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Considering the widespread application of nanotechnology in the food industry, humans are increasingly exposed to food-related engineered nanoparticles (NPs). Upon ingestion, NPs come into contact with human commensal bacteria that play an important role in human health and disease. Therefore, the effects and biotransformation of food-related NPs in the digestive tract, including microbiota, need to be assessed. Herein, artificial saliva was used as a physiologically relevant test medium to investigate the effects of Ag, SiO2and TiO2NPs and food-grade TiO2on the growth and antagonistic activity of Streptococcus salivariusK12, a human beneficial bacterium inhabiting the oral cavity, and bacterially induced biotransformation of NPs. SiO2NPs, TiO2NPs and food-grade TiO2at concentrations up to 100 mg L−1did not affect the growth of S. salivariusK12, while Ag NPs were expectedly growth-inhibitory already at 10 mg L−1, both in aerobic and anaerobic conditions. At sub-growth-inhibitory concentrations, NPs and food-grade TiO2significantly modified the transcription of structural genes (salAand sboA) of two bacteriocins (salivaricins) in S. salivariusK12 genome, signal transduction gene (sboK) and bacteriocin immunity conferring gene (sboG, an ABC transporter). Changes in gene expression were accompanied by the increased antagonistic activity of the bacterial strain. Spent artificial saliva, where bacteria had been cultured, markedly affected the transformation of NPs compared to fresh artificial saliva. The transformations included significant agglomeration, increased dissolution of Ag NPs and enhanced bioavailability of SiO2NPs, TiO2NPs and food-grade TiO2, while Ag NPs became less toxic. The results showed that food-related NPs can affect beneficial bacterial traits needed for competitiveness in microbiota and bacterial activity influences the transformation of NPs, potentially affecting the fate and toxicity of NPs in the digestive tract.

Despite available technology and the knowledge that chemical pollution damages human and ecosystem health, chemical pollution remains rampant, ineffectively monitored, rarely prevented, and only occasionally mitigated. We present a framework that helps address current major challenges in the monitoring and assessment of chemical pollution by broadening the use of the sentinel species Daphniaas a diagnostic agent of water pollution. And where prevention has failed, we propose the application of Daphniaas a bioremediation agent to help reduce hazards from chemical mixtures in the environment. By applying “omics” technologies to Daphniaexposed to real-world ambient chemical mixtures, we show improvements at detecting bioactive components of chemical mixtures, determining the potential effects of untested chemicals within mixtures, and identifying targets of toxicity. We also show that using Daphniastrains that naturally adapted to chemical pollution as removal agents of ambient chemical mixtures can sustainably improve environmental health protection. Expanding the use of Daphniabeyond its current applications in regulatory toxicology has the potential to improve both the assessment and the remediation of environmental pollution.

Oxidative stress is a unifying mechanism relating to the adverse effects induced by atmospheric particulate matter (PM). Owing to complex compositions, the role of PM constituents in triggering oxidative stress remains unclear. We employed synthetic particle suspensions with controlled sizes and compositions as PM surrogates to identify the key contributors to oxidative stress. The suspensions consisted of carbon black (CB) particles, polycyclic aromatic hydrocarbon adsorbed on CB, and dissolved metal ions. After the exposure of A549 or BEAS-2B cells to CB particles, the reactive oxygen species (ROS) level increased in a manner that was dependent on the size and concentration of the particles, in the order of 14 nm > 56 nm > 260 nm. Benzo[a]pyrene-coated CB also increased the ROS level, but not as much as the naked CB, and the benzo[a]pyrene-dione coating had no effect. The co-exposure of CB with one of the eight metal ions did not lead to any additional ROS increase. The results indicate that among the three major constituents, CB particles, and the small-sized ones in particular, contributed most to ROS generation. In mechanistic studies, damaged mitochondria cristae were observed, suggesting that mitochondria are one of the target organelles. Both naked and BaP-coated CB decreased the mitochondrial membrane potential and changed the mRNA expression of fusion/fission proteins. ROS inhibition experiments suggest that complex I of the mitochondria was involved, but complex III and the NADPH oxidase (NOX) system were not. It was thus postulated that small-sized particles could enter cells and disrupt the mitochondria, particularly complex I, leading to the elevated generation of ROS. Our work calls for more attention to be paid to the toxicity of the ultrafine fractions of PM.

