Surface-Directed Disparity in Self-Assembled Structures of Small-Peptide l-Glutathione on Gold and Silver Nanoparticles

Bonding states of gold/silver plasmonic nanostructures and sulfur-containing active biological ingredients in biomedical applications: a review

As one of the most instrumental components in the architecture of advanced nanomedicines, plasmonic nanostructures (mainly gold and silver nanomaterials) have been paid a lot of attention. This type of nanomaterial can absorb light photons with a specific wavelength and generate heat or excited electrons through surface resonance, which is a unique physical property. In innovative biomaterials, a significant number of theranostic (therapeutic and diagnostic) materials are produced through the conjugation of thiol-containing ingredients with gold and silver nanoparticles (Au and Ag NPs). Hence, it is essential to investigate Au/Ag-S interfaces precisely and determine the exact bonding states in the active nanobiomaterials. This study intends to provide useful insights into the interactions between Au/Ag NPs and thiol groups that exist in the structure of biomaterials. In this regard, the modeling of Au/Ag-S bonding in active biological ingredients is precisely reviewed. Then, the physiological stability of Au/Ag-based plasmonic nanobioconjugates in real physiological environments (pharmacokinetics) is discussed. Recent experimental validation and achievements of plasmonic theranostics and radiolabelled nanomaterials based on Au/Ag-S conjugation are also profoundly reviewed. This study will also help researchers working on biosensors in which plasmonic devices deal with the thiol-containing biomaterials (e.g., antibodies) inside blood serum and living cells.

Perturbation of Fermi Resonance on Hydrogen-Bonded > C═O: 2D IR Studies of Small Ester Probes

We utilized linear and 2D infrared spectroscopy to analyze the carbonyl stretching modes of small esters in different solvents. Particularly noteworthy were the distinct carbonyl spectral line shapes in aqueous solutions, prompting our investigation of the underlying factors responsible for these differences. Through our experimental and theoretical calculations, we identified the presence of the hydrogen-bond-induced Fermi resonance as the primary contributor to the varied line shapes of small esters in aqueous solutions. Furthermore, our findings revealed that the skeletal deformation mode plays a crucial role in the Fermi resonance for all small esters. Specifically, the first overtone band of the skeletal deformation mode intensifies when hydrogen bonds form with the carbonyl group of esters, whereas such coupling is rare in aprotic organic solvents. These spectral insights carry significant implications for the utilization of esters as infrared probes in both biological and chemical systems.

Noble Metal Nanoparticles with Nanogel Coatings: Coinage Metal Thiolate-Stabilized Glutathione Hydrogel Shells

Developing biocompatible nanocoatings is crucial for biomedical applications. Noble metal colloidal nanoparticles with biomolecular shells are thought to combine diverse chemical and optothermal functionalities with biocompatibility. Herein, we present nanoparticles with peptide hydrogel shells that feature an unusual combination of properties: the metal core possesses localized plasmon resonance, whereas a few-nanometer-thick shells open opportunities to employ their soft framework for loading and scaffolding. We demonstrate this concept with gold and silver nanoparticles capped by glutathione peptides stacked into parallel β-sheets as they aggregate on the surface. A key role in the formation of the ordered structure is played by coinage metal(I) thiolates, i.e., Ag(I), Cu(I), and Au(I). The shell thickness can be controlled via the concentration of either metal ions or peptides. Theoretical modeling of the shell's molecular structure suggests that the thiolates have a similar conformation for all the metals and that the parallel β-sheet-like structure is a kinetic product of the peptide aggregation. Using third-order nonlinear two-dimensional infrared spectroscopy, we revealed that the ordered secondary structure is similar to the bulk hydrogels of the coinage metal thiolates of glutathione, which also consist of aggregated stacked parallel β-sheets. We expect that nanoparticles with hydrogel shells will be useful additions to the nanomaterial toolbox. The present method of nanogel coating can be applied to arbitrary surfaces where the initial deposition of the seed glutathione monolayer is possible.

