Reduction Of HAuCl4 Research Articles

Synthesis of Gold Nanoparticles Using <i>p</i>-Aminobenzoic Acid and <i>p</i>-Aminosalicylic Acid as Reducing Agent

Synthesis of gold nanoparticles (AuNPs) by reduction of HAuCl4 with p-aminobenzoic acid and p-aminosalicylic acid as a reducing agent was investigated. This work was conducted in order to determine the optimum condition of AuNPs synthesis and examine the effect of the hydroxyl group in p-aminosalicylic acid towards the size, shape, and stability of the synthesized gold nanoparticles (AuNPs). The optimum condition of the gold nanoparticles synthesis was determined by UV/Vis spectrophotometer, the shape and size of gold nanoparticles were measured by Transmission Electron Microscope (TEM). The synthesis process was started by reacting HAuCl4 and the reducing agents in an aqueous solution at 86 ºC. The initial gold concentration, reducing agents concentration and pH were varied in order to obtain the optimum condition. In the optimum condition, the results showed that p-aminosalicylic acid containing both hydroxyl and amino groups performed higher reduction ability compared to p-aminobenzoic acid that only containing an amino group. Reducing agents which have a hydroxyl group (p-aminosalicylic acid) could produce AuNPs with a smaller concentration of HAuCl4 than p-aminobenzoic acid. Gold nanoparticles that were synthesized with p-aminosalicylic acid were more stable and had a smaller particle size compared to its counterpart that is synthesized with p-aminobenzoic acid.

Synthesis, characterization and application of plasmonic hollow gold nanoshells in a photothermal therapy—New particles for theranostics

This article describes the work on synthesis, surface functionalization and characterization of hollow gold nanoshells (HGNs), and their application in a photothermal tumor therapy. The studied gold nanoshells were synthesized using a method based on a reduction of HAuCl4 onto silver nanoparticle templates. A selected aptamer - AS1411 – selective towards nucleolin, with a terminal thiol group was conjugated to HGNs. Surface functionalization of synthesized nanoparticles was necessary to gain the affinity to tumor cells, thus allowing the selective delivery of the modified nanoparticles to target cells. As expected, an increased selectivity of nanoconjugates towards tumor cells (A375) in a comparison to normal ones (HaCaT) was observed (2.67 times). In the framework of our studies the biological activity of the obtained nanoconjugates was evaluated using MTT assay. For this aim, both normal and tumor cell cultures respresenting skin tissue were exposed to gold nanoparticles solutions. It was found, that HGN-AS1411 conjugates cause less than 10% loss in a cell viability in the case of both cell lines at the highest tested concentration. The potential of the developed nanoconjugates as agents in PTT of skin cancer was investigated in a subsequent stage of our research. It was found, that A375 cell viability amounted to less than 40% for 75μM of nanoconjugates (expressed as a concentration of Au atoms) as a result of the laser irradiation of this cell culture after desired accumulation of the tested nanoconjugates inside A375 cells.

Colorimetric detection of the β-agonist ractopamine in animal feed, tissue and urine samples using gold–silver alloy nanoparticles modified with sulfanilic acid

ABSTRACTA highly sensitive, selective and simple method was proposed for colorimetric detection of ractopamine on the basis of the interaction between ractopamine and sulfanilic acid-modified gold–silver alloy nanoparticles (AuAgNPs). The AuAgNPs were prepared by the reduction of HAuCl4 and AgNO3 with sodium citrate in aqueous medium and further modified by sulfanilic acid. The interaction of ractopamine with sulfanilic acid induced rapid aggregation of sulfanilic acid-modified AuAgNPs along with an optical colour change, leading to precise quantification which could be detected by absorptiometry. Under the optimum conditions, the absorbance ratio (A600/A435) of sulfanilic acid-modified AuAgNPs exhibited a linear relationship with the concentration of ractopamine in the range of 4.5–31.6 ng/mL. The detection limit of ractopamine was 1.5 ng/mL. The established novel colorimetric detection method showed high selectivity towards ractopamine. The method was successfully applied to detect ractopamine in spiked pork, swine feed and swine urine samples with excellent recoveries from 94.4% to 112.5%. These results demonstrated that the proposed new method has a good potential for practical applications.

