Gold Salts Research Articles

Green Synthesis and Characterization of Gold Nanoparticles (Au-NPs) using Stem Extract of Euphorbia neriifolia L. and Evaluation of Their Antibacterial and Antifungal Potential

Nanotechnology is an emerging science in the world and attracted the interest of researchers due to their vast biological application. In this study, we Synthesized the gold nanoparticles (Au-NPs) using the stem extract of Euphorbia neriifolia L. The reduction of gold salt with the extract of E. neriifolia stem resulted in the formation of Au-NPs. The pathway is based on the reduction of AuCl4 by the extract of E. neriifolia stem. This method is simple, efficient, economic and nontoxic. Gold nanoparticles were characterized by UV-Vis spectroscopy, FT-IR Spectroscopy, X-ray Diffraction (XRD), Energy dispersive X-ray spectroscopy (EDX) and Scanning electron microscopy (SEM). The UV-Vis spectra gave surface plasmon resonance (SPR) at 520–570 for gold nanoparticles. FT-IR spectrum indicated the presence of different functional groups present in the biomolecules capping the nanoparticles. XRD showed face-centered cubic structure of gold nanocrystals with an average size of 22[Formula: see text]nm. Gold nanoparticles were mostly spherical in shape and 23–25[Formula: see text]nm in size, confirmed through SEM. Further, the synthesized Au-NPs were examined for their antibacterial and antifungal activity which showed better antibacterial and antifungal potential compared to the stem extract.

Disease-Modifying Antirheumatic Drugs and Risk of Parkinson Disease: Nested Case-Control Study of People With Rheumatoid Arthritis.

Background and ObjectivesEpidemiologic studies have suggested a link between rheumatoid arthritis and Parkinson disease (PD). Disease-modifying antirheumatic drugs (DMARDs) might explain this association. The aim of this work was to evaluate the association between DMARDs and risk of PD in persons with rheumatoid arthritis.MethodsThis nested nationwide case-control study was conducted within the Finnish Parkinson's Disease (FINPARK) cohort, which includes 22,189 Finnish persons with clinically verified PD diagnosed in 1996 to 2015. The cases had recorded diagnosis of PD in the Special Reimbursement Register and had no exclusion diagnoses with symptoms that may be confused with PD within 2 years of PD diagnosis. This study included cases with PD diagnosed during 1999 to 2015 and rheumatoid arthritis diagnosed >3 years before PD. Rheumatoid arthritis was identified from the Finnish Care Register for Health Care and Special Reimbursement Register. Cases were matched with up to 7 controls by age, sex, duration of rheumatoid arthritis, and region. DMARDs were categorized into 5 classes, and data on purchased prescriptions were identified from the Prescription Register since 1995. Associations were studied with conditional logistic regression adjusted for confounders.ResultsAltogether, 315 cases with PD and 1,571 matched controls were included. The majority (>60%) were women, and the median duration of rheumatoid arthritis on matching date was 11.6 years for controls and 12.6 years for cases. Use of DMARDs was not associated with risk of PD with a 3-year lag period applied between exposure and outcome except chloroquine/hydroxychloroquine, which associated with decreased risk (adjusted odds ratio [OR] 0.74, 95% confidence interval [CI] 0.56–0.97). Other DMARDs, including sulfasalazine, methotrexate, gold preparations, and immunosuppressants, were not associated with PD.DiscussionOur results suggest that the lower risk of PD in people with rheumatoid arthritis is not explained by DMARD use because these drugs in general did not modify the risk of PD among persons with rheumatoid arthritis. Association between chloroquine/hydroxychloroquine and lower risk of PD and the possible underlying mechanisms should be further investigated.Classification of EvidenceThis study provides Class II evidence that in individuals with rheumatoid arthritis using DMARDs, only chloroquine/hydroxychloroquine was associated with a potentially decreased risk of developing PD (adjusted OR 0.74, 95% CI 0.56–0.97).

Microwave-Assisted Synchronous Nanogold Synthesis Reinforced by Kenaf Seed and Decoding Their Biocompatibility and Anticancer Activity.

