Solvent effect on the electronic spectra of azine dyes under alkaline condition

On-site SERS analysis and intelligent multi-identification of fentanyl class substances by deep machine learning

As the types of fentanyl class substances continue to grow, a universal SERS sensor is essential for the application of discriminant detection of fentanyl substances. A new nanomaterial SERS sensor-Ag@Au NPs-paper was developed. The SERS sensitivity and stability of Ag@Au NPs-paper were investigated by using R6G molecule, and the results showed that Ag@Au NPs-paper has excellent performance. In combination with visual analysis and machine learning methods, Ag@Au NPs-paper has been successfully applied to the analysis of fentanyl class substances and the component identification of binary fentanyl mixtures, and thus it can be effectively used in food safety, environmental toxicants and other fields.

Raspberry-Like Plasmonic Nanoaggregates with Programmable Hierarchical Structures for Reproducible SERS Detection of Wastewater Pollutants and Biomarkers

Conventional solid-based SERS substrates often face challenges with inconsistent sample distribution, while liquid-based SERS substrates are prone to aggregation and precipitation, resulting in irreproducible signals in both cases. In this study, we tackled this dilemma by designing and synthesizing raspberry-like plasmonic nanoaggregates that exhibit a high density of hotspots and are colloidally stable at the same time. In particular, the nanoaggregates consist of a core made of functionalized polystyrene (PS) microspheres, which act as a template for rapid self-assembly of Au@Ag core-shell nanoparticles to form raspberry-like hierarchical nanoaggregates within 5 min of mixing. The optimized nanoaggregates can be used as reproducible and stable SERS substrates for a range of wastewater pollutants (e.g., rhodamine 6G (R6G) and malachite green (MG)) and nucleobases (e.g., adenine and uracil), with the detection limits as low as 1 × 10-10, 1 × 10-16, 3 × 10-8, and 3 × 10-7 M, respectively. Additionally, the trace detection of adenine in clinical urine samples has been successfully demonstrated. Our modular assembly approach opens up new possibilities in SERS substrate design and advanced trace-chemical detection technologies.

Novel mixed heterovalent (Mo/Co)Ox-zerovalent Cu system as bi-functional electrocatalyst for overall water splitting

A novel hybrid ternary metallic electrocatalyst of amorphous Mo/Co oxides and crystallized Cu metal was deposited over Ni foam using a one-pot, simple, and scalable solvothermal technique. The chemical structure of the prepared ternary electrocatalyst was systematically characterized and confirmed via XRD, FTIR, EDS, and XPS analysis techniques. FESEM images of (Mo/Co)Ox-Cu@NF display the formation of 3D hierarchical structure with a particle size range of 3-5 µm. The developed (Mo/Co)Ox-Cu@NF ternary electrocatalyst exhibits the maximum activity with 188 mV and 410 mV overpotentials at 50 mA cm-2 for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), respectively. Electrochemical impedance spectroscopy (EIS) results for the (Mo/Co)Ox-Cu@NF sample demonstrate the minimum charge transfer resistance (Rct) and maximum constant phase element (CPE) values. A two-electrode cell based on the ternary electrocatalyst just needs a voltage of about 1.86 V at 50 mA cm-2 for overall water splitting (OWS). The electrocatalyst shows satisfactory durability during the OWS for 24 h at 10 mA cm-2 with an increase of only 33 mV in the cell potential.

Photocatalytic removal of benzo[a]pyrene and antibacterial efficacy of Graphitic Carbon Nitride-silver-nickel (g-C3N4-Ag-Ni) mediated nanocomposites

A few PAHs (polycyclic aromatic hydrocarbons) which are known to be pervasive and are of high priority are found to be detrimental pollutants having high potential in the destruction of the network. Hence, photocatalytic disintegration of these PAHs, namely benzo [a]pyrene, found in water is explored. A novel nanocomposite of Ag-Ni on g-C3N4 was fabricated. The prepared nanocomposites were characterized by techniques like UV, XRD, SEM-EDAX, FTIR, and DLS to understand their nature. The activity of the same as a catalyst in the deterioration of the benzopyrene molecule in water was investigated under different conditions including change in the concentration of the PAH, dosage of the catalyst prepared, pH of the reaction mixture, and by changing the source of irradiation. In addition, antibacterial analysis of the prepared nanocomposite material was conducted to determine whether it could be applied to environmental cleanup strategies of high quality.

Design of Silica@Au Hybrid Nanostars for Enhanced SERS and Photothermal Effect

Core-shell nanostructures of silicon oxide@noble metal have drawn a lot of interest due to their distinctive characteristics and minimal toxicity with remarkable biocompatibility. Due to the unique property of localized surface plasmon resonance (LSPR), plasmonic nanoparticles are being used as surface-enhanced Raman scattering (SERS) based detection of pollutants and photothermal (PT) agents in cancer therapy. Herein, we demonstrate the synthesis of multifunctional silica core - Au nanostars shell (SiO2 @Au NSs) nanostructures using surfactant free aqueous phase method. The SERS performance of the as-synthesized anisotropic core-shell NSs was examined using Rhodamine B (RhB) dye as a Raman probe and resulted in strong enhancement factor of 1.37×106 . Furthermore, SiO2 @Au NSs were also employed for PT killing of breast cancer cells and they exhibited a concentration-dependent increase in the photothermal effect. The SiO2 @Au NSs show remarkable photothermal conversion efficiency of up to 72 % which is unprecedented. As an outcome, our synthesized NIR active SiO2 @Au NSs are of pivotal importance to have their dual applications in SERS enhancement and PT effect.

