Colloidal AuNPs Research Articles

One‐Pot Synthesis of Gold Nanoparticles and Aluminum Hydroxide Hydrogels‐Based Nanocomposites with Modulated Optical Properties

AbstractIn this work, the one‐pot synthesis of composites constituted by gold nanoparticles (AuNPs) and aluminum hydroxide hydrogels (AlHG) by employing the Epoxide Route is presented. To modulate the optical properties of the final composites, different anions (X= , , and ) were used as nucleophile, complexing and growth directing agents of the AuNPs. In addition, the concentration of the reactants, e. g., the X : Cl ratio, was set in such a way to preserve the alkalization rate, the transparency of the hydrogels supporting the AuNPs, and the stability of the final composites. Consequently, the composites exhibit different plasmonic properties, resulting from the AuNPs with different sizes and morphologies, as confirmed through transmission electron microscopy, depending on the nature of the employed anion, exclusively. Furthermore, this versatile one‐pot synthesis strategy was employed to design new composites with different I : Cl ratio and synthesize stable colloidal AuNPs within an aluminum hydroxide sol (AuNP@Alsol) without adding any conventional capping agent. This AuNP@Alsol composite can be used as seed to accelerate the extremely slow AuNPs formation kinetics in AuNP@AlHG(SCN), demonstrating the potential of this synthesis method to create composites susceptible to be applied in the photonic and catalysis areas.

Probing the Adsorption Sites of 5‐amino‐2‐mercaptobenzimidazole Conformations on Colloidal Gold Nanoparticles Investigated by SERS and DFT

AbstractGold nanoparticles (AuNP) have shown great potential in biomedical applications due to their unique and tunable properties. Understanding the ligand conformation on AuNP has profound interest in nanoparticle research leading to a precise drug delivery system. Colloidal AuNPs were synthesized using trisodium citrate as reducing agent. Normal Raman spectrum (NRS) in solid and aqueous phase identifies that 5‐amino‐2‐mercaptobenzimidazole (5A2MBI) mainly exist as thione form. Surface enhanced Raman scattering (SERS) investigation of 5A2MBI depending on pH was performed to explore the adsorption mechanism of thiolate and thione conformations on AuNPs. Density functional theory (DFT) calculations were used to find the band assignments and molecular electrostatic potential (MEP) mapping to identify the electron rich site where metal can interact preferentially. Using SERS spectral analysis and DFT results, surface adsorption scheme was proposed. At basic pH, 5A2MBI adsorbs on AuNP as thiolate form bidentately via Sulfur and nitrogen atom of imidazole ring with tilted geometry. However, in acidic condition the thione form adsorbs on nanosurface with perpendicular orientation.

Stealth and Biocompatible Gold Nanoparticles through Surface Coating with a Zwitterionic Derivative of Glutathione.

Gold nanoparticles (AuNPs) hold promise in biomedicine, but challenges like aggregation, protein corona formation, and insufficient biocompatibility must be thoroughly addressed before advancing their clinical applications. Designing AuNPs with specific protein corona compositions is challenging, and strategies for corona elimination, such as coating with polyethylene glycol (PEG), have limitations. In this study, we introduce a commercially available zwitterionic derivative of glutathione, glutathione monoethyl ester (GSHzwt), for the surface coating of colloidal AuNPs. Particles coated with GSHzwt were investigated alongside four other AuNPs coated with various ligands, including citrate ions, tiopronin, glutathione, cysteine, and PEG. We then undertook a head-to-head comparison of these AuNPs to assess their behavior in biological fluid. GSHzwt-coated AuNPs exhibited exceptional resistance to aggregation and protein adsorption. The particles could also be readily functionalized with biotin and interact with streptavidin receptors in human plasma. Additionally, they exhibited significant blood compatibility and noncytotoxicity. In conclusion, GSHzwt provides a practical and easy method for the surface passivation of AuNPs, creating "stealth" particles for potential clinical applications.

