Formation Of Gold Nanoparticles Research Articles

Combination of distance-based paper analytical devices with ionic liquid-based dispersive liquid-liquid microextraction for enzyme-free bilirubin quantification

This article introduces the first demonstration of integrating distance-based paper analytical devices (dPADs) with ionic liquid-based dispersive liquid-liquid microextraction (IL-DLLME) for the quantitative detection of bilirubin levels in human samples. In this approach, bilirubin is preconcentrated and extracted into a small droplet of the extraction solvent using IL-DLLME. The resulting solution is then introduced into an economical and straightforward dPAD sensor. Detection relies on a colorimetric reaction between bilirubin and gold ions (Au3+), leading to the in-situ formation of gold nanoparticles (AuNPs) on the paper substrate. The observed red-purple distance length is directly proportional to the bilirubin level. Under optimization, a linear range between 0.25 nM and 5.0 nM (R2 = 0.9979) and a detection limit (LOD) of 250.0 pM were achieved. The assay exhibits notable precision and selectivity without any interference. With its distance readout feature, this method is simpler and more cost-effective, offering greater sensitivity compared to other methods requiring expensive reagents and instruments. Moreover, the technique shows high accuracy and precision for bilirubin quantification in human control samples, with recoveries ranging from 98.33% to 102.00%. No significant difference was observed between our method and the enzyme-linked immunoassay (ELISA) method. By combining a low-cost microfluidic device with a simple microextraction method, this strategy holds great potential as an alternative analytical method for determining bilirubin. It can be expanded for further applications in analytical sensing for point-of-care (POC) diagnostics.

Facile Preparation of Gold Nanoparticles Silica Composite Film Embedded in Anodized Aluminium Oxide-Glass Substrate

Thin film based on gold nanoparticles or AuNPs is typically used as catalyst in the industrial processes due to their high stability and good reusability. In this work, a thin AuNPs-silica composite film was fabricated firstly from sol-gel method by mixing gold pyrazolate complex to a medium comprised of ethanol, deionized water, and hydrochloric acid followed by addition of tetrabutyl orthosilicate as silica source. Next, 70 microliters of the sol-gel solution were spin-coated on several type of substrates such as glass, anodized aluminium oxide or AAO, and combination of both to yield gold complex-silica composite film. It was found that gold complex-silica composite film fabricated on combination of both AAO-glass substrate gave the best quality based on its surface thickness, layer uniformity and film brittleness. Later, the film was selected and subjected to thermal hydrogen reduction at 210 degrees Celsius for 2 hours to facilitate the formation of gold nanoparticles to give AuNPs-silica in AAO-glass film. Before the heat treatment, the light-brownish colour of the original gold complex-silica in AAO-glass film in daylight will appear as a pinkish red film under UV light, suggesting the interaction between gold atoms and supported by its luminescence spectrum at 692 nm. Upon heat treatment, the resulting AuNPs-silica in AAO-glass film gave a deep-red colour indicating the successful formation of AuNPs. The presence of AuNPs in the film was further confirmed based on the absorption peak at 545 nm, X-ray diffraction pattern at 38.20 degrees for d111 plane in wide-angle region, transmission electron microscopy images showing a small and sphere shape particles as well as its elemental composition in energy dispersive X-ray analysis. Moreover, scanning electron microscope images also suggested that the AAO pores is fully filled with the composite and is in accordance with its surface roughness study via atomic force microscopy analysis.

A gold speciation that adds a second layer to synergistic gold-copper toxicity in Cupriavidus metallidurans.

