Gold Nanosurface Research Articles

A new and selective nanogold surface molecularly imprinted methacrylic acid RRS nanoprobe for the determination of trace 4-methylimidazole

A new gold nanosurface molecularly imprinted polymer spectral probe (AuNP-MIP) for the detection of 4-methylimidazole (MI) was synthesized by microwave irradiation, using AuNP as the nanosubstrate, the azo compound (AC) of MI as the template molecule and methacrylic acid (MAA) as the functional monomer. The probe was found to exhibit strong resonance Rayleigh scattering (RRS) effects and to specifically recognize AC. With the increase of MI concentration, the AC increased, the RRS energy transfer (RRS-ET) was enhanced, and the intensity of RRS signal at 370 nm decreased linearly. Accordingly, a new RRS-ET method was developed for the simple, sensitive and selective determination of MI, with the linear range of 0.0375–0.13125 μg/mL, and the detection limit of 0.0022 μg/mL MI. It was applied to analysis of MI in samples, with the recoveries of 91%–100% and relative standard deviations of 1.1%–8.5%.

Computational Insights into the Adsorption of Ligands on Gold Nanosurfaces.

We study the adsorption process of model peptides, nucleobases, and selected standard ligands on gold through the development of a computational protocol based on fully atomistic classical molecular dynamics (MD) simulations combined with umbrella sampling techniques. The specific features of the interface components, namely, the molecule, the metallic substrate, and the solvent, are taken into account through different combinations of force fields (FFs), which are found to strongly affect the results, especially changing absolute and relative adsorption free energies and trends. Overall, noncovalent interactions drive the process along the adsorption pathways. Our findings also show that a suitable choice of the FF combinations can shed light on the affinity, position, orientation, and dynamic fluctuations of the target molecule with respect to the surface. The proposed protocol may help the understanding of the adsorption process at the microscopic level and may drive the in-silico design of biosensors for detection purposes.

A plasmonic gold nano-surface functionalized with the estrogen receptor for fast and highly sensitive detection of nanoplastics

Nanoplastics are a global emerging environmental problem whose effects might pose potential threats to the human’s health. Despite the relevance of the issue, fast, reliable and quantitative in situ analytical approaches to determine nanoplastics are not yet available. The aim of this work was to devise an optical sensor with the goal of direct detecting and quantifying nanoplastics in seawater without sample pre-treatments. To this purpose, a nano-plasmonic biosensor was developed by exploiting an Estrogen Receptor (ER) recognition element grafted onto a polymer-based gold nanograting (GNG) plasmonic platform. The ER-GNG biosensor required just minute sample volumes (2 μL), allowed rapid detection (3 min) and enabled to determine nanoplastics in simulated seawater with a linear dynamic concentrations range of 1–100 ng/mL, thus encompassing the expected environmental loads. The nanostructured grating (GNG) provided remarkable performance enhancements, extending the measurement range across five orders of magnitude, thanks to the both the SPR and the localized SPR phenomena occurring at the GNG chip. At last, the ER-GNG biosensor was tested on real seawater samples collected in the Naples area and the results (∼30 ng/mL) were verified by a conventional approach (filtration and evaporation), confirming the ER-GNG sensor offers a straightforward and highly sensitive method for the direct in-field nanoplastics monitoring.

Naringenin-Functionalized Gold Nanoparticles and Their Role in α-Synuclein Stabilization

Misfolding and self-assembly of several intrinsically disordered proteins into ordered β-sheet-rich amyloid aggregates emerged as hallmarks of several neurodegenerative disorders such as Alzheimer's and Parkinson's diseases. Here we show how the naringenin-embedded nanostructure effectively retards aggregation and fibril formation of α-synuclein, which is strongly associated with the pathology of Parkinson's-like diseases. Naringenin is a polyphenolic compound from a plant source, and in our current investigation, we reported the one-pot synthesis of naringenin-coated spherical and monophasic gold nanoparticles (NAR-AuNPs) under optimized conditions. The average hydrodynamic diameter of the produced nanoparticle was ∼24 nm and showed a distinct absorption band at 533 nm. The zeta potential of the nanocomposite was ∼-22 mV and indicated the presence of naringenin on the surface of nanoparticles. Core-level XPS spectrum analysis showed prominent peaks at 84.02 and 87.68 eV, suggesting the zero oxidation state of metal in the nanostructure. Additionally, the peaks at 86.14 and 89.76 eV were due to the Au-O bond, induced by the hydroxyl groups of the naringenin molecule. The FT-IR analysis further confirmed strong interactions of the molecule with the gold nanosurface via the phenolic oxygen group. The composite surface was found to interact with monomeric α-synuclein and caused a red shift in the nanoparticle absorption band by ∼5 nm. The binding affinity of the composite nanostructure toward α-synuclein was in the micromolar range (Ka∼ 5.02 × 106 M-1) and may produce a protein corona over the gold nanosurface. A circular dichroism study showed that the nanocomposite can arrest the conformational fluctuation of the protein and hindered its transformation into a compact cross-β-sheet conformation, a prerequisite for amyloid fibril formation. Furthermore, it was found that naringenin and its nanocomplex did not perturb the viability of neuronal cells. It thus appeared that engineering of the nanosurface with naringenin could be an alternative strategy in developing treatment approaches for Parkinson's and other diseases linked to protein conformation.

