Zhicheng Lu

Hierarchical nanogaps within bioscaffold arrays as a high-performance SERS substrate for animal virus biosensing.

A three-dimensional (3D) biomimetic SERS substrate with hierarchical nanogaps was formed on the bioscaffold arrays of cicada wings by one-step and reagents-free ion-sputtering techniques. This approach requires a minimal fabrication effort and cost and offers Ag nanoislands and Ag nanoflowers with four types of nanogaps (<10 nm) on the chitin nanopillars to generate a high density of hotspots (∼2000/μm2). The 3D biomimetic substrate shows a low detection limit to Rhodamine 6G (10(-13) M), high average enhancement factor (EF, 5.8×10(7)), excellent signal uniformity (5.4%), good stability, and suitability in biosensing. Furthermore, the finite-difference time-domain (FDTD) electric-field-distribution simulations illustrate that the 3D biomimetic SERS substrate provides the high-density hotspot area within a detection volumem, resulting in enormous SERS enhancement. In addition, the conspicuous far-field plasmon resonance peaks were not found to be a strong requirement for a high EF in 3D biomimetic substrates. Additionally, the novel substrate was applied in label-free animal viruses detection and differentiation with small amounts (1.0 μL) and low concentrations of analyte (1×10(3) PFU/mL), and it exhibited potential as an effective SERS platform for virus detection and sensing.

Antiviral Activity of Graphene Oxide: How Sharp Edged Structure and Charge Matter.

Graphene oxide and its derivatives have been widely explored for their antimicrobial properties due to their high surface-to-volume ratios and unique chemical and physical properties. However, little information is available on their effects on viruses. In this study, we report the broad-spectrum antiviral activity of GO against pseudorabies virus (PRV, a DNA virus) and porcine epidemic diarrhea virus (PEDV, an RNA virus). Our results showed that GO significantly suppressed the infection of PRV and PEDV for a 2 log reduction in virus titers at noncytotoxic concentrations. The potent antiviral activity of both GO and rGO can be attributed to the unique single-layer structure and negative charge. First, GO exhibited potent antiviral activity when conjugated with PVP, a nonionic polymer, but not when conjugated with PDDA, a cationic polymer. Additionally, the precursors Gt and GtO showed much weaker antiviral activity than monolayer GO and rGO, suggesting that the nanosheet structure is important for antiviral properties. Furthermore, GO inactivated both viruses by structural destruction prior to viral entry. The overall results suggest the potential of graphene oxide as a novel promising antiviral agent with a broad and potent antiviral activity.

Carbon-Dot and Quantum-Dot-Coated Dual-Emission Core–Satellite Silica Nanoparticles for Ratiometric Intracellular Cu2+ Imaging

Copper (Cu(2+)) is physiologically essential, but excessive Cu(2+) may cause potential risk to plants and animals due to the bioaccumulative properties. Hence, sensitive recognition is crucial to avoid overintake of Cu(2+), and visual recognition is more favored for practical application. In this work, a dual-emission ratiometric fluorescent nanoprobe was developed possessing the required intensity ratio, which can facilitate the sensitive identification of Cu(2+) by the naked eye. The probe hybridizes two fluorescence nanodots (quantum dots (QDs) and carbon dots (CDs)). Although both of them can be viable fluorescence probes for metal ion detection, rarely research has coupled this two different kinds of fluorescence material in one nanosensor to fabricate a selectively ratiometric fluorescence probe for intracellular imaging. The red emitting CdTe/CdS QDs were capped around the silica microsphere to serve as the response signal label, and the blue-emitting CDs, which is insensitive to the analyte, were covalently attached to the QDs surface to act as the reference signal. This core-satellite hybrid sphere not only improves the stability and brightness of QDs significantly but also decreases the cytotoxicity toward HeLa cells tremendously. Moreover, the Cu(2+) could quench the QDs emission effectively but have no ability for reduction of the CDs emission. Accordingly, a simple, efficient, and precise method for tracing Cu(2+) was proposed. The increase of Cu(2+) concentration in the series of 0-3 × 10(-6) M was in accordance with linearly decrease of the F650/F425 ratio. As for practical application, this nanosensor was utilized to the ratiometric fluorescence imaging of copper ions in HeLa cells.