The combination of green-nanotechnology and biology may contribute to anticancer therapy. In this regard, using gold nanoparticles (GNPs) as therapeutic molecules can be a promising strategy. Herein, we proposed a novel biocompatible nanogold constructed by simply microwave-heating (MWI) Au3+ ions and kenaf seed (KS) extract within a minute. The phytoconstituents of KS extract have been utilized for safe synthesis of gold nanoparticles (KS@GNPs). The biogenic KS@GNPs were characterized by UV-vis Spectra, TEM, HR-TEM, XRD, FTIR, DLS, EDX, and SEAD techniques. The legitimacy and toxicity concern of KS@GNPs were tested against RAW 264.7 and NIH3T3 cell lines. The anticancer efficacy was verified using LN-229 cells. The pathways of KS@GNPs synthesis were optimized by varying the KS concentration (λmax 528 nm), gold salt amount (λmax 524 nm), and MWI times (λmax 522 nm). TEM displayed spherical shape and narrow size distribution (5–19.5 nm) of KS@GNPs, whereas DLS recorded Z-average size of 121.7 d·nm with a zeta potential of −33.7 mV. XRD and SAED ring patterns confirmed the high crystallinity and crystalline face centered cubic structure of gold. FTIR explored OH functional group involved in Au3+ ions reduction followed by GNPs stabilization. KS@GNPs exposure to RAW 264.7 and NIH3T3 cell lines did not induce toxicity while dose-dependent overt cell toxicity and reduced cell viability (26.6%) was observed in LN-229 cells. Moreover, the IC50 (18.79 µg/mL) treatment to cancer cell triggered cellular damages, excessive ROS generation, and apoptosis. Overall, this research exploits a sustainable method of KS@GNPs synthesis and their anticancer therapy.

Arylated gold nanostars aided SERS study of breast cancer cells

Anisotropic gold nanomaterials are opening new approaches for the study of cancer cells using high-performance diagnostic devices. Aryldiazonium gold salt, AgNO3, and ascorbic acid were used as shape-directing agent to promote the growth of spikes over the seeds. We synthesized covalently aryl functionalized gold nanostars via diazonium route using three AgNO3 concentrations of 1 × 10−1, 5 × 10−1, and 1 × 10−4 M for spikes length optimization. The seed and growth solutions were mixed and left undisturbed for 24 h. Transmission electron microscopy results showed that the spike sharpness and length were decreased with increasing AgNO3 concentration. The biocompatible AuNS were incubated with human breast cancer cells MDA-MB-231 and the cellular uptake was estimated using confocal microscopy. Different cancer cell concentrations range of 10–500 cells/mL were used for SERS study. Our results highlight the significance of nano spike-morphology in SERS study on cellular components and efficient cellular uptake of AuNS by MDA-MB-231 compared to normal cells, jointly is important for developing nanomedicines for cancer therapy.

A Highly Efficient Graphene Gold Based Green Supercapacitor Coin Cell Device for Energy Storage

Inclination to exploit renewable energy and their potential storage by facile, cost-effective, and above all in a green way are exactly what the current alternative energy research is looking for. The high-performance supercapacitor devices made up with the electrode materials synthesized in a simple and ecofriendly way are in utmost demand and the ultimate goal for widespread commercialization. Keeping these points in view, one pot green synthesis of active electrode material rGO-Au composite is achieved which not only performs as a very good supercapacitor in three-electrode configuration but also demonstrates extremely well as a coin cell device, ready to use. Ascorbic acid, which is commonly found in citrus fruits, plays an important role to reduce graphene oxide into rGO and simultaneously gold salt into gold nanoparticles, resulting in rGO-Au composite. The maximum recorded specific capacitance by CV measurement is 303.02 Fg−1at a scan rate of 5 mVs−1. Hindrance in the commercialization is caused by the differences in the supercapacitor performances between three electrode configurations and finally the proposed device. Here the proposed coin cell device exhibits maximum areal and mass specific capacitance of 62.43 mFcm−2and 56.09 Fg−1, respectively, that is very high among all reported graphene based composite devices benefitted over with commercially viable high capacity retention up to 80% even after 10,000 cycles. The proposed device demonstrates high energy density (∼ ED= 7.79 Wh/Kg) comparable to batteries and an optimum power density (∼ PD= 2512.9 W/Kg) close to supercapacitor insinuating it is an effective green supercapacitor for commercialization.

