Modeling Absorption Dynamics of Differently Shaped Gold Glioblastoma and Colon Cells Based on Refractive Index Distribution in Holotomographic Imaging.

Herein, it is demonstrated that the toxic effect of gold nanoparticles (Au NPs) on three different cancer cell lines (U-118 and LN-299 glioblastoma and HCT-116 colon) depends on their absorption dynamics by cells, related to the shapes of the NPs. This hypothesis is confirmed by showing that i) based on refractive index (RI) values, typical for cell components and gold nanoparticles, it is possible to show the absorption dynamics and accumulation locations of the latter ones inside and outside of the cells. Moreover, ii) the saturation of the accumulated Au NPs volume in the cells depends on the nanoparticle shape and is reached in the shortest time for star-shaped Au NPs (AuS NPs) and in the longest time for spherical Au NPs (AuSph NPs) and on the cancer cells, where the longest and the shortest saturation are noticed for HCT-116 and LN-229 cells, respectively. A physical model of Au NPs absorption dynamics is proposed, where the diameter and shape of the Au NPs are used as parameters. The obtained theoretical data are consistent with experimental data in 85-98%.

Analysis and experimental assessment of an optimized SERS substrate used to detect thiabendazole in apples with high sensitivity.

Pesticides that linger in the environment and ecosystems for an extended period can cause severe and dangerous health problems in humans. To detect pesticides in foods, the development of high-sensitivity and quick screening technologies was required. This research investigated the performance of Au@Ag NPs with varying thicknesses of the silver shell for detecting trace quantities of thiabendazole (TBZ) in apples using surface-enhanced Raman spectroscopy (SERS). The Au@Ag NPs were synthesized by coating 32 nm gold seeds with different thicknesses of silver shell ranging from 2.4 to 8.7 nm, achieved by adjusting the incorporation of AgNO3 and ascorbic acid. The optimized Au@Ag NPs with a 7.3 nm silver shell demonstrated outstanding SERS activity, high sensitivity, and a detection limit of 0.05 µg/mL for TBZ. The R2 values, representing the goodness of fit, were found to be 0.990 and 0.986 for standard and real TBZ samples, respectively, indicating a strong correlation between the measured signal and the TBZ concentration. The recovery analysis showed a reliable and accurate detection capability (96 to 105%), suggesting good reliability and accuracy of the SERS-based detection using the optimal Au@Ag NPs. Overall, this research highlights the potential of SERS with optimal Au@Ag NPs for rapid and effective monitoring of pesticides in the food industry.

Photocatalytic Deposition of Au Nanoparticles on Ti3C2Tx MXene Substrates for Surface-Enhanced Raman Scattering.

Surface-enhanced Raman scattering (SERS) is a promising technique for sensitive detection. The design and optimization of plasma-enhanced structures for SERS applications is an interesting challenge. In this study, we found that the SERS activity of MXene (Ti3C2Tx) can be improved by adding Au nanoparticles (NPs) in a simple photoreduction process. Fluoride-salt-etched MXene was deposited by drop-casting on a glass slide, and Au NPs were formed by the photocatalytic growth of gold(III) chloride trihydrate solutions under ultraviolet (UV) irradiation. The Au-MXene substrate formed by Au NPs anchored on the Ti3C2Tx sheet produced significant SERS through the synergistic effect of chemical and electromagnetic mechanisms. The structure and size of the Au-decorated MXene depended on the reaction time. When the MXene films were irradiated with a large number of UV photons, the size of the Au NPs increased. Hot spots were formed in the nanoscale gaps between the Au NPs, and the abundant surface functional groups of the MXene effectively adsorbed and interacted with the probe molecules. Simultaneously, as a SERS substrate, the proposed Au-MXene composite exhibited a wider linear range of 10-4-10-9 mol/L for detecting carbendazim. In addition, the enhancement factor of the optimized SERS substrate Au-MXene was 1.39 × 106, and its relative standard deviation was less than 13%. This study provides a new concept for extending experimental strategies to further improve the performance of SERS.