The metal-resistant bacterium Cupriavidus metallidurans occurs in metal-rich environments. In auriferous soils, the bacterium is challenged by a mixture of copper ions and gold complexes, which exert synergistic toxicity. The previously used, self-made Au(III) solution caused a synergistic toxicity of copper and gold that was based on the inhibition of the CupA-mediated efflux of cytoplasmic Cu(I) by Au(I) in this cellular compartment. In this publication, the response of the bacterium to gold and copper was investigated by using a commercially available Au(III) solution instead of the self-made solution. The new solution was five times more toxic than the previously used one. Increased toxicity was accompanied by greater accumulation of gold atoms by the cells. The contribution of copper resistance determinants to the commercially available Au(III) solution and synergistic gold-copper toxicity was studied using single- and multiple-deletion mutants. The commercially available Au(III) solution inhibited periplasmic Cu(I) homeostasis, which is required for the allocation of copper ions to copper-dependent proteins in this compartment. The presence of the gene for the periplasmic Cu(I) and Au(I) oxidase, CopA, decreased the cellular copper and gold content. Transcriptional reporter gene fusions showed that up-regulation of gig, encoding a minor contributor to copper resistance, was strictly glutathione dependent. Glutathione was also required to resist synergistic gold-copper toxicity. The new data indicated a second layer of synergistic copper-gold toxicity caused by the commercial Au(III) solution, inhibition of the periplasmic copper homeostasis in addition to the cytoplasmic one.IMPORTANCEWhen living in auriferous soils, Cupriavidus metallidurans is not only confronted with synergistic toxicity of copper ions and gold complexes but also by different gold species. A previously used gold solution made by using aqua regia resulted in the formation of periplasmic gold nanoparticles, and the cells were protected against gold toxicity by the periplasmic Cu(I) and Au(I) oxidase CopA. To understand the role of different gold species in the environment, another Au(III) solution was commercially acquired. This compound was more toxic due to a higher accumulation of gold atoms by the cells and inhibition of periplasmic Cu(I) homeostasis. Thus, the geo-biochemical conditions might influence Au(III) speciation. The resulting Au(III) species may subsequently interact in different ways with C. metallidurans and its copper homeostasis system in the cytoplasm and periplasm. This study reveals that the geochemical conditions may decide whether bacteria are able to form gold nanoparticles or not.

Dissolved black carbon mediated photo-reductive formation of colloidal-stable gold nanoparticles

Gold nanoparticles (AuNPs) have garnered attention as an emerging class of nanomaterials due to their wide range of applications across various sectors. This study reported that the dissolved black carbon (DBC) can mediate Au(III) photoreduction and form uniform and colloidal-stable AuNPs in aqueous solutions at room temperature under sunlight irradiation. Transmission electron microscopy images revealed that the average diameter of the photo-formed AuNPs was approximately 16 nm, and these nanoparticles maintained considerable colloidal-stability over time. Notably, no change in average size was observed following a 23-day storage period at 4°C in a light-free environment. The photo-formed superoxide (O2·-) is the crucial reductant in this reaction. O2·-, generated by DBC, reduces Au(III) to Au(I), which is then further reduced to Au(0), culminating in the formation of AuNPs. Furthermore, our findings illustrate that an increase in reaction pH shifts the predominant species of Au(III) in the solution toward forms with a lower redox potential, thereby decreasing the oxidizability of Au(III) and consequently decelerating the photoreduction process. A mildly acidic environment is more favorable for the DBC-mediated photoformation of AuNPs. This study elucidates that DBC can be observed as a novel reductant to complete the photo-reductive formation of AuNPs under low-cost conditions, opening up a new possibility for the green synthesis of AuNPs.

Synthesis of Gold Clusters and Nanoparticles Using Cinnamon Extract-A Mechanism and Kinetics Study.

In this work, UV-Vis spectrophotometry, High Resolution Scanning Transmission Electron Microscopes and selected experimental conditions were used to screen the colloidal system. The obtained results complement the established knowledge regarding the mechanism of nanoparticle formation. The process of gold nanoparticles formation involves a two-step reduction of Au ions to Au(0); atom association and metastable cluster formation; autocatalytic cluster growth; ultra-small particle formation (1-2 nm, in diameter); particle growth and larger particles formation; and further autocatalytic crystal growth (D > 100 nm). As a reductant of Au(III) ions, a cinnamon extract was used. It was confirmed that eugenol as one of the cinnamon extract compounds is responsible for fast Au(III) ion reduction, whereas cinnamaldehyde acts as a gold-particle stabilizer. Spectrophotometry studies were carried out to track kinetic traces of gold nanoparticle (D > 2 nm) formation in the colloidal solution. Using the Watzky-Finke model, the rate constants of nucleation and autocatalytic growth were determined. Moreover, the values of energy, enthalpy and entropy of activation for stages related to the process of nanoparticle formation (Index 1 relates to nucleation, and Index 2 relates to the growth) were determined and found to be E1 = 70.6 kJ, E2 = 19.6 kJ, ΔH1 = 67.9 kJ/mol, ΔH2 = 17 kJ/mol, ΔS1 = -76.2 J/(K·mol), ΔS2 = -204.2 J/(K·mol), respectively. In this work the limitation of each technique (spectrophotometry vs. HRSTEM) as a complex tool to understand the dynamic of the colloidal system was discussed.