Gold conjugated carbon dots nano assembly: FRET paired fluorescence probe for cysteine recognition

The detection and discrimination of Cys amino acid from numerous other related biomolecules has great importance in clinical field for diagnosis of various diseases. Herein, to detect the Cys, we embedded the carbon dots (CDs), gold, and naphthalimide (L1) into a single ratiometric fluorescence sensor assembly. Sensor assembly works on the principle of FRET mechanism between CDs and naphthalimide when CDs and L1 adhered on gold nanoparticles surface. Gold metal was turned into solid support by in situ reduction of HAuCl4 in the presence of CDs and L1. When the assembly was excited at 360 nm, emission maxima at 568 nm corresponded to naphthalimide emission was emerged that signifies the existence of a FRET between the CDs and naphthalimide fluorophores. With the addition of Cys, the FRET mechanism eliminated and the change in the fluorescence emission at two different wavelengths (450 nm and 568 nm) was recorded. The endogenous images of Cys was recorded by collecting the fluorescence images of HeLa cells under fluorescence microscope and also applied for the assay of Cys in blood serum. Cytotoxicity studies of CDs and sensor assembly were evaluated by performing the MTT assay.

Label-Free Detection of Human Serum Using Surface-Enhanced Raman Spectroscopy Based on Highly Branched Gold Nanoparticle Substrates for Discrimination of Non-Small Cell Lung Cancer

Surface-enhanced Raman spectroscopy (SERS) is a good candidate for the development of fast and easy-to-use diagnostic tools, possibly used on serum in screening tests. In this study, a potential label-free serum test based on SERS spectroscopy was developed to analyze human serum for the diagnosis of the non-small cell lung cancer (NSCLC). We firstly synthesized novel highly branched gold nanoparticles (HGNPs) at high yield through a one-step reduction of HAuCl4 with dopamine hydrochloride at 60°C. Then, HGNP substrates with good reproducibility, uniformity, and high SERS effect were fabricated by the electrostatically assisted (3-aminopropyl) triethoxysilane-(APTES-) functionalized silicon wafer surface-sedimentary self-assembly method. Using as-prepared HGNP substrates as a high-performance sensing platform, SERS spectral data of serum obtained from healthy subjects, lung adenocarcinoma patients, lung squamous carcinoma patients, and large cell lung cancer patients were collected. The difference spectra among different types of NSCLC were compared, and analysis result revealed their intrinsic difference in types and contents of nucleic acids, proteins, carbohydrates, amino acids, and lipids. SERS spectra were analyzed by principal component analysis (PCA), which was able to distinguish different types of NSCLC. Considering its time efficiency, being label-free, and sensitivity, SERS based on HGNP substrates is very promising for mass screening NSCLC and plays an important role in the detection and prevention of other diseases.

Nanocomposite material based on nanoporous oxide of aluminum with additives of silver and gold nanoparticles

Porous films of anodized aluminum oxide with pore sizes of 50-60 nm were obtained. Silver nanoparticles in porous alumina have been synthesized by the method of controlled single-jet crystallization. The synthesis of gold nanoparticles in the pores was carried out by the reduction of HAuCl4 with NaOH alkali in the pores of aluminum oxide.

Post-assay growth of gold nanoparticles as a tool for highly sensitive lateral flow immunoassay. Application to the detection of potato virus X.

This article demonstrates a new kind of a highly sensitive lateral flow immunoassay (LFIA). It is based on the enlargement of the size of gold nanoparticles (GNPs) directly on the test strip after a conventional LFIA. Particle size enlargement is accomplished through the catalytic reduction of HAuCl4 in the presence of H2O2 and through the accumulation of additional gold on the surface of the GNPs. To attain maximal enhancement of the coloration of the zone in the test strip and toachieve a minimal background, the concentration of precursors, the pH value, and the incubation time were optimized. GNPs on the test strip are enlarged from 20 to 350nm after a1-min treatment at room temperature. The economically important and widespread phytopathogen potato virus X (PVX) was used as the target analyte. The use of the GNP enlargement method results in a 240-fold reduction in the limit of the detection of PVX, which can be as low as 17pg·mL-1. The total duration of the assay, including virus extraction from the potato leaves, lateral flow, and the enhancement process, is only 12min. The diagnostic efficiency of the technique was confirmed by its application to the analysis of potato leave samples. No false positives or false negatives were found. The technique does not depend on specific features of the target analyte, and it is conceivablyapplicable to numerous GNP-based LFIAs for important analytes. Graphical abstract An enlargement solution (containing HAuCl4 and H2O2) was dripped on the strip after common lateral flow immunoassay. Gold nanoparticles on the strip (20nm) catalyze gold reduction and the formation of larger particles (up to 350nm), resulting in a 240-fold lower detection limit within 1min.