Off-resonance high-performance surface-enhanced Raman scattering-active substrate by trapping gold nanoparticles using Bessel beam

The surface-enhanced Raman scattering (SERS) technique provides outstanding molecular fingerprint identification and high sensitivity of analytes. Herein, colloidal sphere-shaped gold nanoparticles (Au-NPs) trapped in concentric rings of the Bessel beam generated from the optical fiber-based negative axicon has been reported as a SERS substrate. With the trapping of Au-NPs, the SERS ability of colloidal Au-NPs improved, and the average enhancement factor (AEF) of the rhodamine-6G (R6G) and 4-aminothiophenol (4-ATP) molecules can reach up to the order of 107. Control experiments were also carried out with the trapping of Au-NPs by Gaussian beam illumination, without any illumination of the light and with the trapping of Au-NPs by the Bessel beam illumination on a silver (Ag)-coated silicon (Si) substrate with a self-assembled monolayer (SAM) of 4-ATP. Theoretical studies were also carried out using the finite element method (FEM) to identify the hotspots generated in the gaps formed between the Au-NPs, leading to an enhancement in the SERS signal of the molecules, and the results were consistent with the experimentally determined AEFs. The obtained results demonstrate that the proposed SERS technique is stable. This study has significant potential applications in clinical diagnosis, food safety, environment safety, chemical sensing, and biosensing.

Light-enhanced catalytic activity of stable and large gold nanoparticles in homocoupling reactions.

Validating the direct photocatalytic activity of colloidal plasmonic nanoparticles is challenging due to their limited stability and needed support materials that can often contribute to the chemical reactions. Stable gold nanoparticles (AuNPs) with tunable sizes are prepared across porous polymer particles without any chemical bonds where the resulting composite particles exhibit intense surface plasmon resonances (SPRs) in the visible region. These composite particles are then tested as photocatalysts under a broadband solar-simulated light source to examine the contribution degree of photothermal heating and SPR coming from the incorporated AuNPs in the C-C bond forming homocoupling reaction. Generally, the thermal and photothermal heating are the main driving force to increase the reactivity of relatively smaller AuNPs (~ 44 nm in diameter) with a narrower SPR band. However, the SPR-induced catalytic activity is much greater for the composite particles containing larger AuNPs (~ 87 nm in diameter) with a broader SPR. As the polymer particle matrix does not influence the catalytic activity (e.g., inducing charge delocalization and/or separation), the unique SPR role of the colloidal AuNPs in the catalytic reaction is assessable under light irradiation. This study experimentally demonstrates the possibility of evaluating the direct contribution of SPRs to photocatalytic chemical reactions.

Size and concentration effects of gold nanoparticles on the plasmonic sensing of Cr(VI)

It is very important to determine the presence of toxic Cr(VI) in aqueous environment. Detection of Cr(VI) using AuNPs has been carried out based on the oxidation or etching principle, which results in the change of localized surface plasmon resonance. In this work, the effects of size and concentration of colloidal AuNPs on the Cr(VI) sensing characteristics were studied by both simulation and experiment. In the simulation study using MNPBEM toolbox, the etching process was described as shrinking of AuNPs with total volume loss reflecting the concentration of Cr(VI) as oxidizing ions. The experiment was carried out by exposing colloidal AuNPs with different size and concentration to Cr(VI). The AuNPs were obtained from laser-induced photochemical process, in which aqueous solution of Au ions were subjected to femtosecond laser irradiation. The simulation results showed wider blue-shift of λLSPR per total volume loss when larger AuNPs were employed and higher intercept value of extinction decrease per total volume loss when more AuNPs were present in the system. Correspondingly, the experiment demonstrated more distinct color change and wider λLSPR per Cr(VI) concentration when larger AuNPs were used. More concentrated colloid showed still-red color after Cr(VI) etching, representing higher intercept value of extinction decrease per Cr(VI). Both simulation and experiment results show that, in etching-based Cr(VI) sensing, large AuNPs displayed wider LSPR wavelength shift compared to the small nanoparticles. On the other hand, concentration of AuNPs contributes to the intensity change and higher concentration of AuNPs offers higher Cr(VI) sensing range. This result provided an insight on how colorimetric sensor performance might be affected by the choice of nanoparticle size and concentration used in the system.

Green synthesized gold nanoparticles and CuO-based nonenzymatic sensor for saliva glucose monitoring.