Preparation and characterization of AChE immobilized magnetic bio-nanocomposites (Fe3O4@Cht/Au) for pesticide detection.

Free enzymes cause difficulties in many applications due to their insufficient stability, loss of activity in a short time, and most importantly, although they are costly, they are used only once in reactions, lose their effect and cannot be recovered from the environment. Magnetic nanoparticles coated with biocompatible polymeric material are potential candidates for promising enzyme carriers due to their multifunctional pore surfaces, easy removal from the environment provided by the magnetization, ability to main stability under various harsh conditions. This study prepared a biosensor candidate based on the inhibiting acetylcholinesterase enzyme by organophosphate pesticides from chitosan-coated magnetic nanoparticles doped with gold. Transmission electron microscopy, scanning electron microscopy, X-ray diffraction diffractometry, and Fourier transform infrared spectroscopy analysis confirmed the structure of synthesized nanocomposites. Magnetic characteristics of the nanocomposites were assessed using VSM. Bio-nanocomposite (Fe3O4@Cht/Au/AChE) was used to determine environmental pollutants qualitatively. Remediation of organophosphate-containing wastewater is an essential issue for environmental sustainability. In this work, Dichlorvos and Chlorpyrifos were selected as organic pollutants to assess the enzymatic activity of immobilized Fe3O4@Cht/Au/AChE. Optimum conditions for AChE enzyme were immobilized nanostructures (Fe3O4@Cht/Au/AChE) were determined. The optimum pH for the immobilized enzyme was found to be 8, and the optimum temperature was found to be 60 °C. Retained immobilized enzyme activity is found to be around 50% for the 20th reuse. In the presence of 150 µL pesticide, retained immobilized enzyme activity is found to be around 25%. Method validation was performed for pesticides. When using immobilized AChE, the LOD (limit of detection)-LOQ (limit of quantitation) values for Dichlorovos and Chlorpyrifos was obtained in the range of 0.0087-0.029 nM and 0.0014-0.0046 nM, respectively. The relative standard deviation (RSD%) values, which are indicators of precision, were found to be below 2%.

Plasmon mediated SERS and photocatalysis enhancement in Au nanoparticle decorated 2D-TiSe2.

The combination of 2D materials and noble metallic nanostructure is becoming an attractive research domain for label-free, highly sensitive surface-enhanced Raman spectroscopy (SERS) applications. This study demonstrated photocatalysis degradation and SERS enhancements of organic fluorophore (Rhodamine 6G) on two-dimensional (2D) TiSe2using Raman spectroscopy. The Au nanoparticles (NPs) were decorated on TiSe2thin films by thermal annealing at variable temperatures. The selective deposition of Au NPs on the hexagonal TiSe2nanocrystals increases surface roughness, creating a larger surface area for molecule adsorption. It has been observed that the Au decoration at 250 °C on TiSe2exhibits efficient detection capabilities for R6G with the Raman intensity enhancement factors of the order of ≈105along with the significantly improved visible light-induced photodegradation efficiency. The optimized Au NP size creates large electromagnetic hot spots produced by strong plasmon coupling that assists in the charge transfer mechanism among TiSe2, Au NPs, and R6G for enhanced SERS and photocatalysis activities. It has been observed that the intensity of Raman scattering decreases as the Au NP size increases on the TiSe2material. A possible charge transfer mechanism is proposed with an energy band diagram. The simultaneous measurement of SERS and photocatalytic dye degradation in Au decorated TiSe2can be used as a sensitive technique for water pollution treatment and biodegradable organic contaminants for the environmental ecosystem.

Colorimetric and Raman dual-mode lateral flow immunoassay detection of SARS-CoV-2 N protein antibody based on Ag nanoparticles with ultrathin Au shell assembled onto Fe3O4 nanoparticles.

