Concentration Of HAuCl4 Research Articles

A New Tropical Wild Fern for the Green Synthesis of Gold Nanoparticles: Comprehensive Characterization and Application in Water Treatment

Utilizing natural plant extracts to synthesize of gold nanoparticles (AuNPs) has emerged as a sustainable and eco-friendly alternative to conventional methods. Nephrolepis biserrata (NB), a tropical perennial fern, is rich in bioactive phytochemicals such as alkaloids, tannins, and flavonoids, which can effectively serve as reducing and stabilizing agents in the green synthesis of AuNPs. UV-visual spectrophotometry was employed to optimize synthesis parameters, including the reactant ratio of chloroauric acid (HAuCl₄) to NB, HAuCl₄ concentration, and reaction temperature. Optimal AuNP synthesis was achieved at a 1:0.25 HAuCl₄ ratio, a concentration of 0.25 mM HAuCl₄, and a reaction temperature of 70 °C, yielding nanoparticles with an absorbance of 1.449 ± 0.039 at a λmax of 531 nm. The synthesized AuNPs were characterized using FTIR, Zeta potential, FESEM/EDX, and XRD analyses. FTIR results indicated that the hydroxyl (O–H) and carbonyl (C=O) groups in NB facilitated the reduction of Au³⁺ ions. Zeta potential measurements confirmed AuNPs’ stability at -15.1 mV. The FE-SEM images and EDX analysis verified that the AuNPs were predominantly spherical, with minimal variation in shape. The average particle size was measured to be 28.184 ± 7.87 nm. The EDX spectrum showed strong signals for atomic gold at 2.12 and 2.14 keV, indicating that gold constituted approximately 48.49% of the sample by weight, which can be attributed to the bio-reductants in the plant extracts.The peaks in the X-ray diffractogram that correspond to Bragg’s reflection values of 38°, 44°, 64°, and 77° at 2θ indicate the formation of the face-centered cubic crystalline structure of AuNPs. These nanoparticles demonstrated high catalytic efficiency in the degradation of methylene blue (MB) dye, following a pseudo-first-order reaction in the presence of NaBH₄. These findings suggest that NB-mediated AuNPs offer a promising and eco-friendly approach for catalytic applications in wastewater treatment.

Influence of various concentrations of chloroauric acid on the fabrication of gold nanoparticles: Green synthesis using Elaeis guineensis Jacq leaf extract and characterizations

This work studies a green method for synthesizing gold nanoparticles (AuNPs) using Elaeis Guineensis Jacq. (oil palm) leaf extract (EGE) using a precursor of chloroauric acid (HAuCl4). The influence of various HAuCl4 concentrations on the formation of AuNPs by the green method was investigated. Characterization methods were employed to analyze the optical properties, size, shape, structure, and SERS applicability of the AuNPs. The findings suggest that EGE contains biomolecules like flavonoids and phenols, which fulfil the roles of reducing and capping agents during the synthesis of AuNPs. The AuNPs were fabricated spectroscopically at around 525 nm and validated by UV–Vis spectrophotometer. FT-IR result presents that the stretching vibrations of the hydroxyl (O–H) molecule are indicated by the large peak absorption at 3336 cm−1, demonstrating the O–H functional groups in the derivatives of phenols. The carbonyl (CO) stretching vibrations, generated by the carboxylic acid in flavonoids and phenols, exhibited a robust absorption at 1602 cm−1. An optimal HAuCl4 concentration of 0.69 mM resulted in AuNPs with uniform spherical morphology and a 10–30 nm size range confirmed by TEM analysis. This concentration also led to the strongest Raman intensity, indicating the potential of these biogenic AuNPs for SERS applications. Overall, the study demonstrates a sustainable and efficient method for AuNP synthesis using a readily available plant extract, paving the way for their use in advanced sensing technologies.

