Jianbo Liu

Au@Pt nanostructures as oxidase and peroxidase mimetics for use in immunoassays

In this paper, we demonstrated that Au nanorods coated with a shell composed of Pt nanodots (Au@Pt nanostructures) exhibited intrinsic oxidase-like, peroxidase-like and catalase-like activity, catalyzing oxygen and hydrogen peroxide reduction and the dismutation decomposition of hydrogen peroxide to produce oxygen. Based on these findings, we established an Au@Pt nanostructures based enzyme linked immunosorbent assay (ELISA) for the detection of mouse interleukin 2 (IL-2). In comparison with natural enzymes, Au@Pt nanostructures have advantages of low cost, easy preparation, better stability, and tunable catalytic activity (compared with HRP), which make them a promising enzyme mimetic candidate and may find potential applications in biocatalysis, bioassays, and nano-biomedicine such as reactive oxygen species (ROS)-related fields (anti-aging and therapeutics for neurodegenerative diseases and cancers).

Formation of PdPt Alloy Nanodots on Gold Nanorods: Tuning Oxidase-like Activities via Composition

The island growth mode of Pt was employed to guide the forma-tion of PdPt alloy nanodots on gold nanorods (Au@PdPt NRs). Well-defined alloy nanodots, with tunable Pd/Pt ratios from 0.2 to 5, distribute homogeneously on the surface of the Au NR. Formation of nanodots shell leads to the red-shift and broadening of the longitudinal surface plasmon resonance (LSPR) band of the Au NRs. The Au@PdPt alloy NRs exhibit catalytic activity toward oxidation of often-used chromogenic substrates by dissolved oxygen under mild conditions, suggesting a new type of oxidase mimics. Composition dependence catalytic activity is observed for the oxidation of ascorbic acid (AA) and 3,3,5,5-tetramethylbenzidine (TMB) and for the reduction of p-nitrophenol. For AA and TMB, catalytic activity enhances quickly at lower Pd/Pt ratios and tends to saturate at higher Pd/Pt ratios. For p-nitrophenol reduction, catalytic activity shows a nice linear relationship with Pd/Pt ratio owing to much higher catalytic activity of Pd. In conclusion, proper alloying of Pd and Pt presents an effective route to tailor the catalytic activity. Interesting, alloy nanodots can also catalyze the oxidation of Fe (II) to Fe (III) by dissolved oxygen. Thus, based on the competitive oxidation of TMB and Fe (II), selective detection of the latter can be achieved.

Enhanced Optical Responses of Au@Pd Core/Shell Nanobars

A Pd nanoshell was epitaxially grown on a Au nanorod (NR) via simple seed-mediated growth. Compared with the cylindrical shape of the Au NR, the Au core/Pd shell (Au@Pd) nanorods change to a rectangular shape due to the disappearance of {110} facets. The Au NRs exhibit a strong longitudinal surface plasmon resonance (LSPR). As Pd is deposited, damping and broadening occur to the LSPR band. Interestingly, the LSPR band maximum first shows a small red-shift (ca. 40 nm) which then is followed by a blue-shift as the amount of Pd is increased. A thickness-dependent LSPR feature of the Pd shell is believed to contribute to the shift. At a thinner Pd thickness, the Au@Pd nanobars exhibit a well-defined LSPR band in the visible and near-infrared region, which demonstrates a higher dielectric sensitivity than that of the corresponding Au NRs. It thus opens up the potential of Pd nanostructures for SPR-based sensing. Investigations on the surface-enhanced Raman scattering (SERS) indicate that the SERS activities of the Au@Pd nanobars at thicknesses smaller than 2.5 nm mainly originate from the Au cores; thus, the SERS activities can be improved by tuning the aspect ratio of the Au core and/or the Pd shell thickness.

Formation of AgPt Alloy Nanoislands via Chemical Etching with Tunable Optical and Catalytic Properties

An effective way is developed to fabricate AgPt alloy nanoislands on gold nanorods based on the galvanic replacement between Ag and PtCl(4)(2-) in the presence of cetyltrimethylammonium bromide (CTAB). The optical and catalytic properties benefit from the porous structure composed of AgPt nanoislands. A large red shift (265 nm) after etching is observed for longitudinal surface plasmon resonance (SPR) in comparison with Au@Pt0.1@Ag. Alloy compositions in bulk miscibility gap can be obtained and finely tuned from Ag(0.56)Pt(0.44) to Ag(0.38)Pt(0.62). A unique composition dependence is found for both electrocatalytic oxidation of methanol and catalytic oxidation of o-phenylenediamine (OPD) by hydrogen peroxide. In both systems, the highest catalytic activity is achieved at the alloy composition of Pt(0.62)Ag(0.38). Proper alloying with Ag not only improves the CO poisoning of Pt catalyst but also enhances the catalytic activity greatly.