BIOSYNTHESIS OF GOLD NANOPARTICLES BY BACTERIA FROM HYPERALKALINE SPRING AND EVALUATION OF THEIR INHIBITORY ACTIVITY AGAINST PYOCYANIN PRODUCTION

Nanoparticles are used in wide range of applications given their unique optical, chemical and electronic properties. Microbial biosynthesis of nanoparticles has offered a milder and eco-friendly alternative to physical and chemical methods of synthesis. One potential use of nanoparticles is for the inhibition of quorum sensing-mediated processes by microorganisms during pathogenic colonization and infection. In this study, bacteria from hyperalkaline spring (pH 11) were isolated using various enrichment media. The isolates, phylogenetically related to Lysinibacillus sp. and Pseudomonas stutzeri, were investigated for their ability to biosynthesize gold nanoparticles (AuNPs) via reduction of chloroauric acid (HAuCl4) at pH 9. Extracellular synthesis of gold nanoparticles was confirmed by UV-Vis absorption analysis which showed a peak at 500-600 nm wavelength range corresponding to the surface plasmon resonance of AuNPs. The AuNPs synthesized were of spherical and irregular shapes as revealed by SEM analysis. The presence of elemental gold was further confirmed by EDX analysis. FTIR results showed that various functional groups are possibly involved in the reduction of HAuCl4 and stabilization of synthesized gold nanoparticles. The inhibitory effect of biosynthesized AuNPs was tested on the growth and pyocyanin production of Pseudomonas aeruginosa PA01 during a 72-hour incubation period. Although the biosynthesized AuNPs showed no toxicity to the test organism, an increasing inhibition level of pyocyanin production was observed with increasing volumes of nanoparticles used. The levels of pyocyanin in setups treated with biosynthesized gold nanoparticles at 10, 30 and 50 L were significantly lower compared to the untreated setups (P ≤ 0.05). Our findings demonstrate that bacteria adapted to alkaline conditions can be used for efficient biosynthesis of AuNPs, which exhibited potential biomedical application in inhibiting pyocyanin production.

One-step synthesis of highly-branched gold nanostructures and its application in fabrication of SERS-active substrates

In this paper, we reported a simple one-step synthesis of highly-branched gold nanostructures (HGNs) in high yields. The reduction of HAuCl4 was accomplished by dopamine hydrochloride in the reaction system. By varying the amount of dopamine hydrochloride, HAuCl4 and the reaction temperature, we managed to tune the size of the HGNs from 200 to 600 nm. Systematic analysis revealed that the optical properties and surface-enhanced Raman scattering (SERS) activities of the HGNs were highly dependent on their morphology and size. In terms of their SERS activities, it was found that the HGNs synthesized at 60 °C with 2.0 mL dopamine hydrochloride (53 mM), 0.4 mL HAuCl4 (50 mM) exhibited the largest SERS enhancement. When the HGNs were assembled onto the silicon wafers, outstanding SERS efficiency was obtained with a detection limit of 5×10-10 M of 4-mercaptobenzoic acid (4-MBA) and the analytical enhancement factor (AEF) was calculated to be 7×107. Besides, the 3-aminopropyltriethoxysilane (APTES)-functionalized substrates with the HGNs displayed remarkable signal reproducibility with relative standard deviation (RSD) of 3.57%. All these results demonstrated that the SERS-active substrates held great promise to be applied in trace-level molecule detection in the future.

