Shape-controlled synthesis of gold icosahedra and nanoplates using Pluronic P123 block copolymer and sodium chloride

Gold icosahedra with an average diameter of about 600 nm were easily prepared by heating an aqueous solution of the amphiphilic block copolymer, poly(ethylene oxide)₂₀-poly(propylene oxide)₇₀-poly(ethylene oxide)₂₀ (Pluronic P123), and hydrogen tetrachloroaurate(III) trihydrate (HAuCl₄·3H₂O) at 60 °C for 25 min. When sodium chloride (NaCl:HAuCl₄ molar ratio=10:1) was added to this aqueous solution, gold nanoplates were produced. The chloride ion was found to be a key component in the formation of the gold nanoplates by facilitating the growth of {111} oriented hexagonal/triangular gold nanoplates, because similar gold nanoplates were produced when LiCl or KCl was added to the aqueous solution instead of NaCl, while gold nanocrystals having irregular shapes were produced when NaBr or NaI was added.     

Sensitive electrochemical detection of arsenic (III) using gold nanoparticle modified carbon nanotubes via anodic stripping voltammetry

Gold nanoparticles were deposited electrolessly on multiwalled carbon nanotubes (CNTs) via in situ reduction of HAuCl₄ by NaBH₄. The resulting gold covered nanotubes were immobilised onto the surface of a glassy carbon electrode via evaporation of a suspension in chloroform. Anodic stripping voltammetry was performed with the modified electrode in As(III) solutions. A limit of detection (LOD based on 3σ) of 0.1 μg L⁻¹ was obtained but more importantly a sensitivity of 1985 μA μM⁻¹ was obtained with square wave voltammetry (SWV) in an optimised system with a deposition time of 120 s. These values, particularly the high sensitivity compare favourably with previously reported methods in the area of electrochemical arsenic detection.     

新形金纳米片的简单制备与生长机制

在室温(~30 ℃)条件下,氯金酸(HAuCl₄)均匀混合在粘稠的表面活性剂聚乙烯吡咯烷酮(PVP)胶体(水为溶剂)中,HAuCl₄可以被PVP还原,从而形成纳米片. 本工作中,通过调整晶体生长条件,成功合成了大量新形貌的单晶金纳米片(厚度数十纳米,尺寸为数个微米). 例如,在晶体生长初期阶段,通过引入温度变化(如降温10-20 ℃),形成的金纳米片主要是六角星形,并伴有盾状、内凹外凸的三角状、截角的、三叉的及多台阶等新形纳米片. 结合理论计算,阐明了金纳米片的生长机制：在一定条件下,金(111)晶面不仅可以沿着<110>方向生长成为常规的三角或六角纳米片,还可以沿<211>、<321>等不同方向生长成含有更高指数侧面的新形金纳米片.     

Synthesis of gold/polydopamine composite surfaces on glass substrates for localized surface plasmon resonance and catalysis

Composite materials of polydopamine (PDA) and gold nanoparticles on glass substrates (Au/PDA@slide) were obtained via a simple chemical process. First, PDA films (PDA@slide) were formed by immersing slides in 20 mg ml⁻¹ dopamine aqueous solution at pH = 8.5 for 1 h. Then, PDA@slide was dipped in 0.02 M chloroauric acid (HAuCl₄) aqueous solution for a certain time, Au/PDA@slide being formed. Gold nanoparticles were obtained by the reductive properties of PDA. The morphology and chemical composition of the composite material were characterized using scanning electron microscopy, X‐ray diffraction and X‐ray photoelectron spectroscopy. The catalytic properties of Au/PDA@slide were evaluated using the reduction of 4‐nitrophenol (4‐NP) in the presence of sodium borohydride (NaBH₄) aqueous solution at room temperature. The catalytic activity of the optimal Au/PDA@slide was so satisfactory that the reduction of 4‐NP was completed within 10 min. Moreover, the Au/PDA@slide composite material was stable up to five cycles without significant loss of its catalytic activity. In addition, Au/PDA@slide also exhibited photocatalytic ability, photodegrading 2.5 ml of 17.5 mg l⁻¹ methyl orange in 100 min. By measuring the UV–visible absorption bands of Au/PDA@slide, it was proved that the condition of the strongest surface plasmon resonance of Au/PDA@slide was the optimal condition for catalytic reduction of 4‐NP.     