In in vitrocell assays, nominal concentrations of a test chemical are most frequently used in the description of its dose–response curves. Although the biologically effective concentration (BEC) is considered as the most relevant dose metric, in practice, it is very difficult to measure. In this work, we attempted to determine the BEC of long-chain perfluoroalkyl carboxylic acids (PFCAs) in peroxisome proliferator-activated receptor γ (PPARγ) activity assays. In both adipogenesis and transcriptional activity assays with human and mouse cells, PPARγ activity of 7 PFCAs first increased and then decreased with their carbon chain length. The binding affinity of these PFCAs with the ligand-binding domain of PPARγ was measured by fluorescence competitive binding assay and showed very poor correlation with their receptor activity (r2= 0.002–0.047). Internal concentrations of the PFCAs in the cells were measured by LC–MS/MS. Although their correlation with the receptor activity increased significantly, it is still low (r2= 0.41–0.82). Using the binding affinity constant, internal concentration, and PPARγ concentration measured by immunoassays, concentrations of receptor-bound PFCAs in cells were calculated, which exhibited excellent correlation with PPARγ activity in both adipogenesis and transcriptional activity assays (r2= 0.91–0.93). These results demonstrate that the concentration of receptor-bound PFCA is the BEC that dictates its activity on human and mouse PPARγ in cell assays. In the absence of any direct detection method, our approach can be used to calculate the target-site concentration of other ligands.

Despite many studies on the toxicity of nanoplastic particles (NPPs) to aquatic invertebrates, the effects of ecological constituents such as humic substances (HSs) are often neglected. In our study, Daphnia magnawas used to evaluate the effects of three HSs, natural organic matter (NOM), fulvic acid (FA), and humic acid (HA), on NPP toxicity and corona formation. Acute toxicities of NPPs were reduced by all HSs at environmentally relevant concentrations. NPPs elicited the upregulation of all genes related to detoxification, oxidative stress, and endocrine activity after 7 days of exposure. The presence of NOM or HA resulted in the mitigation of gene expression, whereas significantly higher upregulation of all of the genes was observed with FA. The presence of FA led to increased protein adsorption on NPPs in D. magnaculture medium (eco-corona, EC) and homogenates (protein corona, PC), while there was less adsorption in the presence of HA. The highly abundant proteins identified in EC are involved in immune defense, cell maintenance, and antipredator response, while those in PC are responsible for lipid transport, antioxidant effects, and estrogen mediation. Our findings revealed the key influence of HSs on the toxicity of NPPs and provide an analytical and conceptual foundation for future study.

The potential causal relationship between exposure to environmental contaminants and diabetes is troubling. Exposure of perfluoroalkyl substances (PFASs) is found to be associated with hyperinsulinemia and the enhancement of insulin secretion by islet β cells in humans, but the underlying mechanism is still unclear. Here, by combining in vivostudies with both wild type and gene knockout mice and in vitrostudies with mouse islet β cells (β-TC-6), we demonstrated clearly that 1 h exposure of perfluorooctanesulfonate (PFOS) stimulated insulin secretion and intracellular calcium level by activating G protein-coupled receptor 40 (GPR40), a vital free fatty acid regulated membrane receptor on islet β cells. We further showed that the observed effects of PFASs on the mouse model may also exist in humans by investigating the molecular binding interaction of PFASs with human GPR40. We thus provided evidence for a novel mechanism for how insulin-secretion is disrupted by PFASs in humans.