Colorimetric Sensing of Antioxidant Capacity via Auric Acid Reduction Coupled to ABTS Oxidation.

In this study, a simple and sensitive colorimetric assay has been developed for total antioxidant capacity measurement. The assay is based on the absorption measurement of the bluish-green oxidized product (ABTS·+) formed as a result of the oxidation reaction of the chromogenic reagent ABTS (2,2'-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) with gold(III). However, in the presence of antioxidants, the ABTS oxidation process is effectively suppressed due to the reduction of gold(III) ions to the zerovalent state forming gold nanoparticles (AuNPs). Relatively lighter colors and a significant decrease in absorbance are observed depending on the total antioxidant capacity. Taking advantage of this situation, qualitative and quantitative total antioxidant capacity (TAC) measurements, with the naked eye and UV-vis spectroscopy, respectively, could be successfully performed. The assay is named "auric reducing antioxidant capacity" (AuRAC) because the gold(III) ion-reducing ability of antioxidants is measured. The AuRAC assay was applied to dietary polyphenols, vitamin C, thiol-type antioxidants, and their synthetic mixtures. Trolox equivalent antioxidant capacity (TEAC) values obtained with the AuRAC assay were found to be compatible with those of the reference CUPRAC (cupric reducing antioxidant capacity) assay. The AuRAC assay was validated through linearity, additivity, precision, and recovery, demonstrating that the assay is reliable and robust. Compared to the simple TAC assays in the literature based on AuNP formation with subsequent surface plasmon resonance (SPR) absorbance measurement, this indirect assay has a smoother linear range starting from lower antioxidant concentrations. This method displays much higher molar absorption coefficients for antioxidant compounds than other conventional single electron transfer (SET) assays because 3-e- reduction of trivalent gold (i.e., Au(III) → Au(0)) produces three chromophore cation radicals (ABTS·+) of the assay reagent. The sensor has been successfully applied to complex matrices, such as tea infusions and pharmaceutical samples. The AuRAC assay stands out with its high molar absorptivity connected to enhanced sensitivity as well as its potential to convert into a paper-based colorimetric sensor.

Biosynthesis of Gold Nanoparticles Using Aqueous Extract of Paramignya trimera Roots and Its Anticancer Activity

Developing environment-friendly processes for metal nanoparticle synthesis without using toxic chemical is very necessary to meet the demand for biological and medical applications. In this work, biosynthesis of gold nanoparticles (AuNPs) using aqueous extract of Paramignya trimera roots as the reducing and stability agents was carried out. The formation of gold nanoparticles was confirmed by the presence of an absorption peak at 550 nm using UV–Visible spectrophotometry. The size and morphology of gold nanoparticles was monitored by Field emission scanning electron microscopy (FE-SEM) and High resolution transmission electron microscopy (HR-TEM). Analysis of these particles showed the synthesized AuNPs were spherical in shape, with the particle size range of 10 nm–15 nm. The element gold and the crystalline nature of AuNPs were finalized using Energy dispersive X-ray (EDX) and X-ray diffraction (XRD) spectrometer, respectively. Fourier transform infrared (FTIR) spectroscopy revealed possible involvement of reductive groups on the surfaces of nanoparticles. The synthesized AuNPs are evaluated for its activity against MCF-7, HepG2, KB, LU-1 and MKN7 cancer cell lines with inhibition concentration 50% (IC50) of 2.01, 7.60, 3.89, 3.99 and 3.53 ppm respectively after 72 hours of treatment.