Nanogold – IgY antibodies. An immunoconjugated for the detection of house dust mite (Dermatophagoides) allergens

Conjugation of avian IgY antibodies to nanosensors has been extensively explored for the diagnostics of virus and parasite infection, as well as for the detection of pharmaceutically and toxicologically relevant molecules. However, to date this strategy has only been minimally applied the detection of allergens. In this study, gold nanoparticles (GNPs) were conjugated to a polyvalent IgY antibodies raised against Dermatophagoides group I allergens. GNPs were synthesized by HAuCL4 reduction using 1% trisodium citrate, and characterized them by absorption spectroscopy and transmission electron microscopy (TEM). The most stable immunoconjugates were obtained with 18-nm monodisperse GNPs and a minimal concentration of 12.5 μg/mL of IgY at pH 7.5. The immunoconjugate was capable of detecting up to 1.5 μg of a total Dermatophagoides farinae protein extract in an immuno-dot blot assay. This immunoreactant conjugate represents a new tool for the detection and control of indoor dust mite allergens.

Dendronized triazolyl-containing ferrocenyl polymers as stabilizers of gold nanoparticles for recyclable two-phase reduction of 4-nitrophenol

A series of small-sized (about 2.0 nm) gold nanoparticles (AuNPs) with apparent lattice fringes are synthesized by NaBH4 reduction of HAuCl4 in the presence of stabilizing linear or dendronized 1,2,3-triazolyl-containing ferrocenyl polymers. These AuNPs show high catalytic activity for biphasic 4-nitrophenol (4-NP) reduction to 4-aminophenol (4-AP) by NaBH4. The lower generation G1 dendronized polymers (DPs) is a more efficient stabilizer for AuNP catalytic activity in the reduction of 4-NP than linear G0 polymers or bulky G2 DPs. The G1 DP-stabilized AuNPs are robust and easily recyclable, and the catalyst is recovered and reused at least twenty times with progressive smooth AuNP size increase along with some decrease of catalytic activity.

Fabrication and characterization of gold nanoparticle-doped electrospun PCL/chitosan nanofibrous scaffolds for nerve tissue engineering.

In the field of nerve tissue engineering, nanofibrous scaffolds could be a promising candidate when they are incorporated with electrical cues. Unique physico-chemical properties of gold nanoparticles (AuNPs) make them an appropriate component for increasing the conductivity of scaffolds to enhance the electrical signal transfer between neural cells. The aim of this study was fabrication of AuNPs-doped nanofibrous scaffolds for peripheral nerve tissue engineering. Polycaprolactone (PCL)/chitosan mixtures with different concentrations of chitosan (0.5, 1 and 1.5) were electrospun to obtain nanofibrous scaffolds. AuNPs were synthesized by the reduction of HAuCl4 using chitosan as a reducing/stabilizing agent. A uniform distribution of AuNPs with spherical shape was achieved throughout the PCL/chitosan matrix. The UV-Vis spectrum revealed that the amount of gold ions absorbed by nanofibrous scaffolds is in direct relationship with their chitosan content. Evaluation of electrical property showed that inclusion of AuNPs significantly enhanced the conductivity of scaffolds. Finally, after 5 days of culture, biological response of Schwann cells on the AuNPs-doped scaffolds was superior to that on as-prepared scaffolds in terms of improved cell attachment and higher proliferation. It can be concluded that the prepared AuNPs-doped scaffolds can be used to promote peripheral nerve regeneration.

Dithiothreitol-Facilitated Synthesis of Bovine Serum Albumin–Gold Nanoclusters for Pb(II) Ion Detection on Paper Substrates and in Live Cells

In this work, a bright red fluorescent protein-capped gold nanocluster, AuNC@BSA, is developed in a green synthesis approach, and its application as a sensor for detection of Pb(II) ion in water and in live cells is demonstrated. AuNC@BSA is prepared by dithiothreitol (DTT)-mediated activation of bovine serum albumin (BSA) followed by the reduction of HAuCl4 in an aqueous medium. The incorporation of DTT assists in the reduction of disulfide bridges present in cysteine residues, which in turn increases the reducing power of BSA forming a significant number of the Au25 clusters that enhances the bright red fluorescence of AuNC@BSA at 660 nm when excited at 520 nm with a highest quantum yield of ∼20.0% reported so far. AuNC@BSA as nanosensor selectively detect Pb(II) ion in water with a detection limit of 1.0 ppb, lower than the World Health Organization limit (10.0 ppb), and follow quenching-based sensing mechanism through metallophilic interaction between Au(I) and Pb(II) ion. In presence of a strong chel...