Characterization of gold nanoparticles electrochemically deposited on amine-functioned mesoporous silica films and electrocatalytic oxidation of glucose

This study reports the preparation and characterization of gold nanoparticles deposited on amine-functioned hexagonal mesoporous silica (NH₂–HSM) films and the electrocatalytic oxidation of glucose. Gold nanoparticles are fabricated by electrochemically reducing chloroauric acid on the surface of NH₂–HSM film, using potential step technology. The gold nanoparticles deposited have an average diameter of 80 nm and show high electroactivity. Prussian blue film can form easily on them while cycling the potential between −0.2 and 0.6 V (vs saturated calomel electrode) in single ferricyanide solution. The gold nanoparticles loading NH₂–HSM-film-coated glassy carbon electrode (Au–NH₂–HSM/GCE) shows strong catalysis to the oxidation of glucose, and according to the cathodic oxidation peak at about 0.16 V, the catalytic current is about 2.5 μA mM⁻¹. Under optimized conditions, the peak current of the cathodic oxidation peak is linear to the concentration of glucose in the range of 0.2 to 70 mM. The detection limit is estimated to be 0.1 mM. In addition, some electrochemical parameters about glucose oxidation are estimated.     

Colorimetric detection of fluoride ion in an aqueous solution using a thioglucose-capped gold nanoparticle

The thioglucose-capped gold nanoparticles have been prepared by the chemical reduction of HAuCl₄ using thioglucose as the reducing and capping agent, which displays selective colorimetric detection of fluoride ion in 10 mM HEPES buffer at physiological pH.     

Voltammetry of immobilized cytochrome c on novel binary self-assembled monolayers of thioctic acid and thioctic amide modified gold electrodes

Horse heart cytochrome c (cyt c) was adsorbed on the binary self-assembled monolayers (SAMs) composed of thioctic acid (T-COOH) and thioctic amide (T-NH₂) at gold electrodes via electrostatic interaction. The cyt c adsorbed on the modified gold electrode exhibited well-defined reversible electrochemical behavior in 10 mM phosphate buffer solution (PBS, pH 7.0). The surface concentration (Γ) of electroactive species, cyt c, on the binary SAMs was higher than that in single-component SAMs of T-COOH, and reached a maximum value of 9.2 × 10⁻¹² mol cm⁻² when the ratio of T-COOH to T-NH₂ in adsorption solution was of 3:2, and the formal potential (E^0′=(E_pa+E_pc)/2) of cyt c was −0.032 V (vs. Ag|AgCl (3 M NaCl)) in a 10 mM PBS. The interaction between cyt c and the binary SAMs made the E^0′ shift negatively when compared with that of cyt c in solution (+0.258 V vs. NHE, i.e., +0.058 V vs. Ag|AgCl (3 M NaCl)). The fractional coverage of bound cyt c was a 0.64 theoretical monolayer. The standard electron transfer rate constant of cyt c immobilized on the binary SAMs was also higher than that on single-component SAMs of T-COOH, and the maximum value of 15.8 ± 0.6 s⁻¹ was obtained when the ratio of T-COOH to T-NH₂ in adsorption solution was at 3:2. The results suggest that the electrode modified with the binary SAMs functions better than the electrode modified with single-component SAMs of T-COOH.     

Ultra-sensitive immunosensor for detection of hepatitis B surface antigen using multi-functionalized gold nanoparticles

The signal amplification for analytical purposes has considerable potential in detecting trace levels of analytes for clinical, security or environmental applications. In the present report a strategy based on a sandwich type immunoassay system was designed for the detection of hepatitis B surface antigen which exploits the specific affinity interaction between streptavidin and biotin recognition systems. The method involves the specific coupling of multi-functionalized gold nanoparticles (bearing biotin and luminol molecules) to the streptavidin modified by secondary antibody. The chemiluminescent signal is produced by the gold nanoparticles in the presence of HAuCl₄ as catalyst and hydrogen peroxide as oxidant. The immunosensor was able to detect hepatitis B surface antigen in the linear concentration range from 1.7 to 1920 pg mL⁻¹ and the detection limit of 0.358 pg mL⁻¹, at signal/noise = 3.     

