Synthesis, Structural Analysis, and Peroxidase-Mimicking Activity of AuPt Branched Nanoparticles.

Bimetallic nanomaterials have generated significant interest across diverse scientific disciplines, due to their unique and tunable properties arising from the synergistic combination of two distinct metallic elements. This study presents a novel approach for synthesizing branched gold-platinum nanoparticles by utilizing poly(allylamine hydrochloride) (PAH)-stabilized branched gold nanoparticles, with a localized surface plasmon resonance (LSPR) response of around 1000 nm, as a template for platinum deposition. This approach allows precise control over nanoparticle size, the LSPR band, and the branching degree at an ambient temperature, without the need for high temperatures or organic solvents. The resulting AuPt branched nanoparticles not only demonstrate optical activity but also enhanced catalytic properties. To evaluate their catalytic potential, we compared the enzymatic capabilities of gold and gold-platinum nanoparticles by examining their peroxidase-like activity in the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB). Our findings revealed that the incorporation of platinum onto the gold surface substantially enhanced the catalytic efficiency, highlighting the potential of these bimetallic nanoparticles in catalytic applications.

Exo â ¢-assisted amplification signal strategy synergized with Au@Pt NFs/CoSe2 for sensitive detection of enrofloxacin.

Overuse of enrofloxacin (ENR) has posed a potential threat to ecosystems and public health, so it is critical to sensitive and accurate determination of ENR residues. In this work, a novel ultra-sensitive and specific electrochemical aptasensor was fabricated based on the cobalt diselenide loaded gold and platinum nanoflowers (Au@Pt NFs/ CoSe2) and Exonuclease III (Exo III)-assisted cycle amplification strategy for the detection of ENR. Au@Pt NFs/ CoSe2 nanosheets as the substrate material, with large surface area, accelerate electron transfer and attach more DNA probes on the electrode substrate, have effectively enhanced the electrochemical performance of the electrode. With the existence of Enrofloxacin (ENR), the aptamer recognizes and binds to ENR, thus the signal probe cDNA was released and immobilized onto the electrode surface to hybridized with methylene blue (MB) labelled DNA (MB-DNA), thereby triggering the Exo III-assisted cycle for further signal amplification. As expected, the prepared aptasensor demonstrated excellent sensitivity and selectivity, with a wide linear range from 5.0 × 10-6 ng/mL to 1.0 × 10-2 ng/mL for ENR, a low detection limit of 1.59 × 10-6 ng/mL. Consequently, this strategy provided a promising avenue for ultrasensitive and accurate detection of ENR in milk samples.

Synthesis of Structure-Adjustable R-Au/Pt-CdS Nanohybrids with Strong Plasmon Coupling and Improved Photothermal Conversion Performance.

Noble metal nanomaterials with a localized surface plasmon resonance effect exhibit outstanding advantages in areas such as photothermal therapy and photocatalysis. As a unique plasmonic metal nanostructure, gold nanobipyramids have been attracting much interest due to their strong specific local electric field intensity, large optical cross sections, and high refractive index sensitivity. In this study, we propose a novel three-component hetero-nanostructure composed of rough gold nanobipyramids (R-Au NBPs), Pt, and CdS. Initially, purified gold nanobipyramids are regrown to form R-Au NBPs that have a certain degree of roughness. These R-Au NBP substrates with a rough surface provide more hotspots and strengthen the intensity of localized electric fields. Subsequently, Pt and CdS nanoparticles are selectively deposited onto the surface of R-Au NBPs. Pt nanoparticles can provide more active sites. Each component of this hetero-nanostructure directly contacts others, creating multiple electron transfer channels. This novel design allows for tunable localized plasmon resonance wavelengths ranging from the visible to near-infrared regions. These factors contribute to the final superior photothermal conversion performance of the R-Au/Pt-CdS nanohybrids. Under the irradiation of near-infrared light (1064 nm), the photothermal conversion efficiency of R-Au/Pt-CdS reached 38.88%, which is 4.49, 1.5, and 1.22 times higher than that of Au NBPs, R-Au NBPs, and R-Au NBPs/Pt, respectively.