Synthesis of cationic β-cyclodextrin functionalized silver nanoparticles and their drug-loading applications

Silver nanoparticles have attracted great attention owing to their distinct physicochemical properties, which inspire the development of their synthesis methodology and their potential biomedical applications. In this study, a novel cationic β-cyclodextrin (C-β-CD) containing a quaternary ammonium group and amino group was applied as a reducing agent as well as a stabilizing agent to prepare C-β-CD modified silver nanoparticles (CβCD-AgNPs). Besides, based on the inclusion complexation between drug molecules and C-β-CD, the application of CβCD-AgNPs in drug loading was explored by the inclusion interaction with thymol. The formation of AgNPs was confirmed by ultraviolet-visible spectroscopy (UV-vis) and X-ray diffraction spectroscopy (XRD). Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) showed the prepared CβCD-AgNPs were well dispersed with particle sizes between 3-13 nm, and the zeta potential measurement result suggested that the C-β-CD played a role in preventing their aggregation in solution. 1H Nuclear magnetic resonance spectroscopy (1H-NMR) and Fourier transform infrared spectroscopy (FT-IR) revealed the encapsulation and reduction of AgNPs by C-β-CD. The drug-loading action of CβCD-AgNPs was demonstrated by UV-vis and headspace solid-phase microextraction gas chromatography mass spectrometry (HS-SPME-GC-MS), and the results of TEM images showed the size increase of nanoparticles after drug loading.

Self-Assembly of Cyclodextrin-Coated Nanoparticles:Fabrication of Functional Nanostructures for Sensing and Delivery

In recent years, the bottom-up approach has emerged as a powerful tool in the fabrication of functional nanomaterials through the self-assembly of nanoscale building blocks. The cues embedded at the molecular level provide a handle to control and direct the assembly of nano-objects to construct higher-order structures. Molecular recognition among the building blocks can assist their precise positioning in a predetermined manner to yield nano- and microstructures that may be difficult to obtain otherwise. A well-orchestrated combination of top-down fabrication and directed self-assembly-based bottom-up approach enables the realization of functional nanomaterial-based devices. Among the various available molecular recognition-based "host-guest" combinations, cyclodextrin-mediated interactions possess an attractive attribute that the interaction is driven in aqueous environments, such as in biological systems. Over the past decade, cyclodextrin-based specific host-guest interactions have been exploited to design and construct structural and functional nanomaterials based on cyclodextrin-coated metal nanoparticles. The focus of this review is to highlight recent advances in the self-assembly of cyclodextrin-coated metal nanoparticles driven by the specific host-guest interaction.

Plasmonic nanogels for naked-eye sensing of food adulterants

Cellulose based nanoplasmonic sensors gained immense attention for various applications due to their advantageous physicochemical characteristics such as ease of fabrication, low density, chirality, surface functionalization and disposal. Herein, a hydrogel based nanoplasmonic sensor probe was fabricated and evaluated for the detection of melamine (MA). Plasmonic nanomaterials (AuNPs) were synthesized by the redox reaction using a dual reducing agent (β-cyclodextrin (βCD) and citrate). The physicochemical characteristics of the synthesized AuNPs were extensively determined by various spectroscopic and microscopic techniques. The colorimetric sensing of melamine (MA) was carried out in solution and hydrogel phases. Upon the addition of MA, AuNPs tend to aggregate and exhibit color changes from orange-red to purple due to surface plasmon resonance (SPR) coupling. This nanosensor probe showed high selectivity and sensitivity for detection of MA with a detection limit of 3 × 10^-7 M. Plasmonic hydrogels were prepared using the cellulose acetate (CA) polymer and optimized for stability and interaction with melamine. The βCD-citrate stabilized AuNPs showed color changes with the CA hydrogels. The hydrogel-based sensor probe exhibits similar characteristics with respect to the selective and sensitive detection of MA under optimized conditions. The fabricated nanoreactor based sensor probe has high potential for food sensor applications.

Development of a β-cyclodextrin-modified gold nanoparticle-assisted electromembrane extraction method followed by capillary electrophoresis for methadone determination in plasma

In this study, gold nanoparticles (AuNPs) modified with β-cyclodextrin (β-CD) were used to assist with electromembrane extraction (EME) and were coupled with capillary electrophoresis (CE) and ultraviolet (UV) detection (CE-UV) for the extraction and measurement of methadone from plasma samples. A β-CD-modified AuNP-reinforced hollow fiber (HF) was utilized in this work. The β-CD-modified AuNPs act as an absorbent and provide an extra pathway for the analyte extraction. For obtaining the effect of the presence of β-CD-modified AuNPs in the HF pores, the extraction efficiency of the EME and β-CD-modified AuNPs/EME techniques were compared. Different parameters influencing the extraction efficacy of the EME and β-CD-modified AuNPs/EME methods were optimized. Optimal extractions were performed with 1-octanol as the organic solvent in the supported liquid membrane (SLM), with an applied voltage of 10 V as the driving force across the SLM, and with pH 7.0 in the donor solutions with a stirring speed of 1000 rpm after 20 min and 25 min for the β-CD-modified AuNPs/EME and EME methods, respectively. Under optimal conditions, compared with the EME method, the β-CD-modified AuNPs/EME method exhibited increased extraction efficacy in a short time. The β-CD-modified AuNPs/EME technique demonstrated a lower limit of detection (5.0 ng mL^-1), higher extraction recovery (68%), and a more optimal preconcentration factor (135). Furthermore, this method was successfully utilized for measuring methadone in real plasma samples.