Peptide Stereochemistry Effects from pKa-Shift to Gold Nanoparticle Templating in a Supramolecular Hydrogel.

The divergent supramolecular behavior of a series of tripeptide stereoisomers was elucidated through spectroscopic, microscopic, crystallographic, and computational techniques. Only two epimers were able to effectively self-organize into amphipathic structures, leading to supramolecular hydrogels or crystals, respectively. Despite the similarity between the two peptides' turn conformations, stereoconfiguration led to different abilities to engage in intramolecular hydrogen bonding. Self-assembly further shifted the pKa value of the C-terminal side chain. As a result, across the pH range 4-6, only one epimer predominated sufficiently as a zwitterion to reach the critical molar fraction, allowing gelation. By contrast, the differing pKa values and higher dipole moment of the other epimer favored crystallization. The four stereoisomers were further tested for gold nanoparticle (AuNP) formation, with the supramolecular hydrogel being the key to control and stabilize AuNPs, yielding a nanocomposite that catalyzed the photodegradation of a dye. Importantly, the AuNP formation occurred without the use of reductants other than the peptide, and the redox chemistry was investigated by LC-MS, NMR, and infrared scattering-type near field optical microscopy (IR s-SNOM). This study provides important insights for the rational design of simple peptides as minimalistic and green building blocks for functional nanocomposites.

The effect of photolysis of sodium citrate treated with gold chloride using coloured light on the generation of gold nanoparticles and the repression of WiDr colon cancer cells

Gold nanoparticles (GNPs) are usually formed via a wet chemical method using gold (III) chloride trihydrate (GC), which is treated with stable reducing agents such as sodium citrate (SC). This study determines the effect of coloured light on the formation of GNPs by irradiation of SC after the addition of GC (SCGC) and the effect of the SCGC photolytic procedure on the suppression of WiDr colon cancer cells by forming reactive oxygen species. The absorbance of surface plasmon resonance peaks at 523 nm are 0.069 and 0.219 for SCGC when treated with blue light illumination (BLI) and violet light irradiation (VLI), respectively, whereas green and red light treatments have little or no effect. Most GNPs have diameters ranging from 3 to 15 nm, with a mean of 6 nm, when SCGC is exposed to VLI for 1.5 h. Anionic superoxide radicals (O2•−) are formed in a charge-transfer process after SCGC under VLI treatment; however, BLI treatment produces no significant reaction. Moreover, SCGC under VLI treatment proves to be considerably more effective at inhibiting WiDr cells than BLI treatment, as firstly reported in this study. The reduction rates for WiDr cells treated with SCGC under BLI and VLI at an intensity of 2.0 mW/cm2 for 1.5 h (energy dose, 10.8 J/cm2) are 4.1% and 57.7%, respectively. The suppression rates for WiDr cells treated with SCGC are inhibited in an irradiance-dependent manner, the inhibition percentages being 57.7%, 63.3%, and 80.2% achieved at VLI intensities of 2.0, 4.0, and 6.0 mW/cm2 for 1.5 h, respectively. Propidium iodide is a fluorescent dye that detects DNA changes after cell death. The number of propidium iodide-positive nuclei significantly increases in WiDr cells treated with SCGC under VLI, suggesting that SCGC photolysis under VLI is a potential treatment option for the photodynamic therapy process.

Tunable formation of gold nanoparticles on polymer by keV ion beam irradiation

The formation of nanostructures from a thin Au film deposited on a polystyrene and polymethylmethacrylate substrate under keV monatomic P, Ta and molecular PF4 ion irradiation is studied. The formation of nanoparticles on both kinds of polymers is shown. Heavy Ta ions are most effective in altering the Au layer, whereas its transformation by light P or molecular PF4 ions is less pronounced. Irradiation with PF4 ions has a much smaller effect on the PS and PMMA substrate bulk compared to that with monatomic P ions. The crucial role of collision cascade density in the process of thin metallic film coagulation on polymer substrate is revealed. During ion bombardment, transmitted IR light intensity increases proportionally to the area covered by the metal film, which makes it possible to use FTIR as a rapid technique to estimate the state of the nanoparticle formation process.