Glucose, essential for brain and muscle functions, requires careful monitoring in diabetes and other chronic disease management. While blood glucose monitoring provides precise information about these diseases, it remains an invasive method. Saliva glucose monitoring could offer an alternative approach, but the glucose concentration in saliva is very low. In this work, we report a simple, low-cost, highly sensitive nonenzymatic electrochemical glucose sensor. We developed this sensor using green synthesized gold nanoparticles (AuNPs) and wet chemical synthesized copper oxide (CuO) nanoparticles on a screen-printed carbon electrode (Au/CuO/SPCE). The sensor's high sensitivity results from dual amplification strategies using AuNPs and CuO nanomaterials, each demonstrating catalytic activity towards glucose. This shows promising potential for saliva glucose monitoring. The AuNPs were synthesized using an Au precursor and orange peel extract (OPE), yielding stable colloidal AuNPs with a mean diameter of about 37 nm, thus eliminating the need for additional capping agents. Under optimal conditions, amperometric tests revealed that the sensor responded linearly to glucose concentrations ranging from 2 μM to 397 μM with a sensitivity of 236.70 μA mM-1 cm-2. Furthermore, the sensor demonstrated excellent reproducibility, stability and high selectivity for glucose in the presence of different biomolecules. We validated the sensor's efficacy by measuring glucose in human saliva, showing its potential for noninvasive glucose monitoring. This research advances the development of point-of-care devices, positioning the sensor as a promising tool for noninvasive glucose monitoring and improved diabetes management.

Micro-interdigitated electrodes genosensor based on Au-deposited nanoparticles for early detection of cervical cancer

Genosensor-based electrodes mediated with nanoparticles (NPs) have tremendously developed in medical diagnosis. Herein, we report a facile, rapid, low cost and highly sensitive biosensing strategy for early detection of HPV 18 using gold-nanoparticles (AuNPs) deposited on micro-IDEs. This study represents surface charge transduction of micro-interdigitated electrodes (micro-IDE) alumina insulated with silica, independent and mini genosensor modified with colloidal gold NPs (AuNPs), and determination of gene hybridization for early detection of cervical cancer. The surface of AuNPs deposited micro-IDE functionalized with optimized 3-aminopropyl-triethoxysilane (APTES) followed by hybridization with deoxyribonucleic acid (DNA) virus to develop DNA genosensor. The results of ssDNA hybridization with the ssDNA target of human papillomavirus (HPV) 18 have affirmed that micro-IDE functionalized with colloidal AuNPs resulted in the lowest detection at 0.529 aM. Based on coefficient regression, micro-IDE functionalized with AuNPs produces better results in the sensitivity test (R2 = 0.99793) than unfunctionalized micro-IDE.

Investigation of in vitro antimicrobial, antioxidant and antiproliferative activities of Nostoc calcicola biosynthesized gold nanoparticles.

The cyanobacteria are the promising candidate for synthesizing gold nanoparticles (AuNPs), due to their ability to accumulate heavy metals from the cellular environment and additionally contain varied bioactive compounds as reducing and stabilizing agents. This study describes the N2-fixing cyanobacterium Nostoc calcicola-mediated bioreduction of AuNPs and the inherent antimicrobial, antioxidant, and antiproliferative activities in vitro. Biosynthesized Nc-AuNPs were characterized by spectral characterization techniques. The formation of AuNPs was physically confirmed by the colour change from pale green to dark violet. The UV-Vis analysis, further, proved the reduction in Nc-AuNPs with the cyanobacterium and showed a spectral peak at 527nm. FESEM-EDX images suggested the surface morphology of the NPs as spherical, cuboidal, and size between 20 and 140nm. The antimicrobial studies of Nc-AuNPs were carried out by agar-well diffusion method and MIC values against five pathogenic bacterial and two fungal strains were noted. The AuNPs exhibited potential antimicrobial activity against h-pathogenic bacteria with inhibitory zones ranging at 11-18mm; against fungi ranging at 13-17mm. Significant antioxidant potentialities were explored by a DPPH assay with an IC50 value of 55.97μg/ mL. Furthermore, in the anticancer efficacy assay, the Nc-AuNPs inhibited cellular proliferation in human breast adenocarcinoma and cervical cancer cell lines at IC50 concentration, 37.3μg/ml, and 44.5μg/ml, respectively. Conclusively, N. calcicola would be an excellent source for synthesizing stable colloidal AuNPs that had significant credibility as phycological (algal) nanomedicines as novel prodrugs with multiple bioactivities.