Chlorinated polyfluoroalkylether sulfonic acids (Cl-PFESAs) have been shown to have potential thyroid hormone (TH) disruption effects. Here, we further investigated their estrogenic effects and underlying mechanisms. In vivo results revealed that exposure of zebrafish to Cl-PFESAs induced disorder of sex hormones during the early embryonic stages and caused histopathological lesions in the gonads of adult zebrafish relative to control groups. To find out whether the estrogen receptor is the molecular target of Cl-PFESAs, the binding interaction between Cl-PFESAs and ERs was investigated using a series of in vitro assays. We found that all tested chemicals could bind directly to ERs and exhibit relatively weak agonistic activity toward ERs, suggesting that the ER-mediated signaling pathway is directly involved in the estrogenic effects of Cl-PFESAs. The internal dose of 8:2 Cl-PFESA was significantly higher than the others, which explained why it obviously displayed an ER agonistic effect despite its weak ER binding affinity. Taken together, these results uncover that, in addition to the TH disruption effect, Cl-PFESAs might also cause estrogenic effects by activating ER pathways.

The growing evidence of the microbiome's crucial role in human health and disease has prompted research on understanding the impacts of engineered nanomaterials (ENMs) on commensal microorganisms. Accordingly, the number of studies addressing the ENM effects on intestinal microbiota has been rapidly increasing over the past few years. The focus on the gut microbiota is justified due to established metabolic and immunological functions of gut microbes, however, respiratory tract and skin microbiota also play important roles in host health and immunity. Here we review the composition and functions of microbiota inhabiting the major human organs that are prone to ENM exposure – skin, respiratory and digestive tract. We discuss the mechanisms of ENM actions relevant to physiological conditions and microbiota, and describe recently developed in vitromodels for elucidating the ENM impacts on the gut microbiota. We find that studies pertinent to the oxygen levels prevailing in the digestive tract, are still limited. Finally, we analyze the results of in vivostudies conducted in vertebrate models – zebrafish, mice and rats – exposed to ENMs viaingestion. The relative abundances of bacterial phyla indicate that ENMs have a potential to modulate intestinal microbiota and induce harmful or beneficial effects in the host. Future perspectives include identification of the factors driving ENM-caused dysbiosis and the ENM impacts on microbiota with deviated composition, e.g., under compromised health conditions. Understanding the interplay between ENMs and the human microbiota is crucial for the continued development of nanomedicine and protection of human health against accidental exposure to hazardous ENMs.

Occurrence of brominated flame retardants especially tetrabromobisphenol A (TBBPA) in water bodies poses a serious threat to aquatic ecosystems. Heterogeneous photocatalysis is a versatile technology that can efficiently degrade organic contaminants. However, existing studies on photocatalytic degradation of TBBPA are all achieved under intense light irradiation and high initial concentrations of TBBPA, which are far from real environmental conditions and not conducive to practical application. In this study, series of Z-scheme heterojunctions of WO3/ZnIn2S4photocatalysts were prepared and used for the high-efficiency photocatalytic degradation of TBBPA at lower light irradiation intensity (100 W) and lower TBBPA concentration (5.4 mg/L). Among them, WO3/ZnIn2S4-3 (molar ratio of 1:3) exhibited the highest photocatalytic activity due to the formation of Z-Scheme heterojunction which effectively facilitated the separation of photogenerated charges and endowed WO3/ZnIn2S4-3 higher redox ability. Thus, under light illumination, 91.6% degradation of TBBPA was achieved at an initial pH of 8.0 within 150 min, with a pseudo-first-order rate constant of 0.01572 min−1. Electron spin resonance spectroscopy and radical scavenger experiments confirmed that ·O2−radicals were the primary reactive oxygen species driving the TBBPA degradation. By applying LC-MS/MS, the degradation products were identified and possible degradation pathways were proposed. Finally, potential toxicity for PBBPA and generated intermediates were evaluated using luminescent bacteria, which revealed the toxicity of PBBPA was reduced effectively during the photocatalytic degradation process. Overall, the Z-scheme WO3/ZnIn2S4photocatalyst provides a promising way for the application of photocatalytic technology in actual wastewater treatment.