Serological antibody tests are useful complements of nuclei acid detection for SARS-CoV-2 diagnosis, which can significantly improve diagnostic accuracy. However, antibody detection in serum or plasma remains challenging to do with high sensitivity. In this study, Ag nanoparticles with ultra-thin Au shells embedded with 4-mercaptobenzoic acid (MBA) (AgMBA@Au) were manufactured and then assembled onto Fe3O4 surface by electrostatic interaction to construct the Fe3O4-AgMBA@Au nanoparticles (NPs) with magnetic-Raman-colorimetric properties. Based on the composite nanoparticles, a colorimetric and Raman dual-mode lateral flow immunoassay (LFIA) for ultrasensitive identification of SARS-CoV-2 nucleocapsid (N) protein antibody was constructed. The magnetic nanoparticles (Fe3O4 NPs) were acted as the core and coated a layer of AgMBA@Au particles on the surface by electrostatic interaction to prepare Fe3O4-AgMBA@Au NPs, which can amplify the SERS signal due to multiple AgMBA@Au particles concentrated on a single magnetic nanoparticle. Moreover, the Fe3O4-AgMBA@Au NPs facilitated pre-purifying sample using magnetic separation, and complex matrix interference would be greatly decreased in the detection. The Fe3O4-AgMBA@Au NPs modified with N protein recognized and bound with N protein antibodies, which were trapped on the T-line, forming color band for observing detection. Under optimal conditions, the N protein antibodies could be qualitatively detected in colorimetric mode with the visual limit of 10-8 mg/mL and quantitatively detected by SERS signals between 10-6 and 10-10 mg /mL with 0.08 pg/mL detection limit. The coefficients variations (CV) of intra-assay was 8.0%, whereas of inter-assay was 11.7%, confirming of good reproducibility. Finally, this approach was able to discriminate between positive, negative, and weakly positive samples when detecting 107 clinical serum samples. The process enables highly sensitive quantitative assays that are valuable for evaluating disease processes and guiding treatment. Colorimetric and Raman dual-mode LFIA detection of SARS-CoV-2 N protein antibody based on Fe3O4-AgMBA@Au nanoparticles.

MOF@Au NPs/aptamer fluorescent probe for the selective and sensitive detection of thiamethoxam.

The luminescence performance of fluorescent reagents plays a crucial role in fluorescence analysis. Therefore, in this study, a novel bi-ligand Zn-based metal-organic framework, Au nanoparticle (NP) fluorescent material was synthesized using a hydrothermal method with Zn as the metal source. Simultaneously, a DNA aptamer was introduced as a molecular recognition element to develop a Zn-based MOF@Au NPs/DNA aptamer fluorescent probe for the ultra-trace detection of thiamethoxam residues in agricultural products. The probe captured different concentrations of the target molecule, thiamethoxam, through the DNA aptamer, causing a conformational change in the DNA aptamer and bursting the fluorescence of the probe, therefore establishing a fluorometric method for thiamethoxam detection. This method is highly sensitive due to the excellent luminescence properties of the Zn-based MOF@Au NPs, and the DNA aptamer can specifically recognize thiamethoxam, offering high selectivity. The linear range of the method was 2.5-6000 × 10-11  mol L-1 , with a detection limit of 8.33 × 10-12  mol L-1 . This method was applied to the determination of actual samples, such as bananas, and the spiked recovery rate was found to be in the range 84.05-109.07%. Overall, the proposed probe has high sensitivity, high selectivity, and easy operation for the detection of thiamethoxam residues in actual samples.

A signal-off photoelectrochemical sandwich-type immunosensor based on WO3/TiO2 Z-scheme heterojunction.

A sandwich "signal-off" type photoelectrochemical (PEC) immunosensor was fabricated based on a composite heterojunction of tungsten oxide/titanium oxide microspheres (WO3/TiO2) acting as signal amplification platform and carbon microspheres loaded by gold nanoparticles (Cs@Au NPs) utilized as the label for detecting antibody. WO3/TiO2 had excellent photoelectric performance, and the results of Mott-Schottky plots, open-circuit voltage, and electron spin resonance spectroscopy indicated that it belonged to the Z-scheme heterojunction transfer mechanism of photogenerated carriers. To achieve the sensitization of PEC immunosensor, Cs@Au NP-labeled immunocomplex can effectively reduce the photocurrent signal. The PEC immunosensors were fabricated under the optimal conditions of 1:1 WO3/TiO2 (molar ratio), 2.0 mg mL-1 WO3/TiO2, and 1.5 mg mL-1 Cs@Au NPs. Through comparison of the detection results of label-free and sandwich-type PEC immunosensors for nucleocapsid (N) protein of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), we found that the sensitivity of the sandwich type was 2.53 times the label-free type, and the limit of detection was 0.006 ng mL-1, i.e., 3.17 times lower than the label-free type. This demonstrates that the developed sandwich-type PEC immunosensor will have a brighter application prospect.