Surface-enhanced Raman spectroscopy for detection of fentanyl and its analogs by using Ag-Au nanoparticles

The problem of opioid abuse has become a global problem. Thus, creating an urgent need for highly sensitive detection of opioid substances. In this work, we developed a method for the controllable preparation of Ag@Au nanocrystals (Ag@Au NCs) for highly sensitive SERS detection of fentanyl and its analogs. By regulating the concentration of ligands on the surface of silver seed, we successfully prepared Ag@Au NCs with three different morphologies, including core-satellite, yolk shell and hollow structure. Firstly, we explored the SERS-enhancing effect of Ag@Au NCs with different morphology using rhodamine 6G as the molecule to be tested. The results show that the core-satellite Ag@Au NCs has the best SERS effect, and the lowest detection concentration for R6G reached to 10^-10 M. Furthermore, we used the prepared core-satellite Ag@Au NCs to detect fentanyl and its five analogs, including carfentanyl, furanylfentanyl, thiofentanyl, 4-fluorobutyrfentanyl and N-4-piperidylacetanilide. Trace detection was achieved for the above six substances. For the environmental water samples spiked with fentanyl, the calculated recovery was 89.2% with an RSD value of 7.3%. Moreover, in order to realize the qualitative analysis of the characteristic peaks of different fentanyl analogs, we performed DFT calculations on the Raman spectra of the above-mentioned 6 substances. By analyzing the DFT calculation results, conventional Raman spectroscopy and SERS spectroscopy, we realized the distinction of six fentanyl analogs with similar structures.

Inconsistent hydrogen bond-mediated vibrational coupling of amide I

Using infrared spectroscopy and density functional theory (DFT) calculations, we scrutinized an amide (dimethylformamide) as a "model" compound to interpret the interactions of amide 1 with different phenol derivatives (para-chlorophenol (PCP) and para-cresol (CP)) as "model guest molecules". We established the involvement of amide I in vibrational coupling with symmetric and asymmetric C[double bond, length as m-dash]C modes of different phenolic derivatives and how their coupling was dependent upon different guest aromatic phenolic compounds. Interestingly, substitution of phenol perturbed the pattern of vibrational coupling with amide I. The symmetric and asymmetric C[double bond, length as m-dash]C modes of PC were coupled significantly with amide 1. For PCP, the symmetric C[double bond, length as m-dash]C mode coupled significantly, but the asymmetric mode coupled negligibly, with amide I. Here, we reveal the nature of vibrational coupling based on the structure of a guest molecule hydrogen-bonded with amide I. Our conclusions could be valuable for depiction of the unusual dynamics of coupled amide-I modes as well as the dependency of vibrational coupling on altered factors.

Nanotechnology-Enabled Biosensors: A Review of Fundamentals, Design Principles, Materials, and Applications

Biosensors are modern engineering tools that can be widely used for various technological applications. In the recent past, biosensors have been widely used in a broad application spectrum including industrial process control, the military, environmental monitoring, health care, microbiology, and food quality control. Biosensors are also used specifically for monitoring environmental pollution, detecting toxic elements' presence, the presence of bio-hazardous viruses or bacteria in organic matter, and biomolecule detection in clinical diagnostics. Moreover, deep medical applications such as well-being monitoring, chronic disease treatment, and in vitro medical examination studies such as the screening of infectious diseases for early detection. The scope for expanding the use of biosensors is very high owing to their inherent advantages such as ease of use, scalability, and simple manufacturing process. Biosensor technology is more prevalent as a large-scale, low cost, and enhanced technology in the modern medical field. Integration of nanotechnology with biosensors has shown the development path for the novel sensing mechanisms and biosensors as they enhance the performance and sensing ability of the currently used biosensors. Nanoscale dimensional integration promotes the formulation of biosensors with simple and rapid detection of molecules along with the detection of single biomolecules where they can also be evaluated and analyzed critically. Nanomaterials are used for the manufacturing of nano-biosensors and the nanomaterials commonly used include nanoparticles, nanowires, carbon nanotubes (CNTs), nanorods, and quantum dots (QDs). Nanomaterials possess various advantages such as color tunability, high detection sensitivity, a large surface area, high carrier capacity, high stability, and high thermal and electrical conductivity. The current review focuses on nanotechnology-enabled biosensors, their fundamentals, and architectural design. The review also expands the view on the materials used for fabricating biosensors and the probable applications of nanotechnology-enabled biosensors.

Selective detection of tartaric acid using amino acid interlinked silver nanoparticles as a colorimetric probe

A variety of biomolecules with different functional groups play critical roles in almost all the processes occurring in living cells. Interaction of metallic nanoparticles (NPs) with various biomolecules generates a layer of molecules on their surface, and this biomolecular rich layer formed on the NP surface is described as a "biomolecular corona". The physicochemical properties of the NPs, including size, adsorption affinity, and charge on the particles' surfaces are the major factors influencing the characteristics of this corona. The formation of various biomolecular corona has been studied well, whereas the amino acid corona is relatively new by exploring their stability. In the present study, a novel formation of an amino acid corona with a fundamental interaction mechanism for a selective detection procedure using a colorimetric platform has been proposed. Herein, amino acid-coated silver NPs (AgNPs) have been used as a template with spectroscopic (steady state UV-Vis, FTIR) and imaging (HR-TEM, DLS) techniques. Our findings demonstrated that among different amino acid coronas, glutathione (GSH) stabilized AgNPs show a rapid reaction with tartaric acid. The extent and thermodynamics of the formed complex between the GSH/AgNPs and tartaric acid have also been studied and this suggested that the complex formed is spontaneous and energy releasing in nature.

