Gold Salts Research Articles

Mechanistic insights of the reduction of gold salts in the Turkevich protocol.

This paper presents fundamental understanding of the mechanism of the Turkevich protocol, the method recommended by the National Institute of Standards and Technology for the synthesis of gold nanoparticles using sodium citrate as reducing agent. Herein, we reveal that the Turkevich mechanism consists of two consecutive reduction steps (Au3+→ Au+→ Au0) rather than a reduction followed by the disproportionation reaction as conventionally believed. This new understanding has profound implications: i. the second reduction step (Au+→ Au0), rather than the previously postulated first reduction step, is the rate-limiting reduction step and ii. the formation of acetone dicarboxylate (DC2-) as an intermediate product through the oxidation of citrate has a key role as stabilizer and as a reducing agent (stronger than sodium citrate). This knowledge enables the synthesis of monodispersed gold nanoparticles with sizes ranging from 5.2 ± 1.7 nm to 21.4 ± 3.4 nm, with the lower end considerably smaller than previously reported through the Turkevich route. This work provides fundamental guidance for the controllable synthesis of nanoparticles using DC2- as a reducing agent directly applicable to other precious metals.

Photothermal conversion of SiO2@Au nanoparticles mediated by surface morphology of gold cluster layer.

Photothermal effects in SiO2@Au core–shell nanoparticles have demonstrated great potential in various applications for drug delivery, thermo-photovoltaics and photothermal cancer therapy, etc. However, the photothermal conversion of SiO2@Au nanoparticles partially covered by disconnected gold clusters has rarely been investigated systematically. Here, we control the surface morphology of gold clusters on the photothermal conversion performance of SiO2@Au core–shell nanoparticles by means of chemically adjusting the synthesis parameters, including amounts of gold salts, pH value and reducing agent. The macroscopic variations of the photothermal heating of different nanoparticle dispersions are significantly influenced by the nanoscale differences of gold cluster morphologies on the silica core. The temperature rise can be enhanced by the strong near-field coupling and collective heating among gold clusters with a relatively uniform distribution on the silica core. A numerical model of the simplified photothermal system is formulated to interpret the physical mechanism of the experimental observation, and shows a similar trend of temperature rise implying a reasonably good agreement with experimental data. Our work opens new possibilities for manipulating the light-to-heat conversion performance of SiO2@Au core–shell nanoparticles and potential applications of heat delivery with spatial resolution on the nanoscale.

In situ preparation of gold-polyester nanoparticles for biomedical imaging.

The synthesis and application of gold nanoparticles (AuNPs) have attracted much attention due to their interesting optical and chemical properties, as well as their utility in imaging, therapeutics, sensors, electronics, and catalysis. AuNPs are synthesized using multiple approaches, followed by chemical modification or encapsulation, to enhance their colloidal stability, biocompatibility, and targeting. Here, we report the one-step synthesis of gold-polyester nanoparticles for use as an imaging agent. The AuNPs were prepared inside polymeric NPs by means of ultraviolet irradiation of a gold salt in the presence of Irgacure I-2959 photoinitiator. We monitored the kinetic growth and nucleation of AuNPs (in vitro and ex vivo) over time using spectral analysis. Moreover, we investigated the cytotoxicity, localized plasmonic surface resonance (LSPR), and cellular imaging capabilities of the Au-polyester nanoparticles. The resulting Au-polyester NPs were characterized by Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), X-ray diffraction (XRD), dynamic light scattering (DLS), and transmission electron microscopy (TEM) to probe their chemical structure, size, zeta potential (ζ), and morphology, respectively. Furthermore, in vitro experiments showed that the NP formulation is stable over time and exhibits negligible toxicity against 3T3 fibroblast and U-87 MG glioblastoma cells. The results also demonstrated that the Au-polyester NPs exhibit excellent cellular imaging properties. This one-step strategy goes beyond current syntheses of gold-polyester nanoparticles because it can be used to synthesize the imaging agent in situ (i.e., in living cells) in lieu of conventional ex situ approaches.