A photoelectrochemical sensor for Hg2+ detection with enhanced cathodic photocurrent via BiOI/Bi2S3 photoanode of self-sacrifice.

Due to the inherent merits of the anodic photoelectrochemical (PEC) sensor, it was widely utilized in the field of analytical chemistry. However, it must be noted that the anodic PEC sensor was susceptible to interference in practical applications. The situation with the cathodic PEC sensor was exactly the opposite. Therefore, this work fabricated a PEC sensor combining photoanode and photocathode that solved the defects of conventional PEC sensors in detecting Hg2+. Specifically, Na2S solution was carefully dropped on the BiOI-modified indium-tin oxide (ITO) to obtain ITO/BiOI/Bi2S3 directly by self-sacrifice method and the resulting electrode was used as photoanode. In addition, a sequential modification process was employed to decorate the ITO substrate with Au nanoparticles (Au NPs), Cu2O, and L-cysteine (L-cys), thereby realizing the fabrication of the photocathode. Moreover, the presence of Au NPs further amplified the photocurrent of the PEC platform. During the detection process, when Hg2+ is present it will bind to the L-cys, resulting in an increase in current, thus enabling sensitive detection of Hg2+. The proposed PEC platform exhibited good stability and reproducibility, providing a new idea for the detection of other heavy metal ions.

Electrochemical biosensor based on antibody-modified Au nanoparticles for rapid and sensitive analysis of influenza A virus.

To cope with the easy transmissibility of the avian influenza A virus subtype H1N1, a biosensor was developed for rapid and highly sensitive electrochemical immunoassay. Based on the principle of specific binding between antibody and virus molecules, the active molecule-antibody-adapter structure was formed on the surface of an Au NP substrate electrode; it included a highly specific surface area and good electrochemical activity for selective amplification detection of the H1N1 virus. The electrochemical test results showed that the BSA/H1N1 Ab/Glu/Cys/Au NPs/CP electrode was used for the electrochemical detection of the H1N1 virus with a sensitivity of 92.1 µA (pg/mL)-1 cm2, LOD of 0.25 pg/ml, linear ranges of 0.25-5 pg/mL, and linearity of (R 2 = 0.9846). A convenient H1N1 antibody-based electrochemical electrode for the molecular detection of the H1N1 virus will be of great use in the field of epidemic prevention and raw poultry protection. Supplementary Information: The online version contains supplementary material available at 10.1007/s11581-023-04944-w.

Heterogeneous Cu2O-Au nanocatalyst anchored on wood and its insight for synergistic photodegradation of organic pollutants.

In this study, a Cu2O-Au nanoparticles (NPs) heterojunction catalyst anchored on wood was developed by in situ reduction and hydrothermal treatment, and the properties of the catalyst were systematically characterized. The catalyst exhibited prominent photocatalysis of methyl orange (MO, 0.169 min- 1), and tetracycline (TC, 0.122 min-1) which were degraded completely within 20 min. Even after four recyclings, the efficiency of MO degradation by the catalyst remained at 80%. The natural wood with three-dimensional porous structures acted as a reducing agent and a stabilizer for Au NPs and Cu2O, which helped to maintain high performance and reusability. The presence of Au NPs mediated the light-induced electron transfer and enhanced the absorption of visible light for promoting photocatalytic activity. The intermediates of contaminants within the degradation process were characterized by liquid chromatography-mass spectrometry. Additionally, the photogenerated superoxide radicals and holes were identified by electron spin resonance. Thus, the potential degradation mechanism catalyzed by the Cu2O-Au NPs-wood was proposed. This findings of this study valorizes biomass as a photocatalyst for wastewater remediation.