CTAB-Co-MOFs@AuPt NPs as signal probes for the electrochemical detection of carcinoembryonic antigen 15-3.

A sensitive electrochemical strategy for carcinoembryonic antigen 15-3 (CA15-3) detection is reported using CTAB-Co-MOFs@AuPt NPs as signal probes. The electrochemical strategy was designed as follows: First, the graphene aerogel@gold nanoparticles (GA@Au NPs) nanocomposites were employed to modify the sensing surface for promoting electron transfer rate and primary antibody (Ab1) immobilization due to GA possesses a large specific surface area, eminent conductivity, and a 3D network structure. Cobalt metal-organic frameworks (CTAB-Co-MOFs) synthesized were then used as a carrier for AuPt NPs and secondary antibody (Ab2) immobilization (notes: labelled-Ab2). With sandwich immunoreaction, the labelled-Ab2 was captured on the surface of the GA@Au NPs nanocomposites. Finally, differential pulse voltammetry (DPV) was employed to register the electrochemical signal of the immunosensor at the potential of - 0.85 V (vs SCE) in phosphate buffer saline (PBS) containing 2.5 mM H2O2. It was verified that the electrochemical reduction signal from Co3+ to Co2+ was recorded. The AuPt NPs could catalyze the reaction of H2O2 oxidizing Co2+ to Co3+, resulting in the amplification of the electrochemical signal. Under the selected conditions, the immunosensor can detect CA15-3 in the range 10 µU/mL to 250 U/mL with a low detection limit of 1.1 µU/mL. In the designed strategy, the CTAB-Co-MOFs were not only employed as carriers for AuPt NPs, but also acted as signal probes. The CTAB-Co-MOFs were investigated including SEM, TEM, XPS, and XRD. The application ability of the immunosensor was evaluated using serum sample, demonstrating the immunosensor can be applied to clinic serum analysis.

One-pot synthesized Au@Pt nanostars-based lateral flow immunoassay for colorimetric and photothermal dual-mode detection of SARS-CoV-2 nucleocapsid antibody.

In addition to confirming virus infection, quantitative identification of the antibodies to severe acute respiratory syndrome coronavirus 2(SARS-CoV-2) also evaluates persons immunity to guide personal protection. However, portable assays for fast and accurate quantification of SARS-CoV-2 antibodies remain challenging. In this work, we synthesized Au@Pt star-like nanoparticles (NPs) quickly and easily by a one-pot wet-chemical approach, allowing the stellate Au core to be partially decorated by Pt nanoshells. The nanoparticles were used as probe in a lateral flow immunoassay (LFIA) that operated in both colorimetric and photothermal dual modes, which could detect the antibodies to the SARS-CoV-2 nucleocapsid (N) protein with high sensitivity. Due to the sharp tips on the external region of nanostars and surface plasmon coupling effect between the Au core and Pt shell, the NIR absorption capacity and photothermal performance of these NPs were exceptional. Under optimal conditions, the colorimetric mode's detection limit for SARS-CoV-2 N protein antibody was 1 ng mL-1, which is significantly lower by 2-order of magnitude compared to commercially available colloidal gold strips. And the detection limit for the photothermal mode was as low as 24.91 pg mL-1, which was approximately 40-fold more sensitive than colorimetric detection. Moreover, the method demonstrated favorable specificity, reproducibility and stability. Finally, the approach was employed for the successful identification of actual serum samples. Therefore, the dual-mode LFIA can be applied for screening and tracking the early immunological reaction to SARS-CoV-2, and it has great promise for clinical application.

"Three-in-One" Nanozyme Composite for Augmented Cascade Catalytic Tumor Therapy.