A synthetic protocol for (−)-ketorolac; development of asymmetric gold(I)-catalyzed cyclization of allyl alcohol with pyrrole ring core

An asymmetric synthesis of (−)- and (+)-ketorolac was achieved with 89% ee using a novel Friedel–Crafts (FC) type C–C bond forming cyclization of an allyl alcohol containing a pyrrole ring core in the presence of a bimetallic gold(I) salt complex prepared from a 2:2:1 combination of AuCl·SMe2, AgOTf and chiral Quinaphos.

Unexpected intracellular biodegradation and recrystallization of gold nanoparticles

Gold nanoparticles are used in an expanding spectrum of biomedical applications. However, little is known about their long-term fate in the organism as it is generally admitted that the inertness of gold nanoparticles prevents their biodegradation. In this work, the biotransformations of gold nanoparticles captured by primary fibroblasts were monitored during up to 6 mo. The combination of electron microscopy imaging and transcriptomics study reveals an unexpected 2-step process of biotransformation. First, there is the degradation of gold nanoparticles, with faster disappearance of the smallest size. This degradation is mediated by NADPH oxidase that produces highly oxidizing reactive oxygen species in the lysosome combined with a cell-protective expression of the nuclear factor, erythroid 2. Second, a gold recrystallization process generates biomineralized nanostructures consisting of 2.5-nm crystalline particles self-assembled into nanoleaves. Metallothioneins are strongly suspected to participate in buildings blocks biomineralization that self-assembles in a process that could be affected by a chelating agent. These degradation products are similar to aurosomes structures revealed 50 y ago in vivo after gold salt therapy. Overall, we bring to light steps in the lifecycle of gold nanoparticles in which cellular pathways are partially shared with ionic gold, revealing a common gold metabolism.

Poly(vinyl alcohol) triggers Au nanoparticles formation for near‐infrared radiation‐responsive gels and nanofibers

ABSTRACTThe capability of poly(vinyl alcohol) (PVA) to reduce noble metal ions and, in turn, to prepare one‐step hybrid systems that exhibit near‐infrared radiation (NIR) light‐responsiveness has been barely explored. The aim of this work was to elucidate whether gold nanoparticles (Au NPs) could be spontaneously formed in PVA gels suitable to be used as syringeable depots or to prepare electrospun nanofibers. To check the hypothesis of that the gold counterion may play a role in the Au NPs formation process, two different gold salts (HAuCl4 and AuAc3) were used. Localized surface plasmon resonance bands were monitored during the incubation of PVA‐gold salt gels, and the photoresponsive capability of the newly formed Au NPs inside gels was investigated during laser irradiation at 808 nm. HET‐CAM assay suggested good biocompatibility. Then, the feasibility of producing electrospun hybrid PVA‐based mats that exhibit light‐responsive photothermal features was explored here for the first time. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020, 137, 48811.

Green pyomelanin-mediated synthesis of gold nanoparticles: modelling and design, physico-chemical and biological characteristics