Electrochemical Aptasensor Based on Au Nanoparticles Decorated Porous Carbon Derived from Metal-Organic Frameworks for Ultrasensitive Detection of Chloramphenicol.

A facile and sensitive electrochemical aptamer sensor (aptasensor) based on Au nanoparticles-decorated porous carbon (AuNPs/PC) composite was developed for the efficient determination of the antibiotic drug chloramphenicol (CAP). AuNPs modified metal-organic framework (AuNPs/ZIF-8) is applied as a precursor to synthesize the porous carbon with homogeneous AuNPs distribution through a direct carbonization step under nitrogen atmosphere. The as-synthesized AuNPs/PC exhibits high surface area and improved conductivity. Moreover, the loading AuNPs could enhance the attachment of the aptamers on the surface of electrode through the Au-S bond. When added to CAP, poorly conductive aptamer-CAP complexes are formed on the sensor surface, which increases the hindrance to electron transfer resulting in a decrease in electrochemical signal. Based on this mechanism, the developed CAP aptasensor represents a wide linear detection range of 0.1 pM to 100 nM with a low detection limit of 0.03 pM (S/N = 3). In addition, the proposed aptasensor was employed for the analysis of CAP in honey samples and provided satisfactory recovery.

In situ reduced graphene-based aerogels embedded with gold nanoparticles for real-time humidity sensing and toxic dyes elimination.

Hybrid aerogels are promising candidates for energy storage, biosensing, and medical applications, but the conventional fabrication methods, being time-consuming and complex, limit their widespread utilization. The critical issues affecting their functionality include the un-controllable particle dispersity, loading of active materials, and the porosity. We report a simple and efficient method to synthesize in situ reduced Au nanoparticles@graphene (Au@graphene) hybrid aerogel using near-infrared radiation (NIR), resulting the uniform loading of well-dispersed Au nanoparticles (Au-NPs) as well as in situ reduction of graphene oxide (GO) with enhanced conductivity. The concentration of iso-propylacrylamide and GO can be adjusted to control the aerogel pore size during the freeze-drying process. Reduction of HAuCl4 and GO to high extent under NIR light was confirmed with advanced characterization techniques. Density functional theory based calculations with generalized gradient-corrected functional (GGA/PW91) in the hybrid aerogel system, and dnd basis sets are used for the confirmation of possible interactions between the GO, Au-NPs, and the polymer. The as-designed highly porous and conductive aerogel shows an excellent humidity response (30-97%) and successfully removes the methylene blue pollutant from the aqueous solution to a high extent (90%). Therefore, Au@graphene hybrid aerogel is potentially an exciting candidate for a wide range of applications in the humidity sensing and biomedical disease detection.

Photochemical Synthesis of Gold and Silver Nanoparticles-A Review.

Nanomaterials have supported important technological advances due to their unique properties and their applicability in various fields, such as biomedicine, catalysis, environment, energy, and electronics. This has triggered a tremendous increase in their demand. In turn, materials scientists have sought facile methods to produce nanomaterials of desired features, i.e., morphology, composition, colloidal stability, and surface chemistry, as these determine the targeted application. The advent of photoprocesses has enabled the easy, fast, scalable, and cost- and energy-effective production of metallic nanoparticles of controlled properties without the use of harmful reagents or sophisticated equipment. Herein, we overview the synthesis of gold and silver nanoparticles via photochemical routes. We extensively discuss the effect of varying the experimental parameters, such as the pH, exposure time, and source of irradiation, the use or not of reductants and surfactants, reagents' nature and concentration, on the outcomes of these noble nanoparticles, namely, their size, shape, and colloidal stability. The hypothetical mechanisms that govern these green processes are discussed whenever available. Finally, we mention their applications and insights for future developments.

Assembling PVP-Au NPs as portable chip for sensitive detection of cyanide with surface-enhanced Raman spectroscopy.