Cascade catalytic reaction exhibits simple procedure and high efficiency, such as that from the orderly assembly of different enzymes in biological systems. Mimicking of the natural cascade procedure becomes critical, but the orderly assembly of different enzymes is still challenging. Herein, single Au-Pt nanozyme is reported with "three-in-one" functions to initiate cascade conversions for O2 supply as mimic catalase, H2 O2 production with its glucose oxidase-like property, and • OH generation as mimic peroxidase for chemodynamic therapy (CDT). Thus, the complex assembly and cross-talk among the different enzymes are avoided. To this end, metastable Cu2 O NPs, as scaffolds, are used to anchor ultrasmall Au-Pt nanozyme, while metal-organic framework (MOF) is used to encapsulate the nanozyme for tumor microenvironment response and shielding protein adsorption. Pluronic F127 is then modified on the surface to improve hydrophilicity and biocompatibility of the composite. The endogenous acidity and glutathione in tumor degrade MOF to expose nanozyme for cascade catalytic CDT. The high photothermal conversion ability also enhances the CDT, while Cu2+ ions consume GSH to further improve CDT efficiency as augmented cascade catalytic tumor therapy. Thus, a new paradigm is provided with drug-free single nanozyme for improving tumor therapeutic efficacy and minimizing side effects.

Kinetically Controlled Nucleation Enabled by Tunable Microfluidic Mixing for the Synthesis of Dendritic Au@Pt Core/Shell Nanomaterials.

The nucleation stage plays a decisive role in determining nanocrystal morphology and properties; hence, the ability to regulate nucleation is critical for achieving high-level control. Herein, glass microfluidic chips with S-shaped mixing units are designed for the synthesis of Au@Pt core/shell materials. The use of hydrodynamics to tune the nucleation kinetics is explored by varying the number of mixing units. Dendritic Au@Pt core/shell nanomaterials are controllably synthesized and a formation mechanism is proposed. As-synthesized Au@Pt exhibited excellent ethanol oxidation activity under alkaline conditions (8.4 times that of commercial Pt/C). This approach is also successfully applied to the synthesize of Au@Pd core/shell nanomaterials, thus demonstrating its generality.

Tuning the plasmonic and catalytic signals of Au@Pt nanoparticles for dual-mode biosensing.

Dual-mode biosensors have gained great attention due to their excellent detection accuracy provided by the mutual verification of output signals. However, current strategies for dual-mode sensing mainly rely on a signal probe exhibiting dual properties that may encounter unreliability. Herein, we report a dual-mode biosensing strategy by modulating the plasmonic and catalytic activities of nanoparticles through a surface growing approach. Ascorbic acid enables the growing of Au shell on Au@Pt NPs to tune both their peroxidase-like activity and plasmonic signal. Enzyme-catalyzed reactions can generate ascorbic acid to modulate the plasmonic and catalytic activities of nanoparticles. Combined with enzyme-linked immunosorbent assay, it enables dual-mode immunoassays of carbofuran with both a colorimetric readout by a spectrometer down to 0.1 ppb and a naked-eye readout of 5 ppb. This dual-mode biosensing technique advantages in tunable sensitivity and robustness, holding promise as an analytical platform for biomedical diagnosis and food safety.

Au-Nanorods Supporting Pd and Pt Nanocatalysts for the Hydrogen Evolution Reaction: Pd Is Revealed to Be a Better Catalyst than Pt.

Ordered thin films of Au nanorods (NRs) on Ti/Au/Si heterostructure substrates are electrodeposited in thin film aluminum oxide templates and, after template removal, serve as supports for Pd and Pt nanocatalysts. Based on previous work which showed a better electrocatalytic performance for layered Au/Pd nanostructures than monolithic Pd, electrodeposited 20 nm Pd discs on Au-NRs are first investigated in terms of their catalytic activity for the hydrogen evolution reaction (HER) and compared to monolithic 20 nm Pd and Pt discs. To further boost performance, the interfacial interaction area between the Au-NRs supports and the active metals (Pt and Pd) was increased via magnetron sputtering an extremely thin layer of Pt and Pd (20 nm overall sputtered thickness) on the Au-NRs after template removal. In this way, the whole NR surface (top and lateral) was covered with Pt and Pd nanoparticles, ensuring a maximum interfacial contact between the support and the active metal. The HER performance obtained was substantially higher than that of the other nanostructures. A Salient result of the present work, however, is the superior activity obtained for sputtered Pd on Au in comparison to that of sputtered Pt on Au. The results also show that increasing the Au-NR length translates in a strong increase in performance. Density functional theory calculations show that the interfacial electronic interactions between Au and Pd lead to suitable values of hydrogen adsorption energy on all possible sites, thus promoting faster (barrier-free diffusion) hydrogen adsorption and its recombination to H2. A Volmer-Heyrovsky mechanism for HER is proposed, and a volcano plot is suggested based on the results of the Tafel plots and the calculated hydrogen adsorption energies.