BackgroundSynthesis of nanoparticles (NPs) and their incorporation in materials are amongst the most studied topics in chemistry, physics and material science. Gold NPs have applications in medicine due to their antibacterial and anticancer activities, in biomedical imaging and diagnostic test. Despite chemical synthesis of NPs are well characterized and controlled, they rely on the utilization of harsh chemical conditions and organic solvent and generate toxic residues. Therefore, greener and more sustainable alternative methods for NPs synthesis have been developed recently. These methods use microorganisms, mainly yeast or yeast cell extract. NPs synthesis with culture supernatants are most of the time the preferred method since it facilitates the purification scheme for the recovery of the NPs. Extraction of NPs, formed within the cells or cell-wall, is laborious, time-consuming and are not cost effective. The bioactivities of NPs, namely antimicrobial and anticancer, are known to be related to NPs shape, size and size distribution.ResultsHerein, we reported on the green synthesis of gold nanoparticles (AuNPs) mediated by pyomelanin purified from the yeast Yarrowia lipolytica. A three levels four factorial Box–Behnken Design (BBD) was used to evaluate the influence of temperature, pH, gold salt and pyomelanin concentration on the nanoparticle size distribution. Based on the BBD, a quadratic model was established and was applied to predict the experimental parameters that yield to AuNPs with specific size. The synthesized nanoparticles with median size value of 104 nm were of nanocrystalline structure, mostly polygonal or spherical. They exhibited a high colloidal stability with zeta potential of − 28.96 mV and a moderate polydispersity index of 0.267. The absence of cytotoxicity of the AuNPs was investigated on two mammalian cell lines, namely mouse fibroblasts (NIH3T3) and human osteosarcoma cells (U2OS). Cell viability was only reduced at AuNPs concentration higher than 160 µg/mL. Moreover, they did not affect on the cell morphology.ConclusionOur results indicate that different process parameters affect significantly nanoparticles size however with the mathematical model it is possible to define the size of AuNPs. Moreover, this melanin-based gold nanoparticles showed neither cytotoxicity effect nor altered cell morphology.

Preparation and Deep Characterization of Composite/Hybrid Multi-Scale and Multi-Domain Polymeric Microparticles.

Polymeric microparticles were produced following a three-step procedure involving (i) the production of an aqueous nanoemulsion of tri and monofunctional acrylate-based monomers droplets by an elongational-flow microemulsifier, (ii) the production of a nanosuspension upon the continuous-flow UV-initiated miniemulsion polymerization of the above nanoemulsion and (iii) the production of core-shell polymeric microparticles by means of a microfluidic capillaries-based double droplets generator; the core phase was composed of the above nanosuspension admixed with a water-soluble monomer and gold salt, the shell phase comprised a trifunctional monomer, diethylene glycol and a silver salt; both phases were photopolymerized on-the-fly upon droplet formation. Resulting microparticles were extensively analyzed by energy dispersive X-rays spectrometry and scanning electron microscopy to reveal the core-shell morphology, the presence of silver nanoparticles in the shell, organic nanoparticles in the core but failed to reveal the presence of the gold nanoparticles in the core presumably due to their too small size (c.a. 2.5 nm). Nevertheless, the reddish appearance of the as such prepared polymer microparticles emphasized that this three-step procedure allowed the easy elaboration of composite/hybrid multi-scale and multi-domain polymeric microparticles.

Coinage Metal (Bisfluorosulfonyl)imide Complexes: Preparation, Characterization, and Catalytic Applications

Triflate (–OTf) and triflimide (–NTf2) represent two most widely used weakly coordinating counteranions in transition metal catalysis, yet their high price hinders large‐scale application. Herein, we report the preparation, characterization, and catalytic applications of silver(I), gold(I), and copper(II) (bisfluorosulfonyl)imide (–FSI) complexes, showing –FSI as a low cost alternative of –OTf and –NTf2. These complexes, including AgFSI·2MeCN (1), AgFSI·MeCN (2), AgFSI·H2O (3), (AgFSI)6·(H2O)4 (4), AgFSI (5), LAuFSI (6a–6e), and CuFSI2·4H2O (7), are prepared conveniently starting from KFSI, an inexpensive chemical, and shown interesting structural features and some unprecedented coordination modes. In comparison with the corresponding coinage metal triflimides, the FSI complexes have exhibited comparable or better catalytic performance in a series of the model chemical transformations.