Cyanide (C≡N) can lead to blood, cardiovascular system, and nervous system disorders owing to the acute and chronic toxicity; thus, aiming at the group or individual poisoning incidents, it is necessary to develop the sensitive and credible method for rapid on-site detection of poisons cyanide. Surface-enhanced Raman spectroscopy (SERS) with the advantages of providing fingerprint information of target molecules and single-molecules sensitivity has been widely used in on-site analysis; however, the SERS measurements always suffer from the problem of the stability of substrates. Here, the polyvinylpyrrolidone (PVP)-stabilized Au NPs (PVP-Au NPs) have been assembled through the simple, convenient evaporation-induced strategy with the large-scale hotspots substrates. The presence of PVP can not only facilitate the assembly of Au NPs but also prevent the corrosion of CN- towards the Au NPs with the formation of [Au (CN)2]-1, providing high stable and reproducible SERS signals. Moreover, the PVP-Au NPs have been assembled on the Si wafer to fabricate the portable SERS chip for rapid on-site detection of CN- with an RSD of 5.8% and limitation of 100 ppb. Furthermore, by coupling a portable Raman spectrometer, the SERS spectra of CN- spiked into different specimens to simulate the poison samples have been collected and analyzed on SERS chips with the recovery of 89-103% and RSD not higher than 11.3%. Consequently, the fabricated SERS chip with assembled PVP-Au NPs can provide sensitive and credible detection for CN- in different specimens, and then would satisfy the rapid on-site evaluation of CN- in poisoning incidents with the portable Raman spectrometer. Graphical Abstract.

A label-free electrochemical magnetic aptasensor based on exonuclease III-assisted signal amplification for determination of carcinoembryonic antigen.

A novel label-free and exonuclease III (Exo III)-assisted signal amplification electrochemical aptasensor was constructed for the determination of carcinoembryonic antigen (CEA) via magnetic field-induced self-assembly of magnetic biocomposites (Fe3O4@Au NPs-S1-S2-S3). The magnetic biocomposites were acquired by modifying double-stranded DNA (S1-S2-S3) on the surface of Fe3O4@Au nanoparticles (Fe3O4@Au NPs). Among them, Fe3O4@Au NPs were used as carriers for magnetic separation, thiolated single-stranded DNA (S1) provided signal sequence, CEA aptamer (S2) worked as a recognition element, and complementary strand (S3) was used to form double strands. In the presence of CEA, S2 bonded with CEA competitively; the exposed S1 could not be cleaved since Exo III was inactive against ssDNA. The G-quadruplex/hemin complexes finally formed with the existence of K+, and the high electrochemical signal of G-quadruplex/hemin complexes was recorded by differential pulse voltammetry (DPV) at - 0.6 V. Conversely, in the absence of CEA, dsDNA was cleaved from the 3' blunt end by Exo III; the disappearance of G-rich sequence blocked the generation of the signal. This method exhibited good selectivity and sensitivity for the determination of CEA; the linear range was from 0.1 to 200 ng mL-1 and the limit of detection was 0.4 pg mL-1. Graphical abstract.

Influences of simulated gastrointestinal environment on physicochemical properties of gold nanoparticles and their implications on intestinal epithelial permeability.

Gold nanoparticles (Au NPs) hold great promise in food, industrial and biomedical applications due to their unique physicochemical properties. However, influences of the gastrointestinal tract (GIT), a likely route for Au NPs administration, on the physicochemical properties of Au NPs has been rarely evaluated. Here, we investigated the influence of GIT fluids on the physicochemical properties of Au NPs (5, 50, and 100 nm) and their implications on intestinal epithelial permeability in vitro. Au NPs aggregated in fasted gastric fluids and generated hydroxyl radicals in the presence of H2O2. Cell studies showed that GIT fluids incubation of Au NPs affected the cellular uptake of Au NPs but did not induce cytotoxicity or disturb the intestinal epithelial permeability.

A "turn-on" fluorometric assay for kanamycin detection by using silver nanoclusters and surface plasmon enhanced energy transfer.