Anomalous Infrared Absorbance of S═O: A Perturbation Study of α-C-H/D

Solvatochromic shifts of S═O vibrational probes describe the strength of the surrounding electric fields and the hydrogen bonding status. Herein, we demonstrated how the solvents alter the infrared (IR) spectra of the S═O vibrating mode. The experimental measurement of the involvement of α-H/D isotopic interactions with different solvents and their effects on the IR absorbance spectra of the vibrational probe provides detailed knowledge of the microsolvation environment despite the complexity of overlapping bands in the spectra. Herein, we discover how the solvents interact differently with DMSO and DMSO-d6, while being electronically and structurally the same. Interestingly, the IR spectrum of the S═O mode remains unaltered during α-isotopic replacement in the presence of aprotic solvents (acetone, acetonitrile, and dichloromethane), but in strongly coordinating polar solvents (D2O), it is altered remarkably. There is a lack of quantitative information about the influence of the α-H atom or α-isotopic substitution on the vibrational probe in the literature. Our experiments provide a detailed molecular understanding of the structure of DMSO in DMSO-solvent binary mixtures. As DMSO plays an important role in virtually all subdisciplines of chemistry and biology, we believe that our work will be of interest to a large diversity of studies in these fields.

Detection and imaging of Hg(II) in vivo using glutathione-functionalized gold nanoparticles

The optical and biological properties of functionalized gold nanoparticles (GNPs) have been widely used in sensing applications. GNPs have a strong binding ability to thiol groups. Furthermore, thiols are used to bind functional molecules, which can then be used, for example, to detect metal ions in solution. Herein, we describe 13 nm GNPs functionalized by glutathione (GSH) and conjugated with a rhodamine 6G derivative (Rh6G2), which can be used to detect Hg(II) in cells. The detection of Hg²⁺ ions is based on an ion-catalyzed hydrolysis of the spirolactam ring of Rh6G2, leading to a significant change in the fluorescence of GNPs-GSH-Rh6G2 from an "OFF" to an "ON" state. This strategy is an effective tool to detect Hg²⁺ ions. In cytotoxicity experiments, GNPs-GSH-Rh6G2 could penetrate living cells and detect mercury ions through the fluorescent "ON" form.

On-Off Infrared Absorption of the S═O Vibrational Probe of Dimethyl Sulfoxide

Dimethyl sulfoxide (DMSO), a polar solvent molecule, is used in a wide range of therapeutic and pharmacological applications. Different intermolecular interactions, such as dimerization and hydrogen bonding with water, are crucial to understanding the role of DMSO in applications. Herein, we study DMSO in various solvation environments to decipher the environment-dependent dimerization and hydrogen-bonding propensity. We use a combination of infrared spectroscopy, quantum mechanical calculations, and molecular dynamics simulations to reach our conclusions. Although DMSO can exist in a dynamic equilibrium between monomers and dimers, our results show that the relative intensity of the S═O stretch and the CH₃ rocking modes is a spectroscopic indicator of the extent of DMSO dimerization in solution. The dimerization (self-association) is seen to be maximum in neat DMSO. When dissolved in different solvents, the dimerization propensity decreases with increasing solvent polarity. In the presence of a protic solvent, such as water, DMSO forms a hydrogen bond with the solvent molecules, thereby reducing the extent of dimerization. Further, we estimate the hydrogen-bond occupancy of DMSO. Our results show that DMSO predominantly exists as doubly hydrogen-bonded in water.

Solution NMR methods for structural and thermodynamic investigation of nanoparticle adsorption equilibria

Characterization of dynamic processes occurring at the nanoparticle (NP) surface is crucial for developing new and more efficient NP catalysts and materials. Thus, a vast amount of research has been dedicated to developing techniques to characterize sorption equilibria. Over recent years, solution NMR spectroscopy has emerged as a preferred tool for investigating ligand-NP interactions. Indeed, due to its ability to probe exchange dynamics over a wide range of timescales with atomic resolution, solution NMR can provide structural, kinetic, and thermodynamic information on sorption equilibria involving multiple adsorbed species and intermediate states. In this contribution, we review solution NMR methods for characterizing ligand-NP interactions, and provide examples of practical applications using these methods as standalone techniques. In addition, we illustrate how the integrated analysis of several NMR datasets was employed to elucidate the role played by support-substrate interactions in mediating the phenol hydrogenation reaction catalyzed by ceria-supported Pd nanoparticles.