As alternatives to perfluorooctanoic acid (PFOA), hexafluoropropylene oxide (HFPO) homologues, including hexafluoropropylene oxide dimer acid (HFPO-DA), hexafluoropropylene oxide trimer acid (HFPO-TA), and hexafluoropropylene oxide tetramer acid (HFPO-TeA), have been used in the fluoropolymer industry for a long period of time. These compounds have attracted widespread attention in recent years due to their environmental ubiquity and high bioaccumulation capability, as well as their toxicity. In our study, we evaluated the potential estrogenic effects of HFPOs in comparison to PFOA by ligand binding, transcriptional activity, and in vivo assays. Fluorescence ligand binding assays showed that both HFPO-TA and HFPO-TeA exhibited higher binding affinity to estrogen receptor ligand binding domains (ER-LBDs) than PFOA, with 2.5- and 57.5-fold higher affinity to ERα-LBD and 2.6- and 41.8-fold higher affinity to ERβ-LBD, respectively, whereas HFPO-DA exhibited weaker binding affinity than PFOA. Unlike PFOA, HFPO-TA and HFPO-TeA exhibited antagonistic activity toward the ERs’ signaling pathway, with HFPO-TeA displaying the strongest potency. In silico study revealed that while PFOA binds with ERs in a similar fashion as 17β-estradiol, the HFPOs display an antagonistic binding mode. Using a zebrafish model, we further found that exposure to HFPO homologues significantly altered the levels of sex steroid hormones and vitellogenin. In general, both in vivo and in vitro results indicate that HFPO homologues might exert higher estrogenic effects than PFOA.

Hexafluoropropylene oxide trimer acid (HFPO-TA) and hexafluoropropylene oxide dimer acid (HFPO-DA) have been used as perfluorooctanoic acid (PFOA) alternatives in the fluoropolymer industry for years. Their widespread environmental distribution, high bioaccumulation capability, and human exposure have caused great concern. Nevertheless, their potential toxicity and health risk remain largely unknown. In the present study, we compared potential disruption effects of HFPO-TA, HFPO-DA, and PFOA on peroxisome proliferator-activated receptor γ (PPARγ) via the investigation of receptor binding, receptor activity, and cell adipogenesis effects. The receptor binding experiment showed HFPO-TA exhibited 4.8–7.5 folds higher binding affinity with PPARγ than PFOA, whereas HFPO-DA exhibited weaker binding affinity than PFOA. They also showed agonistic activity toward PPARγ signaling pathway in HEK 293 cells in the order of HFPO-TA > PFOA > HFPO-DA. Molecular docking simulation indicated HFPO-TA formed more hydrogen bonds than PFOA, whereas HFPO-DA formed fewer hydrogen bonds than PFOA. HFPO-TA promoted adipogenic differentiation and lipid accumulation in both mouse and human preadipocytes with potency higher than PFOA. Adipogenesis in human preadipocytes is a more sensitive end point than mouse preadipocytes. Collectively, HFPO-TA exerts higher binding affinity, agonistic activity, and adipogenesis activity than PFOA. The potential health risk of HFPO-TA should be of concern.