Clean Synthesis of an Economical 3D Nanochain Network of PdCu Alloy with Enhanced Electrocatalytic Performance towards Ethanol Oxidation

A one-pot method for the fast synthesis of a 3D nanochain network (NNC) of PdCu alloy without any surfactants is described. The composition of the as-prepared PdCu alloy catalysts can be precisely controlled by changing the precursor ratio of Pd to Cu. First, the Cu content changes the electronic structure of Pd in the 3D NNC of PdCu alloy. Second, the 3D network structure offers large open pores, high surface areas, and self-supported properties. Third, the surfactant-free strategy results in a relatively clean surface. These factors all contribute to better electrocatalytic activity and durability towards ethanol oxidation. Moreover, the use of copper in the alloy lowers the price of the catalyst by replacing the noble metal palladium with non-noble metal copper. The composition-optimized Pd80 Cu20 alloy in the 3D NNC catalyst shows an increased electrochemically active surface area (80.95 m(2)  g(-1) ) and a 3.62-fold enhancement of mass activity (6.16 A mg(-1) ) over a commercial Pd/C catalyst.

Ultrasensitive detection of aflatoxin B1 by SERS aptasensor based on exonuclease-assisted recycling amplification

Aflatoxin B1 (AFB1) is one of the most abundant and carcinogenic food-contaminating mycotoxins around the world. In this study, we proposed a surface enhanced Raman scattering (SERS) sensing strategy for the determination of AFB1. An aptamer for AFB1 partially hybridized with complementary-DNA, which was released after the recognition of AFB1 and immediately hybridized with hairpin DNA on the surface of sputtering Au film. Exonuclease III hydrolyzed the double-stranded DNA, leaving short single-stranded DNA on the Au surface and releasing complementary-DNA for next ring opening and digestion. SERS tag was captured on Au surface by DNA hybridization. Agarose gel electrophoresis and dynamic light scattering showed that SERS tag was successfully prepared. The detection principle was validated by electrochemical impedance spectroscopy and SERS at each step. High sensitivity and good selectivity for AFB1 detection were observed. The results showed that there was a good linear relation when the AFB1 concentration was from 1×10-6 to 1ng/mL, and the limit of detection (LOD) was 0.4 fg/mL. This sensor was also applied for quantifying AFB1 levels in spiked peanuts samples, the recoveries was in the range of 89-121%.

Highly sensitive enzyme-free immunosorbent assay for porcine circovirus type 2 antibody using Au-Pt/SiO2 nanocomposites as labels

Improving the performance of conventional enzyme-linked immunosorbent assay (ELISA) is of great importance to meet the demand of early clinical diagnosis of various diseases. Herein, we report a feasible enzyme-free immunosorbent assay (EFISA) system using antibody conjugated Au-Pt/SiO2 nanocomposites (APS NCs) as labels. In this system, Au-Pt/SiO2 nanospheres (APS NPs) were first synthesized by wet chemical method and exhibited intrinsic peroxidase and catalase-like activity with excellent water-solubility. Then APS NCs were utilized as labels to replace HRP conjugated antibody, and Fe3O4 magnetic beads (MBs) to entrap the analyte. To discuss the performance of EFISA system, Human IgG was served as a model analyte, and porcine circovirus type 2 (PCV2) serums as real samples. The system boosted the detection limit of HIgG to 75pgmL(-1) with a RSD below 5%, a 264-fold improvement as compared with conventional ELISA. This is the first time that APS NCs have been used and successfully optimized for the sensitive dilution detection of PCV2 antibody (5:10(7)) in ELISA. Besides, APS NCs have advantages related to low cost, easy preparation, good stability and tunable catalytic activity, which make them a potent enzyme mimetic candidate and may find potential applications in bioassays and clinical diagnostics.

Hydrogen-bonding recognition-induced aggregation of gold nanoparticles for the determination of the migration of melamine monomers using dynamic light scattering

The migration of melamine monomers from food contact materials has aroused particular attention since the 2008 melamine-tainted milk scandal in China. However, the determination of melamine monomers migratory quantity (MMMQ) has remained an open question because of the complex sample pretreatment and the low sensitivity. Based on the hydrogen bonding interaction between DNA thymine and melamine, this paper described a simple and rapid method focusing on the measurement of MMMQ from melamine tableware by gold nanoparticles (GNPs) and dynamic light scattering (DLS). With the presence of probe DNA (p-DNA), the GNPs were stable in NaCl solution (0.06 M), whereas they became aggregated when the p-DNA hybridized with melamine. The change in the hydrodynamic diameter of GNPs could be detected by DLS technology. Under the optimal conditions, the average diameter increased linearly with the concentration of melamine over the range from 5.0 to 320.0 μg L(-1), and showed a detection limit of 2.0 μg L(-1) (3σ/slope). The MMMQ was investigated within a range from 6.00×10(-4) to 2.58×10(-1) mg dm(-2) (n≥3) in four different food simulants at different temperatures and time points. The results suggest that the DLS method has great potential in the analysis of the migration of melamine monomers.