Impact of BSA and Au3+ concentration on the formation and fluorescence properties of Au nanoclusters.

Bovine serum albumin-stabilized Au nanoclusters (BSA-Au NCs) have emerged as promising contenders for imaging agents and highly sensitive fluorescence sensors due to their biocompatibility and strong photoluminescence. Optimizing the synthesis conditions of BSA-Au NCs is crucial for enhancing fluorescence imaging and other nanocluster applications. In this study, for the first time, we systematically investigated the effects of BSA concentration and Au3+ on both particle size and optical characteristics of BSA-Au NCs. When the two components achieved a suitable concentration ratio, it was beneficial to form BSA-Au NCs with a high quantum yield (QY = 74.30%) and good fluorescence stability. In contrast, an inappropriate concentration ratio would lead to the formation of gold nanoparticles (Au NPs), and their internal filtration effect (IFE) would attenuate the fluorescence emission of BSA-Au NCs. The BSA-Au NCs were then employed as efficient fluorescence sensors for detecting Hg2+. Furthermore, the growth mechanism of BSA-Au NCs was elucidated by monitoring fluorescence changes during different incubation times. The BSA-Au NCs with a high quantum yield introduce a novel synthetic concept for sensitive fluorescent probes and expanding versatile applications of BSA-Au NCs in catalysis, chemical sensing and biomedicine.

Group 11 complexes of a bulky triazene ligand.

A new triazene ligand was prepared by the reaction of the bulky aryl azide, TerMesN3, (2,6-bis(2,4,6-trimethylphenyl)phenyl azide), with the bulky N-heterocyclic carbene (NHC), SIPr (N,N'-2,6-bis(diisopropylphenyl)-3,4-dihydroimidazol-2-ylidene). The steric bulk of these two groups leads to perpendicular bonding of the NHC-N3 plane and the aryl group which provides immense steric crowding around the triazene core. The corresponding π-conjugated triazene ligand was utilized as a neutral, monodentate ligand which results in monomeric Cu(I)Cl, Ag(I)OTf, and Au(I)Cl complexes. Instability of the π-conjugated triazene Au(I)Cl complex was observed, even under inert conditions. When dissolved and photolyzed in THF with workup in isopropanol, the compound decomposes forming [(SIPrNH)2Au(I)][Au(I)Cl2] a relatively stable compound to light, moisture, and water - alongside the formation of gold nanoparticles which were characterized using scanning electron microscopy with energy dispersive spectroscopy.

Design of a gold nanoparticles site in an engineered lipase: an artificial metalloenzyme with enantioselective reductase-like activity.

The conjugation of gold complexes with proteins has proved to be interesting and effective in obtaining artificial metalloenzymes as catalysts with improved properties such as higher stability, activity and selectivity. However, the design and precise regulation of their structure as protein nanostructured forms level remains a challenge. Here, we have designed and constructed a gold nanoparticles-enzyme bioconjugate, by tailoring the in situ formation of gold nanoparticles (AuNPs) at two specific sites on the structure of an alkalophilic lipase from Geobacillus thermocatenulatus (GTL). For this purpose, two genetically modified variants of GTL were created by inserting a unique cysteine residue into the catalytic active site by replacing the active serine (GTL-114) and into the lid site (GTL-193). The enzyme, after a first protein-gold coordination, induced the in situ formation of AuNPs, generating a homogeneous artificial enzyme. The size and morphology of the nanoparticles in the AuNPs-enzyme conjugate have been controlled by specific pH conditions in synthesis and the specific protein region where they are formed. Reductase activity of all of them was confirmed in the hydrogenation of nitroarenes in aqueous media. The protein area seemed to be key for the AuNPs, with the best TOF values obtained for the bioconjugates with AuNPs in the lid site. Finally, the protein environment and the asymmetric properties of the AuNPs were tested in the reduction of acetophenone to 1-phenylethanol in aqueous medium at room temperature. A high reductive conversion and an enantiomeric excess of up to 39% towards (R)-1-phenylethanol was found using Au-Mt@GTL-114 pH 10 as a catalyst. Moderate enantioselectivity towards the opposite isomer was also observed using the Au-Mt@GTL-193 pH 10 conjugate.