Green synthesis of Au nanoparticles by Scutellaria barbata extract for chemo-photothermal anticancer therapy

IntroductionThe combination of photothermal therapy and chemotherapy has emerged as a promising strategy for cancer treatment. The green synthesis of gold nanoparticles (Au NPs) using extracts from traditional Chinese medicine Scutellaria barbata D. Don (Scu) has revealed an economical, sustainable, and eco-friendly approach for the outstanding anticancer activities. MethodsScu extract was mixed with HAuCl4 solution to fabricate Scu-Au NPs. The synthesis process was optimized by varying the reaction temperature, reaction time, and HAuCl4 concentration. The changes in the components of Scu before and after synthesis were analyzed using the 3,5-dinitrosalicylic acid (DNS) reduction test, the rutin colorimetric method, and the Folin–Ciocalteu method. The morphology, size, and structure of Scu-Au NPs were characterized by TEM, DLS, XRD, and XPS. The photothermal characteristics induced by near-infrared (NIR) irradiation were assessed by continuously monitoring the temperature elevation. The anticancer activity and mechanisms of Scu-Au NPs were investigated using MTT assay, cell uptake studies, ROS level detection, cell apoptosis and necrosis assays, flow cytometry analysis, intracellular Caspase-3 protein activity fluorescence detection, and Western blot analysis on A549, 4T1, and RAW264.7 cells. ResultsScu-Au NPs were successfully fabricated using Scu extract as a reducing agent. The Scu-Au NPs were spherical with a size of 50 nm. During the synthesis process, the levels of reducing sugars, flavonoids, and polyphenols in the Scu extract decreased by 80.8%, 54.3%, and 70.1%, respectively. Scu-Au NPs demonstrated excellent photothermal responsiveness, thermostability, and biocompatibility. For chemo-photothermal anticancer therapy, the cytotoxicity of Scu-Au NPs on 4T1 cells reached approximately 85% upon exposure to 808 nm NIR irradiation. The anticancer activity was attributed to the induction of apoptosis and necrosis, achieved by increasing intracellular ROS levels, causing cell cycle arrest at the S phase, and modulating the expression of apoptosis-related proteins. DiscussionOur synthesized Scu-Au NPs exhibit favorable photothermal conversion characteristics, demonstrating excellent therapeutic efficacy and safety for cancer treatment.

Biosynthesized gold nanoparticles for enhanced determination of nicotine in heated tobacco products

An electrochemical sensor for nicotine determination in heated tobacco products (HTPs) was developed using biosynthesized AuNPs from Ceiba pentandra leaf extract. The biosynthesis process was optimized by investigating the effects of HauCl4 concentration, extract volume, reaction temperature, and time on the formation of gold nanoparticles (AuNPs). The biosynthesized AuNPs were characterized using various techniques, confirming their crystallinity, spherical morphology, and uniform size distribution with an average diameter of 19.8 ± 3.6 nm. The AuNP modified glassy carbon electrode (AuNP/GCE) exhibited enhanced electrochemical performance compared to the bare GCE, facilitating efficient oxidation of nicotine. The AuNP/GCE sensor demonstrated a wide linear range of 0.02–280 µmol L−1 and a low limit of detection of 0.01 µmol L−1 for nicotine determination. The sensor showed excellent selectivity towards nicotine in the presence of common interfering substances, with negligible responses (<5 % change) to uric acid, paracetamol, glucose, melamine, L-cysteine, and dopamine. The AuNP/GCE sensor's applicability was validated by analyzing nicotine levels in real HTP samples, with excellent recovery rates (97.6–102.4 %) and good agreement with the HPLC (R2 = 0.998). The biosynthesized AuNP-based electrochemical sensor offers a rapid, sensitive, eco-friendly, and cost-effective approach for nicotine determination in HTPs, providing a valuable tool for quality control and regulatory purposes.

Proving the automatic benchtop electrochemical station for the development of dopamine and paracetamol sensors

The introduced work represents an implementation of the automatic benchtop electrochemical station (BES) as an effective tool for the possibilities of high-throughput preparation of modified sensor/biosensors, speeding up the development of the analytical method, and automation of the analytical procedure for the determination of paracetamol (PAR) and dopamine (DOP) as target analytes. Within the preparation of gold nanoparticles modified screen-printed carbon electrode (AuNPs-SPCE) by electrodeposition, the deposition potential EDEP, the deposition time tDEP, and the concentration of HAuCl4 were optimized and their influence was monitored on 1 mM [Ru(NH3)6]3+/2+ redox probe and 50 μM DOP. The morphology of the AuNPs-SPCE prepared at various modification conditions was observed by SEM. The analytical performance of the AuNPs-SPCE prepared at different modification conditions was evaluated by a construction of the calibration curves of DOP and PAR. SPCE and AuNPs-SPCE at modification condition providing the best sensitivity to PAR and DOP, were successfully used to determine PAR and DOP in tap water by “spike-recovery” approach. The BES yields better reproducibility of the preparation of AuNPs-SPCE (RSD = 3.0%) in comparison with the case when AuNPs-SPCE was prepared manually by highly skilled laboratory operator (RSD = 7.0%).Graphical abstract