Metal-mediated Fe3O4@polydopamine-aptamer capture nanoprobe coupling multifunctional MXene@Au@Pt nanozyme for direct and portable photothermal analysis of circulating breast cancer cells.

Breast cancer (BC) is the most common cancer in the world and circulating tumor cells (CTCs) are reliable biomarkers for early breast cancer diagnosis in a non-invasive manner. However, effective isolation and sensitive detection of BC-CTCs by portable devices in human blood samples are extremely challenging. Herein, we proposed a highly sensitive and portable photothermal cytosensor for direct capture and quantification of BC-CTCs. To achieve efficient isolation of BC-CTCs, aptamer functionalized Fe3O4@PDA nanoprobe was facilely prepared through Ca2+-mediated DNA adsorption. To further detect the captured BC-CTCs with high sensitivity, multifunctional two-dimensional Ti3C2@Au@Pt nanozyme was synthesized, which not only possessed superior photothermal effect but also exhibited high peroxidase-like activity for catalyzing 3,3',5,5'-tetramethylbenzidine (TMB) to produce TMB oxide (oxTMB) with a strong photothermal characteristic, combining with Ti3C2@Au@Pt to synergistically amplify the temperature signal. Moreover, numerous Ti3C2@Au@Pt nanocomposites would be selectively attained on the BC-CTCs surface through multi-aptamer recognition and binding strategy, which further enhanced the specificity and facilitated signal amplification. Therefore, direct separation and highly sensitive detection of BC-CTCs was successfully achieved in human blood samples. More significantly, the controlled release of the captured BC-CTCs without affecting cell viability could be straightforwardly realized by a simple strand displacement reaction. Thus, with the distinct features of portability, high sensitivity, and easy operation, the current method holds great promise for early diagnosis of breast cancer.

In situ enzymatic generation of Au/Pt nanoparticles as an analytical photometric system: proof of concept determination of tyramine.

In situ enzymatic generation of bimetallic nanoparticles, mainly Au/Pt, overcomes the drawbacks (continuous absorbance drift, modest LOQ, and long-time reaction) observed when AuNP alone are produced. In this study, Au/Pt nanoparticles have been characterized by EDS, XPS, and HRTEM images using the enzymatic determination of tyramine with tyramine oxidase (TAO) as a model. Under experimental conditions, the Au/Pt NPs show an absorption maximum at 580 nm which can be related to the concentration of tyramine in the range 1.0 × 10-6M to 2.5 × 10-4M with a RSD of 3.4% (n = 5, using 5 × 10-6M tyramine). The Au/Pt system enables low LOQ (1.0 × 10-6 M), high reduction of the absorbance drift, and a significant shortening of the reaction time (i.e., from 30 to 2 min for a [tyramine] = 1 × 10-4M); additionally, a better selectivity is also obtained. The method has been applied to tyramine determination in cured cheese and no significant differences were obtained compared to a reference method (HRP:TMB). The effect of Pt(II) seems to involve the previous reduction of Au(III) to Au(I) and NP generation from this oxidation state. Finally, a three-step (nucleation-growth-aggregation) kinetic model for the generation of NPs is proposed; this has enabled us to obtain a mathematical equation which explains the experimentally observed variation of the absorbance with time.