Solution-based Supramolecular Hierarchical Assembly of Frenkel Excitonic Nanotubes Driven by Gold Nanoparticle Formation and Temperature.

Translating nature's successful design principle of solution-based supramolecular self-assembling to broad applications─ranging from renewable energy and information technology to nanomedicine─requires a fundamental understanding of supramolecular hierarchical assembly. Though the forces behind self-assembly (e.g., hydrophobicity) are known, the specific mechanism by which monomers form the hierarchical assembly still remains an open question. A crucial step toward formulating a complete mechanism is understanding not only how the monomer's specific molecular structure but also how manifold environmental conditions impact the self-assembling process. Here, we elucidate the complex correlation between the environmental self-assembling conditions and the resulting structural properties by utilizing a well-characterized model system: well-defined supramolecular Frenkel excitonic nanotubes (NTs), self-assembled from cyanine dye molecules in aqueous solution, which further self-assemble into bundled nanotubes (b-NTs). The NTs and b-NTs inhabit distinct spectroscopic signatures, which allows the use of steady-state absorption spectroscopy to monitor the transition from NTs to b-NTs directly. Specifically, we investigate the impact of temperature (ranging from 23 °C, 55 °C, 70 °C, 85 °C, up to 100 °C) during in situ formation of gold nanoparticles to determine their role in the formation of b-NTs. The considered time regime for the self-assembling process ranges from 1 min to 8 days. With our work, we contribute to a basic understanding of how environmental conditions impact solution-based hierarchical supramolecular self-assembly in both the thermodynamic and the kinetic regime.

Optimization of Gold Nanoparticles Electrodeposition Duration on Screen Printed Electrode to Enhance Electrochemiluminescence of Nitrogen-doped Carbon Dots

In this work, the electrodeposition method was utilized to form gold nanoparticles on a carbon screen-printed electrode (SPE) using chronoamperometry at -0.4 V with various durations from 50 to 200 seconds. Scanning Electron Microscopy (SEM) images have proven that the electrodeposition method is capable of uniformly forming AuNPs on SPE (AuNPs- SPE). Apart from that, electrodeposition durations have increased the size of AuNPs by up to 66% based on average size measurements using ImageJ software. It can be observed that long electrodeposition durations permit the agglomeration of AuNPs on the electrode surface. The effect of electrodeposition duration on electrocatalytic performance in potassium ferricyanide and electrochemiluminescence (ECL) intensity of nitrogen-doped carbon dots (NCDs) was evaluated. Cyclic voltammetry (CV) of ferricyanide demonstrates that as the electrodeposition duration increases, AuNPs-SPE shows better electrochemical performance than bare SPE. ECL of NCDs displays that 100 s electrodeposition durations give the highest ECL intensity of 184% compared to bare SPE and have been chosen as the optimum parameter. The ECL mechanisms of bare SPE and AuNPs-SPE reveal that AuNPs- SPE has greater electrochemical and ECL performance than bare SPE, as evidenced by the CV of AuNPs-SPE having a faster reduction current, which rises to 87.2% ECL intensity and 510 mV faster ECL occurrence. These phenomena confirmed that the electrodeposition of AuNPs has improved the conductivity of SPE.

Anisotropic Gold Nanoparticles Synthesized using Litchi chinensis Leaf Extract and their Effect on Breast Cancer

