Impact of Graphene Oxide on SERS Enhancement of Arylated Gold Nanospheres: Mechanistic Insight.

The performance of gold nanospheres as substrates for surface-enhanced Raman spectroscopy (SERS) investigation has been compromised by their low adsorption efficiency, high colloidal dispersibility, and diminishing hot spots. However, gold nanosphere substrates modified using aryldiazonium gold(III) chemistry via durable gold-carbon bonds are promising for SERS enhancement due to their controlled organic layer density. In this study, arylated gold nanospheres AuNSs-COOH have shown SERS enhancement when incorporated into graphene oxide (GO) to form nanocomposites (NCs) labeled AuNSs-COOH/GO (AuNCs). Our investigation using X-ray photoelectron spectroscopy (XPS) surface analysis showed that the gold-aryl nanospheres reached their maximum SERS enhancement with an optimal coating. The evaluation included the Au 4f chemical environment and compact graphitic layers for the SERS substrate optimization. The fabricated AuNC substrates demonstrated superior efficiency and reproducibility. A broad linear range of 10-3-10-7 M 4-nitrophenol detection was obtained with exceptional repeatability, as evidenced by the relative standard deviation (RSD) of 9.32%. A detailed investigation of the energy profiles, particularly the valence band maximum (VBM) and band gap values of the substrate and analyte, depicted the electromagnetic (EM) and charge-transfer-induced enhancement and the role of GO inclusion in substrate efficiency in SERS enhancement mechanisms. The finite-difference time domain (FDTD) simulation results revealed that AuNCs incorporated with graphitic nanostructures exhibited the most substantial SERS effect through an EM field enhancement mechanism. This study demonstrated significant SERS enhancement using gold-aryl nanospheres when modified with GO, in contrast to the typical reliance on anisotropic nanostructures.

Flexible Copper Films Modification via Spontaneous Reduction of Aryldiazonium Gold Salts: Unraveling Surface Properties and Energy Profile.

In this study, we report the modification of flexible copper films via the spontaneous reduction of aryldiazonium gold salts [X-4-C6H4N≡N]AuCl4 (X═COOH, NO2). The electroless modification involves dipping of flexible copper films in the aryldiazonium gold solutions for a few seconds, under ambient conditions, followed by a washing step with deionized water to obtain a mechanically robust gold-aryl coating. The chemical composition, morphology, electronic structure, and optical properties of the gold-aryl layer and the flexibility of the modified copper films are supported by the results from X-ray photoelectron spectroscopy (XPS), electrochemistry, contact angle, scanning electron microscopy (SEM), and ultraviolet photoelectron spectroscopy (UPS). XPS surface analysis showed metallic gold in addition to C-C, C-O/C-N, and C═O functional groups from the grafted aryls. Cu 2p showed metallic copper as a major component and a small amount of Cu(II) ions. Wettability studies showed that Au-COOH@Cu increased the contact angle of the bare copper films from 68.0 ± 0.7° to 82.0° ± 0.7°, while Au-NO2@Cu increased the contact angle to 134.0° ± 0.3°. UPS energy profile analysis of [HOOC-4-C6H4N≡N]AuCl4 (valence band maximum = 1.91 eV) exhibited greater reducibility than [O2N-4-C6H4N≡N]AuCl4 (valence band maximum = 2.91 eV). The lower ionization potential of [HOOC-4-C6H4N≡N]AuCl4 (IP = 4.33 eV) enhanced the reactivity upon copper film contact, potentially inducing efficient energy level alignment, compared with [O2N-4-C6H4N≡N]AuCl4 (IP = 5.62 eV). UPS results were further supported by electrochemistry investigation which revealed that [HOOC-4-C6H4N≡N]AuCl4 is easily reducible compared with [O2N-4-C6H4N≡N]AuCl4. The findings presented here hold significant implications for developing flexible copper films and pave the way for future advancements in electronic material modification for industrial applications.

Correlation notice on the electrochemical dealloying and antibacterial properties of gold-silver alloy nanoparticles.

Galvanic replacement reaction was used in the synthesis of bimetallic gold-silver alloy nanoparticles (Au-Ag NPs), where pre-synthesized Ag nanoparticles-polyvinylpyrrolidone (AgNPs-PVP) were used to reduce the aryldiazonium tetrachloroaurate(III) salt in water. TEM images and EDS elemental analysis showed the formation of spherical Au-Ag NPs with sizes of 12.8 ± 4.9 nm and 25.6 ± 14.4 nm for corresponding Au-Ag ratios and termed as Au0.91Ag0.09 and Au0.79Ag0.21, respectively, with different concentrations of the gold precursor. The hydrodynamic sizes measured using dynamic light scattering are 46.4 nm and 74.8 nm with corresponding zeta potentials of - 44.56 and - 25.09 mV in water, for Au0.91Ag0.09 and Au0.79Ag0.21 respectively. Oxidative leachability of Ag ion studies from the starting AgNPs-PVP in 1 M NaCl showed a significant decrease in the plasmon peak after 8 h, indicating the complete dissolution of Ag ions, however, there is enhanced oxidation resistivity of Ag from Au-Ag NPs even after 24 h. Electrochemical studies on glassy carbon electrodes displayed a low oxidation peak in aqueous solutions of 20 mM KCl at 0.16 V and KNO3 at 0.33 V vs. saturated calomel electrode (SCE). We studied the antibacterial activity of Au-Ag alloy nanoparticles against gram-positive Staphylococcus aureus, Staphylococcus epidermidis, Enterococcus faecalis, and gram-negative Escherichia coli, Salmonella typhimurium, and Pseudomonas aeruginosa. Our findings demonstrated superior antibacterial activity of Au-Ag NPs compared with AgNPs-PVP. Moreover, the nanoparticles inhibited the S. epidermidis biofilm formation.