Process optimization for gold nanoparticles biosynthesis by Streptomyces albogriseolus using artificial neural network, characterization and antitumor activities

Gold nanoparticles (GNPs) are highly promising in cancer therapy, wound healing, drug delivery, biosensing, and biomedical imaging. Furthermore, GNPs have anti-inflammatory, anti-angiogenic, antioxidants, anti-proliferative and anti-diabetic effects. The present study presents an eco-friendly approach for GNPs biosynthesis using the cell-free supernatant of Streptomyces albogriseolus as a reducing and stabilizing agent. The biosynthesized GNPs have a maximum absorption peak at 540 nm. The TEM images showed that GNPs ranged in size from 5.42 to 13.34 nm and had a spherical shape. GNPs have a negatively charged surface with a Zeta potential of − 24.8 mV. FTIR analysis identified several functional groups including C–H, –OH, C–N, amines and amide groups. The crystalline structure of GNPs was verified by X-ray diffraction and the well-defined and distinct diffraction rings observed by the selected area electron diffraction analysis. To optimize the biosynthesis of GNPs using the cell-free supernatant of S. albogriseolus, 30 experimental runs were conducted using central composite design (CCD). The artificial neural network (ANN) was employed to analyze, validate, and predict GNPs biosynthesis compared to CCD. The maximum experimental yield of GNPs (778.74 μg/mL) was obtained with a cell-free supernatant concentration of 70%, a HAuCl4 concentration of 800 μg/mL, an initial pH of 7, and a 96-h incubation time. The theoretically predicted yields of GNPs by CCD and ANN were 809.89 and 777.32 μg/mL, respectively, which indicates that ANN has stronger prediction potential compared to the CCD. The anticancer activity of GNPs was compared to that of doxorubicin (Dox) in vitro against the HeP-G2 human cancer cell line. The IC50 values of Dox and GNPs-based treatments were 7.26 ± 0.4 and 22.13 ± 1.3 µg/mL, respectively. Interestingly, treatments combining Dox and GNPs together showed an IC50 value of 3.52 ± 0.1 µg/mL, indicating that they targeted cancer cells more efficiently.

Development of Hollow Gold Nanoparticles for Photothermal Therapy and Their Cytotoxic Effect on a Glioma Cell Line When Combined with Copper Diethyldithiocarbamate.

Gold-based nanoparticles hold promise as functional nanomedicines, including in combination with a photothermal effect for cancer therapy in conjunction with chemotherapy. Here, we synthesized hollow gold nanoparticles (HGNPs) exhibiting efficient light absorption in the near-IR (NIR) region. Several synthesis conditions were explored and provided monodisperse HGNPs approximately 95-135 nm in diameter with a light absorbance range of approximately 600-720 nm. The HGNPs were hollow and the surface had protruding structures when prepared using high concentrations of HAuCl4. The simultaneous nucleation of a sacrificial AgCl template and Au nanoparticles may affect the resulting HGNPs. Diethyldithiocarbamate (DDTC) is metabolized from disulfiram and is a repurposed drug currently attracting attention. The chelation of DDTC with copper ion (DDTC-Cu) has been investigated for treating glioma, and here we confirmed the cytotoxic effect of DDTC-Cu towards rat C6 glioma cells in vitro. HGNPs alone were biocompatible and showed little cytotoxicity, whereas a mixture of DDTC-Cu and HGNPs was cytotoxic in a dose dependent manner. The temperature of HGNPs was increased by NIR-laser irradiation. The photothermal effect on HGNPs under NIR-laser irradiation resulted in cytotoxicity towards C6 cells and was dependent on the irradiation time. Photothermal therapy by HGNPs combined and DDTC-Cu was highly effective, suggesting that this combination approach hold promise as a future glioma therapy.