Electrochemical determination of chromium(VI) using metallic nanoparticle-modified carbon screen-printed electrodes

Carbon screen-printed electrodes (CSPEs) modified with metal nanoparticles present an interesting alternative in the determination of chromium(VI) by differential pulse voltammetry (DPV).Metallic silver and gold nanoparticle deposits have been obtained by electrochemical deposition. Scanning electron microscopy measurements show that the electrochemically synthesized silver and gold nanoparticles are deposited in aggregated form.The detection limit for the analytical procedures developed in this work were 8.5 × 10⁻⁷ and 4.0 × 10⁻⁷ M for silver and gold nanoparticle-modifed CSPE, respectively.In terms of reproducibility, the precision of the above-mentioned method was calculated at 6.7% in %R.S.D. values for silver and 3.21% for gold nanoparticle CSPE.     

UV irradiation induced formation of single-crystal gold nanonetworks with controllable pore distribution

Single-crystal gold nanonetworks and nanoplates with novel porous structures were synthesized through a continuous UV irradiation method. The structures of the porous nanonetworks and the nanoplates were found to be citric acid concentration dependent. Transmission electron microscopy (TEM) showed that the two-dimensional (2-D) nanonetworks prepared at the lower citric acid concentration (0.5 mM) had irregular pores and bigger area. Increasing the citric acid concentration resulted in formation of gold nanoplates with hexagonal, triangular or truncated triangular pores. When the acid concentration came to 2 mM, the nanoplates with single and double pores were observable. The selected area electron diffraction (SAED) patterns showed that both the nanonetworks and porous nanoplates were single-crystal. The presence of 1/3{4 2 2} reflections indicated that the surface of the gold nanonetwork and nanoplates is atomically flat.     

A new organic compound for the synthesis of gold nanoparticles

2,3,5,6-Tetrakis-(morpholinomethyl)hydroquinone (1) is used for the first time in the preparation of gold nanoparticles by the reduction of HAuCl₄ in water–methanol medium without using any capping agent. Compound 1 was prepared by Mannich-type aminomethylation of hydroquinone with morpholine. It is characterized by elemental analysis, FT-IR, UV–Vis and mass spectra and finally by single crystal X-ray diffraction. The ratio of HAuCl₄ and compound 1 played a vital role in controlling the shape and size of gold nanoparticles. The samples were characterized by Transmission Electron Microscopy (TEM), XRD, FT-IR, UV–Vis measurements. With the increasing amount of gold(III) solution with respect to compound 1, two different morphologies such as self-assembled and spherical gold nanoparticles have been observed. The results indicate that the morphology of gold nanoparticles with different sizes can be controlled by changing the concentrations of compound 1 and gold(III) solution.     

Synthesis and Characterization of Gold Nanoparticles with Surface Ligands Derived from a Primary Phosphine

Reduction of HAuCl₄ · 3H₂O with NaBH₄ in THF/H₂O in the presence of the primary phosphine PH₂Mes* (Mes* = 2,4,6-(t-Bu)₃C₆H₂) gave a mixture of ca. 1.3 nm diameter gold nanoparticles (1) and the known oligomers [Au(PHMes*)]_n (2). Nanoclusters 1 might contain phosphido (PHMes*) or phosphinidene (PMes*) surface ligands, or both; they were characterized by elemental analysis, TGA, XPS, TEM, NMR, IR, and UV–Vis spectroscopies, and by their reactions with dodecanethiol, which gave PH₂Mes*. Solid-state ³¹P-NMR cross-polarization studies of 1 and 1D (prepared using NaBD₄ and PD₂Mes* in THF/D₂O) were consistent with the presence of phosphinidene surface groups.     

Flexible superhydrophobic gold film for magnetical manipulation of droplets

Herein, we present a simple, efficient, and economical approach for the preparation of superhydrophobic gold film embedded on polydimethylsiloxane (PDMS) sheets without the requirement of surface pretreatment. The reduction reaction between chloroauric acid (HAuCl₄) and sodium formate (HCOONa) at room temperature was performed to generate the aggregated gold microstructures on a PDMS sheet without chemical residuals. Superhydrophobic property was achieved when deposition time was reached to 2 h with water contact angle >160° and low contact angle hysteresis (H = 1.93°). Systematic investigations of the size, morphology, and mechanism of the generated gold films are presented. The generated gold film contains two different layers involving uniform spherical gold particles attached to the PDMS surface with the complex hierarchical structures on top. The complex structures play an important role in the superhydrophobic property, as they strongly promote the roughness to the PDMS surface. The durability of the fabricated gold film was elucidated by dropping ~7,200 waterdrops and external physical forces (e.g. stretch, bend, and twist). The main structures and their superhydrophobic properties have not disoriented after the tests. Moreover, the surface of the gold film demonstrated the potential applications as magnetical manipulation of droplets and a robust Surface enhanced Raman spectroscopy (SERS substrate).     