Simultaneous electrochemical detection of oxygen (O2) and hydrogen peroxide (H2O2) in neutral media

The simultaneous detection of oxygen (O2) and hydrogen peroxide (H2O2) in neutral media was investigated by cyclic voltammetry using a two-working modified glassy carbon (GC) electrode system. Both electrodes were functionalized either by electrodeposited or by chemically-prepared gold nanoparticles (AuNPs). AuNPs electrodeposition was achieved by constant potential electrolysis either at 0.5 or ‐0.5 V/SHE in acidic HAuCl4 solution. Colloidal AuNPs were obtained according four different procedures (type A to D) derived from the classical Turkevich synthesis and further drop-casted on GC. The kinetics of H2O2 oxidation was studied by recording steady-state voltammograms in a deaerated NaCl/NaHCO3 pH 7.4 neutral solution on all the functionalized electrodes and favorably compared to unmodified GC and bare gold electrodes. Both Koutecky-Levich and Tafel treatment of the current-potential curves showed that the highest anodic transfer coefficient αn (0.78 ± 0.14) was obtained with the electrodeposited AuNPs/GC electrode using the most cathodic deposition potential of ‐0.5 V which provided the highest average number of nanoparticles per square micrometer (555 ± 49 µm-2) of very little average size (25 ± 12 nm) NPs. The simultaneous detection and quantification of O2 and H2O2 was achieved only with electrodes functionalized using D-type Turkevich synthesis. In this case H2O2 was detected at the anode while current corresponding to O2 reduction was selectively recorded at a potential close to ‐0.3 V without interference from H2O2.

Updates on the Biofunctionalization of Gold Nanoparticles for the Rapid and Sensitive Multiplatform Diagnosis of SARS-CoV-2 Virus and Its Proteins: From Computational Models to Validation in Human Samples.

Since the outbreak of the pandemic respiratory virus SARS-CoV-2 (COVID-19), academic communities and governments/private companies have used several detection techniques based on gold nanoparticles (AuNPs). In this emergency context, colloidal AuNPs are highly valuable easy-to-synthesize biocompatible materials that can be used for different functionalization strategies and rapid viral immunodiagnosis. In this review, the latest multidisciplinary developments in the bioconjugation of AuNPs for the detection of SARS-CoV-2 virus and its proteins in (spiked) real samples are discussed for the first time, with reference to the optimal parameters provided by three approaches: one theoretical, via computational prediction, and two experimental, using dry and wet chemistry based on single/multistep protocols. Overall, to achieve high specificity and low detection limits for the target viral biomolecules, optimal running buffers for bioreagent dilutions and nanostructure washes should be validated before conducting optical, electrochemical, and acoustic biosensing investigations. Indeed, there is plenty of room for improvement in using gold nanomaterials as stable platforms for ultrasensitive and simultaneous "in vitro" detection by the untrained public of the whole SARS-CoV-2 virus, its proteins, and specific developed IgA/IgM/IgG antibodies (Ab) in bodily fluids. Hence, the lateral flow assay (LFA) approach is a quick and judicious solution to combating the pandemic. In this context, the author classifies LFAs according to four generations to guide readers in the future development of multifunctional biosensing platforms. Undoubtedly, the LFA kit market will continue to improve, adapting researchers' multidetection platforms for smartphones with easy-to-analyze results, and establishing user-friendly tools for more effective preventive and medical treatments.

Surfactant-Free Colloidal Syntheses of Gold-Based Nanomaterials in Alkaline Water and Mono-alcohol Mixtures.

Gold nanoparticles (Au NPs) and gold-based nanomaterials combine unique properties relevant for medicine, imaging, optics, sensing, catalysis, and energy conversion. While the Turkevich-Frens and Brust-Schiffrin methods remain the state-of-the-art colloidal syntheses of Au NPs, there is a need for more sustainable and tractable synthetic strategies leading to new model systems. In particular, stabilizers are almost systematically used in colloidal syntheses, but they can be detrimental for fundamental and applied studies. Here, a surfactant-free synthesis of size-controlled colloidal Au NPs stable for months is achieved by the simple reduction of HAuCl4 at room temperature in alkaline solutions of low-viscosity mono-alcohols such as ethanol or methanol and water, without the need for any other additives. Palladium (Pd) and bimetallic Au x Pd y NPs, nanocomposites and multimetallic samples, are also obtained and are readily active (electro)catalysts. The multiple benefits over the state-of-the-art syntheses that this simple synthesis bears for fundamental and applied research are highlighted.