The effect of gold nanostructure morphology on label-free electrochemical immunosensor design

In this research, various electrodeposition techniques were used to form gold nanostructures (AuNSs) on the surface of graphite rod electrode (GE). Three distinct AuNS morphologies on GE have been achieved based on the composition of electrodeposition solution. The use of H2SO4 as a supporting electrolyte resulted in the formation of smaller but more numerous AuNSI with a modified electrode’s electroactive surface area (EASA) of 0.213 cm2. Exchanging the supporting electrolyte to KNO3 and increasing HAuCl4 concentration facilitated the formation of bigger AuNSII particles with electrode EASA of 0.116 cm2. Finally, a partial coverage of GE by branched gold nanostructures (AuNSIII) was achieved with an estimated EASA of 0.110 cm2, when the HAuCl4 and KNO3 concentrations were increased. Estimated values of heterogeneous electron transfer rate constant did not depend on AuNS morphology. Electrode modified with AuNSI exhibited the highest bovine serum albumin (BSA) immobilization efficiency and the highest relative response for the detection of specific polyclonal antibodies against BSA (p-anti-BSA) compared to other modified electrodes. The limit of p-anti-BSA detection in PBS buffer was calculated as 0.63 nM, while in blood serum it was 0.71 nM. Linear ranges were from 1 to 7 nM and from 1 to 5 nM, respectively.

Ligand Mediation for Tunable and Oxide Suppressed Surface Gold-Decorated Liquid Metal Nanoparticles.

Gallium-based liquid metal systems hold vast potential in materials science. However, maximizing their possibilities is hindered by gallium's native oxideand interfacial functionalization. In this study, small-molecule ligands are adopted as surfactants to modify the surface of eutectic gallium indium (EGaIn) nanoparticles and suppress oxidation. Different p-aniline derivatives are explored. Next, the reduction of chloroanric acid (HAuCl4 ) onto these p-aniline ligand modified EGaIn nanoparticles is investigated to produce gold-decorated EGaIn nanosystems. It is found that by altering the concentrations of HAuCl4 or the p-aniline ligand, the formation of gold nanoparticles (AuNPs) on EGaIn can be manipulated. The reduction of interfacial oxidation and presence of AuNPs enhances electrical conductivity, plasmonic performance, wettability, stability, and photothermal performance of all the p-aniline derivative modified EGaIn. Of these, EGaIn nanoparticles covered with the ligand of p-aminobenzoic acid offer the most evenly distributed AuNPs decoration and perfect elimination of gallium oxides, resulting in the augmented electrical conductivity, and highest wettability suitable for patterning, enhanced aqueous stability, and favorable photothermal properties. The proof-of-concept application in photothermal therapy of cancer cells demonstrates significantly enhanced photothermal conversion performance along with good biocompatibility. Due to such unique characteristics, the developed gold-decorated EGaIn nanodroplets are expected to offer significant potential in precise medicine.

Photochemical Synthesis of Noble Metal Nanoparticles: Influence of Metal Salt Concentration on Size and Distribution.

This paper explores the photochemical synthesis of noble metal nanoparticles, specifically gold (Au) and silver (Ag) nanoparticles, using a one-component photoinitiator system. The synthesis process involves visible light irradiation at a wavelength of 419 nm and an intensity of 250 mW/cm2. The radical-generating capabilities of the photoinitiators were evaluated using electron spin resonance (ESR) spectroscopy. The main objective of this study was to investigate how the concentration of metal salts influences the size and distribution of the nanoparticles. Proposed mechanisms for the photochemical formation of nanoparticles through photoinitiated radicals were validated using cyclic voltammetry. The results showed that the concentration of AgNO3 significantly impacted the size of silver nanoparticles, with diameters ranging from 1 to 5 nm at 1 wt% and 3 wt% concentrations, while increasing the concentration to 5 wt% led to an increase in the diameter of silver nanoparticles to 16 nm. When HAuCl4 was used instead of AgNO3, it was found that the average diameters of gold nanoparticles synthesized using both photoinitiators at different concentrations ranged between 1 and 4 nm. The findings suggest that variations in HAuCl4 concentration have minimal impact on the size of gold nanoparticles. The photoproduction of AuNPs was shown to be thermodynamically favorable, with the reduction of HAuCl4 to Au0 having ∆G values of approximately -3.51 and -2.96 eV for photoinitiators A and B, respectively. Furthermore, the photoreduction of Ag+1 to Ag0 was demonstrated to be thermodynamically feasible, with ∆G values of approximately -3.459 and -2.91 eV for photoinitiators A and B, respectively, confirming the effectiveness of the new photoinitiators on the production of nanoparticles. The synthesis of nanoparticles was monitored using UV-vis absorption spectroscopy, and their sizes were determined through particle size analysis of transmission electron microscopy (TEM) images.