Interfacial interactions between TiO2nanocrystals and the surrounding environmental media play a critical role in dictating their environmental behaviors. Here two specific-faceted TiO2crystals, {101} facet and {001} facet, were adopted to investigate facet-mediated aggregation kinetics in aquatic environments. In pristine electrolyte solution (NaCl and CaCl2), {001} TiO2exhibited higher stability than {101} TiO2due to the abundant –OH groups on the {001} facet surface. The presence of Suwannee river humic acid (SRHA) significantly improved the stability of TiO2nanocrystals in a facet dependent manner, in which {101} TiO2exhibited a more remarkable improvement in stability than {001} TiO2. At a high SRHA concentration (10 mg L−1), both faceted TiO2displayed comparable stability. The adsorption experiments and attenuated total reflectance Fourier transformation infrared spectroscopy demonstrated that {101} TiO2induced more pronounced adsorption of SRHA molecules than {001} TiO2, probably driven by the efficient bidentate coordination of –COO– groups in SRHA on the {101} facet. This facet-affected colloidal stability behavior would deepen our understanding on nanomaterial transport and exposure in natural waters.

With worldwide environmental accumulation of plastics and their recognized degradation into smaller particles, attention to their impacts on ecological systems and humans has been increasing recently. However, environmental factors and their impacts are seldom considered during their eco-toxicity evaluation. In this study, D. magnaneonates were used to assess and compare the acute toxicities of polystyrene microplastic particles (MPPs) and nanoplastic particles (NPPs) in the absence and presence of humic acids (HAs), an important environmental factor in aquatic systems. Four stress response and detoxification genes (CAT, GST, HSP70, and P-GP) were used to characterize the toxic response of the neonates to the exposure. Our results showed that NPPs were much more toxic than MPPs in that 10 mg L−1NPPs induced over 70% of death in 96 h but MPPs (as high as 400 mg L−1) caused no mortality under all tested conditions. More importantly, we revealed a potent protective role of HA against NPP toxicity at environmentally relevant concentrations. The effect was concentration dependent, as 50 mg L−1HA subdued the NPP (400 mg L−1) toxicity effect completely. NPPs elicited the up-regulation of all examined genes while HA diminished the change appreciably, further confirming its detoxifying role against NPP toxicity. Through fluorescence and dynamic light scattering measurements, we found that HA was adsorbed on NPPs and formed a corona, without causing agglomeration or precipitation, but changed NPP distribution in the D. magnaneonates in a way similar to that of MPPs, leading to alleviated toxicity. Our results suggest that it is essential to consider environmental factors in evaluating and monitoring NPP toxicity as this presents a more relevant exposure state.

Estrogen-related receptor γ (ERRγ) is an orphan nuclear receptor having functional cross-talk with classical estrogen receptors. Here, we investigated whether ERRγ is a potential target of polybrominated diphenyl ethers (PBDEs) and their hydroxylated metabolites (OH-PBDEs). By using a fluorescence competitive binding method established in our laboratory, the binding potencies of 30 PBDEs/OH-PBDEs with ERRγ were determined for the first time. All of the tested OH-PBDEs and some PBDEs bound to ERRγ with Kdvalues ranging from 0.13–13.61 μM. The OH-PBDEs showed much higher binding potency than their parent PBDEs. A quantitative structure–activity relationship (QSAR) model was developed to analyze the chemical binding potencies in relation to their structural and chemical characteristics. The QSAR model indicated that the molecular size, relative ratios of aromatic atoms, and hydrogen bond donors and acceptors were crucial factors for PBDEs/OH-PBDEs binding. By using a reporter gene assay, we found that most of the low-brominated PBDEs/OH-PBDEs exerted agonistic activity toward ERRγ, while high-brominated PBDEs/OH-PBDEs had no effect on the basal ERRγ activity. The docking results showed that the low-brominated PBDEs/OH-PBDEs tended to take an agonistic binding mode while the high-brominated ones tended to take an antagonistic binding mode. Overall, our results suggest ERRγ to be a potential novel target for PBDEs/OH-PBDEs.