Injectable Hydrogels Encapsulating Dual-Functional Au@Pt Core-Shell Nanoparticles Regulate Infarcted Microenvironments and Enhance the Therapeutic Efficacy of Stem Cells through Antioxidant and Electrical Integration.

Injectable functional biomaterials have made significant progress in cardiac regenerative. In addition, how to adjust the abominable infarction microenvironment and introduce therapeutic stem cells to improve the healing effect has become a hotspot. Herein, injectable stem cell vector is prepared by combining natural alginate hydrogel and Au@Pt nanoparticles (Au@Pt/Alg hydrogel) to encapsulate brown adipose stem cells (BASCs). Au@Pt nanoparticles with both antioxidative and conductive properties could effectively eliminate reactive oxygen species, enhance the frequency of action potential release of cardiomyocytes, and further reduce the inflammatory factors of macrophage in vitro. The Au@Pt/Alg hydrogel enhances the antioxidant, differentiation, and paracrine capability of BASCs. The effect of BASCs loaded Au@Pt/Alg hydrogel is evaluated in a rat myocardial infarction (MI) model. The antioxidant, anti-inflammatory, and heart electrical integration are showed in the MI model. More interestingly, Au@Pt/Alg hydrogel can effectively maintain the paracrine efficiency and pro-angiogenesis effects of BASCs in the infarcted area. This study led us to recognize the great value of Au@Pt/Alg hydrogels for their ability to actively regulate the microenvironment and carry stem cells for MI treatment.

Collision Electrochemical Synthesis of Metal Nanoparticles Using Electrons as Green Reducing Agent.

Synthesis of high-quality metal nanoparticles (NPs) is the premise toward their downstream diverse applications. Although some electrochemical synthesis strategies have been developed, the necessary use of high-concentration electrolyte solution as current pathway and reaction medium severely limits the colloidal stability of the growing NPs in the solution and their tunability in size and shape. Herein, we report a collision electrochemical method for the synthesis of metal NPs without the use of electrolyte solution. To this end, we designed an asymmetrical electrochemical cell to control the potential (i.e., to supply electrons) in the reaction system via a separated electrochemical cell, thereby enabling the electrochemical reaction occurring in an electrolyte-free growth solution. Consequently, this collision electrochemical method, using seed-mediated growth of NPs as examples, allows the synthesis of monodisperse homogeneous Au NPs and heterogeneous Pd- and Pt-coated Au NPs at a yield comparable to that achieved in common chemical synthesis. Furthermore, this method allows readily tailoring the morphology of the resultant metal NPs just by changing the concentration of the growth solution. Therefore, our green synthesis method is important for a variety of nanomaterials beyond metal NPs.

An Enzyme-Free Sandwich Amperometry-Type Immunosensor Based on Au/Pt Nanoparticle-Functionalized Graphene for the Rapid Detection of Avian Influenza Virus H9 Subtype.

Avian influenza virus H9 subtype (AIV H9) has contributed to enormous economic losses. Effective diagnosis is key to controlling the spread of AIV H9. In this study, a nonenzymatic highly electrocatalytic material was prepared using chitosan (Chi)-modified graphene sheet (GS)-functionalized Au/Pt nanoparticles (GS-Chi-Au/Pt), followed by the construction of a novel enzyme-free sandwich electrochemical immunosensor for the detection of AIV H9 using GS-Chi-Au/Pt and graphene-chitosan (GS-Chi) nanocomposites as a nonenzymatic highly electrocatalytic material and a substrate material to immobilize capture antibodies (avian influenza virus H9-monoclonal antibody, AIV H9/MAb), respectively. GS, which has a large specific surface area and many accessible active sites, permitted multiple Au/Pt nanoparticles to be attached to its surface, resulting in substantially improved conductivity and catalytic ability. Au/Pt nanoparticles can provide modified active sites for avian influenza virus H9-polyclonal antibody (AIV H9/PAb) immobilization as signal labels. Upon establishing the electrocatalytic activity of Au/Pt nanoparticles on graphene towards hydrogen peroxide (H2O2) reduction for signal amplification and optimizing the experimental parameters, we developed an AIV H9 electrochemical immunosensor, which showed a wide linear range from 101.37 EID50 mL-1 to 106.37 EID50 mL-1 and a detection limit of 100.82 EID50 mL-1. This sandwich electrochemical immunosensor also exhibited high selectivity, reproducibility and stability.