Artificial neural network approach for prediction of AuNPs biosynthesis by Streptomyces flavolimosus, characterization, antitumor potency in-vitro and in-vivo against Ehrlich ascites carcinoma

Gold nanoparticles (AuNPs) have emerged as promising and versatile nanoparticles for cancer therapy and are widely used in drug and gene delivery, biomedical imaging, diagnosis, and biosensors. The current study describes a biological-based strategy for AuNPs biosynthesis using the cell-free supernatant of Streptomyces flavolimosus. The biosynthesized AuNPs have an absorption peak at 530–535 nm. The TEM images indicate that AuNPs were spherical and ranged in size from 4 to 20 nm. The surface capping molecules of AuNPs are negatively charged, having a Zeta potential of − 10.9 mV. FTIR analysis revealed that the AuNPs surface composition contains a variety of functional groups as –OH, C–H, N–, C=O, NH3+, amine hydrochloride, amide group of proteins, C–C and C–N. The bioprocess variables affecting AuNPs biosynthesis were optimized by using the central composite design (CCD) in order to maximize the AuNPs biosynthesis. The maximum yield of AuNPs (866.29 µg AuNPs/mL) was obtained using temperature (35 °C), incubation period (4 days), HAuCl4 concentration (1000 µg/mL) and initial pH level 6. Comparison was made between the fitness of CCD versus Artificial neural network (ANN) approach based on their prediction and the corresponding experimental results. AuNPs biosynthesis values predicted by ANN exhibit a more reasonable agreement with the experimental result. The anticancer activities of AuNPs were assessed under both in vitro and in vivo conditions. The results revealed a significant inhibitory effect on the proliferation of the MCF-7 and Hela carcinoma cell lines treated with AuNPs with IC50 value of 13.4 ± 0.44 μg/mL and 13.8 ± 0.45 μg/mL for MCF-7 and Hela cells; respectively. Further, AuNPs showed potential inhibitory effect against tumor growth in tumor-bearing mice models. AuNPs significantly reduced the tumor volume, tumor weight, and decreased number of viable tumor cells in EAC bearing mice.

Construction of Pt/Pt-Au doped chiral nanostructures using arginine and porphyrin assemblies as templates for enantioselective photocatalysis

Chiral nanomaterials with different functions have been widely developed, but the deep understanding of the structural effects of nanocatalysts on enantioselective photocatalytic efficiency is still highly demanded. Herein, Pt and Pt-Au-bimetal-doped chiral nanostructures with various morphologies and compositions are facilely constructed using L-/D-arginine (L-/D-Arg) and mono-sulfonate tetraphenyl porphyrin (H2TPPS) assemblies as chiral templates. Interestingly, these Pt and Pt-Au-doped chiral nanostructures, including nanorods (NR) and nanospheres (NS), can be well regulated by controlling pH, ionic strength, and reaction time of the assembling system of Arg and H2TPPS. More impressively, specific Au growth direction along the Pt-doped chiral NR (L-/D-Pt-NR) is observed (from tip to middle) during the preparation of Pt-Au-bimetal-doped chiral NR (L-/D-Pt-Au-NR) and their compositions can be finely controlled by simply adjusting the concentrations of HAuCl4. As expected, the chiral nanostructures exhibit superior enantioselective photocatalytic ability toward chiral organics under visible light: the oxidation rate of L-dihydroxy-phenylalanine (L-DOPA) catalyzed by L-Pt-NR (or D-DOPA catalyzed by D-Pt-NR) is about 60% higher than that of L-DOPA catalyzed by D-Pt-NR (or L-DOPA catalyzed by D-Pt-NR). This study provides a facile strategy to construct chiral nanostructures for the photocatalytic conversion of chiral organics.

The spectral and microscopical study of phytosynthesized plasmonic gold nanoparticles

Here, we present a facile and environmentally friendly method for the synthesis of gold nanoparticles (Au NPs) with an infrared response. The structure of the obtained Au NPs was investigated by transmission electron microscopy. Small and large Au NPs with different morphologies, including spheres, triangles, and hexagons, were imaged and studied, and the reasons for the morphological diversity were discussed. From the selected area diffraction data, the Au NPs showed sufficient crystallinity. The optical properties of the Au nanocolloids, investigated by UV-visible absorption spectroscopy, confirmed the presence of localized surface plasmon resonance (LSPR) peaks at 500…540 nm for Au NPs smaller than 30 nm. An increase in absorption intensity in the 600…1050 nm region indicates the formation of larger non-spherical Au NPs. The optical absorption spectra show the redshift of the second LSPR peak to the near-infrared region with a longer wavelength with increasing HAuCl4 concentration in the synthesis solution. In addition, we recorded the maxima of photoluminescence (PL) bands at 370 and 458 nm for the water-diluted Au colloids under 320 nm excitation and considered the possible reasons for PL. Attempts were made to elucidate the optical and PL behavior of the nanocolloids within the known models