Fabrication and characterization of conductive silk fibroin–gold nanocomposite films

This research proposes a one-step fabrication of novel conducting silk fibroin (SF) nanocomposites (NCs) in which in situ generation of nanoparticles from their precursor are achieved. Here, the gold salt (HAuIIICl4·H2O) is reduced to gold nanoparticles (AuNPs) using SF, a renewable natural biopolymer, and SF–AuNPs NCs are developed via solution casting method. The optical absorption spectra recorded using the UV–Visible spectroscopy (UV–Vis) witnesses the generation of anisotropic particles by showing two absorption bands. Also, the calculated optical band gap energy (Eg) value decreases from 4.2 to 2.4 eV with the increasing concentration of AuNPs. The X-ray diffraction (XRD) profile of the NCs confirms the presence of AuNPs. The scanning electron microscopy (SEM) micrographs clearly admit the successful formation of AuNPs in the host polymer matrix with homogeneous dispersion. The size and evolution of the different shaped AuNPs are confirmed by the transmission electron microscopy (TEM) study. An increase in DC conductivity from 1.48 × 10−9 to 7.12 × 10−9 S/cm and decrease in frequency-dependent dielectric constant are observed with the increase in AuNPs. The obtained result suggests that the insulating behaviour of the SF can be effectively changed into a conducting nature with the in situ creation of AuNPs in the SF matrix.

Comparative study of the antitumoral activity of phosphine-thiosemicarbazone gold(I) complexes obtained by different methodologies

A series of phosphino-thiosemicarbazone gold(I) dinuclear complexes obtained by two different synthetic procedures have been prepared. All the compounds have been spectroscopically characterized including single crystal X ray diffraction analysis in some of cases. [Au2(HL1)Cl2] (1), [Au2(HL2)2]Cl2 (2) and [Au2(HL3)2]Cl2 (3) have been prepared by chemical synthesis using a gold(III) salt as precursor; while [Au2(L1)2] (4), [Au2(L2)2]∙2CH3CN (5) and [Au2(L3)2] (6) have been isolated from an electrochemical synthesis (HLn = 2-[2-(diphenylphosphanyl)-benzylidene]-N-R-thiosemicarbazone; HL1: R = methyl, HL2: R = methoxyphenyl, HL3: R = nitrophenyl). The in vitro cytotoxic activity of these gold(I) complexes was tested against some human tumor cell lines: HeLa 229 (cervical epithelial carcinoma), MCF-7 (ovarian adenocarcinoma), NCI-H460 (non-small-cell lung cancer) and MRC5 (normal human lung fibroblast), and the IC50 values compared with those of cisplatin. The neutral methyl-substituted complexes 1 and 4 and methoxyphenyl 5 displayed significant cytotoxic activities in all investigated cancer cell lines, being 1 and 4 the most effective. The ability of complexes 1 and 4 to induce cell death by apoptosis in Hela 229 was also investigated by fluorescence microscopy using the apoptotic DNA fragmentation as marker. These results indicated that the inhibition of cell proliferation is mainly due to an apoptotic process. In order to obtain more information about the mechanism of action of these metallocompounds, the interactions of complexes 1 and 4 with the thioredoxin reductase (TrxR) enzyme were analyzed. Both complexes exhibited a strong inhibition of the thioredoxin reductase activity.

The Influence of the Parameters of a Gold Nanoparticle Deposition Method on Titanium Dioxide Nanotubes, Their Electrochemical Response, and Protein Adsorption.

The goal of this research was to find the best conditions to prepare titanium dioxide nanotubes (TNTs) modified with gold nanoparticles (AuNPs). This paper, for the first time, reports on the influence of the parameters of cyclic voltammetry process (CV) -based AuNP deposition, i.e., the number of cycles and the concentration of gold salt solution, on corrosion resistance and the capacitance of TNTs. Another innovation was to fabricate AuNPs with well-formed spherical geometry and uniform distribution on TNTs. The AuNPs/TNTs were characterized using scanning electron microscopy, X-ray photoelectron spectroscopy, electrochemical impedance spectroscopy, and open-circuit potential measurement. From the obtained results, the correlation between the deposition process parameters, the AuNP diameters, and the electrical conductivity of the TNTs was found in a range from 14.3 ± 1.8 to 182.3 ± 51.7 nm. The size and amount of the AuNPs could be controlled by the number of deposition cycles and the concentration of the gold salt solution. The modification of TNTs using AuNPs facilitated electron transfer, increased the corrosion resistance, and caused better adsorption properties for bovine serum albumin.