Peptide-tailored assembling of Au nanorods

By investigating the influence of peptides on the assembling process of Au nanorods induced by 4-mercaptopyridine, two kinds of peptides were identified. The nature of peptides plays an important role in tailoring assembling, which makes potential peptide recognition and detection possible.

Ferroxidase-like activity of Au nanorod/Pt nanodot structures and implications for cellular oxidative stress

Platinum nanoparticles (NPs) are reported to mimic various antioxidant enzymes and thus may produce a positive biological effect by reducing reactive oxygen species (ROS) levels. In this manuscript, we report Pt NPs as an enzyme mimic of ferroxidase by depositing platinum nanodots on gold nanorods (Au@Pt NDRs). Au@Pt NDRs show pH-dependent ferroxidase-like activity and have higher activity at neutral pH values. Cytotoxicity results with human cell lines (lung adenocarcinoma A549 and normal bronchial epithelial cell line HBE) show that Au@Pt NDRs are taken up into cells via endocytosis and translocate into the endosome/lysosome. Au@Pt NDRs have good biocompatibility at NDR particle concentrations lower than 0.15 nΜ. However, in the presence of H2O2, lysosomelocated NDRs exhibit peroxidase-like activity and therefore increase cytotoxicity. In the presence of Fe2+, the ferroxidase-like activity of the NDRs protects cells from oxidative stress by consuming H2O2. Thorough consideration should be given to this behavior when employing Au@Pt NDRs in biological systems.

Highly sensitive and robust peroxidase-like activity of Au–Pt core/shell nanorod-antigen conjugates for measles virus diagnosis

BackgroundAs a promising candidate for artificial enzymes, catalytically active nanomaterials show several advantages over natural enzymes, such as controlled synthesis at low cost, tunability of catalytic activities, and high stability under stringent conditions. Rod-shaped Au–Pt core/shell nanoparticles (Au@Pt NRs), prepared by Au nanorod-mediated growth, exhibit peroxidase-like activities and could serve as an inexpensive replacement for horseradish peroxidase, with potential applications in various bio-detections. The determination of measles virus is accomplished by a capture-enzyme-linked immunosorbent assay (ELISA) using Au@Pt NR-antigen conjugates.ResultsBased on the enhanced catalytic properties of this nanozyme probe, a linear response was observed up to 10xa0ng/mL measles IgM antibodies in human serum, which is 1000 times more sensitive than commercial ELISA.ConclusionsHence, these findings provide positive proof of concept for the potential of Au@Pt NR-antigen conjugates in the development of colorimetric biosensors that are simple, robust, and cost-effective.

Diagnosis of rubella virus using antigen-conjugated Au@Pt nanorods as nanozyme probe

Background As nanotechnology advances rapidly, the nanozymes which could replace protein enzymes in bioanalytical assays bring a new opportunity to the development of simple and sensitive diagnostic tools. Purpose Antibody-conjugated Au-Pt core/shell nanorods (Au@Pt NRs) have been used for nanozyme probes for diagnosis of rubella virus. Au@Pt NRs, prepared by Au nanorod-mediated growth, exhibit peroxidase-like activities and could serve as an inexpensive replacement for horseradish peroxidase (HRP) in conjugation of antigen. Method Using a capture enzyme-linked immunosorbant assay for the determination of rubella virus. Results Compared with antibody-conjugated HRP, the antigen-conjugated Au@Pt NRs are more stable and more robust, but less expensive. Based on the enhanced catalytic properties of this nanozyme probe, it was found that the antigen-conjugated Au@Pt NRs-based enzyme-linked immunosorbant assay exhibited good sensitivity. Conclusion Our results indicate that these antigen-conjugated Au@Pt NRs represent a suitable nanozyme probe for future clinical applications under various conditions.

Pt-guided formation of Au nanoislands on Au nanorods and its optical properties

Core–shell nanostructures exhibit unique optical and catalytic properties that are dependent on their morphology and composition. In this paper, a general and facile way was developed to prepare Au-nanoisland-coated Au nanorods with porous structures. Pt nanodots were first formed on Au nanorods by using a simple successive reduction growth. Then, the island growth mode of Pt on the Au rod was employed to guide the growth behavior of Au-nanoisland. Because of the high dielectric sensitivity of the Au nanostructures, tiny changes in the shell structure can be readily seen from absorption spectra and electromagnetic field enhancement. Simulations of absorption spectra and the electromagnetic field enhancement using the finite difference time domain (FDTD) method and taking into account the real shapes of the core–shell nanostructures were reported. The accuracy and validity of the FDTD method were verified. The results presented here indicated that surface plasmon resonances of these core–shell metallic nan...