FRET-based fluorescent probe for drug assay from amino acid@gold-carbon nanoparticles.

Biocompatible and luminescent nanostructures synthesized by capping gold-carbon nanoparticles (HOOC-4-C6H4-AuNPs) with amino acids tyrosine, tryptophan, and cysteine were used for the quantitative estimation of ranitidine (RNH), a peptic ulcer and gastroesophageal reflux drug. We applied a fluorescence quenching mechanism to investigate the viability of the energy transfer based on gold-carbon nanosensors. Förster resonance energy transfer (FRET) calculations showed a donor-acceptor distance of 1.69 nm (Tyr@AuNPs), 2.27 nm (Trp@AuNPs), and 2.32 nm (Cys@AuNPs). The constant time-resolved fluorescence lifetime measurements supported the static quenching nature. This method was successfully utilized in the detection and quantification of RNH, with a limit of detection (LOD) of 0.174, 0.56, and 0.332 µM for Tyr@AuNP, Trp@AuNP, and Cys@AuNP bioconjugates, respectively. This approach was also successful in the quantification of RNH in spiked serum samples.

Doping matters in carbon nanomaterial efficiency in environmental remediation.

Carbon nanomaterials (CNMs) are rapidly emerging in materials science research due to their widespread environmental applications. They are useful for environmental pollutants' remediation through various methods. Heteroatom doping resulted in reliable approaches to overcome pristine CNMs challenges. The engineering of the dopants is believed to be a promising route to improve the efficiency of CNMs in environmental remediation. The idea of doping has been attractive since it allows the control of electronic properties due to the electron transfer between dopants and the host material and the dopants along with the bonding between analogous atoms and carbon atoms. This mini-review, through computational and experimental studies, puts special emphasis on the role of doping different CNMs as an efficient approach to enhance the environmental remediation.

Gold Nanoparticle-Mediated Gene Therapy.

Gold nanoparticles (AuNPs) have gained increasing attention as novel drug-delivery nanostructures for the treatment of cancers, infections, inflammations, and other diseases and disorders. They are versatile in design, synthesis, modification, and functionalization. This has many advantages in terms of gene editing and gene silencing, and their application in genetic illnesses. The development of several techniques such as CRISPR/Cas9, TALEN, and ZFNs has raised hopes for the treatment of genetic abnormalities, although more focused experimentation is still needed. AuNPs, however, have been much more effective in trending research on this subject. In this review, we highlight recently well-developed advancements that are relevant to cutting-edge gene therapies, namely gene editing and gene silencing in diseases caused by a single gene in humans by taking an edge of the unique properties of the AuNPs, which will be an important outlook for future research.

Lysozyme and Human Serum Albumin Proteins as Potential Nitric Oxide Cardiovascular Drug Carriers: Theoretical and Experimental Investigation.

Nitric oxide-containing drugs present a critical remedy for cardiovascular diseases. Nitroglycerin (NG, O-NO) and S-nitrosoglutathione (SNG, S-NO) are the most common nitric oxide drugs for cardiovascular diseases. Insights regarding the binding affinity of NO drugs with lysozyme and human serum albumin (HSA) proteins and their dissociation mechanism will provide inquisitive information regarding the potential of the proteins as drug carriers. For the first time, the binding interactions and affinities are investigated using molecular docking, conventional molecular dynamics, steered molecular dynamics, and umbrella sampling to explore the ability of both proteins to act as nitric oxide drug carriers. The molecular dynamics simulation results showed higher stability of lysozyme-drug complexes compared to HSA. For lysozyme, cardiovascular drugs were bound in the protein cavity mainly by the electrostatic and hydrogen bond interactions with residues ASP53, GLN58, ILE59, ARG62, TRP64, ASP102, and TRP109. For HSA, key binding residues were ARG410, TYR411, LYS414, ARG485, GLU450, ARG486, and SER489. The free energy profiles produced from umbrella sampling also suggest that lysozyme-drug complexes had better binding affinity than HSA-drug. Binding characteristics of nitric oxide-containing drugs NG and SNG to lysozyme and HSA proteins were studied using fluorescence and UV-vis absorption spectroscopy. The relative change in the fluorescence intensity as a function of drug concentrations was analyzed using Stern-Volmer calculations. This was also confirmed by the change in the UV-vis spectra. Fluorescence quenching results of both proteins with the drugs, based on the binding constant values, demonstrated significantly weak binding affinity to NG and strong binding affinity to SNG. Both computational and experimental studies provided important data for understanding protein-drug interactions and will aid in developing potential drug carrier systems in cardiovascular diseases.