectroscopy (ICP-OES) and laundering durability tests showed that AgNP adhesion was aided by the presence of the rGO host matrix allowing for robust immobilisation of silver nanostructures with relatively high stability, which offered a rapid, convenient, scalable route to conformal NP-decorated and nanocomposite soft matter coatings.