Chlorinated polyfluoroalkylether sulfonates (Cl-PFAESs) have been used as perfluorooctanesulfonate (PFOS) alternatives in the chrome plating industry for years. Although Cl-PFAESs have become ubiquitous environmental contaminants, knowledge on their toxicological mechanism remains very limited. We compared potential thyroid hormone (TH) disruption effects of Cl-PFAESs and PFOS via the mechanisms of competitive binding to TH transport proteins and activation of TH receptors (TRs). Fluorescence binding assays revealed that 6:2 Cl-PFAES, 8:2 Cl-PFAES and F-53B (a mixture of 6:2 and 8:2 Cl-PFAES) all interacted with a TH transport protein transthyretin (TTR), with 6:2 Cl-PFAES showing the highest affinity. It was also found that the chemicals interacted with TRs, with the affinity following the order of 6:2 Cl-PFAES > PFOS > 8:2 Cl-PFAES. In reporter gene assays the chemicals exhibited agonistic activity toward TRs, with the potency of 6:2 Cl-PFAES comparable to that of PFOS. The chemicals also promoted GH3 cell proliferation, with 6:2 Cl-PFAES displaying the highest potency. Molecular docking and molecular dynamic simulation revealed that both Cl-PFAESs fit into the ligand binding pockets of TTR and TRs with the binding modes similar to PFOS. Collectively, our results demonstrate that Cl-PFAESs might cause TH disruption effects through competitive binding to transport proteins and activation of TRs.

We reported an unprecedented chemiluminescence (CL) behavior of polyamine-functionalized carbon dots induced by Fe3+–H2O2Fenton-like system. The first-step CL intensity increased with the increasing of the concentration of H2O2and Fe3+, when the Fe3+concentration came to 10−3M, the unprecedented two-step CL behavior appeared. The CL intensity of BPEI-CDs induced by Fenton-like system was about 10 times stronger than that of naked CDs. The possible two-step CL mechanism was speculated based on the photoluminescence spectra, CL emission spectra, and the effects of radical scavengers on the CL intensity. Radiative recombination of the injected holes by strong oxidant perferrate formed through Fe3+–H2O2reaction and the ·OH generated from successive Fenton reaction with the thermally excited electrons was proposed, which further facilitate full understanding about the optical properties of carbon dots.

An efficient photocatalytic process involves two closely related steps: charge separation and the subsequent surface redox reaction. Herein, a ternary hybrid photocatalytic system was designed and fabricated by anchoring Cu(II) clusters onto a TiO2/reduced graphene oxide (RGO) composite. Microscopic and spectroscopic characterization revealed that both TiO2nanoparticles and Cu(II) clusters were highly dispersed on a graphene sheet with intimate interfacial contact. Compared with pristine TiO2, the TiO2/RGO/Cu(II) composite yielded an almost 3-fold enhancement in the photodegradation rate toward phenol degradation under UV irradiation. Electron spin resonance (ESR) spectra and electrochemical measurements demonstrated that the improved photocatalytic activity of this ternary system benefitted from the synergetic effect between RGO and Cu(II), which facilitates the interfacial charge transfer and simultaneously achieves in situ generation of H2O2via two-electron reduction of O2. These results highlight the importance to harmonize the charge separation and surface reaction process in achieving high photocatalytic efficiency for practical application.

A graphene-based two-dimensional (2D) nanoplatform provides new opportunities for fabricating 2D heterojunction interfaces to fortify charge transfer in semiconductor assemblies. In this report, TiO2nanosheet/graphene composite based 2D–2D heterojunctions were fabricated by a solvothermal process. Microscopic and spectroscopic characterization revealed a homogeneous sheetlike morphology with intimate interfacial contact between the TiO2nanosheet and graphene due to chemical interactions. Compared with 0D–2D Degussa P25 (TiO2)/graphene and 1D–2D TiO2nanotube/graphene composites, the 2D–2D TiO2nanosheet/graphene hybrid demonstrated higher photocatalytic activity toward the degradation of rhodamine B and 2,4-dichlorophenol under UV irradiation. Radical trapping and ESR experiments revealed the enhanced generation of ·OH and O2•–in the 2D–2D heterojunction system. By analyzing TiO2excited state deactivation lifetime, the interfacial electron transfer rates determined for 0D–2D, 1D–2D, and 2D–2D TiO2/graphene composites were 1.15 × 108s–1, 3.47 × 108s–1, and 1.06 × 109s–1, respectively. It was therefore proposed that the fast charge separation in the TiO2nanosheet/graphene photocatalyst promoted the generation of reactive oxygen species and enhanced the photodegradation reactions. The results underscore the key role of nanomaterial dimensionality in interfacial charge transfer processes.