Electrochemical sensor modified with gold and arenediazonium salts for the determination of copper and mercury in human’s hair

Current article presents the results of using a solid carbon-containing electrochemical sensor modified with arenediazonium salts (ME-ADT-COOH) for the joint determination of copper and mercury in human hair. The sensitivity of the determination of copper and mercury ions using a graphite electrode modified with gold and arenediazonium salts with a substituent carboxy group is higher compared to the other carbon-containing modified electrodes. The influence of the concentration of arenediazonium tosylates with various substituents on the obtained analytical signal was studied. The conditions for the manufacturing the new carbon-containing modified electrochemical sensor have been developed. The effective surface area of the modified electrode was calculated, which was estimated using a cyclic voltammogram against the background of 0.1 M KCl with the addition of potassium hexacyanoferrate (С=5*10-4mol/l) salts and calculated using the Randles-Ševčík equation for the reversible electrode process. A linear range of determined concentrations in the voltametric determination of microelements on the arendiazonium-modified gold-graphite electrode was established - from 0.1 to 12 µg/g. The error of the determination did not exceed 25 %. The correctness of the results of the determination of copper and mercury in real objects by the “introduced-found” method, which correlates well with the known values, has been verified.

Catalytic reduction of 4-nitrophenol and methylene blue by biogenic gold nanoparticles synthesized using Carpobrotus edulis fruit (sour fig) extract

Along with the increasing requirement for efficient organic conversions using green chemistry, there is a need to develop highly efficient and eco-friendly catalytic reaction systems. Gold nanoparticles (AuNPs)-based nanocatalysts are promising candidates for the reduction of environmental pollutants, such as nitroaromatics and dyes. This study reports on the green synthesis of AuNPs using Carpobrotus edulis (C. edulis) fruit aqueous extract (CeFE) and their catalytic activities. The CeFE induced rapid reduction of gold (III) salt to form monodispersed and spherical AuNPs, with a core and hydrodynamic sizes of 40 and 108.7 nm, respectively. CeFE alone had no effect on 4-nitrophenol, whereas incubation with methylene blue (MB) caused reduction of the peak at 665 nm. Addition of CeFE-AuNPs in the presence of NaBH4, caused the reduction of 4-nitrophenol to 4-AP, and MB to leucoMB within 10 min. These reactions followed the pseudo first-order kinetics. Therefore, biogenic CeFE-AuNPs could be used for the elimination of noxious environmental pollutants.

Silver-mediated intramolecular P–C coupling

Silver(I) salts mimic copper(I) but not gold(I) salts in the reaction with peri-iodo naphthyldiisopropylphosphine. The formation of the corresponding peri-cyclic phosphonium derivatives represents the first example of silver-mediated P–C coupling through a two-electron redox sequence.

A study on the optical and dielectric behavior of Au-PVA nanocomposite films

In the current work, gold nanoparticles (AuNPs) embedded poly(vinyl alcohol) (PVA) composites were fabricated via solution casting technique. The AuNPs were synthesised in situ by the reduction of the metal precursor in the PVA matrix, acts as reducing and stabilising agent. The Plasmon resonance bands registered around 562–564 nm wavelength range of UV–Visible (UV–Vis) absorption spectra evidenced AuNPs’ generation in PVA. X-ray diffraction (XRD) studies revealed the FCC crystalline structure of the formed AuNPs. The generation of AuNPs in PVA has significantly reduced the optical energy gap for both direct and indirect transitions. Dielectric properties of the nanocomposites were investigated in the frequency range of 50 Hz-50 MHz revealed that dielectric constant and dielectric loss are enhanced in nanocomposites. Cole-Cole plot shows semi-circular arc originating from single point implying broad relaxation exists in nanocomposites. DC conductivity was enhanced with increase in gold salt concentration in Au-PVA nanocomposite, which is two orders of magnitude higher than the pristine PVA films.

Plasmon-controlled shaping of gold nanostar photothermal therapy agents.

Tunable gold nanostars were synthesized through the reduction of gold salt by an aminosugar, N-methyl-D-glucamine, in a seed-less route. The nanoparticle morphology and size were facilely tuned through adjustments in reaction pH and LED light-mediated synthesis. The materials demonstrated low inherent cytotoxicity and high potential for photothermal therapy.