Preparation of reversibly photo-cross-linked nanogels from pH-responsive block copolymers and use as nanoreactors for the synthesis of gold nanoparticles

Reversibly photo-cross-linkable pH-responsive block copolymer poly(ethylene oxide)-b-poly((2-(diethylamino)ethyl methacrylate-co-4-methyl-[7-(methacryloyl)oxyethyloxy] coumarin)) (PEO-b-P(DEA-co-CMA)) was synthesized via atom transfer radical polymerization (ATRP). Block copolymer nanogels could be easily prepared by first photo-cross-linking of the micelles at pH > 7 and then adjusting the solution to pH < 7. The photo-cross-linking was proved to be reversibly controlled under alternative irradiation of UV light at 365 nm and 254 nm. As a result, the cross-linking degrees and sizes of the nanogels can be easily controlled by alternatively UV light irradiation. Finally, the nanogels can serve as nanoreactors for the synthesis of gold nanoparticles. The protonated DEA units were first coordinated with HAuCl₄, and then the electrostatically bounded AuCl⁴⁻ anions were reduced to gold nanoparticles by NaBH₄. The nanogel-supported gold nanoparticles were used in chemical catalysis. The pH-responsive photo-cross-linked nanogels have been characterized using dynamic light scattering, transmission electron microscopy, UV-vis spectra and ¹H NMR spectroscopy measurements, respectively.     

Selective detection and recovery of gold at tannin-immobilized non-conducting electrode

A tannin-immobilized glassy carbon electrode (TIGC) was prepared via electrochemical oxidation of the naturally occurring polyphenolic mimosa tannin, which generated a non-conducting polymeric film (NCPF) on the electrode surface. The fouling of the electrode surface by the electropolymerized film was evaluated by monitoring the electrode response of ferricyanide ions as a redox marker. The NCPF was permselective to HAuCl₄, and the electrochemical reduction of HAuCl₄ to metallic gold at the TIGC electrode was evaluated by recording the reduction current during cyclic voltammetry measurement. In the mixed electrolyte containing HAuCl₄ along with FeCl₃ and/or CuCl₂, the NCPF remained selective toward the electrochemical reduction of HAuCl₄ into the metallic state. The chemical reduction of HAuCl₄ into metallic gold was also observed when the NCPF was inserted into an acidic gold solution overnight. The adsorption capacity of Au(III) on tannin-immobilized carbon fiber was 29 ± 1.45 mg g⁻¹ at 60 °C. In the presence of excess Cu(II) and Fe(III), tannin-immobilized NCPF proved to be an excellent candidate for the selective detection and recovery of gold through both electrochemical and chemical processes.     

In situ polymerization and reduction to fabricate gold nanoparticle‐incorporated polyaniline as supercapacitor electrode materials

Nanocomposites of gold nanoparticles and polyaniline are synthesized by using HAuCl₄ and ammonium peroxydisulfate as the co‐oxidant involving in situ polymerization of aniline and in situ reduction of HAuCl₄. Through these in situ methods, the synthesized Au nanoparticles of ca. 20 nm embedded tightly and dispersed uniformly in polyaniline backbone. With the Au content in composite increasing from 4.20 to 24.72 wt.%, the specific capacitance of the materials first increased from 334 to 392 F g⁻¹ and then decreased to 298 F g⁻¹. Based on the real content of PANI in composite material, the highest specific capacitance is calculated to be 485 F g⁻¹ at the Au amount of 19.15 wt.%, which remains 55.6% after 5000 cycles at the current density of 2 A g⁻¹. Finally, the asymmetric supercapacitor of AuNP/PANI||AC and the symmetric supercapacitor of AuNP/PANI||AuNP/PANI are assembled. The asymmetric supercapacitor device shows a better electrochemical performance, which delivers the maximum energy density of 7.71 Wh kg⁻¹ with power density of 125 W kg⁻¹ and maximum power density of 2500 W kg⁻¹ with the energy density of 5.35 Wh kg⁻¹.     