Luminescent Self-Assembled Monolayer on Gold Nanoparticles: Tuning of Emission According to the Surface Curvature

Until now, the ability to form a self-assembled monolayer (SAM) on a surface has been investigated according to deposition techniques, which in turn depend on surface-coater interactions. In this paper, we pursued two goals: to form a SAM on a gold nanosurface and to correlate its formation to the nanosurface curvature. To achieve these objectives, gold nanoparticles of different shapes (spheres, rods, and triangles) were functionalized with a luminescent thiolated bipyridine (Bpy-SH), and the SAM formation was studied by investigating the photo-physics of Bpy-SH. We have shown that emission wavelength and excited-state lifetime of Bpy-SH are strongly correlated to the formation of specific aggregates within SAMs, the nature of these aggregates being in close correlation to the shape of the nanoparticles. Micro-Raman spectroscopy investigation was used to test the SERS effect of gold nanoparticles on thiolated bipyridine forming SAMs.

Effect asymmetry of diffraction efficiency in LC cells with different command surfaces

We report the new results on the measurements of diffraction efficiency in liquid crystal (LC) cells with different orienting surfaces in the presence of a DC electric field. Diffraction gratings were recorded in combined cells with E7 liquid crystal. We used LC cells with thickness of ∼10 µm. Gold nanoparticles, chalcogenide and ITO nano-surfaces were used as command surfaces. Diffraction gratings were formed during irradiation of LC cells by 2-beam spatially modulated laser light (λ = 532 nm) with linear p-polarization in experiments of two-wave mixing. As a result, we found an asymmetry in the diffraction efficiency of the recorded gratings in different cells, which depends on the type of command surface and the polarity of applied voltage. The obtained results are appropriately described in the terms of surface-induced photorefractive mechanism, when a diffraction grating arises due to the formation of an unstable charge in pure liquid crystal. We believe that unstable charge depends on a surface on which different types of charge carriers are excited by light.

Comparison of the Stability of 2H Nanosurfaces by the Adsorption of Small Molecules : A DFT Study

Density functional theory (DFT) calculations were carried out to understand the structural stability of 2D nanosheets of gold and silver in hexagonal phase of 2H by the adsorption of small molecules. In this work, we have obtained the bonding and adsorption properties of such small molecules as H2O, H2O2, and C2H5OH on 2H phase of gold and silver nanosurfaces, through DFT method using Quantum Expresso (QE) code. The high absorption energy values of (-2.45 eV, -2,46 eV, -2, 41 eV) for H2O, H2O2, and C2H5OH molecules on 2H-Au surfaces, respectively obtained than that of 2H-silver surfaces that the interaction between small molecules and both 2H nanosurfaces corresponds to physisorption. However, during the adsorption, the gold surface in the 2H phase (2H-Au) seems to preserve its atomic structure, while 2H-Ag surface changes from 2H to the fcc structure. Based on the analysis of electronic and physicochemical properties, the composite systems of 2H-gold/2H-silver-small molecules exhibit semiconductor behaviour. While 2H-Ag surfaces have short recovery time values for hydrogen peroxide (H2O2), this time is quite long for 2H-Au surfaces. Because of the long recovery time, Au-2H reported surfaces can be a candidate for possible applications of viral capture. Thus, the reported results are significant, and they would stimulate the experimental and further studies.

4-Iodophenylboronic Acid Stabilized Gold Cluster as a New Fluorescent Chemosensor for Saccharides Based on Excimer Emission Quenching.