The New Strategy for Studying Drug-Delivery Systems with Prolonged Release: Seven-Day In Vitro Antibacterial Action

The new method of antibacterial-drug-activity investigation in vitro is proposed as a powerful strategy for understanding how carriers affect drug action during long periods (7 days). In this paper, we observed fluoroquinolone moxifloxacin (MF) antibacterial-efficiency in non-covalent complexes, with the sulfobutyl ether derivative of β-cyclodextrin (SCD) and its polymer (SCDpol). We conducted in vitro studies on two Escherichia coli strains that differed in surface morphology. It was found that MF loses its antibacterial action after 3-4 days in liquid media, whereas the inclusion of the drug in SCD led to the increase of MF antibacterial activity by up to 1.4 times within 1-5 days of the experiment. In the case of MF-SCDpol, we observed a 12-fold increase in the MF action, and a tendency to prolonged antibacterial activity. We visualized this phenomenon (the state of bacteria, cell membrane, and surface morphology) during MF and MF-carrier exposure by TEM. SCD and SCDpol did not change the drug's mechanism of action. Particle adsorption on cells was the crucial factor for determining the observed effects. The proteinaceous fimbriae on the bacteria surface gave a 2-fold increase of the drug carrier adsorption, hence the strains with fimbriae are more preferable for the proposed treatment. Furthermore, the approach to visualize the CD polymer adsorption on bacteria via TEM is suggested. We hope that the proposed comprehensive method will be useful for the studies of drug-delivery systems to uncover long-term antibacterial action.

Multifunctional phototheranostic agent ZnO@Ag for anti-infection through photothermal/photodynamic therapy

To overcome the limitations of traditional therapeutics, nanotechnology offers a synergistic therapeutic approach for the treatment of bacterial infection and biofilms that has attracted attention. Herein, we report on a ZnO@Ag nanocomposite with good biocompatibility synthesized by doping ZnO NPs with silver nanoparticles (Ag NPs). ZnO@Ag nanocomposites were synthesized with varying ratios of Ag NPs (0.5%, 2%, 8%). Under the same experimental conditions, ZnO@8%Ag exhibited outstanding properties compared to the other nanocomposites and the pristine ZnO NPs. ZnO@8%Ag demonstrated excellent photothermal and photodynamic properties. Also, ZnO@8%Ag demonstrated over 99% inhibition of Staphylococcus aureus (S. aureus) under photothermal therapy (PTT) or photodynamics therapy (PDT) as a result of the excessive generation of reactive oxygen species (ROS) by the Ag+ released, while the pristine ZnO showed an insignificant inhibition rate compared to the PBS group (control). Furthermore, ZnO@8%Ag completely disrupted S. aureus biofilm under a combined PTT/PDT treatment, a synergetic trimodal therapy, although the molecular mechanism of biofilm inhibition remains unclear. Hence, the excellent photothermal, photodynamic, biocompatibility, and bactericidal properties of ZnO@8%Ag present it as an appropriate platform for bacterial and biofilm treatment or other biomedically related applications.

Cyclodextrins and Their Polymers Affect the Lipid Membrane Permeability and Increase Levofloxacin’s Antibacterial Activity In Vitro

Cyclodextrins (CDs) are promising drug carriers that are used in medicine. We chose CDs with different substituents (polar/apolar, charged/neutral) to obtain polymers (CDpols) with different properties. CDpols are urethanes with average Mw of ~120 kDa; they form nanoparticles 100–150 nm in diameter with variable ζ-potential. We studied the interaction of CD and CDpols with model (liposomal) and bacterial membranes. Both types of CD carriers cause an increase in the liposomal membrane permeability, and for polymers, this effect was almost two times stronger. The formation of CD/CDpols complexes with levofloxacin (LV) enhances LV’s antibacterial action 2-fold in vitro on five bacterial strains. The most pronounced effect was determined for LV-CD complexes. LV-CDs and LV-CDpols adsorb on bacteria, and cell morphology influences this process dramatically. According to TEM studies, the rough surface and proteinaceous fimbria of Gram-negative E. coli facilitate the adsorption of CD particles, whereas the smooth surface of Gram-positive bacteria impedes it. In comparison with LV-CDs, LV-CDpols are adsorbed 15% more effectively by E. coli, 2.3-fold better by lactobacilli and 5-fold better in the case of B. subtilis. CDs and CDpols are not toxic for bacterial cells, but may cause mild defects that, in addition to LV-CD carrier adsorption, improve LV’s antibacterial properties.

Design and fabrication of bimetallic plasmonic colloids through cold nanowelding

The integration of Au and Ag into nanoalloys has emerged as an intriguing strategy to further tailor and boost the plasmonic properties of optical substrates. Conventional approaches for fabricating these materials via chemical reductions of metal salts in solution suffer from some limitations, such as the possibility of retaining the original morphology of the monometallic substrate. Spontaneous nanowelding at room temperature has emerged as an alternative route to tailor Au/Ag nanomaterials. Herein, we perform a thorough study on the cold-welding process of silver nanoparticles onto gold substrates to gain a better understanding of the role of different variables in enabling the formation of well-defined bimetallic structures that retain the original gold substrate morphology. To this end, we systematically varied the size of silver nanoparticles, dimensions and geometries of gold substrates, solvent polarity and structural nature of the polymeric coating. A wide range of optical and microscopy techniques have been used to provide a complementary and detailed description of the nanowelding process. We believe this extensive study will provide valuable insights into the optimal design and engineering of bimetallic plasmonic Ag/Au structures for application in nanodevices.

Electrochemical aspects of coinage metal nanoparticles for catalysis and spectroscopy

Down scaling bulk materials can cause colloidal systems to evolve into microscopically dispersed insoluble particles. Herein, we describe the interesting applications of coinage metal nanoparticles (MNPs) as colloid dispersions especially gold and silver. The rich plasmon bands of gold and silver in the visible range are elaborated using the plasmon resonance and redox potential values of grown metal microelectrode (GME). The gradation of their standard reduction potential values (E 0), as evaluated from the Gibbs free energy change for bulk metal, is ascribed to the variation in their size. Also, the effect of nucleophiles in the electrolytic cell with metal nanoparticles (MNPs) is described. The nucleophile-guided reduction potential value is considered, which is applicable even for bulk noble metals. Typically, a low value (as low as E 0 = +0.40 V) causes the oxidation of metals at the O2 (air)/H2O interface. Under this condition, the oxidation of noble metal particles and dissolution of the noble metal in water are demonstrated. Thus, metal dissolution as a function of the size of metal nanoparticles becomes eventful and demonstrable with the addition of a surfactant to the solution. Interestingly, the reversal of the nobility of gold (Au) and silver (Ag) microelectrodes at the water/electrode interface is confirmed from the evolution of normal and inverted 'core-shell' structures, exploiting visible spectrophotometry and surface-enhanced Raman scattering (SERS) analysis. Subsequently, the effect of the size, shape, and facet- and support-selective catalysis of gold nanoparticles (NPs) and the effect of incident photons on current conversion without an applied potential are briefly discussed. Finally, the synergistic effect of the emissive behaviour of gold and silver clusters is productively exploited.

