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.

Colorimetric determination of uric acid based on the suppression of oxidative etching of silver nanoparticles by chloroauric acid.

A colorimetric method is described for the determination of uric acid (UA). The assay is based on oxidative etching of silver nanoparticles (AgNPs) by chloroauric acid (HAuCl4). The presence of UA suppresses the redox reaction between AgNPs and HAuCl4 because a competitive reaction occurs between HAuCl4 and UA. This results in a color change of the solution from brown to yellow. In parallel, the absorbance is blue shifted from 477 to 428 nm. The method has a detection limit as low as 30 pM (at S/N = 3) and a linear response range that covers the 0.1 nM to 0.1 mM UA concentration range. The reliability of the method was successfully demonstrated by analyzing spiked serum samples. Graphical abstractSchematic representation of a colorimetric method for determination of uric acid (UA) based on oxidative etching of silver nanoparticles by HAuCl4.

One-step synthesis of phyto-polymer coated gold nanospheres as a delivery system to enhance resveratrol cytotoxicity.

This study introduces a simple method for one-step synthesis of highly stable nontoxic polymer-coated gold nanospheres for use in drug delivery, focuses on the ability of chloroauric acid (HAu Cl4 ) to induce polyphenols polymerization, puts up an easy procedure for loading hydrophobic drugs onto gold nanoparticles with ultra-high loading efficiency and studies the cytotoxicity of free and gold nanoparticles-loaded resveratrol. Gold nanospheres were synthesized simply by direct reaction between resveratrol itself and HAu Cl4 in aqueous medium. Synthesized gold nanospheres exhibited high stability in both aqueous and ethanolic solutions. UV-visible spectrum showed that the synthesized gold nanospheres have maximum absorption at 532 nm. TEM imaging, mass and FT-IR spectrometry revealed the presence of a distinct polymeric shell around each nanoparticle. Resveratrol, as a chemopreventive agent, was loaded onto the synthesized gold nanospheres with an ultra-high loading capacity (11.6% w/w). Free resveratrol, free gold nanospheres, and resveratrol-loaded gold nanospheres were examined for cytotoxicity on HepG2 cell line where cytotoxicity of loaded resveratrol was dramatically enhanced to reach about nine folds as that of free resveratrol at the same concentration.

Hydrogel design to overcome thermal resistance and ROS detoxification in photothermal and photodynamic therapy of cancer.

Responsive heat resistance (by heat shock protein upregulation) and spontaneous reactive oxygen species (ROS) detoxification have been regarded as the major obstacles for photothermal/photodynamic therapy of cancer. To overcome the thermal resistance and improve ROS susceptibility in breast cancer therapy, Au ion-crosslinked hydrogels including indocyanine green (ICG) and polyphenol are devised. Au ion has been introduced for gel crosslinking (by catechol-Au3+ coordination), cellular glutathione depletion, and O2 production from cellular H2O2. ICG can generate singlet oxygen from O2 (for photodynamic therapy) and induce hyperthermia (for photothermal therapy) under the near-infrared laser exposure. (-)-Epigallocatechin gallate downregulates heat shock protein to overcome heat resistance during hyperthermia and exerts multiple anticancer functions in spite of its ironical antioxidant features. Those molecules are concinnously engaged in the hydrogel structure to offer fast gel transformation, syringe injection, self-restoration, and rheological tuning for augmented photo/chemotherapy of cancer. Intratumoral injection of multifunctional hydrogel efficiently suppressed the growth of primary breast cancer and completely eliminated the residual tumor mass. Proposed hydrogel system can be applied to tumor size reduction prior to surgery of breast cancer and the complete remission after its surgery.

Ultrahigh Energy and Power Densities of d-MXene-Based Symmetric Supercapacitors.

Here, rational design electrodes are fabricated by mixing MXene with an aqueous solution of chloroauric acid (HAuCl4). In order to prevent MXene from self-restacking, the groups of -OH on the surface of Ti3C2Tx nanosheets underwent a one-step simultaneous self-reduction from AuCl4-, generating spaces for rapid ion transit. Additionally, by using this procedure, MXene's surface oxidation can be decreased while preserving its physio-chemical properties. The interlayered MX/Au NPs that have been obtained are combined into a conducting network structure that offers more active electrochemical sites and improved mass transfer at the electrode-electrolyte interface, both of which promote quick electron transfer during electrochemical reactions and excellent structural durability. The Ti3C2Tx-AuNPs film thus demonstrated a rate performance that was preferable to that of pure Ti3C2Tx film. According to the results of the characterization, the AuNPs effectively adorn the MXene nanosheets. Due to the renowned pseudocapacitance charge storage mechanism, MXene-based electrode materials also work well as supercapacitors in sulfuric acid, which is why MXene AuNPs electrodes have been tested in 3 M and 1 M H2SO4. The symmetric supercapacitors made of MXene and AuNPs have shown exceptional specific capacitance of 696.67 Fg-1 at 5 mVs-1 in 3 M H2SO4 electrolyte, and they can sustain 90% of their original capacitance for 5000 cycles. The highest energy and power density of this device, which operates within a 1.2 V potential window, are 138.4 Wh kg-1 and 2076 W kg-1, respectively. These findings offer a productive method for creating high-performance metal oxide-based symmetric capacitors and a straightforward, workable approach for improving MXene-based electrode designs, which can be applied to other electro-chemical systems that are ion transport-restricted, such as metal ion batteries and catalysis.

Rapid in-situ growth of gold nanoparticles on cationic cellulose nanofibrils: Recyclable nanozyme for the colorimetric glucose detection.