Fabrication of Thermoresponsive Polymer-Functionalized Cellulose Sponges: Flexible Porous Materials for Stimuli-Responsive Catalytic Systems.

In this present work, a thermoresponsive and recyclable catalytic system was prepared by grafting poly( N-isopropylacrylamide)- co-poly(glycidyl methacrylate) (PNIPAM- co-PGM) to a cellulose sponge, which was reinforced by polydopamine (PDA) and (3-aminopropyl)triethoxysilane(APTMS). Au nanoparticles (Au NPs) were loaded via in situ reduction of HAuCl4 with PDA. Fourier transform infrared, X-ray photoelectron spectroscopy, scanning electron microscopy, transmission electron microscopy, and thermogravimetric analysis results revealed that the Au NPs (<10 nm) were homogenously dispersed on the surface of the sponge. Catalytic experiments with sponges prepared without PNIPAM- co-PGM demonstrated an increased reaction rate when the temperature of the reaction medium was elevated. However, in the presence of PNIPAM-i co-PGM in the sponges, the reaction rate was decreased when the reaction temperature was higher than the lower critical solution temperature of the polymer. The sponge could be conveniently separated from the reactions and reused up to 22 cycles.

Nano–silica functionalized with thiol–based dendrimer as a host for gold nanoparticles: An efficient and reusable catalyst for chemoselective oxidation of alcohols

In this paper, we present the synthesis of Au nanoparticles supported on nanosilica thiol based dendrimer, nSTDP. The catalyst was prepared by reduction of HAuCl4 with NaBH4 in the presence of nSTDP. The resulting Aunp–nSTDP materials were characterized by FT–IR and UV–vis spectroscopic methods, SEM, TEM, TGA, XPS and ICP analyses. The characterization of the catalyst showed that Au nanoparticles with the size of 2–6 nm are homogeneously distributed on the nSTDP dendrimer with a catalyst loading of about 0.19 mmol/g of catalyst. The Aunp–nSTDP catalyst was used in the oxidation of alcohols with tert–butyl hydroperoxide (TBHP) as oxidant. The influence of vital reaction parameters such as solvent, oxidant and amount of catalyst on the oxidation of alcohols was investigated. These reactions were best performed in an acetonitrile/water mixture (3:2) in the presence of 0.76 mol% of the catalyst on the basis of the Au content at 80 °C under atmospheric pressure of air to afford the desired products in high yields (80–93% for benzyl alcohols). The Aunp–nSTDP catalyst exhibited a high selectivity toward the corresponding aldehyde and ketone (up to 100%). Reusabiliy and stability tests demonstrated that the Aunp–nSTDP catalyst can be recycled with a negligible loss of its activity. Also this catalytic exhibited a good chemoselectivity in the oxidation of alcohols.

A simple gold nanoplasmonic SERS method for trace Hg2+ based on aptamer‐regulating graphene oxide catalysis

The as-prepared graphene oxide (GO) exhibited a strong catalytic effect on reduction of HAuCl4 by trisodium citrate to form gold nanoplasmons (AuNPs) with a strong surface-enhanced Raman scattering (SERS) effect at 1615cm-1 in the presence of molecular probe Victoria blue 4R (VB4r). SERS intensity increased with nanocatalyst GO concentration due to the formation of more AuNP substrates. The aptamer (Apt) of Hg2+ can bind to GO to form Apt-GO complexes, which can strongly inhibit nanocatalysis. When target Hg2+ is present, the formed stable Hg2+ -Apt complexes are separated from the GO surface, which leads to GO catalysis recovery. The enhanced SERS signal was linear to Hg2+ concentration in the range 0.25-10nmol/L, with a detection limit of 0.08nmol/L Hg2+ . Thus, a new gold nanoplasmon molecular spectral analysis platform was established for detecting Hg2+ , based on Apt regulation of GO nanocatalysis.