Electrochemical sensing of limonene using thiol capped gold nanoparticles and its detection in the real breath sample of a cirrhotic patient

• Molar ratio of gold salt to thiol compound (2:1) synthesised best performing AuNPs. • Hexanethiolated capped AuNPs electrochemically detected limonene (LOD= 0.2 mmol L −1 ). • Limonene was detecteded in a cirrhotic patient breath sample using Hexanethiolated capped AuNPs. • Quantitative electrochemical detection of limonene was confirmed vusing GCMSto be 800 ppm. Volatile organic compounds (VOCs) are a major constituent of human breath which is being investigated as potential targets to be sensed in e-nose biosensors. Limonene is found in the breath of cirrhotic liver patients and can be used for early diagnosis using electrochemical biosensors. In the current study, electrochemical detection of limonene was performed using monolayer thiolated gold nanoparticles. Three different types of monolayer thiol capped AuNPs were synthesized by the modified biphasic method with the different molar ratios (2:1 and 1:1) of hydrogen tetrachloroaurate (III) (HAuCl 4 ·2H 2 O) and thiol groups: dodecanethiol, decanethiol, and hexanethiol. Thiol capped AuNPs were characterized physiochemically and for electrochemical sensing at different factors such as pHs, scan rate, current stability. Based on the best presented electrochemical results, hexanethiol AuNPs were selected as a sensor for analyzing the electrochemical detection of limonene as an analyte. Hexanethiol capped AuNPs based biosensing platform showed high sensitivity with a LOD of 0.2 mmol L −1 as observed via its DPV, and high specificity when was used against another VOC standard. The sensor was also used to detect limonene in the real breath sample of the clinical patient, besides testing the lab standard of limonene. The breath sample of cirrhotic patients was collected and tested for the presence of limonene by using GC–MS. The quantity of limonene measured via GC–MS was 800 ppm in cirrhotic patients and electrochemical sensor measurements of limonene were almost the same providing confidence over quantitative detection of the synthesized hexanethiol capped AuNPs based biosensing platform in this study.

Rowan Berries: A Potential Source for Green Synthesis of Extremely Monodisperse Gold and Silver Nanoparticles and Their Antimicrobial Property.

Rowanberries (Sorbus aucuparia) are omnipresent in Europe. The medicinal importance of rowanberries is widely known and corresponds to the active ingredients present in the fruits, mainly polyphenols, carotenoids, and organic acids. In the current study, we explored rowanberries for the reduction of gold and silver salts into nanoparticles. Rowanberries-mediated gold nanoparticles (RB-AuNPs) formed within 5 s at room temperature, and silver nanoparticles (RB-AgNPs) formed in 20 min at 90 °C. The produced nanoparticles were thoroughly characterized by UV-Vis spectroscopy, scanning electron microscopy (SEM), energy dispersive X-ray (EDX), transmission electron microscopy (TEM), dynamic light scattering (DLS), single-particle inductively coupled plasma–mass spectrometry (sp-ICP-MS), thermogravimetric analysis (TGA), Fourier transform-infrared spectroscopy (FT-IR) and matrix-assisted laser desorption/ionization time of flight mass spectrometry (MALDI-TOF). The characterization confirmed that the nanoparticles are highly monodisperse, spherical, stable over long periods, and exhibit a high negative zeta potential values. The produced RB-AuNPs and RB-AgNPs were 90–100 nm and 20–30 nm in size with a thick biological corona layer surrounding them, providing extreme stability but lowering the antimicrobial activity. The antimicrobials study of RB-AgNPs revealed that the nanoparticles have antimicrobial potential with an MBC value of 100 µg/mL against P. aeruginosa and 200 µg/mL against E. coli.

Evaluation of the Sorption Capacity of a Maleic Acid Copolymer Towards Gold(III) Ions and Production of Catalytically Active Gold Nanoparticles on Its Base

Two spectrophotometric approaches are suggested for the assessment of the concentration of gold(III) cations in an aqueous solution: direct recording of the optical density of gold cations and galvanic substitution of silver atoms in polymer-stabilized silver nanoparticles with gold cations. The sorption capacity of a maleic acid copolymer towards gold cations is estimated. A colloidal composite containing gold nanoparticles is obtained from the polymeric gold salt. The catalytic properties of the resulting polymer-stabilized nanogold are studied in the aerobic oxidation of glucose to gluconic acid.