Interface engineering with self-assembling Au@Ag@β-cyclodextrin bimetal nanoparticles to fabricate a ring-like arrayed SERS substrate for sensitive recognition of phthalate esters based on a host-guest interaction and the coffee ring effect

Herein, Au@Ag@β-cyclodextrin (β-CD) nanoparticles with a relatively uniform shape and size of ∼13 nm in diameter have been successfully synthesized, and the surfaces of the synthesized nanoparticles are successful modified by β-CD. A highly efficient synthetic approach was developed for the preparation of a surface-enhanced Raman spectroscopy (SERS) substrate, which self-assembles Au@Ag@β-CD nanoparticles and analytes into a coffee ring pattern via the coffee ring effect. The coffee ring effect can make phthalates (PAEs) aggregate to the edge together with the Au@Ag@β-CD nanoparticles and concentration enrichment can be achieved. In addition, the surface of the core-shell Au@Ag@β-CD is modified with β-CD with a cavity structure, which can enrich analyte concentration by adsorbing the analytes into the hydrophobic cavity using host-guest recognition. This enrichment process not only improves the concentration of the surface of the analyte but also effectively distinguishes it from other substances in the analyte solution. The mechanism of enrichment and host-guest recognition is verified by subsequent molecular docking simulation. Thus, a ring-like arrayed SERS substrate with dual-strategy enrichment is used to detect PAEs. The experiments using the ring-like arrayed SERS substrate, gave a limit of detection of 0.2 nM for DOP detection, the recovery rate of the spiked samples ranged from 92.3% to 106.6%, and an RSD of less than 6% for PAE detection is obtained. This work provided a simple, rapid, low-cost, highly sensitive and stable method for PAE detection in life and the environment.

Facile tuning of tip sharpness on gold nanostars by the controlled seed-growth method and coating with a silver shell for detection of thiram using surface enhanced Raman spectroscopy (SERS)

Developing SERS substrates based on individual gold and silver metals, either with rough surfaces or bare nanoparticles, has certain limitations in practical analysis applications. In order to improve the range of applications of the noble metallic substrates, a comprehensive approach has been proposed for preparing non-traditional SERS nano-substrates by combining tip-enhanced gold nanostars and Raman signal amplification of the silver layer. This preparation process is conducted in two steps, including tuning the sharpness and length of tips by a modified seed growth method followed by coating the silver layer on the formed star-shaped nanoparticles. The obtained AuNS-Ag covered with an average size of around 100 nm exhibited interesting properties as a two-component nano-substrate to amplify the activities in SERS for detecting thiram. The controllable and convenient preparation route of gold nanostars is based on the comproportionation reaction of Au seed particles with Au(iii) ions, achieved by governing the stirring times of the mixture of the Au seed and the growth solution. Thus, the citrate-seed particles decreased in size (below 2 nm) and grew into nanostars with sharp tips. The thickness of Ag covering the Au particles' surface also was appropriately controlled and the tips were still exposed to the outside, which is a benefit for matching with the source excitation wavelength to achieve good SERS performance. The Raman signals of thiram can be instantly and remarkably detected with the enhancement of the substrates. Thiram can be determined without any pretreatment. It was found that the limit of detection for thiram is 0.22 ppm, and the limit of quantification is 0.73 ppm. These experimental results shed some light on developing the SERS method for detecting pesticide residue.

Developing SERS substrates based on the star-like morphology of gold nanoparticles covered by a silver layer to overcome limitations in practical analysis application.

DNA Origami-Templated Bimetallic Nanostar Assemblies for Ultra-Sensitive Detection of Dopamine

The abundance of hotspots tuned via precise arrangement of coupled plasmonic nanostructures highly boost the surface-enhanced Raman scattering (SERS) signal enhancements, expanding their potential applicability to a diverse range of applications. Herein, nanoscale assembly of Ag coated Au nanostars in dimer and trimer configurations with tunable nanogap was achieved using programmable DNA origami technique. The resulting assemblies were then utilized for SERS-based ultra-sensitive detection of an important neurotransmitter, dopamine. The trimer assemblies were able to detect dopamine with picomolar sensitivity, and the assembled dimer structures achieved SERS sensitivity as low as 1 fM with a limit of detection of 0.225 fM. Overall, such coupled nanoarchitectures with superior plasmon tunability are promising to explore new avenues in biomedical diagnostic applications.

Voltammetric sensor based on bimetallic nanocomposite for determination of favipiravir as an antiviral drug

A novel and sensitive voltammetric nanosensor was developed for the first time for trace level monitoring of favipiravir based on gold/silver core–shell nanoparticles (Au@Ag CSNPs) with conductive polymer poly (3,4-ethylene dioxythiophene) polystyrene sulfonate (PEDOT:PSS) and functionalized multi carbon nanotubes (F-MWCNTs) on a glassy carbon electrode (GCE). The formation of Au@Ag CSNPs/PEDOT:PSS/F-MWCNT composite was confirmed by various analytical techniques, including X-ray diffraction (XRD), ultraviolet–visible spectroscopy (UV–Vis), transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDX), and field-emission scanning electron microscopy (SEM). Under the optimized conditions and at a typical working potential of + 1.23 V (vs. Ag/AgCl), the Au@Ag CSNPs/PEDOT:PSS/F-MWCNT/GCE revealed linear quantitative ranges from 0.005 to 0.009 and 0.009 to 1.95 µM with a limit of detection 0.46 nM (S/N = 3) with acceptable relative standard deviations (1.1-4.9 %) for pharmaceutical formulations, urine, and human plasma samples without applying any sample pretreatment (1.12–4.93%). The interference effect of antiviral drugs, biological compounds, and amino acids was negligible, and the sensing system demonstrated outstanding reproducibility, repeatability, stability, and reusability. The findings revealed that this assay strategy has promising applications in diagnosing FAV in clinical samples, which could be attributed to the large surface area on active sites and high conductivity of bimetallic nanocomposite.