Bioinspired synthesis of multiple-functional nanocomposite platform showing optically and thermally responsive affinity: Application to environmentally responsive separation membrane

A tremendous effort has been made for the synthesis and multifunction of environmentally responsive and selective separation membranes. With the bioinspired design of polydopamine (pDA)-assisted inorganic film, we proposed a simple, yet efficient, thermo-responsive cell culture substrate. Herein, a Ag/TiO2/pDA-based nanocomposite structure was initially obtained, and the ciprofloxacin-imprinted membranes (MINCMs) with thermo-responsive recognition sites were then synthesized by using NIPAm as backbone monomer. The opto-thermally responsive molecularly imprinted membranes (OT-MIMs) were obtained through in situ reduction of HAuCl4 on membrane surfaces, Au nanoparticles were used as the light-heat converters. The light-switching principle was elaborated as well as the energy conversions that took place in this system. These conformational changes finally allowed the constructions or destructions of ciprofloxacin-imprinted sites. Due to the formation of the opto-thermally responsive ciprofloxacin-imprinted sites, rapid adsorption dynamics and opto-thermally responsive perm-selectivity toward templates were both achieved. Therefore, 58.65 mg/g of adsorption capacity and 4.91 of permselectivity factor from OT-MIMs were successfully obtained. Importantly, the as-designed bioinspired strategy led to a state-of-the-art design that was capable of reversibly controlling the flow rate (J) of ciprofloxacin from 12.10 to 4.93 mg min−1 cm−2 in less than a few minutes using light.

Effect of Phenolic Compounds on the Synthesis of Gold Nanoparticles and its Catalytic Activity in the Reduction of Nitro Compounds.

Gold nanoparticles (AuNPs) were prepared using an eco-friendly approach in a single step by reduction of HAuCl4 with polyphenols from tea extracts, which act as both reducing and capping agents. The obtained AuNPs were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), ultraviolet–visible spectroscopy (UV–vis), and X-ray photoelectron spectroscopy (XPS). They act as highly efficient catalysts in the reduction of various aromatic nitro compounds in aqueous solution. The effects of a variety of factors (e.g., reaction time, type and amount of reducing agent, shape, size, or amount of AuNPs) were studied towards the optimization of the processes. The total polyphenol content (TPC) was determined before and after the catalytic reaction and the results are discussed in terms of the tea extract percentage, the size of the AuNPs, and their catalytic activity. The reusability of the AuNP catalyst in the reduction of 4-nitrophenol was also tested. The reactions follow pseudo first-order kinetics.

(Invited) Acceleration of Electrocatalytic Reaction By Photoexciting Localized Surface Plasmon of Octahedral Au@Pt Core-Shell Nanoparticles