Polyallylamine assisted synthesis of 3D branched AuNPs with plasmon tunability in the vis-NIR region as refractive index sensitivity probes

This paper describes the synthesis of highly branched gold nanoparticles (AuNPs) through a facile seeded growth approach using poly(allylamine hydrochloride) (PAH) as shape inducing agent. The obtained branched AuNPs present highly tunable optical properties in the Vis-NIR region from ca. 560 nm to 1260 nm. We controlled the morphology, and therefore the optical response, of the NPs by either changing the gold salt to seeds ratio or by fine-tuning the solution pH. We proposed that the formation of size-dependent PAH-AuCl4- aggregates as demonstrated by dynamic light scattering measurements, together with pH-dependent gold salt speciation might be responsible for the branched morphology. Advanced electron microscopy techniques demonstrated the polycrystalline nature of the AuNPs and facilitated a better understanding of branched morphology. Additionally, the refractive index sensitivity estimated by the inflection point of the Localized Surface Plasmon Resonance (LSPR) band can be controlled by tuning the nanoparticle branching. Furthermore, the versatility of the PAH chemistry allowed the easy functionalization of the synthesized NPs.

Folate-targeted doxorubicin delivery to breast and cervical cancer cells using a chitosan-gold nano-delivery system

Nanoparticles (NPs) are ideal candidates for safe, directed and effective delivery of chemotherapeutic agents to cancer cells. Herein, we report the synthesis of a gold NP (GNP) based delivery system as a platform for doxorubicin (DOX) delivery to cancer cells. GNPs synthesized by citrate reduction of the gold salt was used to encapsulate DOX, using sodium tripolyphosphate (TPP) as a linking agent. The subsequent functionalization of the DOX-GNP with chitosan (CS) and folate-linked chitosan (F-CS) resulted in the formation of CS-GNP-DOX and F-CS-GNP-DOX delivery systems. The synthesized DOX nanocarriers were characterized using UV–visible and ATR-FTIR spectroscopy, transmission electron microscopy (TEM) and nanoparticle tracking analysis (NTA). Drug release and kinetic evaluations were done in simulated tumour and physiological microenviroments. The drug-nanocomplexes were evaluated in an in vitro MTT assay for their effect on cell proliferation with further assessments on the mechanisms associated with the toxicity. The NPs and nanocomplexes were spherically shaped, colloidally stable, and displayed a pH-dependent DOX release that closely followed a first or zero-order kinetic model. CS-GNP-DOX and F-CS-GNP-DOX displayed higher chemotherapeutic activity in the human breast (MCF-7), cervical (HeLa) and hepatocellular (HepG2) carcinoma cell lines when compared to free DOX. The lowest IC50 obtained for CS-GNP-DOX and F-CS-GNP-DOX in the cancer cells was significantly lower than that for free DOX. The F-CS-GNP-DOX nanocomplex displayed superior anticancer effects over CS-GNP-DOX in the breast and cervical cancer cells, predominantly due to enhanced cellular uptake via their over-expressed folate receptors (FRα). These nanocomplexes also induced mitochondrial membrane depolarization and activated downstream caspases during apoptotic induction in the breast and cervical cancer cells. Overall, these DOX-nanocomplexes have the potential for clinical application and are be promising lead candidates for further development.

Retention of Activity by Antibodies Immobilized on Gold Nanoparticles of Different Sizes: Fluorometric Method of Determination and Comparative Evaluation.

Antibody–nanoparticle conjugates are widely used analytical reagents. An informative parameter reflecting the conjugates’ properties is the number of antibodies per nanoparticle that retain their antigen-binding ability. Estimation of this parameter is characterized by a lack of simple, reproducible methods. The proposed method is based on the registration of fluorescence of tryptophan residues contained in proteins and combines sequential measurements of first the immobilized antibody number and then the bound protein antigen number. Requirements for the measurement procedure have been determined to ensure reliable and accurate results. Using the developed technique, preparations of spherical gold nanoparticles obtained by the most common method of citrate reduction of gold salts (the Turkevich–Frens method) and varying in average diameter from 15 to 55 nm have been characterized. It was shown that the number of antibodies (immunoglobulins G) bound by one nanoparticle ranged from 30 to 194 during adsorptive unoriented monolayer immobilization. C-reactive protein was considered as the model antigen. The percentage of antibody valences that retained their antigen-binding properties in the conjugate increased from 17 to 34% with an increase in the diameter of gold nanoparticles. The proposed method and the results of the study provide tools to assess the capabilities of the preparations of gold nanoparticles and their conjugates as well as the expediency of seeking the best techniques for various practical purposes.