Functionalization of gold nanoparticles by β-cyclodextrin as a probe for the detection of heavy metals in water and photocatalytic degradation of textile dye

Gold nanoparticles (AuNPs) and AuNPs functionalized by β-cyclodextrin (β-CD/AuNPs) were prepared successfully through chemical reduction method. The structural, morphological, optical, compositional and vibrational studies for the AuNPs and β-CD/AuNPs were carried out. Functionalization of AuNPs by β-CD was confirmed with FT-IR results. The UV-visible absorption spectra exhibit a red-shift with decreasing average particle size. This sustains the enhancement in surface area (SA) to volume (V) ratio that is one of the peculiar characteristics of nanoparticles. TEM results show that β-CD/AuNPs formed were monodispersed and self assembled. Also it shows a decrease in average particle size and improved distribution. The use of β-CD in the synthesis of AuNPs are revealed not only create uniform small sized nanoparticles but these water soluble nanoparticles have very good antibacterial action by inhibiting the growth of bacteria commonly found in water and sensing activity for sensing the concentration of toxic metals in water. The sensitivity of the system towards copper (Cu) concentration was found as 1.788/mM for β-CD/AuNPs and 1.333/mM for AuNPs. The photocatalytic action of the obtained nanoparticles increases with decreasing average particle size. The k_app value of this photocatalytic degradation of textile dyeing waste water in presence of AuNPs was 0.002/min and β-CD/AuNPs was 0.005/min. This is a non-toxic and eco-friendly approach.

Broadband SERS Enhancement by DNA Origami Assembled Bimetallic Nanoantennas with Label-Free Single Protein Sensing

Engineering hotspots in surface-enhanced Raman spectroscopy (SERS) through precisely controlled assembly of plasmonic nanostructures capable of expanding intense field enhancement are highly desirable to enhance the potentiality of SERS as a label-free optical tool for single molecule detection. Inspired by DNA origami technique, we constructed plasmonic dimer nanoantennas with a tunable gap decorated with Ag-coated Au nanostars on origami. Herein, we demonstrate the single-molecule SERS enhancements of three dyes with emission in different spectral regions after incorporation of single dye molecules in between two nanostars. The enhancement factors (EFs) achieved in the range of 10⁹-10¹⁰ for all the single dye molecules, under both resonant and nonresonant excitation conditions, would enable enhanced photostability during time-series measurement. We further successfully explored the potential of our designed nanoantennas to accommodate and detect a single thrombin protein molecule after selective placement in the wide nanogap of 10 nm. Our results suggest that such nanoantennas can serve as a broadband SERS enhancer and enable specific detection of target biological molecules with single-molecule sensitivity.

Hybrid silver-gold nanoparticles suppress drug resistant polymicrobial biofilm formation and intracellular infection

Over decades bacteria have evolved multiple mechanisms to fight antibiotics. Biofilm formation by bacteria is one such mechanism as it forms a barrier and creates an acidic environment that reduces the efficiency of antimicrobials. Bacteria have also developed the ability to persist intracellularly within mammalian cells, causing recurrent infections. Many antibiotics are rendered ineffective due to poor penetration across biofilms and within mammalian cells. In this study, silver-gold hybrid nanoparticles were developed as anti-microbial agents to combat biofilm formation and intracellular infections. Biogenic hybrid silver gold nanoparticles were developed in an organic solvent free single reaction mixture using quercetin, a flavonoid, as the reducing and stabilizing agent. Silver-gold nanoparticles of 40 ± 10 nm diameter were effective against a broad spectrum of bacteria with minimum bactericidal concentrations of 10 μg ml-1 and 20 μg ml-1 for Gram negative and Gram-positive organisms, respectively. These nanoparticles were also effective against mixed infections at 20 μg ml-1. Their mode of action involves generating intracellular oxidative stress in both Gram negative and Gram-positive bacteria, which causes damage to the cell wall. Polymicrobial biofilm formation was suppressed and intracellular infection was reduced by 70% to 90% in fibroblast and monocyte cell lines. These results indicate that hybrid silver gold nanoparticles are promising agents to suppress biofilm formation and tackle intracellular infections.

Cyclodextrins and inorganic nanoparticles: Another tale of synergy

In this review, we summarize the recent research focused on the combination of inorganic nanoparticles and α-, β- and γ- cyclodextrins. Our intention is to highlight the most relevant publications on the synthesis of nanoparticle-cyclodextrin (NP-CD) nanohybrids, with CDs acting as reducing agents or through the post-synthetic modification of inorganic nanoparticles with CDs. We also discuss the new or enhanced properties that arise from the host-guest capabilities of the CDs and inorganic nanoparticles. Finally, we illustrate the potential applications of these materials in numerous research fields.

Au–Ag core–shell composite nanoparticles as a selective and sensitive plasmonic chemical probe for l-cysteine detection in Lens culinaris (lentils)

The present work reported is a simple and selective method for the colorimetrical detection of l-cysteine in Lens culinaris (or lentils) using Au–Ag core–shell (Au core Ag shell) composite nanoparticles as a chemical probe.