Experimental and theoretical study of biodirected green synthesis of gold nanoflowers

We report a very simple, green, and eco-friendly route to synthesize three-dimensional branched gold nanoflowers (AuNFs). The process involved reduction of gold salt in presence of two naturally occurring small biomolecules viz.l-tyrosine and sodium citrate which act as mild reducing and shape-directing agent. A detailed picture of the formation mechanism of AuNFs has been proposed after thorough experimental analysis (electron microscopy, X-ray photoelectron spectroscopy [XPS], circular dichroism [CD], UV-vis spectroscopy, dynamic light scattering [DLS] and nanoparticle tracking analysis [NTA]) as well as by theoretical simulations (cellular automata and diffusion-limited aggregation [DLA] simulations). Experimental analysis and numerical simulation pointed out that l-tyrosine molecules self-assemble in a complex way which controls the flower-like shape and structure, whereas trisodium citrate plays a crucial role in controlling the particle diameter. A second shape (quasi-spherical) could also be obtained with same formulation by just changing the sequence of addition of reactants. As such the effect of the shape on surface enhanced Raman spectroscopy [SERS] enhancement has also been evaluated. Finally, in vitro studies were performed on a model cell line of mouse brain endothelium (bEnd.3) to assess biocompatibility.

Nanostructured Hematite Decorated with Gold Nanoparticles for Functionalization and Biocompatibility

Iron oxides have attracted the attention of researchers due to their abundance, low cost, low toxicity, and versatility of applications. According to the composition and crystalline structure, iron oxides may have characteristics of semiconductors and magnetic materials, such as hematite (α‐Fe2O3) and magnetite (Fe3O4), respectively. The property of biocompatibility of hematite is essential to be applied in the construction of micro‐/nanorobots (MNRs). Herein, the decoration of hierarchically structured core/shell Fe3O4/Fe2O3 microtubes and foils with gold nanoparticles (AuNPs) for functionalization and enhancement of biocompatibility that favor the use in MNR fabrication is presented. In this case, the synthesis of AuNPs takes advantage of the capacity of hematite to reduce Au3+ photochemically under excitation by a sunlight simulator. The yield of AuNPs covering the microtube surface is dependent on the gold salt concentration used for the synthesis. The AuNP‐decorated hematite surfaces of the microtube and foil are functionalized with thiol poly(ethylene glycol) fluorescein, exhibiting increase in conductivity favored by irradiation with visible light. AuNPs also favor cell adherence and proliferation with the maintenance of mitochondrial transmembrane potential. Therefore, the hematite surface of the microtubes decorated with AuNPs is a promising material for the application in micro‐/nanorobots and bioelectronics.

Biogenic Gold Nanoparticles from Fusarium oxysporum: The Impact of Fungal Morphology and Localization Studies

The synthesis of nanoparticles from biological sources has gained significant attention recently, however, with much emphasis on the novelty of sources. This study aims to provide a comprehensive overview on the aspects of fungal age and type of cultivation on the properties of the nanoparticles. The effect of age of Fusarium oxysporum developed in submerged culture and on solid agar medium was evaluated. When the gold salt solution was added to the fungal colony on agar medium, a deep purple colored radial zone developed in the 3 days old mycelium. The nanoparticles in the radial purple zone had two distinct characteristics when the agar blocks were dried by either lyophilization or heating in a hot air oven. The lyophilized sample contained square bi-pyramidal particles (1 to 2 μm). The oven-dried sample contained abundant truncated triangular nanoplates (150 to 500 nm), decahedrons and icosahedrons (20 to 70 nm), and a few triangular and hexagonal nanoplates (50 nm). The mycelium when suspended in 1 mM HAuCl4·3H2O presented distinct geometries of the nanoparticles in the cytoplasm and periplasm. The formation of gold nanoparticles of different morphologies within the cytoplasm, and the periplasm has implications in Surface Enhanced Raman Spectroscopic (SERS) measurements. HRTEM images of hyphae of Fusarium oxysporum suspended in 1 mM HAuCl4·3H2O for 24 h. The nanoparticles present in the electron dense cytoplasm are markedly different from those in the periplasmic space.