The binding interactions between ligands and receptors play a vital role in their biological functions. In this work, a label-free indirect competitive binding assay based on surface plasmon resonance (SPR) detection was developed, using fatty acid–human serum albumin (HSA) as a model system. In the assay, a fatty acid analog was immobilized on the surface of an SPR gold chip by self-assembly, and was allowed to bind with HSA in solution. Addition of a ligand under investigation into the solution set up a competition with the analog for the protein, causing a reduction in the SPR signal. Due to the asymmetric structure of the ligand binding channel, HSA exhibited remarkable selectivity for the orientation of the fatty acid analog on a gold surface. When the carboxylic acid group of the analog was exposed on the sensor surface, the amount of bound HSA was very low. However, it increased by more than 7 fold when the alkyl chain was exposed. Dilution of the surface coverage of the fatty acid analog also enhanced HSA binding by reducing steric hindrance on the surface. Using a 1 : 4 mercaptoundecanoic acid–mercaptohexanol modified surface derivatized with octylamine, competitive binding assays for octanoic acid and perfluorooctane sulfonate with HSA were conducted. Using a derived kinetic equilibrium model, the equilibrium association constant was determined to be 4.57 × 105M−1and 2.11 × 105M−1, respectively, which are consistent with the values measured by other established methods. The engineered sensor chip surface can be used to study the binding interactions of other chemicals with this important serum transport protein.

Abstract: Nanometer sized materials have been shown to possess excellent chemical and electrochemical catalytic properties. In this work, a gold nanoparticle (AuNP) modified indium tin oxide (ITO) electrode was employed for investigating its electro-catalytic property. AuNP was deposited on the 3-aminopropyltriethoxysilane (APTES) modified ITO electrode by self-assembly, and was characterized by scanning electron microscopy and cyclic voltammetry. Although the electrochemical reaction of dopamine was very sluggish on the ITO/APTES electrode, it was significantly enhanced after AuNP deposition. The cyclic voltammogram exhibited apparent dependence on the surface coverage of 11 nm AuNPs, which could be rationalized by different modes of mass diffusion. Among the different sizes of AuNP investigated, the lowest anodic peak potential was observed on 11 nm AuNP. However, the potential was still about 50 mV more positive than that obtained on a bulk gold electrode of similar geometry. It is therefore concluded that there is no nanometer size effect of AuNP modified ITO on the electrochemistry of dopamine.

Quantitation of biological affinity reactions by a newly developed chemically amplified electrochemical detection method was demonstrated with the biotin-avidin binding pair. In the method, ruthenium tris2,2′-bipyridine Ru-bipy was used as an electrochemical signal-generating tag. Its oxidation current on an indium tin oxide ITO electrode was amplified with a sacrificial electron donor, oxalate. Because oxalate itself produced negligible current on the electrode, the signal-to-background ratio was greatly enhanced in comparison with other chemical amplification systems. Although the Ru-bipyoxalate redox couple has been employed previously in electrochemiluminescent and photoelectrochemical detection, its use in a catalytic amperometric detection of biological binding assays has not been reported. To implement the method in the detection of biotin–avidin recognition, avidin was immobilized on an ITO electrode, and was reacted with biotin in solution. Immobilization of avidin by passive adsorption was found to be relatively stable under the condition of the affinity reaction. In the direct assay, biotin labelled with Ru-bipy was recognized by avidin and accumulated on the electrode surface, which was then detected electrochemically in the presence of oxalate. A linear relationship between electrochemical current and biotin concentration was obtained in the range of 1–300 ng mL−1. In the competitive assay, a mixed solution of unlabelled biotin the analyte of various concentrations and 100 ng mL−1labelled biotin was reacted with avidin on the surface. As the concentration of the unlabelled biotin increased, less labelled biotin bound to avidin, leading to a reduction in the electro-catalytical response of Ru-bipy. A detection limit of 1 ng mL−1biotin was obtained in the competitive assay, which is close to the sensitivity of some enzyme-labelled amperometric assays.