One-pot generation of gold-polymer hybrid nanoparticles using a miniemulsion reactor system

We investigated one-pot synthesis of gold nanoparticles (AuNPs) and AuNPs-polymer hybrid nanoparticles in a water-in-oil (W/O) miniemulsion. Water nanodroplets were dispersed as a reactor in cyclohexane using dimethicone as a surfactant. First, we intended to generate AuNPs in water nanodroplets, which contained HAuCl4 with a mixture of 1-vinylpyrrolidone (VP) and N,N’-methylenebisacrylamide (MBAAm). Several AuNPs with the size of approximately 10–20 nm were generated in each nanodroplet via reduction of AuCl4- by dimethicone. On the other hand, AuNPs was scarcely generated in water nanodroplets containing HAuCl4 with 2-hydroxyethyl methacrylate (HEMA). Next, we carried out polymerization in water nanodroplets to encapsulate AuNPs into polymer nanoparticles. Several AuNPs were encapsulated within polymer particles by copolymerization of VP and MBAAm with an oil-soluble initiator (V-601), and some AuNPs were present in the oil phase. The encapsulation efficiency of AuNPs was 34%. The encapsulation efficiency of AuNPs was dramatically increased by increasing the concentration of the initiator. The same result was obtained by increasing the concentration of the crosslinker due to rapid gelation of nanodroplets. On the other hand, monodisperse particles could be obtained by polymerization of HEMA using a water-soluble initiator (V-65). After polymerization for 5 d at 65ºC, the color of the suspension changed from opaque blue to blue purple and the encapsulation efficiency of AuNPs (5–20 nm) increased to 99 wt%. The average number of AuNPs encapsulated in a PHEMA nanoparticle increased from 1.5 to 4.6 particle. Furthermore, the size of AuNPs could be tuned by increasing the HAuCl4 concentration, and the corresponding color of the suspensions such as blue, purple, and red could be observed. The number and location of AuNPs in polymer nanoparticles could also be tuned by additives such as L-histidine and polyvinylpyrrolidone. By drop-casting the obtained hybrid nanoparticles, we could obtain gold-polymer hybrid films where AuNPs were evenly distributed within a film. The films exhibited different colors corresponding to their LSPR of AuNPs.

Green synthesis of reduced graphene oxide/chitosan/gold nanoparticles composites and their catalytic activity for reduction of 4-nitrophenol

Gold nanoparticles (AuNPs) have attracted extensive attention in the past few years due to their unique properties and great potential application in catalysis. However, the application of AuNPs remains a significant challenge due to the lack of high efficiency and stability caused by aggregation. Immobilization of AuNPs on appropriate support shows promising results in avoiding aggregation and improving catalytic activity. In this work, reduced graphene oxide/chitosan/gold nanoparticles (rGO/CHS/AuNPs) composites were prepared using chitosan with different molecular weights (MW) as a reducing agent and stabilizer, and characterized by FT-IR, XRD, XPS, SEM, FESEM, EDS, TEM, HRTEM, and TGA. The preparation conditions of rGO/CHS/AuNPs composites, including chitosan MW, CHS/GO mass ratio, reaction temperature and time, and HAuCl4 concentration were investigated in detail. The results indicated that reduction activity of chitosan for GO increased with the decrease of chitosan MW. The C/O ratio of rGO reduced by low molecular weight chitosan (LMWC) with viscosity-average molecular weight (Mv) of 21 kDa was 6.34. Small spherical AuNPs were uniformly immobilized on the rGO surface. The particle size of AuNPs increased from 9.29 to 13.03 nm as chitosan MW decreased from 465 to 21 kDa. The rGO/CHS/AuNPs showed good catalytic activity for the reduction of 4-NP in the presence of NaBH4. The catalytic activity of rGO/CHS/AuNPs was closely related to chitosan MW. rGO/CHS/AuNPs synthesized by LMWC with Mv of 21 kDa showed the highest kinetic rate constant of 0.2067 min−1. The results of this experimental study could be useful in the development of effective catalysts for the reduction of aromatic nitro compounds.