Monitoring Solid-Phase Reactions in Self-Assembled Monolayers by Surface-Enhanced Raman Spectroscopy

Nanopatterned surfaces enhance incident electromagnetic radiation and thereby enable the detection and characterization of self-assembled monolayers (SAMs), for instance in surface-enhanced Raman spectroscopy (SERS). Herein, Au nanohole arrays, developed and characterized as SERS substrates, are exemplarily used for monitoring a solid-phase deprotection and a subsequent copper(I)-catalyzed azide-alkyne cycloaddition "click" reaction, performed directly on the corresponding SAMs. The SERS substrate was found to be highly reliable in terms of signal reproducibility and chemical stability. Furthermore, the intermediates and the product of the solid-phase synthesis were identified by SERS. The spectra of the immobilized compounds showed minor differences compared to spectra of the microcrystalline solids. With its uniform SERS signals and the high chemical stability, the platform paves the way for monitoring molecular manipulations in surface functionalization applications.

Controllable preparation of sea urchin-like Au NPs as a SERS substrate for highly sensitive detection of the toxic atropine

Branched Au nanoparticles (Au NPs) can significantly enhance the Raman signal of trace chemical substances, and have attracted the interest of researchers. However, there are still challenges to accurately prepare the morphology of branched Au NPs. In this work, we have successfully prepared sea urchin-like Au NPs and Au nanowires by using the seed-mediate growth method, with cetyltrimethylammonium bromide (CTAB) and glutathione as ligands, and ascorbic acid as a reducing agent. Using Au NPs with a tetrahexahedron (THH) morphology as seeds, and by simply changing the concentration of glutathione, we explored the growth process of sea urchin-like Au and Au nanowires. At low concentrations of glutathione, Au NPs will preferentially grow along the edges and corners of the THH Au seed, forming a core/satellite structure. As the concentration of glutathione increases, Au NPs will grow along the direction of glutathione, forming sea urchin-like Au NPs. To further increase the concentration of glutathione, we will prepare Au nanowires. In addition, we use the prepared Au NPs as a substrate material for surface-enhanced Raman (SERS) high-sensitivity detection. By using 4-aminothiophenol (4-ATP) as the test molecule, we evaluated the SERS effect of the prepared Au NPs with different morphologies. The results showed that sea urchin-like Au NPs have the best enhancement effect. The lowest concentrations of Rhodamine 6G and 4-ATP were 10-10 M and 10-12 M, respectively, using sea urchin Au NPs as the base material. Furthermore, we conducted a highly sensitive SERS detection of the poison atropine monohydrate, and the lowest detected concentration was 10-10 M.

Nanostructures for Biosensing, with a Brief Overview on Cancer Detection, IoT, and the Role of Machine Learning in Smart Biosensors

Biosensors are essential tools which have been traditionally used to monitor environmental pollution and detect the presence of toxic elements and biohazardous bacteria or virus in organic matter and biomolecules for clinical diagnostics. In the last couple of decades, the scientific community has witnessed their widespread application in the fields of military, health care, industrial process control, environmental monitoring, food-quality control, and microbiology. Biosensor technology has greatly evolved from in vitro studies based on the biosensing ability of organic beings to the highly sophisticated world of nanofabrication-enabled miniaturized biosensors. The incorporation of nanotechnology in the vast field of biosensing has led to the development of novel sensors and sensing mechanisms, as well as an increase in the sensitivity and performance of the existing biosensors. Additionally, the nanoscale dimension further assists the development of sensors for rapid and simple detection in vivo as well as the ability to probe single biomolecules and obtain critical information for their detection and analysis. However, the major drawbacks of this include, but are not limited to, potential toxicities associated with the unavoidable release of nanoparticles into the environment, miniaturization-induced unreliability, lack of automation, and difficulty of integrating the nanostructured-based biosensors, as well as unreliable transduction signals from these devices. Although the field of biosensors is vast, we intend to explore various nanotechnology-enabled biosensors as part of this review article and provide a brief description of their fundamental working principles and potential applications. The article aims to provide the reader a holistic overview of different nanostructures which have been used for biosensing purposes along with some specific applications in the field of cancer detection and the Internet of things (IoT), as well as a brief overview of machine-learning-based biosensing.

Label-free colorimetric detection of glutathione by autocatalytic oxidation of o-phenylenediamine based on Au3+ regulation and its application

A label-free, rapid, and highly sensitive colorimetric assay for the detection of glutathione (GSH) was developed.