In situsmall-angle X-ray scattering investigation of X-ray-induced gold nanoparticle synthesis without stabilizer

The X-ray irradiation of gold salt aqueous solutions in the synthesis of gold nanoparticles (AuNPs) in the absence of any reducing agent or stabilizer is presented. The size, dispersion, number of particles, yield and morphology evolution during the radiolytic formation of AuNPs were followed simultaneously usingin situsmall-angle X-ray scattering. This study provides an insight into the overall kinetics and formation mechanisms at the initial stage of AuNP synthesis without reductants and stabilizers. The pH-dependent speciation of aqueous HAuCl4and its influence on the synthesis, structure and properties of AuNPs were observed. The result sheds light on the key parameters required to obtain stable monomodal particles and the influence of the surface charge and reactivity of the chemical solution on the final particle size and shape.

Development of a Lateral Flow Immunochromatographic Strip for Rapid and Quantitative Detection of Small Molecule Compounds.

Membrane-based lateral flow immunochromatographic strips (ICSs) are useful tools for low-cost self-diagnosis and have been efficiently applied to toxin, physiological index and clinical biomarker detection. In this protocol, we provide a detailed description of the steps to develop a rapid, sensitive and quantitative lateral-flow immunoassay (using AuNPs as a marker and mAbs as a probe). The procedure describes the preparation and characterization of colloidal gold, synthesis of the AuNP-mAb conjugate, assembly of the immunochromatographic strip, and methodological investigation of the assay. The results showed that the final strips can be further utilized for the rapid and convenient self-diagnosis of a small molecule, which may provide an alternative tool in the rapid and precise analysis of physiological and biological indices.

Pyroelectric Synthesis of the Site‐Specific Au‐ZnO Nanorod Array

AbstractThis paper introduces an alternative approach for the synthesis of site‐specific gold‐zinc oxide (Au‐ZnO) nanorod array through the pyroelectric approach. The hydrothermally grown ZnO nanorod array on the Si substrate is served as the pyroelectric catalyst. Under rapid temperature oscillation, the gold salt precursor is reduced into gold nanoparticles around the tip of ZnO nanorods in aqueous solution. The hybrid structure shows a significant photoluminescence quenching in the visible emission spectrum of ZnO, which is due to the interaction of ZnO and gold nanoparticles. A Rhodamine B (RhB) degradation test under full spectrum sunlight illumination is conducted to demonstrate the photocatalytic performance of the Au‐ZnO nanorod array. The mechanism behind the hydrothermal growth of ZnO, pyroelectric reduction of gold nanoparticles, and photoluminescence quenching of Au‐ZnO is discussed. The findings of this work offer possible ways to the sustainable use of thermal energy, including harvesting waste heat through pyroelectric effect, and the site‐specific synthesis of various nanomaterials with enhanced photocatalytic degradation capability.

The thyroid hormone converting enzyme human deiodinase 1 is inhibited by gold ions from inorganic salts, organic substances, and by small-size nanoparticles

The selenocysteine-containing enzyme class deiodinases (DIO) consists of three isoforms. DIOs play a role in regulation of thyroid hormone (TH) signaling through the removal of iodide from TH leading to TH that interact with the hypothalamic-pituitary-thyroid (HPT) axis with differing potency. Some gold-containing organic substances are known to inhibit many selenoenzymes, including DIOs. It is, however, unclear whether the Au-containing substances or the Au ions are causing the inhibition. In this study, five organic and inorganic gold substances as well as three gold nanoparticles (AuNPs) were tested for their potential to inhibit DIO1. The enzyme activity was tested using human liver microsomes as an enzyme source and reverse T3 as a substrate; iodide release was measured by the Sandell-Kolthoff method. The three organic gold substances aurothioglucose, auranofin and sodium aurothiomalate inhibited DIO1 with IC50 between 0.38 and 0.75 μM while their structural analogues lacking the gold ion did not. Likewise, the two tested gold salts, Au(I) and Au(III) chloride, showed a concentration-dependent inhibition of the DIO1 with IC50 values of 0.95 and 0.57 μM. Further, AuNPs of different sizes (100, 30 and 5 nm diameter) were tested with only the 5 nm AuNPs leading to inhibition with an IC50 of 8 × 1014 AuNP/L. This inhibition was not caused by the Au ions released by the AuNP into the incubation media. The exact mechanism of inhibition of DIO1 by 5 nm AuNPs should be further examined. In conclusion, the microsomal DIO1 assay demonstrated the inhibition of DIO1 by gold ions originating from different gold-containing substances, but not by Au released from AuNPs; rather DIO1 is inhibited by 5 nm, but not larger, AuNPs.