Comparative Performance of Citrate, Borohydride, Hydroxylamine and β-Cyclodextrin Silver Sols for Detecting Ibuprofen and Caffeine Pollutants by Means of Surface-Enhanced Raman Spectroscopy

The detection of emerging contaminants in the aquatic environment, such as ibuprofen and caffeine, was studied by means of surface-enhanced Raman spectroscopy (SERS) using Ag nanoparticles (AgNPs) synthesized with β-cyclodextrin (βCD) as a reducing agent. The effect on the SERS signal of different molar ratios of Ag⁺/βCD in the synthesis route and the aging process of AgNPs were investigated by using trans-cinnamic as a test molecule. The SERS effectiveness of these β-cyclodextrin colloids (Ag@βCD) was also checked and compared with that of other silver sols usually employed in SERS synthesized by using other reducing agents such as citrate, borohydride and hydroxylamine. All the synthesized SERS substrates were characterized by different techniques. The experimental results indicate that Ag@βCD with the more diluted Ag⁺/βCD molar ratio showed the best SERS signal, enabling detection at trace concentrations of 0.5 µM in the case of trans-cinnamic acid. The Ag@βCD sols also showed the best sensitivity for detecting ibuprofen and caffeine, reaching the lowest limit of detection (0.1 mM). The proposed synthetic route for Ag@βCD sols provides an improved SERS substrate for detecting organic pollutants with better performance than other standard silver sols.

Fast Microwave Synthesis of Gold-Doped TiO2 Assisted by Modified Cyclodextrins for Photocatalytic Degradation of Dye and Hydrogen Production

A convenient and fast microwave synthesis of gold-doped titanium dioxide materials was developed with the aid of commercially available and common cyclodextrin derivatives, acting both as reducing and stabilizing agents. Anatase titanium oxide was synthesized from titanium chloride by microwave heating without calcination. Then, the resulting titanium oxide was decorated by gold nanoparticles thanks to a microwave-assisted reduction of HAuCl4 by cyclodextrin in alkaline conditions. The materials were fully characterized by UV-Vis spectroscopy, X-Ray Diffraction (XRD), Transmission Electron Microscopy (TEM), and N2 adsorption-desorption measurements, while the metal content was determined by Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES). The efficiency of the TiO2@Au materials was evaluated with respect to two different photocatalytic reactions, such as dye degradation and hydrogen evolution from water.

Chiral Assembly of Gold-Silver Core-Shell Plasmonic Nanorods on DNA Origami with Strong Optical Activity

The spatial organization of metal nanoparticles has become an important tool for manipulating light in nanophotonic applications. Silver nanoparticles, particularly silver nanorods, have excellent plasmonic properties but are prone to oxidation and are therefore inherently unstable in aqueous solutions and salt-containing buffers. Consequently, gold nanoparticles have often been favored, despite their inferior optical performance. Bimetallic, i.e., gold-silver core-shell nanoparticles, can resolve this issue. We present a method for synthesizing highly stable gold-silver core-shell NRs that are instantaneously functionalized with DNA, enabling chiral self-assembly on DNA origami. The silver shell gives rise to an enhancement of plasmonic properties, reflected here in strongly increased circular dichroism, as compared to pristine gold nanorods. Gold-silver nanorods are ideal candidates for plasmonic sensing with increased sensitivity as needed in pathogen RNA or antibody testing for nonlinear optics and light-funneling applications in surface enhanced Raman spectroscopy. Furthermore, the control of interparticle orientation enables the study of plasmonic phenomena, in particular, synergistic effects arising from plasmonic coupling of such bimetallic systems.

Improved SERS Performance and Catalytic Activity of Dendritic Au/Ag Bimetallic Nanostructures Based on Ag Dendrites

Bimetallic nanomaterials, which exhibit a combination of the properties associated with two different metals, have enabled innovative applications in nanoscience and nanotechnology. Here, we introduce the fabrication of dendritic Au/Ag bimetallic nanostructures for surface-enhanced Raman scattering (SERS) and catalytic applications. The dendritic Au/Ag bimetallic nanostructures were prepared by combining the electrochemical deposition and replacement reaction. The formation of Au nanoparticle shell on the surface of Ag dendrites greatly improves the stability of dendritic nanostructures, followed by a significant SERS enhancement. In addition, these dendritic Au/Ag bimetallic nanostructures are extremely efficient in degrading 4-nitrophenol (4-NP) compared with the initial dendritic Ag nanostructures. These experimental results indicate the great potential of the dendritic Au/Ag bimetallic nanostructures for the development of excellent SERS substrate and highly efficient catalysts.

Bimetallic Core-Shell Nanoparticles of Gold and Silver via Bioinspired Polydopamine Layer as Surface-Enhanced Raman Spectroscopy (SERS) Platform

Despite numerous attempts to fabricate the core-shell nanoparticles, novel, simple, and low-cost approaches are still required to produce these efficient nanosystems. In this study, we propose the synthesis of bimetallic core-shell nanoparticles of gold (AuNP) and silver (AgNP) nanostructures via a bioinspired polydopamine (PDOP) layer and their employment as a surface-enhanced Raman spectroscopy (SERS) platform. Herein, the PDOP layer was used as an interface between nanostructures as well as stabilizing and reducing agents for the deposition of silver ions onto the AuNPs. UV-vis absorption spectra and electron microscope images confirmed the deposition of the silver ions and the formation of core-shell nanoparticles. SERS activity tests indicated that both the PDOP thickness and silver deposition time are the dominant parameters that determine the SERS performances of the proposed core-shell system. In comparison to bare AuNPs, more than three times higher SERS signal intensity was obtained with an enhancement factor of 3.5 × 10⁵.