Green Synthesis of AuNPs by Crocus caspius—Investigation of Catalytic Degradation of Organic Pollutants, Their Cytotoxicity, and Antimicrobial Activity

Biogenic methods are an effective alternative to chemical methods in the preparation of nanoparticles. Our study used Crocus caspius extract to synthesize gold nanoparticles (CC-AuNPs) in a green manner. The eco-friendly synthesis of AuNPs was conducted by optimizing the temperature and concentration of HAuCl4 and extract. Synthesized CC-AuNPs were characterized using TEM, SEM, EDX, XRD, FTIR, and UV–Vis spectroscopy. The prepared CC-AuNPs were detected with a size of around 22.66 ± 1.67 nm. The FT-IR analysis of the biomolecules involved in synthesizing CC-AuNPs was performed. Additionally, these biomolecules capped on the AuNPs were revealed by TG/DTA analysis. The EDX study demonstrated the existence of elemental gold. The biosynthesized CC-AuNPs were effectively applied as green catalysts to reduce three organic pollutant dyes—methyl orange (MO), methylene blue (MB), and 4-nitrophenol. In the biological evaluations, the free radical scavenging activity of the eco-friendly CC-AuNPs (DPPH assay) indicated an IC50 value of 29.22 ± 0.47 µg/mL. They displayed effective antibacterial activity against several bacterial strains. Their anticancer activity against AGS and MCF-7 cells showed IC50 concentrations at 48.2 µg/mL and 51.76 µg/mL, respectively. Furthermore, CC-AuNPs presented excellent antileishmanial activity (IC50 = 13.92 µg/mL). Therefore, the green AuNPs are efficient in biomedicine and nanobiotechnology.

In-situ synthesized gold nanoparticles modified Mo2C MXene for surface enhanced Raman scattering

Herein, we demonstrate a proof-of-concept of using Mo2C MXene and gold nanoparticles (NPs) hybrid as an efficient surface-enhanced Raman scattering (SERS) substrate for organic pollutants detection. Mo2C MXene/Au hybrid is synthesized by an in-situ reduction of Au3+ ions onto Mo2C MXene nanosheets and characterized for its optical and structural properties. For the hybrid structures, we first synthesized Mo2C MXene by hydrofluoric acid etching of Mo2Ga2C and subsequent delamination with dimethyl sulfoxide to obtain few-layered nanosheets. The concentration of HAuCl4 for in-situ formation of Au was optimized with UV–Vis spectroscopy and probed with high resolution transmission electron microscopy. X-ray diffraction confirms the presence of Au NPs and MXene, while scanning and transmission electron microscopy analyses reveal the loading of Au NPs with an average size of ~ 9 nm on MXene few-layer particles. Based on our X-ray photoelectron spectroscopy results, we proposed a synthesis mechanism in which the functional groups of Mo2C MXene take an active part in reducing the gold precursor to form gold NPs. The optimized Mo2C/Au hybrid was then coated onto silicon and studied as a potential SERS substrate utilizing methylene blue as a model dye. Further, the comparison of the studies with rhodamine 6G confirms and justifies the role of the Mo2C/Au hybrid in signal enhancement. The preliminary findings demonstrate an enhancement factor of 2.2 × 104 and a detection limit of 0.01 μM (10–8 M) for optimal Au loading for MB. The fabricated SERS substrate is stable for nearly 1 month and exhibits excellent signal reproducibility with ~ 88% retention of the signal. These findings can be further extended to other MXenes to obtain in-situ synthesized hybrid for SERS as well as other applications including sensors, photocatalysis, and electrocatalysis.Graphical abstract

Biosynthesis and Characterization of Gold Nanoparticles Produced Using Rhodococcus Actinobacteria at Elevated Chloroauric Acid Concentrations.