4-iodophenylboronic acid (IPBA) ligated luminescent gold cluster was synthesized by mixing an aqueous solution of IBPA and polyvinylpyrrolidone stabilized gold cluster (Au:PVP) in water at room temperature through chemisorption of iodine on gold nano surface. Transmission Electron microscopy (TEM) and matrix assisted laser desorption ionization (MALDI) analysis revealed that the size of these Au-clusters (1.4±0.2nm) remain unchanged without any noticeable aggregation during synthesis. Owing to the formation of excimer between aryl moieties grafted over Au surface, the cluster exhibit strong emission peak at 335nm. This luminescent gold cluster is used for sensing different saccharides in water at physiological pH through quenching of excimer emission peak. This strong excimer emission is significantly quenched in presence of saccharides through interaction with boronic acid moieties. The selectivity for different saccharides follows the order: fructose > galactose > maltose > glucose ~ ribose > sorbitol with hight affinity for fructose (KSV = 1.54 × 104M-1) with Limit of Detection (LOD) of 100μM.

Surface adsorption of hydroxyanthraquinones on CTAB-modified gold nanosurfaces

Gold nanosurfaces are widely applied to the surface-enhanced Raman spectroscopy (SERS) detection of the biological systems. The surface modification of gold nanoparticles (AuNPs) is often required when the analytes do not efficiently adsorb on the surface. In this paper, an aggregation of AuNPs with cetyltrimethylammonium bromide (CTAB) was introduced for the efficient surface adsorption and strong SERS enhancement for a number of hydroxyanthraquinones (HAQs). The SERS of HAQs including 1,2-dihydroxyanthraquinone (alizarin) were strongly enhanced with CTAB-modified AuNPs and deprotonation of alizarin was clearly observed upon the pH change. The CTAB-modified AuNPs are regarded as efficient SERS substrates for many biological molecules with weak surface adsorption.

Decomposition of Carbon Tetrachloride on Gold Surfaces

Banned for already 20 years, carbon tetrachloride is still used industrially. The ingestion of the halogen compound (inhalation, dermal contact, drinking) is known to induce serious damage to the liver, for which gold particles might represent one of the most efficient treatment. Here, using the temperature-programmed desorption technique, we show that carbon tetrachloride is decomposed by a polycrystalline gold surface producing Cl2 at a minimum rate of 25% of the deposited molecules. The adsorption and decomposition explored via density functional theory (DFT) periodic calculations show that a cooperative decomposition of a pairwise CCl4 is energetically favorable on the (110) surface. Our results may contribute to develop better strategies for optimizing the design of gold nanosurfaces and improve the efficiency of the treatment of the hepatotoxicity induced by carbon tetrachloride.

Surface enhanced Raman spectroscopy as a novel tool for rapid quantification of heroin and metabolites in saliva

BackgroundHeroin can be detected and quantified by certain analytical methods, however, forensic professionals and criminal laboratories study for cheaper and faster detection tools. Surface-enhanced Raman spectroscopy (SERS) rises as a possible alternative tool with its widening application spectra. There are few studies regarding Raman and SERS spectra of heroin and its metabolites, which are unfortunately controversial. In this study, we compared five different surfaces in order to find out more efficient Raman-active substrate for opiate detection and rapid quantification of heroin and its metabolites in saliva.Materials and methodsMorphine standard material was used to identify proper surface for SERS analysis of opiates. Heroin and its metabolites (morphine, morphine-3-ß-glucuronide and 6-monoacetyl morphine) were calibrated between 50 ppb and 500 ppm and quantified on AuNRs with signal enhancement of silver colloids in saliva. Raman microscope with a 785-nm laser source was used.Results and ConclusionObtained results showed that heroin and its metabolites can be detected and quantified in saliva samples using a SERS-based system. Additionally, the present study revealed that synergetic effect of a specific gold nano-surface with ability controlling liquid motion and silver nanoparticles increase band numbers and intensities. Therefore, we suggest a fast, accurate and cost-effective method to detect and quantify heroin in biological fluids.

The Molecular Dynamics Simulation of Peptides on Gold Nanosurfaces.

This chapter contributes a short tutorial on the preparation of molecular dynamics (MD) simulations for a peptide in solution at the interface of an uncoated gold nanosurface. Specifically, the step-by-step procedure will give guidance to set up the simulation of a 16 amino acid long antimicrobial peptide on a gold layer using the program Gromacs for MD simulations.

Adsorption of Collagen-like Peptides onto Gold Nanosurfaces.