Multi-functional nanoparticles possessing magnetic, up-conversion fluorescence and bio-affinity properties were synthesized and characterized. The particles have a coreshell structure. Iron oxide nanoparticles of 5–15 nm diameter were synthesized as the magnetic core. The core was covered with ytterbium and erbium co-doped sodium yttrium fluoride NaYF4:Yb,Er, an efficient infrared-to-visible up-conversion phosphor. The phosphor shell was prepared by co-precipitation of the rare-earth metal salts with fluoride in the presence of EDTA and the magnetic nanoparticle. After the magneticfluorescent hybrid particle was coated with SiO2and activated with glutaraldehyde, streptavidin was immobilized on the particle. The magneticfluorescent nanoparticles were found by transmission electron microscopy to be well-dispersed spherical particles with an average diameter of 68 nm. Both energy dispersive X-ray microanalysis and X-ray fluorescence spectra revealed the existence of iron in the particle. Measurements performed on a vibrating sample magnetometer obtained a strong magnetic response for the particle and fluorescence measurements demonstrated its up-conversion property. X-Ray diffraction analysis suggests the phosphor shell has the same structure as the pure NaYF4:Yb,Er nanoparticles we prepared in a previous study G. S. Yi, H. C. Lu, S. Y. Zhao, Y. Ge, W. J. Yang, L. H. Guo, D. P. Chen and J. Cheng, submitted. Streptavidin-coated magneticfluorescent particles were found to bind specifically to a glass slide spotted with biotinylated IgG and emit up-conversion fluorescence, confirming the successful coating of the protein and retention of its optical activity and bio-affinity.

Multi-functional nanoparticles possessing magnetic, up-conversion fluorescence and bio-affinity properties were synthesized and characterized. The particles have a core/shell structure. Iron oxide nanoparticles of 5–15 nm diameter were synthesized as the magnetic core. The core was covered with ytterbium and erbium co-doped sodium yttrium fluoride (NaYF₄:Yb,Er), an efficient infrared-to-visible up-conversion phosphor. The phosphor shell was prepared by co-precipitation of the rare-earth metal salts with fluoride in the presence of EDTA and the magnetic nanoparticle. After the magnetic/fluorescent hybrid particle was coated with SiO₂ and activated with glutaraldehyde, streptavidin was immobilized on the particle. The magnetic/fluorescent nanoparticles were found by transmission electron microscopy to be well-dispersed spherical particles with an average diameter of 68 nm. Both energy dispersive X-ray microanalysis and X-ray fluorescence spectra revealed the existence of iron in the particle. Measurements performed on a vibrating sample magnetometer obtained a strong magnetic response for the particle and fluorescence measurements demonstrated its up-conversion property. X-Ray diffraction analysis suggests the phosphor shell has the same structure as the pure NaYF₄:Yb,Er nanoparticles we prepared in a previous study (G. S. Yi, H. C. Lu, S. Y. Zhao, Y. Ge, W. J. Yang, L. H. Guo, D. P. Chen and J. Cheng, submitted). Streptavidin-coated magnetic/fluorescent particles were found to bind specifically to a glass slide spotted with biotinylated IgG and emit up-conversion fluorescence, confirming the successful coating of the protein and retention of its optical activity and bio-affinity.