Activity and reusability of immobilized gold nanoparticles for the catalysis of both oxidation and reduction reactions

Colloidal gold nanoparticles (AuNP) are well-known to present a catalytic activity. However, they are characterized by certain limitations, as a rather poor stability and lack of both handling and reusability. Their immobilization on surfaces could help to overcome these drawbacks. This work evaluated the impact of the immobilization of AuNP towards their catalytic activity on reduction and oxidation reactions. Colloidal AuNP stabilized with citrate ions were synthesized, characterized, and immobilized by the dip-coating method, the obtained immobilized AuNP (iAuNP) were characterized. The catalytic activity of AuNP and iAuNP was evaluated and compared to each other through the p-nitrophenol reduction reaction. The kinetic of the catalytic activity of iAuNP was slower than colloidal AuNP. The catalytic activity appeared to be impacted by the less available surface of iAuNP. The reduction efficiency of iAuNP was also evaluated with the DPPH•/DPPH2 reduction reaction. The capacity of iAuNP to catalyze the reduction of DPPH• in DPPH2 was shown even after 130 days and 20 reuses of the nanostructured surface on the contrary to non-reusable colloidal AuNP. The oxidation efficiency of iAuNP was measured by the ability to catalyze the auto-oxidation of curcumin (HPLC-UV/vis). For all these experiments, the addition of 4-mercapto-phenol on the surface of iAuNP passivated the surface, decreasing the catalytic activity of the materials. In conclusion, iAuNP are redox catalysts with both anti- and pro-oxidant effects and high reusability over a very long period.

A Colorimetric Detection of Noradrenaline in Wastewater Using Citrate-Capped Colloidal Gold Nanoparticles Probe

This study reports a simple, fast, and low-cost detection of noradrenaline (NA) in wastewater using citrate-capped colloidal gold nanoparticles (AuNPs). The addition of NA to citrate-capped colloidal AuNPs generates a colour modulation that the bare eye can detect due to the aggregation of the colloidal AuNPs. The relationship between the NA concentration and colloidal AuNPs aggregation was further monitored by ultraviolet–visible light (UV–vis) spectroscopy in an aqueous solution. The method displayed a linear range of 0–500 μM with R2 = 0.99 and an LOD and LOQ of 42.2 and 140.5 μM. Application in an environmental sample collected from the Darville Wastewater Treatment Plant shows that this work provided a cost-effective and spectrophotometric method that could be used for monitoring contamination in wastewater.

Impact of Sterilization on the Colloidal Stability of Ligand-Free Gold Nanoparticles for Biomedical Applications.

Sterilization is a major prerequisite for the utilization of nanoparticle colloids in biomedicine, a process well examined for particles derived from chemical synthesis although highly underexplored for electrostatically stabilized ligand-free gold nanoparticles (AuNPs). Hence, in this work, we comprehensively examined and compared the physicochemical characteristics of laser-generated ligand-free colloidal AuNPs exposed to steam sterilization and sterile filtration as a function of particle size and mass concentration and obtained physicochemical insight into particle growth processes. These particles exhibit long-term colloidal stability (up to 3 months) derived from electrostatic stabilization without using any ligands or surfactants. We show that particle growth attributed to cluster-based ripening occurs in smaller AuNPs (∼5 nm) following autoclaving, while larger particles (∼10 and ∼30 nm) remain stable. Sterile filtration, as an alternative effective sterilizing approach, has no substantial impact on the colloidal stability of AuNPs, regardless of particle size, although a mass loss of 5-10% is observed. Finally, we evaluated the impact of the sterilization procedures on potential particle functionality in proton therapy, using the formation of reactive oxygen species (ROS) as a readout. In particular, 5 nm AuNPs exhibit a significant loss in activity upon autoclaving, probably dedicated to specific surface area reduction and surface restructuring during particle growth. The filtered analog enhanced the ROS release by up to a factor of ∼2.0, at 30 ppm gold concentration. Our findings highlight the need for carefully adapting the sterilization procedure of ligand-free NPs to the desired biomedical application with special emphasis on particle size and concentration.