For its medicinal potential, especially in cancer therapy, eco-friendly gold nanoparticles (GNPs) have gained a lot of interest. This investigation used Litchi chinensis leaf extract (LLE) as a reducing agent for the one-step synthesis of regulated-size GNPs. Fourier transform infrared (FTIR) spectrum shows that the bio-molecules act as capping and reducing agents. The formation of GNPs has been confirmed using UV-vis absorption spectra. Effect of various synthesized parameters, i.e., reaction time (5–120 minutes), temperature (25–100°C), solvent quantity (5–45 μL), metal ion concentration (0.25–2 mM) and pH (2–10) has been studied. The size, distribution, and morphology (anisotropic) have been studied using field emission scanning electron microscopy (FESEM) and dynamic light scattering (DLS) techniques in the range of 10 to 70 nm. X-Ray diffraction (XRD) reveals that the particles were crystalline and had face-centered cubic (FCC) structure, and transmission electron microscopy (TEM) images revealed anisotropic morphology (spherical, hexagonal, and triangular). In-vitro studies of GNPs on breast cancer cell lines show cytotoxicity with cellular structural alterations and caused DNA damage without the micronuclei formation.

The high-efficiency PEC material prepared by porphyrin grafted with Au nanoparticles embedded in porous carbon for PTK-7 detection

Photoelectrochemical (PEC) analysis has attracted accumulated attention on diagnosis of diseases and high-efficiency photosensitizers are urgently needed. In this work, N-doped sheet-like porous carbon (N-PC) was prepared by thermal stripping of Zn2+ from zeolitic imidazole framework-8 (ZIF-8), followed by in situ formation of gold nanoparticles (Au NPs) embedded in the N-PC (termed Au NPs@N-PC). Also, the zinc meso-tetra (4-carboxyphenyl) porphine (ZnP) behaved as photosensitizer, which was covalently linked with Au NPs@N-PC (ZnP-Au NPs@N-PC), achieving the 9.2-fold enhancement in the photocurrents by using dopamine (DA) as donor. Next, the PEC mechanism was strictly discussed by UV–vis diffuse reflectance (DLS) spectroscopy, fluorescence (FL) and density functional theory (DFT) calculations. By virtue of the excellent PEC property, a label-free “signal off” PEC aptasensor was constructed based on the ZnP-Au NPs@N-PC for ultrasensitive detection of protein tyrosine kinase (PTK-7). The established biosensor showed a wider linear range of 10.00 pg mL−1 to 1.00 μg mL−1 (R2 = 0.99) and a lower limit of detection (LOD, 1.42 pg mL−1), coupled by showing acceptable results for diagnosis of gliomas. Hence, this research opens a valuable avenue for synthesis of advanced photosensitizer and holds huge potential in biomedical field.

Polyhydroxy Fullerene for Synthesizing Noble Metal Nanoparticles

The redox properties of fullerene and its derivatives enable them to function as electron relays through either oxidation or reduction. Polyhydroxy fullerene (PHF), also known as fullerol or fullerenol, is highly water-soluble derivative and a well-known antioxidant. We have found that PHF is also very effective in reducing noble metal precursors and stabilizing metal nanoparticles by forming covalent M-O bonds. Traditionally, noble metal nanoparticles, such as gold are synthesized using a reducing agent like sodium borohydride (NaBH4) or sodium citrate at elevated temperatures and alkaline pH, with stabilizers added during nucleation to control the size and dispersion of the nanoparticles. While sodium citrate is sometimes used as a single reducing and stabilizing agent, it is not an effective stabilizer and is often replaced with polymers to improve colloidal dispersion. In contrast, PHF can be used as a single reducing and stabilizing agent for metal nanoparticles. The nanoparticles were synthesized by simply mixing the metal precursors with PHF in an aqueous phase and stirring at room temperature. The size and morphology of synthesized nanoparticles were characterized with high-resolution transmission electron microscopy, aberration corrected TEM, and dynamic light scattering. These nanoparticles were monodisperse with size ranging from 2 nm to 100 nm in diameter, which could be controlled by changing the concentration of the two reactants. We utilized multiple tools to investigate the mechanism of reduction and nanoparticle formation. We propose a kinetic agglomerate-dissociation mechanism to describe the formation of gold nanoparticles using PHF. Kinetic agglomerates form instantaneously upon mixing the two reactants due to electrostatic interactions. During the reduction process reactive carbonyl peaks were observed with electron energy loss spectroscopy. The carbonyl moieties were observed only after agglomerate formation and subsequently changed to Au-O bonds between PHF and synthesized gold nanoparticles, which was confirmed with Fourier-transform infrared spectroscopy and density-functional theory calculations, and X-ray photoelectron spectroscopy. Further, we demonstrated that the synthesis of gold nanoparticles using PHF can be affected by pH due to changes in hemiketal structure of PHF. Compared to citrate ions, PHF-coated gold nanoparticles are more stable, remaining so for over two years. The novel PHF-mediated synthesis method can also be applied to other noble metals like platinum, palladium, and silver and create bimetallic nanoparticles. The surface PHF coating on noble metal nanoparticles integrates the properties of both metal and carbon nanoparticles, resulting in superior functional applications. Our findings open up new opportunities for metallic nanoparticle preparation methods, properties, and applications.