The non-covalent complexes of α- or γ-cyclodextrin with divalent metal cations determined by mass spectrometry

Noncovalent complexes between cyclodextrin (CD) and divalent metal cations drew growing attentions due to their applications in the pharmaceutical industry for molecular recognition. In this study, gas-phase binding of noncovalent complexes between α-, or γ-CD and divalent metal cations was investigated by electrospray ionization mass spectrometry (ESI-MS), demonstrating the formation of 1:1 stoichiometric noncovalent complexes. The binding of the complexes were furtherly confirmed by collision-induced dissociation (CID) with tandem mass spectrometry. The CID revealed the fragmentation pattern were strongly dependent on the electronic configuration of the cations and the charge separation reaction frequently took place in the cyclodextrin-complexes with transition metal cations. For the non-covalent complexes of α-CD with Mg²⁺, Ca²⁺, Sr²⁺ or Ba²⁺ at a collision energy of 25 eV, the fragments attributed to [α-CD + cation-nGlucose unit]²⁺ were observed (named series A). However, for the γ-CD complexes with transition metal cations Co²⁺, Ni²⁺, Cu²⁺ or Zn²⁺, apart from fragments of series A, it were observed fragment ions of [γ-CD + cation-nGlucose unit]⁺ (named series B), together with the Glucose unit (m/z 163.2) and its products with loss of H₂O (m/z 145.2 and 126.8). The CID performed at a collision energy from 10 to 50 eV showed that the binding strength of complexes increase in the order of [α-CD + Mg]²⁺, [α-CD + Ca]²⁺, [α-CD + Sr]²⁺ and [α-CD + Ba]²⁺. Through mass spectrometric titrations, the values of dissociation constant K_d (in μmol•L^-1) for the complexes of α-CD with Ca²⁺ or Ni²⁺ were obtained, which were 4.30 and 4.26, respectively.

Smart phone assisted, rapid, simplistic, straightforward and sensitive biosensing of cysteine over other essential amino acids by β-cyclodextrin functionalized gold nanoparticles as a colorimetric probe

Herein, we have attempted the synthesis of β-CD functionalized AuNPs and then applied them as a colorimetric assay for the quantification of Cys over other different essential amino acids.

Controllable "Clicked-to-Assembled" Plasmonic Core-Satellite Nanostructures and Its Surface-Enhanced Fluorescence in Living Cells

The assembly of noble-metal core-satellite (CS) nanostructures is an appealing means to control their plasmonic properties for their applications such as surface-enhanced fluorescence or Raman scattering. However, till now there is a lack of some rapid or convenient methods to construct stable CS nanostructures. Here, we proposed a "clicked-to-assembly" strategy based on the fast and specific "click chemistry" reaction between trans-cyclooctene (TCO) and 1,2,4,5-tetrazine (Tz). The CS nanostructures were constructed within 8 min by simple mixing of TCO- or Tz-modified nanoparticles (TCO-NPs or Tz-NPs) without any catalysts or heating required. Transmission electron microscopy experiments show that the constructed CS nanostructures are uniform, and particularly the number of "satellite" nanoparticles in the core surface is controllable by simply adjusting the feeding ratio of TCO-NPs or Tz-NPs in the reaction. The strong surface plasmon coupling effect (SPCE) was observed in these CS nanostructures, which was dependent on the coverage degree, size and composition of the satellite, and core NPs. The nanostructures with tuned surface plasmon resonance (SPR) effect were tried for the surface-enhanced fluorescence in living cells. Such well-defined CS nanostructures could potentially serve as efficient SPR-enhanced fluorescent probes as diagnostics or biomedical imaging agents in nanomedicine.

Inhibiting Analyte Theft in Surface-Enhanced Raman Spectroscopy Substrates: Subnanomolar Quantitative Drug Detection

Quantitative applications of surface-enhanced Raman spectroscopy (SERS) often rely on surface partition layers grafted to SERS substrates to collect and trap-solvated analytes that would not otherwise adsorb onto metals. Such binding layers drastically broaden the scope of analytes that can be probed. However, excess binding sites introduced by this partition layer also trap analytes outside the plasmonic “hotspots”. We show that by eliminating these binding sites, limits of detection (LODs) can effectively be lowered by more than an order of magnitude. We highlight the effectiveness of this approach by demonstrating quantitative detection of controlled drugs down to subnanomolar concentrations in aqueous media. Such LODs are low enough to screen, for example, urine at clinically relevant levels. These findings provide unique insights into the binding behavior of analytes, which are essential when designing high-performance SERS substrates.

One-Step Photochemical Green Synthesis of Water-Dispersible Ag, Au, and Au@Ag Core-Shell Nanoparticles

A simple and green synthetic protocol for the rapid and effective preparation of Ag, Au and Au@Ag core-shell nanoparticles (NPs) is reported based on the light irradiation of a biocompatible, water-soluble dextran functionalized with benzophenone (BP) in the presence of AgNO₃ , HAuCl₄ , or both. Photoactivation of the BP moiety produces the highly reducing ketyl radicals through fast (<50 ns) intramolecular H-abstraction from the dextran scaffold, which, in turn, ensures excellent dispersibility of the obtained metal NPs in water. The antibacterial activity of the AgNPs and the photothermal action of the Au@Ag core-shell are also shown.

Unraveling Structural Information of Turkevich Synthesized Plasmonic Gold-Silver Bimetallic Nanoparticles

For the synthesis of gold-silver bimetallic nanoparticles, the Turkevich method has been the state-of-the-art method for several decades. It is presumed that this procedure results in a homogeneous alloy, although this has been debatable for many years. In this work, it is shown that neither a full alloy, nor a perfect core-shell particle is formed but rather a core-shell-like particle with altering metal composition along the radial direction. In-depth wet-chemical experiments are performed in combination with advanced transmission electron microscopy, including energy-dispersive X-ray tomography, and finite element method modeling to support the observations. From the electron tomography results, the core-shell structure can be clearly visualized and the spatial distribution of gold and silver atoms can be quantified. Theoretical simulations are performed to demonstrate that even though UV-vis spectra show only one plasmon band, this still originates from core-shell type structures. The simulations also indicate that the core-shell morphology does not so much affect the location of the plasmon band, but mainly results in significant band broadening. Wet-chemistry experiments provide the evidence that the synthesis pathway starts with gold enriched alloy cores, and later on in the synthesis mainly silver is incorporated to end up with a silver enriched alloy shell.