Novel microwave-assisted green in-situ synthesis of positively charged gold nanoparticles (AuNPs) supported by cationic cellulose nanofibrils (C.CNF) within 30 s and devoid of additional reducing agent is reported. Peroxidase activity of these positive AuNPs was studied and that appeared to be superior over its negative charged counterpart. Further the AuNPs@C.CNF is casted into a film which makes it reusable. Using TMB substrate, simple and sensitive colorimetric detection methods for H2O2 and glucose were established. Under optimal conditions, the linear ranges were found to be 0.5-30 µM and 1-60 µM, and the detection limits were 0.30 and 0.67 µM for H2O2 and glucose, respectively. The film was potentially reused for the detection of glucose up to five cycles without a decrease in the activity. Further, this technique was employed to quantify glucose in human serum samples, and the obtained results were comparable with those of the standard GOD-POD method.

One-pot synthesis of an anionic cyclodextrin-stabilized bifunctional gold nanoparticles for visual chiral sensing and catalytic reduction.

A facile one-pot synthetic method for preparing gold nanoparticles by employing sugammadex (SUG), a carboxylic acid functionalized γ-cyclodextrin derivative, as reducing-cum-stabilizing agent herein was reported for the first time. The SUG protected gold nanoparticles (SUG-AuNPs) can work as a colorimetric sensor for visual chiral recognition of α-amino acids enantiomers, especially for lysine (Lys) and asparagine (Asn) enantiomers. The chiral recognition assay was successfully applied to determining the enantiometric excess of L-Lys and L-Asn ranging from -100 % to 100 % respectively. Moreover, the prepared SUG-AuNPs was found to exhibit efficient catalytic activity towards the reduction of toxic 4-nitrophenol by NaBH4 and the efficiency of the system was further demonstrated through the reduction of other typical nitroaromatics under mild condition. The as-synthesized SUG-AuNPs shows good performance for both chiral sensing and reduction activity and thus may facilitate the practical application in the area of both chiral discrimination and catalysis.

Patulin removal from apple juice using a novel cysteine-functionalized metal-organic framework adsorbent.

Patulin (PAT) is one of the most common toxic contaminants of apple juice, which causes severe food safety issues throughout the apple industry. In order to remove PAT efficiently, a metal-organic framework-based adsorbent (UiO-66(NH2)@Au-Cys) was successfully synthesized and used for PAT removal from juice-pH simulation solution and real apple juice. Batch adsorption experiments were systematically performed to study the adsorption behavior for PAT. The results showed that adsorption process could be well described by the Pseudo-second order model and Freundlich isotherm model. The maximum adsorption capacity (4.38 µg/mg) was 10 times higher than the microbe-based biosorbents. Thermodynamic investigation demonstrated that adsorption process was spontaneous and endothermic. Furthermore, no marked cytotoxicity on NIH 3T3 cell lines was observed when the concentration of the adsorbent was lower than 10 µg/mL. Therefore, UiO-66(NH2)@Au-Cys is a potential adsorbent for PAT removal from apple juice with little quality changes.

Colorimetric aptasensors for determination of tobramycin in milk and chicken eggs based on DNA and gold nanoparticles.

Colorimetric aptasensors were designed for detection of tobramycin (TOB) based on unmodified gold nanoparticles (AuNPs) and single-strand DNA (ssDNA). In the absence of TOB, the DNA aptamer was coated on the surface of AuNPs to keep it against salt-induced aggregation. In the presence of TOB, aptamer will bind with TOB and detach from the surface of AuNPs because of higher affinities between aptamer and TOB. Then less protection of DNA may result in the aggregation of AuNPs by salt and an apparent color change from red to purple-blue. The developed aptasensors showed a high selectivity and sensitivity for TOB detection. The linearity range and the detection limit were 40-200 nM and 23.3 nM respectively. The validity of the procedure and applicability of aptasensors were successfully used to detect TOB in milk and chicken eggs, and the results were excellent in accord with the values obtained by spectrofluorimetric detection.

Simultaneous detection of four nitrofuran metabolites in honey by using a visualized microarray screen assay.

A visualized microarray sensing technique has been developed and applied to the screening of honey samples for residues of banned nitrofuran antibiotics. Using a multiplexed approach, metabolites of four main nitrofuran antibiotics can be detected simultaneously. Individual antigens were spotted onto 96-well plates. An indirective competitive assay format, with visualized signal response, was employed. An extraction method, based on derivatization with 2-nitrobenzaldehyde and partition into ethyl acetate, was used for screening. The limits of detection were 0.10, 0.04, 0.04, and 0.10ngg-1 for 3-amino-5-morpholino-2-oxazolidone (AMOZ), 3-amino-2-oxazolidinone (AOZ), semicarbazide (SEM), and 1-aminohydantoin (AHD), respectively. The recovery rate ranged from 78% to 93% for the four targets. In addition, this method was easy to operate with low detection cost and fast speed. This microarray method possesses the potential to be a fit-for-purpose screening technique in the arena of food safety monitoring.

Vapor-phase preparation of gold nanocrystals by chloroauric acid pyrolysis.

We report that gold nanocrystals can be prepared from vapor phase using chloroauric acid (HAuCl4) as the precursor. By tuning the vapor-phase deposition parameters, the size and space distribution of the gold nanocrystals can be well controlled on substrates. Systematic control experiments demonstrate that intermediate AuCl and AuCl3 products pyrolyzed from HAuCl4 play an essential role in this vapor-phase deposition process. Compared to conventional wet-chemical synthesis process, vapor-phase process enables direct deposition of gold nanoparticles on solid substrates with better coverage and uniformity, which may find applications in surface-enhanced Raman scattering and plasmon-enhanced photocatalysis.