Tungsten-based polyoxometalate nanoclusters with remarkable reactive oxygen species-scavenging activity efficiently quenched luminol-based electrochemiluminescence for sensitive detection of Her-2.

This study aimed to develop a quenching-type electrochemiluminescence (ECL) immunosensor for human epidermal growth factor receptor (Her-2) detection. Firstly, Pd/NiFeOx nanoflowers decorated by in situ formation of gold nanoparticles (Au NPs) and 2D Ti3C2 MXene nanosheets were synthesized (AuPd/NiFeOx/Ti3C2) as carriers to load luminol and primary antibodies. Impressively, AuPd/NiFeOx/Ti3C2 with excellent peroxidase-like activity could accelerate the decomposition of the coreactant H2O2 generating more reactive oxygen species (ROSs) under the working potential from 0 to 0.8V, resulting in highly efficient ECL emission at 435-nm wavelengths. Theintroduction of tungsten-based polyoxometalate nanoclusters (W-POM NCs) which exhibit remarkable ROSs-scavenging activity as secondary antibody labels could improve the sensitivity of immunosensors. TheZnO nanoflowers were employed to encapsulate minute-sized W-POM NCs, and polydopamine was self-polymerized on the surface of Zn(W-POM)O to anchor secondary antibodies. The mechanism of the quenching strategy was explored and it was foundthat W-POM NCs could consume ROSs by the redox reaction of W5+ resulting in W6+. The proposed ECL immunosensor displayed a wide linear response range of 0.1pg·mL-1 to 50ng·mL-1, and a low detection limit of 0.036pgmL-1 (S/N = 3). The recoveries ranged from 93.9 to 99.4%, and the relative standard deviation (RSD) was lower than 10%. This finding is promising for the design of detecting new protein biomarkers.

Phytosynthesizing gold nanoparticles: Characterization, bioactivity, and catalysis evaluation

Worldwide health problem generally due to the lack of widespread and comprehensive early detection methods, the associated poor prognosis of patients diagnosed in later stages of the disease and its increasing incidence on a global scale. Indeed, the struggle to fight cancer is one of the greatest challenges of mankind. Centella Asiatica (CA) and Andrographis Paniculata (AP) are two medicinal plant extracts used in the environmentally friendly extracellular production of metallic gold nanoparticles. The size, shape, stability and crystallinity of the synthesized gold nanoparticles were characterised and various characterization methods were used; UV–Vis spectroscopy, Fourier Transform Infrared Spectroscopy, X-ray diffraction, Zeta potential, Selected Area Electron Diffraction, Energy Dispersive X-ray Spectroscopy, High Resolution Transmission Electron Microscopy equipped with elemental mapping in order to confirm the formation of gold nanoparticles. The TEM results showed that gold nanoparticles were mostly spherical in shape. Their effects on anti-bacterial, catalytic, photocatalytic and anticancer cell lines were examined. The MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide] test was used to confirm the cytotoxic properties of both gold nanoparticles samples and the results showed that both the human lung cancer and human breast cancer cell line growth and proliferation were inhibited. Strong antibacterial activity against gram-negative bacteria and moderate antibacterial activity against gram-positive bacteria were identified. It has also been shown that gold nanoparticles have catalytic properties for reducing 4-nitrophenol to 4-aminophenol. By degrading the two dyes methyl orange and congo red in the presence of nano catalysts, the photocatalytic activity of synthesized nanoparticles has been assessed.