The growing industrial and medical use of gold nanoparticles (AuNPs) requires environmentally friendly methods for their production using microbial biosynthesis. The ability of actinobacteria of the genus Rhodococcus to synthesize AuNPs in the presence of chloroauric acid (HAuCl4) was studied. The effect of elevated (0.8-3.2 mM) concentrations of HAuCl4 on bacterial viability, morphology, and intracellular accumulation of AuNPs by different Rhodococcus species was shown. An increase in surface roughness, a shift of the zeta potential to the positive region, and the formation of cell aggregates of R. erythropolis IEGM 766 and R. ruber IEGM 1135 during nanoparticle synthesis were revealed as bacterial adaptations to toxic effects of HAuCl4. The possibility to biosynthesize AuNPs at a five times higher concentration of chloroauric acid compared to chemical synthesis, for example, using the citrate method, suggests greater efficiency of the biological process using Rhodococcus species. The main parameters of biosynthesized AuNPs (size, shape, surface roughness, and surface charge) were characterized using atomic force microscopy, dynamic and electrophoretic light scattering, and also scanning electron microscopy in combination with energy-dispersive spectrometry. Synthesized by R. erythropolis spherical AuNPs have smaller (30-120 nm) dimensions and are positively (12 mV) charged, unlike AuNPs isolated from R. ruber cells (40-200 nm and -22 mV, respectively). Such differences in AuNPs size and surface charge are due to different biomolecules, which originated from Rhodococcus cells and served as capping agents for nanoparticles. Biosynthesized AuNPs showed antimicrobial activity against Gram-positive (Micrococcus luteus) and Gram-negative (Escherichia coli) bacteria. Due to the positive charge and high dispersion, the synthesized by R. erythropolis AuNPs are promising for biomedicine, whereas the AuNPs formed by R. ruber IEGM 1135 are prone to aggregation and can be used for biotechnological enrichment of gold-bearing ores.

Biosynthesis of gold nanoparticles using Kapok (Ceiba pentandra) leaf aqueous extract and investigating their antioxidant activity

Ceiba pentandra leaf extracts can be used as a reducing agent and capping agent in the green synthesis of gold nanoparticles (AuNPs) because it contains phenolic compounds including flavonoids, alkaloids, saponins, tannins, oxalate, phytate, and anthocyanins. This study aimed to obtain the optimum conditions for biosynthesis of AuNPs using Ceiba pentandra leaf extract (AuNPs-Cp) and investigated the antioxidant activities of the AuNPs-Cp. The effect of several parameters on the synthesis of AuNPs was studied and optimized, including the concentration of HAuCl4 as precursor AuNPs, volume ratio between HAuCl4 and Ceiba pentandra leaf extract, temperature, and reaction time. AuNPs-Cp were characterized using UV-Vis spectroscopy, XRD, TEM, and DLS techniques. The results showed that the synthesis method using 4 mL HAuCl4 2 mM and 8 mL Ceiba pentandra leaf extract at 75°C for 90 min was the optimum condition to synthesize AuNPs-Cp. Based on TEM and DLS data, it is known that AuNPs-Cp are spherical with a size of 21.92 ± 8.88 nm. In vitro antioxidant activity studies using DPPH revealed that the AuNPs-Cp have excellent free radical scavenging activity, with IC50 = 57.82 µg/mL. AuNPs were successfully synthesized using Ceiba pentandra aqueous leaf extract as an environmentally friendly bio-reducing agent and capping agent. DPPH scavenging activity indicated effective free radicals inhibition by AuNPs-Cp than Ceiba pentandra leaf extract.

Gold nanoparticle-based biofuel cell catalytic efficiency reliance on medium pH

Over the past several decades, biology, chemistry, and medicine took advantage of gold nanoparticles (AuNPs) for their fascinating characteristics. Today these nanomaterials can be synthesized in various methods from biosynthesis, when particles are made by microbial culture, to physical. Using the fast scan cyclic voltammetry, AuNPs can be electrodeposited from chloroauric acid (HAuCl4) directly onto the surface of a graphite electrode. This method provides high reproducibility and allows to control the size of the nanoparticles (from 4 to 75 nm) and electrode coverage by changing HAuCl4 concentration, scan speed, and a number of applied cycles. Gold nanoparticles are known to express comparable catalytic activity to natural enzymes such as glucose oxidase or horseradish peroxidase. Despite the advantages over natural enzymes, inorganic enzyme mimicking catalysts exhibit limited catalytical efficiency and selectivity. To increase efficiency, we used low size AuNPs which increase reactivity; the lack of selectivity in a biofuel cell is advantageous since AuNPs can reduce/oxidize several substrates in the medium. Biofuel cell based on AuNP’s has a superior life span, as the main active part of the system is inorganic, and thus it is not affected by oxygen stress, where typical microbial biofuel cells are struggling. The observed catalytic activity had a minimal dependency on temperature change. pH was changed from 4 to 10 with the smallest synthesized AuNPs. However, pH has an impact on the reaction speed. Results showed that biofuel cell is suitable for raw wastewater as it usually deviates from pH 7, and usable current can be generated.