Label-free detection of specific DNA sequence-telomere using unmodified gold nanoparticles as colorimetric probes

A simple and sensitive label-free colorimetric detection of telomere DNA has been developed. It was based on the color change of gold nanoparticles (AuNPs) due to DNA hybridization. UV–vis spectra and transmission electron microscopy (TEM) were used to investigate the change of AuNPs. Under the optimized conditions, the linear range for determination of telomere DNA was 5.7 × 10⁻¹³ to 4.5 × 10⁻⁶ mol/L. The detection limit (3σ) of this method has decreased to pico-molar level.     

Preparation and Characterization of Heparin‐Stabilized Gold Nanoparticles

A simple method for preparing gold nanoparticles in aqueous solution has been developed by using glycosaminoglycan‐heparin as reducing and stabilizing agent and HAuCl₄ as precursor. The obtained gold nanoparticles were characterized by UV‐vis spectroscopy, resonance light scattering spectroscopy (RLS), transmission electron microscopy (TEM) and electrophoresis technology. The influence of reactant concentration for the preparation of gold nanoparticles was investigated. The results indicated that the gold nanoparticles carried negative charges in the aqueous solution and the size and shape of the gold nanoparticles could be controlled by changing the concentration of the heparin. Moreover, the gold nanoparticles obtained with relatively high concentration of heparin were very stable and had relative narrow size distribution.     

Aptamer-functionalized silver nanoparticles for scanometric detection of platelet-derived growth factor-BB

In this work, we reported a scanometric assay system based on the aptamer-functionalized silver nanoparticles (apt-AgNPs) for detection of platelet-derived growth factor-BB (PDGF-BB) protein. The aptamer and ssDNA were bound with silver nanoparticles by self-assembly of sulfhydryl group at 5′ end to form the apt-AgNPs probe. The apt-AgNPs probe can catalyze the reduction of metallic ions in color agent to generate metal deposition that can be captured both by human eyes and a flatbed scanner. Two different color agents, silver enhancer solution and color agent 1 (10 mM HAuCl₄ + 2 mM hydroquinone) were used to develop silver and gold shell on the surface of AgNPs separately. The results demonstrated that the formation of Ag core–Au shell structure had some advantages especially in the low concentrations. The apt-AgNPs probe coupled with color agent 1 showed remarkable superiority in both sensitivity and detection limit compared to the apt-AuNPs system. The apt-AgNPs system also produced a wider linear range from 1.56 ng mL⁻¹ to 100 ng mL⁻¹ for PDGF-BB with the detection limit lower than 1.56 ng mL⁻¹. The present strategy was applied to the determination of PDGF-BB in 10% serum, and the results showed that it had good specificity in complex biological media.     

Polyvinyl alcohol–ionic liquid composition for promoting the direct electron transfer and electrocatalysis of hemoglobin

The direct electron transfer and electrocatalysis of hemoglobin (Hb) entrapped in polyvinyl alcohol (PVA)–room temperature ionic liquid (i.e., 1-octyl-3-methylimidazolium hexafluorophosphate [OMIM]PF₆) composition has been investigated by using cyclic voltammetry and chronocoulometry. It is found that the composition can promote the direct electron transfer of Hb and the heterogeneous electron transfer rate constant (k_s) of immobilized Hb is enhanced to 19.9 s⁻¹. The immobilized Hb also shows high electro-catalytic activity towards the redox of oxygen, hydrogen peroxide and nitrite. The Michaelis constants (K_m) decrease to 1.2 × 10⁻⁴ M (for hydrogen peroxide) and 9.4 × 10⁻³ M (for nitrite). The surface concentration of electroactive Hb is estimated and it is ca. 1.4 × 10⁻¹⁰ mol cm⁻², meaning that several layers of immobilized Hb take part in the electrochemical reaction. When gold nanoparticles (GNP) is introduced into the composition, the resulting PVA–GNP–[OMIM]PF₆ composition presents better performance. The electrochemical characteristic of immobilized Hb is improved further. Thus PVA–GNP–[OMIM]PF₆ composition is more suitable for the immobilization of Hb. Therefore, it is a good strategy to prepare novel composition for protein immobilization by using several materials with different function.