New Chitosan-Grafted Thymol Coated on Gold Nanoparticles for Control of Cariogenic Bacteria in the Oral Cavity

Chitosan-grafted thymol (CST) coated on gold nanoparticles has been synthesized and characterized for the design of antimicrobial materials. CST was synthesized via adapting the Mannich reaction, and it acted as the capping agent for the synthesis of gold nanoparticles (AuNPs). The grafting of thymol onto the side chain of chitosan has provided a degree of substitution value (%DSNMR) of 10.0%, calculated by nuclear magnetic resonance spectroscopy. UV–visible spectrometry and elemental analysis were used to confirm the successful synthesis of CST through adapting the Mannich reaction. The appropriate concentration of CST for AuNP synthesis was found to be 0.020%w/v. A red-wine colloidal AuNP solution of 2.41–3.30 nM particle size exhibits a strong surface plasmon resonance at 502 nm, which shows negative charges at pH = 9 of −36.37 mV. This result evidenced that the AuNPs showed electrostatic repulsion and CST played a role as a capping agent to provide a good dispersion and stability state. CST coated on the AuNP surface was successfully utilized for the control of cariogenic bacteria in the oral cavity. The results obtained from this study show that the tuning of the capping agent used in the synthesis step strongly influences the latter antimicrobial activity of the nanoparticles against Streptococcus mutans ATCC 25175 and Streptococcus sobrinus ATCC 33402 activity, with an inhibition zone of 15.90 and 14.25 mm, respectively. The average minimum inhibitory concentration values against S. mutans ATCC 25175 and S. sobrinus ATCC 33402 were found to be 25 and 100 mg/L, respectively, whereas the minimum bactericidal concentration values were 100 and 200 mg/L, respectively.

Synergy of Adsorption and Plasmonic Photocatalysis in the Au-CeO2 Nanosystem: Experimental Validation and Plasmonic Modeling.

Adsorption-mediated water treatment leaves adsorbents as secondary pollutants in the environment. However, photocatalysis aids in decomposing the contaminant into its nontoxic forms. In this context, we demonstrate an adsorption-photocatalysis pairing in Au-CeO2 nanocomposites for a total methylene blue (MB) removal from water. We synthesized Au-CeO2 through the citrate (cit) reduction method at different Au loading and studied its adsorption capacity with kinetics and thermodynamic models. We observe that the high adsorption capacity of Au-CeO2 is primarily because of the presence of Ce3+ states in CeO2 and citrate ligands on Au NPs. The Ce3+ states interact and transfer their electrons to supported Au NPs, rendering a negative charge over Au. The negatively charged Au surface and the carboxyl (-COO-) group of citrate ligands mediate an electrostatic interaction/adsorption of cationic MB. The total removal of MB is expedited under white light and lasers. A control experiment with Au NPs shows less adsorption-photocatalysis. The size of Au NPs and Au-CeO2 interfacial interaction is responsible for the surface plasmon resonance spectral position at 550-600 nm. Linear sweep voltammetry (LSV) and plasmonic field simulation show surface plasmon-driven photocatalysis in Au-CeO2. LSV shows a 3-fold higher photocurrent density in Au-CeO2 than colloidal Au NPs under white light. The simulated electric field intensity in Au-CeO2 is maximum at SPR excitation and the closest interfacial separation (d = 0 nm). The plasmon-driven photocatalysis in colloidal Au NPs is mainly due to the interaction of hot electrons with the adsorbed MB molecule. Notably, near-field light concentration, hot electrons, and interfacial charge separation are responsible for excellent MB removal in the Au-CeO2 nanosystem. The total MB removal through adsorption-photocatalysis pairing is 99.3% (Au-CeO2), 30.7% (Au NPs), and 13% (CeO2).