The molecular behavior of proteins in the presence of inorganic surfaces is of fundamental biological significance. Examples include extracellular matrix proteins interacting with gold nanoparticles and metallic implant biomaterials, such as titanium and stainless steels. Uncharged inorganic surfaces that interact strongly with the solution phase (hydrophilic surfaces) have been commonly used in disease treatments. A deep understanding of the molecular behavior of body proteins in the presence of hydrophilic surfaces is important in terms of clinical applications. However, the adsorption mechanism of proteins onto hydrophilic surfaces remains not fully understood. Here, comprehensive molecular dynamics simulations are carried out to study the molecular response of a human collagen molecule segment (CMS) to the presence of a planar gold surface (AuNS) in explicit solvent, aiming to unravel the adsorption mechanism of proteins onto hydrophilic surfaces. The results demonstrate that in the presence of AuNS, the CMS first biasedly diffuses toward AuNS, followed by anchoring to the gold surface, and finally adsorbs stepwise onto AuNS, where the protein adjusts its structure to maximize the interaction with AuNS. We conclude that adsorption of proteins onto hydrophilic surfaces adheres to three steps, namely, biased diffusion, anchoring, and stepwise adsorption accompanied by structural adaptation. The obtained adsorption mechanism provides insights into the development of inorganic surfaces for biomedical and therapeutic applications.

Modulation of Excited-State Proton Transfer Dynamics in a Model Lactim–Lactam Tautomeric System by Anisotropic Gold Nanoparticles

The past few decades have witnessed significant advances in the development of functionalized gold nanoparticles (GNPs) for diverse applications in various fields such as chemistry, biology, pharmacy, and physics. However, a recent in vivo toxicity study of GNPs in Drosophila melanogaster demonstrated that GNPs are capable of inducing mutagenesis. Considering mutagenicity and tautomerism (lactim–lactam and amine–imine) of DNA base pairs are correlated with each other, a recent theoretical study reveal the modification of double-proton-transfer process of guanine–cytosine DNA base pairs upon interaction with the gold surface (Au(111)). However, there is a dearth of experimental data about the proton-transfer (PT) process in isolated base pairs on gold nanosurface. In this particular work, we have chosen a model lactim–lactam tautomeric system, namely, 1-(2-hydroxy-5-chloro-phenyl)-3,5-dioxo-1H-imidazo-[3,4-b] isoindole (ADCL), and carried out for the first time a comprehensive study of the modification of excited-state PT dynamics in the presence of synthesized isotropic (spherical) and anisotropic (trianglular, rod, and trigonal bipyramidal) GNPs by means of steady-state and time-resolved fluorescence spectroscopy. The PT process operative in ADCL was experimentally found to be accelerated on the anisotropic gold nanosurface, whereas spherical-shaped GNPs showed little impact on the dynamics of the above-mentioned photophysical phenomenon. Therefore, our experimental results regarding the modification of lactim–lactam tautomerism of a model compound on the gold nanosurface are an indirect evidence of mutation caused by GNPs.

Porphyrin-Gold Nanomaterial for Efficient Drug Delivery to Cancerous Cells.

With an aim to overcome multidrug resistance (MDR), nontargeted delivery, and drug toxicity, we developed a new nanochemotherapeutic system with tetrasodium salt of meso-tetrakis(4-sulfonatophenyl)porphyrin (TPPS) armored on gold nanoparticles (TPPS-AuNPs). The nanocarrier is able to be selectively internalized within tumor cells than in normal cells followed by endocytosis and therefore delivers the antitumor drug doxorubicin (DOX) particularly to the nucleus of diseased cells. The embedment of TPPS on the gold nanosurface provides excellent stability and biocompatibility to the nanoparticles. Porphyrin interacts with the gold nanosurface through the coordination interaction between gold and pyrrolic nitrogen atoms of the porphyrin and forms a strong association complex. DOX-loaded nanocomposite (DOX@TPPS-AuNPs) demonstrated enhanced cellular uptake with significantly reduced drug efflux in MDR brain cancer cells, thereby increasing the retention time of the drug within tumor cells. It exhibited about 9 times greater potency for cellular apoptosis via triggered release commenced by acidic pH. DOX has been successfully loaded on the porphyrin-modified gold nanosurface noncovalently with high encapsulation efficacy (∼90%) and tightly associated under normal physiological conditions but capable of releasing ∼81% of drug in a low-pH environment. Subsequently, DOX-loaded TPPS-AuNPs exhibited higher inhibition of cellular metastasis, invasion, and angiogenesis, suggesting that TPPS-modified AuNPs could improve the therapeutic efficacy of the drug molecule. Unlike free DOX, drug-loaded TPPS-AuNPs did not show toxicity toward normal cells. Therefore, higher drug encapsulation efficacy with selective targeting potential and acidic-pH-mediated intracellular release of DOX at the nucleus make TPPS-AuNPs a “magic bullet” for implication in nanomedicine.