Electron Compensation Effect Suppressed Silver Ion Release and Contributed Safety of Au@Ag Core-Shell Nanoparticles

Silver nanoparticles (Ag NPs) have promising plasmonic properties, however, they are rarely used in biomedical applications because of their potent toxicity. Herein, an electron compensation effect from Au to Ag was applied to design safe Au@Ag core-shell NPs. The Ag shell thickness was precisely regulated to enable the most efficient electron enrichment in Ag shell of Au@Ag_2.4 NPs, preventing Ag oxidation and subsequent Ag⁺ ion release. X-ray photoelectron spectroscopy and X-ray absorption near-edge structure analysis revealed the electron transfer process from Au core to Ag shell, and inductively coupled plasma optical emission spectroscopy analysis confirmed the low Ag⁺ ion release from Au@Ag_2.4 NPs. Bare Au@Ag_2.4 NPs showed much lower toxicological responses than Ag NPs in BEAS-2B and Raw 264.7 cells and acute lung inflammation mouse models, and PEGylation of Au@Ag_2.4 NPs could further improve their safety to L02 and HEK293T cells as well as mice through intravenous injection. Further, diethylthiatri carbocyanine iodide attached pAu@Ag_2.4 NPs exhibited intense surface-enhanced Raman scattering signals and were used for Raman imaging of MCF7 cells and Raman biosensing in MCF7 tumor-bearing mice. This electron compensation effect opens up new opportunity for broadening biomedical application of Ag-based NPs.

Facile method for iodide ion detection via the fluorescence decrease of dihydrolipoic acid/beta-cyclodextrin protected Ag nanoclusters

In this work, novel photoluminescent Ag nanoclusters (Ag NCs) with red emission are synthesized and successfully used for detecting iodide ion (I^-). The dihydrolipoic acid (DHLA) is used as the stabilizing agent and beta-cyclodextrin (β-CD) is used as the auxiliary stabilizing agent. DHLA and β-CD are combined with Ag atoms by the formation of AgS bonds and hydrophobic interaction, respectively. Functionalization of β-CD endows good photoluminescent properties and solubility in water to the Ag NCs. The obtained DHLA and β-CD-protected Ag NCs (DHLA/β-CD-Ag NCs) are spherical and display a dispersed state. However, the DHLA/β-CD-Ag NCs are aggregated in the presence of I^-, accompanied by the decrease in their fluorescence intensity. Because the integrity of β-CD cavities is retained on the surface of DHLA/β-CD-Ag NCs, which preserves their capability for I^- host-guest recognition, the DHLA/β-CD-Ag NCs combine with I^- through the formation of inclusion complexes. Based on this phenomenon, the prepared DHLA/β-CD-Ag NCs can be designed as a novel fluorescent probe for I^- detection. The limit of detection (LOD) is calculated as 0.06 μM, indicating that it is an ideal probe for I^- detection in practical applications.

Catalytic Application and Mechanism Studies of Argentic Chloride Coupled Ag/Au Hollow Heterostructures: Considering the Interface Between Ag/Au Bimetals

For an economical use of solar energy, photocatalysts that are sufficiently efficient, stable, and capable of harvesting light are required. Composite heterostructures composed of noble metals and semiconductors exhibited the excellent in catalytic application. Here, 1D Ag/Au/AgCl hollow heterostructures are synthesized by galvanic replacement reaction (GRR) from Ag nanowires (NWs). The catalytic properties of these as-obtained Ag/Au/AgCl hollow heterostructures with different ratios are investigated by reducing 4-nitrophenol (Nip) into 4-aminophenol (Amp) in the presence of NaBH₄, and the influence of AgCl semiconductor to the catalytic performances of Ag/Au bimetals is also investigated. These hollow heterostructures show the higher catalytic properties than pure Ag NWs, and the AgCl not only act as supporting materials, but the excess AgCl is also the obstacle for contact of Ag/Au bimetals with reactive species. Moreover, the photocatalytic performances of these hollow heterostructures are carried out by degradation of acid orange 7 (AO7) under UV and visible light. These Ag/Au/AgCl hollow heterostructures present the higher photocatalytic activities than pure Ag NWs and commercial TiO₂ (P25), and the Ag/Au bimetals enhance the photocatalytic activity of AgCl semiconductor via the localized surface plasmon resonance (LSPR) and plasmon resonance energy transfer (PRET) mechanisms. The as-synthesized 1D Ag/Au/AgCl hollow heterostructures with multifunction could apply in practical environmental remedy by catalytic manners.

Rapid antibacterial effect of sunlight-exposed silicon nanowire arrays modified with Au/Ag alloy nanoparticles

Au/Ag alloy nanoparticles modified silicon nanowire arrays can kill bacterial cells in several minutes under sunlight due to their photothermal and photocatalytic activities.

Novel Competitive Fluorescence Sensing Platform for L-carnitine Based on Cationic Pillar[5]Arene Modified Gold Nanoparticles

Supramolecular host-guest interaction and sensing between cationic pillar[5]arenes (CP5) and L-carnitine were developed by the competitive host-guest recognition for the first time. The fluorescence sensing platform was constructed by CP5 functionalized Au nanoparticles (CP5@Au-NPs) as receptor and probe (rhodamine 123, R123), which shown high sensitivity and selectivity for L-carnitine detection. Due to the negative charge and molecular size properties of L-carnitine, it can be highly captured by the CP5 via electrostatic interactions and hydrophobic interactions. The host-guest mechanism between PP5 and L-carnitine was studied by ¹H NMR and molecular docking, indicating that more affinity binding force of CP5 with L-carnitine. Therefore, a selective and sensitive fluorescent method was developed. It has a linear response of 0.1–2.0 and 2.0–25.0 μM and a detection limit of 0.067 μM (S/N = 3). The fluorescent sensing platform was also used to detect L-carnitine in human serum and milk samples, which provided potential applications for the detection of drugs abuse and had path for guarding a serious food safety issues.