Synergy of Au-Pt for Enhancing Ethylene Photodegradation Performance of Flower-like TiO2.

Efficient and low-cost degradation of ethylene has always been a difficult problem in the storage and transportation of fruits and vegetables. Although photocatalysis is considered to be a feasible and efficient solution for ethylene degradation, the low degradation ability of conventional catalysts for small non-polar molecules limits its application. TiO2 has the advantage of tunable microstructure, but it also has the defects of wide band gap and low utilization of sunlight. The surface plasmon resonance (SPR) effect of noble metals can effectively improve the visible light absorption range of catalysts, and the synergy of noble metals further enhances the photocatalytic ability. Herein, we developed a series of AuPt catalysts through the photo-deposition method. Benefited from the SPR effect and the synergy of Au and Pt, the efficiency of AuPt-TiO2 was 19.9, 4.64 and 2.42 times that of TiO2, Au-TiO2 and Pt-TiO2, and the photocatalytic degradation ability of AuPt-TiO2 was maintained in five cyclic stability tests. Meanwhile, the transient photocurrent spectra and PL spectra proved that the light absorption capacity and carrier separation efficiency of AuPt-TiO2 were enhanced. This work provides a new direction for enhancing non-polar small-molecule photodegradation of semiconductors.

Ultrasensitive and Selective Detection of Glutathione by Ammonium Carbamate-Gold Platinum Nanoparticles-Based Electrochemical Sensor.

Determining the concentration of glutathione is crucial for developing workable medical diagnostic strategies. In this paper, we developed an electrochemical sensor by electrodepositing amino-based reactive groups and gold-platinum nanomaterials on the surface of glassy carbon electrode successively. The sensor was characterized by cyclic voltammetry (CV), field emission scanning electron microscope (FESEM), energy dispersive X-ray spectroscopy (EDX), and electrochemical impedance spectra (EIS). Results showed that Au@Pt nanoparticles with the size of 20-40 nm were presented on the surface of electrode. The sensor exhibits excellent electrocatalytic oxidation towards glutathione. Based on this, we devised an electrochemical biosensor for rapid and sensitive detection of glutathione. After optimizing experimental and operational conditions, a linear response for the concentration of GSH, in the range of 0.1-11 µmol/L, with low detection and quantification limits of 0.051 µM (S/N = 3), were obtained. The sensor also exhibits superior selectivity, reproducibility, low cost, as well as simple preparation and can be applied in human serum sample detection.

Au-Pt nanozyme-based multifunctional hydrogel dressing for diabetic wound healing.

Diabetic chronic wound healing is a critical clinical challenge due to the particularity of wound microenvironment, including hyperglycemia, excessive oxidative stress, hypoxia, and bacterial infection. Herein, we developed a multifunctional self-healing hydrogel dressing (defined as OHCN) to regulate the complex microenvironment of wound for accelerative diabetic wound repair. The OHCN hydrogel dressing was constructed by integrating Au-Pt alloy nanoparticles into a hydrogel (OHC) that formed through Schiff-base reaction between oxidized hyaluronic acid (OHA) and carboxymethyl chitosan (CMCS). The dynamic cross-linking of OHA and antibacterial CMCS imparted the OHCN hydrogel dressing with excellent antibacterial and self-healing properties. Meanwhile, Au-Pt alloy nanoparticles endowed the OHCN hydrogel dressing with the functions of lowering blood glucose, alleviating oxidative damage, and providing O2 by simulating glucose oxidase and catalase. Through a synergistic combination of OHC hydrogel and Au-Pt alloy nanoparticles, the resulted OHCN hydrogel dressing significantly ameliorated the pathological microenvironment and accelerated the healing rate of diabetic wound. The proposed nanozyme-decorated multifunctional hydrogel offers an efficient strategy for the improved management of diabetic chronic wound.