Chiral N-heterocyclic Carbene Gold Complexes: Synthesis and Applications in Catalysis

N-Heterocyclic carbenes have found many applications in modern metal catalysis, due to the formation of stable metal complexes, and organocatalysis. Among a myriad of N-heterocyclic carbene metal complexes, gold complexes have gained a lot of attention due to their unique propensity for the activation of carbon-carbon multiple bonds, allowing many useful transformations of alkynes, allenes, and alkenes, inaccessible by other metal complexes. The present review summarizes synthetic efforts towards the preparation of chiral N-heterocyclic gold(I) complexes exhibiting C2 and C1 symmetry, as well as their applications in enantioselective catalysis. Finally, the emerging area of rare gold(III) complexes and their preliminary usage in asymmetric catalysis is also presented.

Magnetic/Gold Core-Shell Hybrid Particles for Targeting and Imaging-Guided Photothermal Cancer Therapy.

The development of hybrid particles for tumor diagnosis and therapy has received considerable attention because they are capable of combining tumor diagnosis and treatment concurrently. So far hybrid particles for efficient and safe tumor theranostics are still very limited. Herein we have designed a new type of hybrid particles and evaluated its potential to be used in image-guided cancer diagnosis and therapy without the need of any toxic anticancer or contrast agents. The hybrid particles, consist of magnetic nanoparticles which are embedded in the poly(methyl methacrylate) (PMMA) cores and gold shells on chitosan (CTS) (γ-Fe₂O₃ @PMMA/CTS@Au). The hybrid particles were synthesized through initial formation of the core-shell structured γ-Fe₂O₃ @PMMA/CTS particles containing approximately 20% loading of magnetic nanoparticles. A gold layer was then built on top of the core-shell magnetic particles via a reduction of gold salt by amines from the chitosan assisted with the reducing agent NaBH₄, followed by growing to complete gold shells in the presence of ascorbic acid (42.6% Au content). The properties of the composite particles including their chemical composition, morphology, particle size, size distribution, surface charge, magnetic responsiveness and photothermal ability were systematically characterized. The potential application of the γ-Fe₂O₃ @PMMA/CTS@Au hybrid particles in tumor diagnosis and therapy was assessed in vitro and in vivo using 4T1 tumor cells and 4T1 tumor-bearing mice through combining magnetic targeting, photoacoustic (PA)/computed tomography (CT) imaging and photothermal therapy. Results suggest that the γ-Fe₂O₃ @PMMA/CTS@Au particles can serve as a multifunctional tumor theranostic nanoplatform for magnetically targeted photothermal therapy. Breast cancer has been effectively eliminated without the use of any anticancer drugs or contrast agents. Therefore, this type of core-shell hybrid particles represents a new composite particle design for effective and safe tumor theranostics.

Protein-facilitated gold nanoparticle formation as indicators of ionizing radiation.

