Long Wu

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.

Platinum Dendritic-Flowers Prepared by Tellurium Nanowires Exhibit High Electrocatalytic Activity for Glycerol Oxidation

Dentritic Pt-based nanomaterials with enriched edge and corner atoms have recently attracted considerable attention as electrocatalysts. Meanwhile, Pt(111) facets are generally considered more active for the glycerol oxidation reaction (GOR). Thus, it is significant to construct the rational design and synthesis of dentritic Pt whose surface is mostly enclosed by {111} facets. Reported herein is a unique Pt-branched structure enriched by a large amount of valency unsaturated atoms prepared by the aggravation of the galvanic replacement strategy. The synthesis is developed to generate highly crystallized Pt nanoflowers using Te nanowires as a template. Furthermore, the electrochemical results show that Pt nanoflower is an excellent catalyst with higher mass activity and better structure stability than commercial Pt/C (20% Pt) for glycerol electro-oxidation. Besides, the template-broken approach could provide a novel potential way to synthesize Pt-based or other noble metals/alloys for their advanced functional applications.

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.

Spiny-porous platinum nanotubes with enhanced electrocatalytic activity for methanol oxidation

A facile and general approach is developed to synthesize self-supported spiny-porous Pt nanotubes (SP-PtNTs). The multi-dimensional structure with enriched edge and corner atoms showed 4.3 and 1.53 times higher mass electrocatalytic activity than porous Pt nanotubes (P-PtNTs) and commercial Pt/C (20% Pt), which increased the Pt utilization and decreased the dosage of Pt and the cost of Pt-based catalysts. SP-PtNTs had better stability and dispersibility than P-PtNTs and commercial Pt/C (20% Pt) in the water phase. The brief mechanism for the synthesis of SP-PtNTs could also be extended to synthesize other noble metals, as well as their bimetallic combinations, with excellent catalysis and electrocatalysis. Furthermore, the spiny structure provided extra active sites that might facilitate the application of Pt for use in enzyme-like catalysis or nano-electronic applications.

Enhanced immunoassay for porcine circovirus type 2 antibody using enzyme-loaded and quantum dots-embedded shell–core silica nanospheres based on enzyme-linked immunosorbent assay

Boosting the detection sensitivity of enzyme-linked immunosorbent assay (ELISA) is significant to the early clinical diagnosis of various diseases. Here, we developed a versatile immunosensor using silica nanospheres as carriers for sensitive detection of porcine circovirus type 2 (PCV2) antibody. With HRP enzyme covalently immobilized on the silica nanospheres and CdSe nanocrystals embedded inside, these signal probes were successfully utilized in the sensitive detection of PCV2 antibody by ELISA, fluorometry and square-wave voltammetry (SWV). To further demonstrate the performance of the immunosensor, Human IgG (HIgG) was used as a model analyte. Since more HRP and CdSe QDs were loaded, 5-, 200- and 400-fold enhancements in amplified ELISA, fluorometry and voltammetry responses for HIgG could be achieved compared to conventional ELISA. The respective detection limits of theses methods for HIgG were 3.9, 0.1 and 0.05 ng mL(-1) with a RSD below 5% for amplified ELISA, fluorescence and SWV measurements. Additionally, a 100-fold improvement was obtained in the detection sensitivity for PCV2 antibody immunoassay. The versatile immunosensor exhibits good sensitivity, stability and reproducibility, suggesting its potential applications in 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.

Target triggered self-assembly of Au nanoparticles for amplified detection of Bacillus thuringiensis transgenic sequence using SERS

The research methods for DNA detection have been widely extended since the application of nanotechnology, but it remains a challenge to detect specific DNA sequences or low abundance genes in the biological samples with accuracy and sensitivity. Here we developed a SERS biosensing platform by target DNA (tDNA) triggered self-assembly of Au nanoparticles (Au NPs) probes on DNA nanowires for signal amplification in DNA analysis. Based on the hybridization chain reactions (HCR) and surface enhanced Raman scattering (SERS) technology, the SERS intensity reveals a good linearity with tDNA ranging from 50 pM to 500 pM under optimal conditions. The specific detection of tDNA sequence was realized with a detection limit of 50 pM (S/N=3). To demonstrate the specificity and universality of the strategy, the single-base mismatches in DNA and the Bacillus thuringiensis (Bt) transgenic sequence were successively applied in the SERS assay. The results showed that the sensitivity and accuracy of the SERS-based assay were comparable with real-time PCR. Besides, the method would provide precise and ultra-sensitive detection of tDNA but also informative supplement to the SERS biosensing platform.

Versatile Electrochemiluminescence Assays for PEDV Antibody Based on Rolling Circle Amplification and Ru-DNA Nanotags

The sensitive and accurate detection methods for PEDV antibody have practical significance for the prevention and treatment of PEDV. In this work, a new multiple pathways signal amplification method was proposed to construct a sensitive electrochemiluminescence (ECL) platform for the detection of PEDV antibody. Using Au NP-modified graphene nanosheet (Au-GN) as the substrate, antibody-antigen reaction as the recognition unit, rolling circle amplification (RCA) for signal enhancement, and assembled cascade Ru-DNA nanotags as signal label, the proposed platform behaved with good specificity and sensitivity. The binding system of biotin-streptavidin, RCA, and Ru(bpy)32+-doped silica nanoparticles (Ru SNPs) showed remarkable amplification efficiency, low background signal, and little nonspecific adsorption. Moreover, the proposed ECL sensor exhibited good analytical performance for PEDV antibody with a wide linear range from 0.1 pg mL-1 to 5000 pg mL-1 with a detection limit of 0.05 pg mL-1 ( S/ N = 3). The proposed strategy exhibited the advantages of excellent stability and sensitivity for determination of the PEDV antibody, which was easy to prepare and had a good application prospect.