In situ synthesis and characterization of colloidal AuNPs capped nano-chitosan containing poly(2,5-dimethoxyaniline) nanocomposites for biomedical applications

Herein, we have successfully synthesized a novel nCS-PDMA/AuNPs nanocomposite based on nano-chitosan containing poly(2,5-dimethoxyaniline) capped gold nanoparticle in situ synthesis is reported. The AuNPs were synthesized using the green method without using any harmful chemicals, reducing and stabilizing agents to generate AuNPs, is not needed because these roles are played by nCS. The synthesized nCS-PDMA/AuNPs nanocomposite were characterized by UV-Vis, FT-IR, XRD, SEM, and TEM analysis. The polydispersed nCS-PDMA/AuNPs nanocomposite was observed approximately 25 nm. Furthermore, nCS-PDMA/AuNPs nanocomposite was showed significant antibacterial activity against S. aureus and E. coli. The nCS-PDMA/AuNPs nanocomposite showed strong antioxidant activity by inhibiting the DPPH radicals. In addition, the cytotoxicity of nCS-PDMA/AuNPs nanocomposite was tested in HeLa cells and found to be high toxicity than nCS-PDMA. This work suggests that green synthesized nCS-PDMA/AuNPs nanocomposite may be utilized as an effective antibacterial, antioxidant, and anticancer activity. Research highlights nCS-PDMA capped gold nanoparticles (nCS-PDMA/AuNPs) were prepared. Physical characterization of nCS-PDMA/AuNPs by UV-vis, FTIR, XRD, SEM, and TEM. nCS-PDMA/AuNPs displayed promising inhibitory activity against both bacteria. nCS-PDMA/AuNPs showed significant DPPH radical scavenging activities. nCS-PDMA/AuNPs showed an excellent anticancer activity against HeLa cells.

Thioglycolic acid-functionalized gold nanoparticles: Capping agent-affected color perception stability towards nitrate sensing purpose

In comparison with colorimetric detection of metal ions, inorganic anions sensing on gold nanoparticles (AuNPs) seems to be more challenging and less explored due to their weak affinity towards the surface of such metal nanoparticles. Early efforts to detect nitrate in water mainly focused on amino thiol-functionalized AuNPs, thanks to the gold-sulfur interactions, sometimes adjusting the pH was required. In the present work, thioglycolic acid was preliminarily introduced for functionalizing purpose, in combination with the stability of colloidal AuNPs suspensions capped by either sodium citrate or ascorbic acid, which have not been previously reported. In contrast to the precipitation observed on ascorbic acid-capped AuNPs, the stability of color perception of freshly citrate-capped AuNPs and corresponding functionalized samples during 10 days extended their realistic nitrate sensing applications. A straightforward protocol involving three successive stages (synthesis of AuNPs, functionalizing and colorimetric sensing) exposed the color variations from red to purple and then blue, with the detection limit of nitrate of 50 ppm, qualifying the nitrate limit of drinking water authorized by the World Health Organization (WHO). The color signals were strictly relevant to surface plasmon resonance and particle size, evidenced by ultraviolet – visible spectroscopy (UV–vis) and transmission electron microscopy (TEM), respectively.

Synthesis of Gold Nanoparticles using Endophytic streptomyces and its Bactericidal Activities against Enteric Bacterial Pathogens

The present study aimed to report the rapid and one-step synthesis of gold nanoparticles (AuNPs) using the cell-free supernatant (CFS) of an endophytic Streptomyces sp. BDUSMP S05 isolated from Solanum trilobatum. The synthesized AuNPs were characterized by using UV-visible spectroscopy (UV-vis), Fourier-transform infrared spectroscopy (FTIR), energy dispersive X-ray (EDAX) spectroscopy and X-ray diffraction (XRD). The UV-visible spectroscopy (UV-vis) absorption of colloidal AuNPs displayed a surface plasma resonance (SPR) centred at 533 nm. FESEM micrograph analysis showed that synthesized particles were predominantly spherical with a 20-30 nm size range. Dynamic light scattering (DLS) analysis showed that the average particle size varied between 2-28 nm. Zeta potential analysis indicated the negative value of -35.2 mV characteristic for stable AuNPs. The synthesized AuNPs displayed significant antimicrobial activity against Gram-negative bacteria, including Eescherichia coli, Salmonella typhi and Vibrio cholerae compared to CFS alone. The results revealed that endophytic Streptomyces sp. potential to be used for the synthesis of antibacterial gold nanobased materials.