Stabilization of DOPA Zwitterions on Laser-Generated Gold Nanoparticles: ONIOM Computational Study of the Charge-Dependent Structural and Electronic Changes of DOPA Adsorbed on the Gold Nanosurface

A stable colloidal solution of gold nanoparticle–3,4-dihydroxyphenylalanine (DOPA) zwitterion conjugates (Au NP–z-DOPA) was prepared using nanosecond-laser ablation of a gold target in an aqueous solution of zwitterionic DOPA (z-DOPA). Spectroscopic data revealed that Au NPs strongly interact with z-DOPA, which lead to a significant change in the electronic structure of z-DOPA. The adsorbed z-DOPA is highly stable against oxidation in aqueous solution, indicating a significant stabilizing effect of the Au NPs surface on this zwitterion. The electronic structures and geometries of z-DOPA and the other forms of DOPA (including uncharged, cationic, and anionic forms) adsorbed on the Au(111) nanosurface were determined by ONIOM calculations. The geometry and electronic structure of each DOPA form are significantly affected by the surface upon adsorption. The analysis of the frontier orbitals confirmed the significant stabilizing effect of the Au NPs on z-DOPA. The calculations are consistent with the variatio...

Natural ionophore functionalized nanobiosensor capable of staining Cr3+ in live brine shrimp Artemia

We report the fabrication of gold nanoparticles using a sulfur containing microbial ionophore aeruginic acid (H2L), functioning as a reducing as well as stabilizing agent, to develop a nanobiosensor HL-AuNPs which showed highly selective colorimetric detection of Cr3+ in aqueous (100% water) HEPES buffer at physiological pH. On exposing HL-AuNPs to the aqueous solution of Cr3+, a red shift in the surface plasmon resonance (SPR) band of the probe is observed along with bare eye observable color change of the solution. Mechanistic studies revealed attachement of carboxylate moiety to the gold nanosurface. On addition of Cr3+ to the solution of HL-AuNPs, aggregation occurs as a result of coordination of the phenolate O and imine N with the octahedral Cr3+ center. The nanosensor with lower detection limit (LOD) of 0.5 μM can also be utilized for colorimetric detection and removal of Cr3+ in environmental samples. Being non-toxic and permeable in nature, HL-AuNPs can function as a colorimetric staining reagent for Cr3+ in living whole brine shrimp Artemia. Use of functionalized AuNPs as imaging reagent for Cr3+ in living organim is unprecedented.

Blocking Hot Electron Emission by SiO2 Coating Plasmonic Nanostructures

Noble metallic nanostructures provide a platform for high-sensitivity spectroscopic sensing with significantly enhanced electromagnetic fields due to surface plasmon polaritons. However, target molecules can be transformed into other molecules under irradiation with an excitation laser during the surface-enhanced measurement, which thus disturbs detection of unknown samples. In this paper, we perform Raman measurements of p-aminothiophenol on gold nanosurfaces with and without deposition of SiO2 thin films at the surface. The Raman signals are enhanced on both substrates, but the deposition of the glass thin film clearly prevents the chemical transformation. This indicates that hot electrons are effective for chemical transformation and that thin glass films are sufficient to prevent this while still benefiting from surface plasmons.

Interaction of collagen like peptides with gold nanosurfaces: a molecular dynamics investigation.

In this study, an attempt has been made to understand the interaction between collagen like peptides (CPs) with a gold nanosurface (AuNS) using a classical molecular dynamics simulation. Results reveal that the adsorption of CPs onto the gold surface depends on the amino acid composition of the collagen like peptides. It is evident from the findings that the Hyp residue of collagen interacts favorably with the AuNS. It is interesting to note that the model CP without a Hyp residue does not adsorb well on the surface. Results indicate that gold nanosurfaces or gold nanoparticles can be exploited to detect breast cancer due to the increased content of Hyp residues in the Gly-XAA-YAA triplet of collagen in breast cancer tissues. These results provide useful information for designing collagen based scaffolds for tissues engineering applications.

Refractometric and colorimetric index sensing by a plasmon-coupled hybrid AAO nanotemplate

A highly versatile and low-cost large-area refractive index sensor capable of refractometric and colorimetric sensing was developed using a plasmon-coupled hybrid nanotemplate of anodic aluminum oxide with a deposited gold nanosurface.