Two birds with one stone: innovative ceria-loaded gold@platinum nanospheres for photothermal-catalytic therapy of tumors.

Photothermal therapy (PTT) has been widely employed in tumor treatment due to the non-invasive, highly selective, and low toxic side effects. However, the limited penetration of laser couples with the metastasis and recurrence of tumors, thus failing to eliminate them. Here, we report that ceria-loaded gold@platinum (CeO2/Au@Pt) nanospheres modified with polyethylene glycol (PEG). exhibit dual enzymatic activities for photothermal-catalytic synergistic therapy of tumors. CeO2/Au@Pt nanospheres are constructed through the loading of ultra-small CeO2 into core-shell Au@Pt nanospheres. In such a construct, Au@Pt enables targeted PTT, thanks to exceptional photothermal properties, while CeO2 nanozymes alleviate tumor hypoxia and kill tumor cells by producing highly toxic hydroxyl radicals (·OH) based on catalase- and peroxidase-like activities. Synergistic photothermal-catalytic therapy is achieved by delivering nanozymes to the tumor microenvironment (TME) coupled with PTT. This photothermal-catalytic approach that combines simultaneous exogenous and endogenous activation is a potential option for tumor co-therapy.

Multifunctional Au@Pt@Ag NPs with color-photothermal-Raman properties for multimodal lateral flow immunoassay.

Multimodal lateral flow immunoassay (LFIA) has displayed its potential to improve practicability and elasticity of point-of-care testing. Herein, multifunctional core-shell-shell Au@Pt@Ag NPs loaded with dual-layer Raman reporter molecules of 5,5'-dithiobis-(2-nitrobenzoic acid) (DTNB) with a characteristic combination of color-photothermal-Raman performance were constructed for colorimetric LFIA (CM-LFIA), photothermal LFIA (PT-LFIA) and surface-enhanced Raman scattering-based LFIA (SERS-LFIA), respectively. The highly specific nanoprobes, being obtained through the combination of the resulted dual-layer DTNB modified Au@Pt@Ag NPs with the antibody, were triumphantly utilized in exploring multimodal LFIA with one visual qualitative and two optional quantitative modes with excellent sensing sensitivity. Under optimal conditions, the limit of detection (LOD) for the model hazardous analyte dehydroepiandrosterone (DHEA) were 1.0 ng mL-1 for CM-LFIA, 0.42 ng mL-1 for PT-LFIA, and 0.013 ng mL-1 for SERS-LFIA, three of which were over 100-fold, 200-fold and 7 000-fold more sensitive than conventional visual AuNPs-based LFIA, respectively. In addition, the quantitative PT-LFIA and SERS-LFIA sensors worked well in spiked real samples with acceptable recoveries of 96.2 - 106.7% and 98.2 - 105.2%, respectively. This assay demonstrated that the developed multimodal LFIA had a great potential to be a powerful tool for accurate tracing hazardous analytes in complex samples.

Thermal Activation of Gold Atom Diffusion in Au@Pt Nanorods.

Understanding the thermal stability of bimetallic nanoparticles is of vital importance to preserve their functionalities during their use in a variety of applications. In contrast to well-studied bimetallic systems such as Au@Ag, heat-induced morphological and compositional changes in Au@Pt nanoparticles are insufficiently understood, even though Au@Pt is an important material for catalysis. To investigate the thermal instability of Au@Pt nanorods at temperatures below their bulk melting point, we combined in situ heating with two- and three-dimensional electron microscopy techniques, including three-dimensional energy-dispersive X-ray spectroscopy. The experimental results were used as input for molecular dynamics simulations, to unravel the mechanisms behind the morphological transformation of Au@Pt core-shell nanorods. We conclude that thermal stability is influenced not only by the degree of coverage of Pt on Au but also by structural details of the Pt shell.