Ultrasensitive SERS detection of Bacillus thuringiensis special gene based on Au@Ag NRs and magnetic beads

Highly sensitive and selective detection of specific DNA sequences is of great importance in clinical diagnosis, environmental and food monitoring, but it still remains challenges to develop a facile method for real sample detection in aqueous solution. Here, a simple and recyclable surface enhanced Raman scattering (SERS) sensor was constructed for Bacillus thuringiensis (Bt) special gene fragment detection by Fe3O4 magnetic beads (MBs) and Au-Ag core-shell nanorods (Au@Ag NRs). A hairpin DNA with sulfhydryl and biotin was attached to Au@Ag NRs as indicator, and MBs with streptavidin (SA) were acted as the capture probe. On the basis of the biotin-SA specific interaction, target sequences were first hybridized with the hairpin DNA and exposed the biotin. Subsequently, the Au@Ag NRs were captured by the streptavidin modified MBs, which reduced the suspended NRs and led to the change of Raman intensity. Under the optimal conditions, the SERS intensity revealed a good linearity with Bt transgene fragment ranging from 0.1pM to 1nM with a detection limit of 0.14pM (S/N=3). To demonstrate the specificity of the strategy, the single-base mismatch in DNA was discussed in the SERS assay. The results showed that the sensitivity and accuracy of the proposed method was acceptable in DNA detection, revealing a great potential in special gene detection.

Graphene Oxide-Silver Nanocomposite: Novel Agricultural Antifungal Agent against Fusarium graminearum for Crop Disease Prevention

Nanoparticle-based antibacterial agents have emerged as an interdisciplinary field involving medicine, material science, biology, and chemistry because of their size-dependent qualities, high surface-to-volume ratio, and unique physiochemical properties. Some of them have shown great promise for their application in plant protection and nutrition. Here, GO-AgNPs nanocomposite was fabricated through interfacial electrostatic self-assembly and its antifungal activity against phytopathogen Fusarium graminearum was investigated in vitro and in vivo for the first time. The results demonstrated that the GO-AgNPs nanocomposite showed almost a 3- and 7-fold increase of inhibition efficiency over pure AgNPs and GO suspension, respectively. The spore germination inhibition was stimulated by a relatively low concentration of 4.68 μg/mL (minimum inhibition concentration (MIC)). The spores and hyphae were damaged, which might be caused by an antibacterial mechanism from the remarkable synergistic effect of GO-AgNPs, inducing physical injury and chemical reactive oxygen species generation. More importantly, the chemical reduction of GO mediated by fungal spores was possibly contributed to the high antimicrobial activity of GO-AgNPs. Furthermore, the GO-AgNPs nanocomposite showed a significant effect in controlling the leaf spot disease infected by F. graminearum in the detached leaf experiment. All the results from this research suggest that the GO-AgNPs nanocomposite developed in this work has the potential as a promising material for the development of novel antimicrobial agents against pathogenic fungi or bacteria.

Controlled Synthesis of Au-Island-Covered Pd Nanotubes with Abundant Heterojunction Interfaces for Enhanced Electrooxidation of Alcohol.

Here, we, for the first time, synthesized Pd nanotubes covered by high-density Au-islands, in which abundant exposed Pd–Au heterojunction interfaces are present and the content of element Au can be easily controlled. The optimized nanostructures show remarkably enhanced activity for catalyzing different alcohols in alkaline media than commercial Pd/C. The mass activity is 9.66, 1.83, and 4.60 A mgmetal–1 toward the electrooxidation of ethanol, glycerol, and ethylene glycol in alkaline media, which is about 6, 4, and 7 times that of Pd/C, respectively. Additionally, a model was proposed to explain the relationship between the structure and the catalytic activity.