The use of X-ray radiation in radiotherapy is a common treatment for many cancers. Despite several scientific advances, determination of radiation delivered to the patient remains a challenge due to the inherent limitations of existing dosimeters including fabrication and operation. Here, we describe a colorimetric nanosensor that exhibits unique changes in color as a function of therapeutically relevant radiation dose (3-15 Gy). The nanosensor is formulated using a gold salt and maltose-binding protein as a templating agent, which upon exposure to ionizing radiation is converted to gold nanoparticles. The formation of gold nanoparticles from colorless precursor salts renders a change in color that can be observed visually. The dose-dependent multicolored response was quantified through a simple ultraviolet-visible spectrophotometer and the peak shift associated with the different colored dispersions was used as a quantitative indicator of therapeutically relevant radiation doses. The ease of fabrication, visual color changes upon exposure to ionizing radiation, and quantitative read-out demonstrates the potential of protein-facilitated biomineralization approaches to promote the development of next-generation detectors for ionizing radiation.

Facile protic hydration of acetonitrile to protonated acetamide at oxygen mediated by chloroauric acid: insights from experimental and calculations

Chemical transformations such as nitrile hydration or carbon–oxygen bond formation reactions under gentle conditions are important in the pharmaceutical industry because of the presence of potentially delicate functional groups. We present a non-catalytic hydration reaction of acetonitrile to the corresponding protonated acetamide gold(III) salt [CH3(OH)NH2]AuCl4 under ambient conditions in water using chloroauric acid H[AuCl4] for the first time. ATR-FTIR, Raman and 1H and 13C NMR spectroscopic data in addition to X-ray crystallography supported the isolation of protonated acetamide stabilized with [AuCl4]− anion. The protonation of N–C=O fragment of acetamide, O- versus N-protonation aptitude, was validated experimentally and theoretically. The X-ray crystal structure of the acetamide salt [CH3C(OH)NH2]AuCl4 in the triclinic Pī space group suggested the enolic form. However, the reaction of gold(III) trichloride AuCl3 with acetonitrile in water in the absence of a proton source formed the gold(I)/gold(III) salt [Au(CH3CN)2]AuCl4 without hydration as shown in X-ray structure in the monoclinic P21/c space group. Mapping of HOMO–LUMO energy gap using frontier molecular orbital theory and MESP surfaces of OH and NH conformers of acetamide from DFT calculations clearly shows subsequent changes in their profiles with the change in their protonation states. An energy gap of 56.4 kcal/mol in the optimized energies of OH and NH conformers of acetamide along with computed HOMO–LUMO energy difference represents the relative stability of OH conformer compared to NH conformer, thus leading to the conclusion that OH protonation site is more likely to exist in the acetamide structure as compared to the NH protonation state.

High performance yeast-based microbial fuel cells by surfactant-mediated gold nanoparticles grown atop a carbon felt anode

The behavior of gold nanoparticles grown atop a polyethyleneimine functionalized carbon felt substrate is explored for the first time. This green synthesis growth process utilizes surface-bound seeds and an exploration of the effect of a surfactant ligand mediator on the directional growth of the gold nanoparticles. Rough, irregularly shaped, and wide-spread gold nanoflower structures are developed from the seeds atop the hydrophilic functionalized carbon felt fibers through this process. Nanoparticle growth is acquired by the adaptation of a simple solution consisting of a gold salt reducer (L-ascorbic acid), nanoparticle initiator (chloroauric acid), and a strong ligand (4-mercaptobenzoic acid, MBA). Nanoparticle growth time and the concentration of the directional mediating surfactant MBA are varied to optimize the synthesis. The gold nanoparticle structures are examined through X-ray photoelectron spectroscopy and high-resolution scanning electron microscopy. Furthermore, the effects of attachment, biofilm formation, and coverage activity on the performance of a yeast-based microbial fuel cell are electrochemically evaluated. Results show both favorable and unfavorable conditions for yeast biofilm inhabitancy which are verified through electron microscopy, and a relationship between the surface chemical compositions, incomplete gold salt reduction, presence of residual sulphur, and effective yeast active-surface coverage on modified carbon felt is demonstrated. The best power density achieved was 2771 ± 569 mW·m−2 for the polyethyleneimine-modified carbon felt with gold nanoparticles prepared with 715 μM MBA for 30 min; a value higher than many benchmarks referenced in literature representing a new contribution to the field.