A rapid method is described for the determination of the antibiotic kanamycin. It integrates a kanamycin-binding aptamer and surface plasmon enhanced energy transfer (SPEET) between DNA-templated silver nanoclusters (AgNCs) and gold nanoparticles (AuNPs). The AgNCs and AuNPs were selected as energy donor and energy acceptor, respectively. The aptamer was designed to regulate the energy transfer between AgNCs and AuNPs. The aptamer was adsorbed on the AuNPs. Upon addition of kanamycin, the aptamer-kanamycin complex is formed, and this results in the aggregation of the AuNPs in high salt concentration, the formation of a blue coloration, and in the suppression of the SPEET process. The fluorescence of the AgNCs (with excitation/emission peaks at 560/600 nm) is quenched by the aptamer protected AuNPs in absence of kanamycin. The fluorescence on addition of kanamycin increases linearly in the 5 to 50 nM concentration range, with a lower detection limit of 1.0 nM (at S/N = 3). The assay can be performed within 30 min. It was successfully applied to the determination of kanamycin in spiked milk samples, and recoveries ranged between 90.2 and 95.4%. Conceivably, the strategy has a wide potential for screening by simply changing the aptamer. Graphical abstract Schematic presentation of the aptamer regulated surface plasmon enhance energy transfer (SPEET) between silver nanoclusters (Ag NCs) and gold nanoparticles (Au NCs) in high salt concentration buffer, and of the procedure for the detection of kanamycin.

In-situ generation of gold nanoparticles on MnO2 nanosheets for the enhanced oxidative degradation of basic dye (Methylene Blue).

In this work, the gold nanoparticles (Au-NPs) were in-situ generated on the surface of MnO2 nanosheets to form MnO2/Au-NPs nanocomposite in a simple and cost-effective way. Multiple experiments were carried out to optimize the oxidation of basic dye (Methylene Blue (MB)), including the molar ratio of MnO2 to chloroauric acid (HAuCl4), the pH of the solution and the effect of initial material. Under the optimal condition, the highest degradation efficiency for MB achieved to 98.9% within 60 min, which was obviously better than commercial MnO2 powders (4.3%) and MnO2 nanosheets (74.2%). The enhanced oxidative degradation might attribute to the in-situ generation of ultra-small and highly-dispersed Au-NPs which enlarged the synergistic effect and/or interfacial effect between MnO2 nanosheets and Au-NPs and facilitated the uptake of electrons by MnO2 from MB during the oxidation, thus validating the application of MnO2/Au-NPs nanocomposite for direct removal of organic dyes from wastewater in a simple and convenient fashion.

Enantiomeric separation by microchip electrophoresis using bovine serum albumin conjugated magnetic core-shell Fe3 O4 @Au nanocomposites as stationary phase.

In this work, a novel enantioselective MCE was developed employing BSA-conjugated Fe3 O4 @Au nanoparticles (Fe3 O4 @Au NPs) as stationary phase. Fe3 O4 @Au NPs with high magnetic responsively, excellent solubility, and high dispersibility in water were prepared through a sonochemical synthesis strategy. BSA was then immobilized onto the Fe3 O4 @Au NPs surfaces through the well-developed interaction between Au NPs and amine groups of BSA to form Fe3 O4 @Au NPs-BSA conjugates, which were then locally packed into PDMS microchannels with the help of magnets. The resultant Fe3 O4 @Au NPs-BSA conjugates not only have the magnetism of Fe3 O4 NPs that make them easily manipulated by an external magnetic field, but also have the larger surface and excellent biocompatibility of Au shell, which can incorporate much more biomolecules and well maintain their biological activity. In addition, the successful BSA decorations endowed Fe3 O4 @Au NPs-BSA conjugates with pH-tunable water solubility related to the pI of BSA (pI 4.7) and led to enhanced stability against high ionic strength. Compared with the native PDMS microchannel, the modified surfaces exhibited more stable and suppressed electroosmotic mobility, and less nonspecific adsorption toward analytes. Successful separation of chiral amino acids (tryptophan and threonine) and ofloxacin enantiomers demonstrate that the constructed MCE columns own ideal enantioselectivity. The results are expected to open up a new possibility for high-throughput screening of enantiomers with protein targets as well as a new application of magnetic NPs.