Introduction Localized surface plasmon resonance (LSPR) at the surface of noble metal nanoparticles (NPs), such as, copper, silver and gold, has been intensively investigated in the past decade because they demonstrated enhancement of photochemical reactions and highly sensitive spectroscopies. Recently, the LSPR-induced acceleration of electrocatalytic ethanol oxidation reaction was reported by Wang and co-workers using Pd-Au hetero-nanoparticles, in which photogenerated holes in Au NPs could effectively oxidize ethanol in a solution.1 Platinum is one of the most active catalysts for various reactions in a practical application. However, since Pt NPs hardly exhibit LSPR peak in visible-light region, their application to LSPR-induced catalytic reaction has been little investigated. In this study, we try to enhance the catalytic activity of Pt with LSPR of octahedral Au NPs. An electrochemical technique is used for preparing Pt shell layer on octahedral Au NPs, resulting in the formation of Au@Pt core-shell NPs. The photoexcitation of LSPR peaks of octahedral Au core in Au@Pt NPs can modify the catalytic activity of Pt shell layer for oxygen reduction reaction (ORR) as a model reaction. Experimental Octahedral Au NPs were prepared by reduction of HAuCl4 in diethylene glycol containing poly(diallyldimethylammonium chloride) at 230 °C for 1 h. The underpotential deposition (UPD) of Cu monolayer onto octahedral Au NPs immobilized on an HOPG electrode was carried out with constant potential application at +0.3 V vs. RHE in an aqueous solution containing 1.0 mmol dm-3 CuSO4 and 0.1 mol dm-3 H2SO4. Thus-obtained Cu-deposited Au NPs on HOPG substrate immersed in aqueous solution containing 0.5 mmol dm-3 K2PtCl4 for 10 min to replace Cu monolayer by Pt, resulting in the core-shell structure of octahedral Au@Pt NPs. Results and discussions Prepared Au NPs (> 90%) had an octahedral shape with sharp edges and triangle flat surface of {111} facets. The average edge length was determined to be 65 ± 8 nm by SEM measurement. In the extinction spectrum, a sharp LSPR peak appeared at ca. 600 nm, the peak width of which was relatively narrow (FWHM > 90 nm) probably due to the uniformity of shape and size of octahedral Au NPs. The Pt shell were prepared by the galvanic replacement of Cu UPD layer on Au surface with Pt. The electrochemical surface areas of Pt shell and Au NPs were determined with cyclic voltammetry in a 0.1 mol dm-3 H2SO4 aqueous solution. The deposition of Pt layer on Au NPs decreased a peak current assignable to the reduction of Au oxide layer (ca. 1.15 V vs. RHE), while the peaks originating from reduction of Pt oxide layer and H2 desorption on Pt surface were newly observed for Au@Pt NPs at 0.65 and 0.05 V vs. RHE, respectively. These results indicated that the surface of octahedral Au NPs was partially coated with the Pt shell layer. The Pt surface coverage was successfully estimated to be enlarged from 85 to 94% with an increase in the Pt deposition cycles from 1 to 3. TEM measurement revealed that the average edge length of octahedral NPs (original: 65 nm) increased to 66.5 nm and 69 nm by the Pt deposition cycles of 1 and 3, respectively, indicating that the thin Pt layer of ca. 1-2 nm in thickness was formed on Au surface. Hydrodynamic voltammograms for ORR were measured with or without visible-light irradiation, using a ring-disk-rotating electrode loaded with the octahedral Au@Pt NPs (1 cycle of Pt deposition). A cathodic current for ORR was observed at more negative potential than ca. +0.95 V vs. RHE. The current density at +0.5 V vs. RHE was enhanced from -2.6 mA cm-2 to -3.1 mA cm-2 by the visible-light irradiation. The photocurrent action spectrum of the Au@Pt NPs agreed well with their extinction spectra. These results suggested that the LSPR excitation of the Au core in Au@Pt NPs could enhance the electrocatalytic activity of the Pt shell layer for ORR. Reference 1. Wnag, Q., et al., Power Sou., 2016, 316, 29.

Microwave-assisted in situ synthesis of fluorescent gold nanoclusters with BSA/montmorillonite and application on latent fingermark imaging

A method for in situ preparation of fluorescent gold nanoclusters (AuNCs) with bovine serum albumin/montmorillonite composite powder (AuNC-BSA/MMT) was developed, and the products were used to detect latent fingermarks. In this work, AuNCs were “grown” both inside and on the surface of BSA/MMT clay using one-step reduction of HAuCl4 by BSA. The as-prepared AuNC-BSA/MMT nanocomposites emit intensive red fluorescence under the excitation of UV-visible light and show stable chemical features and low toxicity. The obtained fluorescent powders were characterized by UV-visible absorption spectroscopy, fluorescence spectroscopy, infrared spectroscopy, transmission electron microscopy/high-resolution transmission electron microscopy, scanning electron microscopy, X-ray photoelectron spectroscopy and X-ray diffraction to depict their sizes, structural information and optical features. Given their environmentally friendly preparation, simple operation, low cost, efficient UVvisible radiation-dependent photoluminescence and good affinity with finger residues, the in situ synthesized AuNC-BSA/MMT nanocomposite powders were used as an alternative fluorescent developing reagent for developing latent fingermarks deposited on various object surfaces (such as glass, aluminum foil, painted metal, plastic products and weighing papers) for individual identification. As results, the developed fingermarks with clear patterns and satisfactory level-2 (minutiae points) and level-3 (sweat pores) ridge details were obtained. Notably, treated prints could be excited by red light and emitted near infrared fluorescence, which was beneficial to avoid background interference and reduce the damage caused by UV light. With the advantages of the simple preparation process and good enhancement performance for latent fingermarks, the proposed method might be used in the preparation of various fluorescent probes for detecting trace evidence in forensic sciences.