Shanmin Gao

Highly sensitive recognition of Pb2+ using Pb2+ triggered exonuclease aided DNA recycling

Here, we have demonstrated an ultra-high sensitive detection platform with the detection limit of 5pM for an environmental toxin-Pb(2+). We designed a Pb(2+) triggered exonuclease aided DNA recycling system to improve the detection sensitivity. In our system, a Pb(2+) dependent 8-17 DNAzyme and its substrate were used to form hybridization duplex. In the presence of Pb(2+), the substrate was cleaved and disassociated from the duplex. Then, the released 8-17 DNAzyme was used as a target of the exonuclease aided DNA recycling system which can amplify the fluorescence signal by recycling the 8-17 DNAzyme continuously. Then, the sensitive Pb(2+) detection are accomplished and the detection limit of Pb(2+) was down to 5pM which is about 1000 times lower than the traditional detection method based on the 8-17 DNAzyme.

Graphene-based nanoprobes and a prototype optical biosensing platform

Biochemical and biomedical applications of graphene are critically dependent on the interaction between biomolecules and the nanomaterial. In this work, we developed a graphene-based signal-amplification nanoprobe by combining anti-immunoglobulin G (anti-IgG) and horseradish peroxidase (HRP) with graphene oxide (GO). The structure and function of HRP in the nano-interface of GO were firstly investigated, which demonstrated that the enzyme retained 78% of its native activity and 77% of its native α-helix content. HRP and anti-IgG were then co-adsorbed onto GO to form bifunctional nanoprobes. The nanoprobes provide both improved binding ability and signal-amplification ability. Comparing with conventional bioconjugates such as enzyme-linked antibody, co-adsorption could avoid chemical conjugation between biomolecules, keeping their bioactivity well. As an example for their application, the nanoprobes were used to obtain amplified signals in a sandwich-type immunoassay for cancer marker, instead of conventional colorimetric conjugates. This approach provided a detection limit of 10 pg/mL alpha-fetoprotein (AFP), which was much more sensitive than conventional enzyme-linked immunosorbent assay (ELISA) methods. The easily fabricated GO-based nanoprobes have the potential to become universal probes for molecular diagnostics.

A graphene-based platform for fluorescent detection of SNPs

A novel fluorescent single nucleotide polymorphism (SNP) assay was developed by using Graphene Oxide (GO), which provides a fast, sensitive and simple method for SNP detection. The strategy was based on the single base extension reaction and different absorption capacity of fluorescein labeled dGTP (dGTP-Fl) and double-stranded DNA (dsDNA) to GO. dGTP-Fl is incorporated into the probe by extension reaction for the mutant target but not for the wild target, which leads to recovered fluorescence for the mutant target because of weak interaction between dsDNA and GO and weak fluorescence for the wild target because of the quenched fluorescence of dGTP-Fl by GO. The method shows a linear range for the mutant-type target from 3 nM to 50 nM and 3 nM is the detection limit. It was noted that as low as 10% mutant-type target could be detected in the presence of the wild-type target, in which the concentration is 9 times higher than that of the mutant-type target.

One-step preparation of core-shell Au@poly(m-phenylenediamine) without any extra reagent and electrocatalytic biosensing for H2O2

In this paper, a simple, one-step chemical synthesis of Au@poly(m-phenylenediamine) (PMPD) core-shell nanoparticles by direct dropping aqueous chloroauric acid aqueous solution to m-phenylenediamine aqueous solution was reported, which is a facile and green method. We further evaluate the use of the obtained Au@PMPD to modify glassy carbon electrode and for H2O2 electrocatalytic biosensing. The results indicate that the aggregated small Au nanoparticles in the inner part of PMPD could be an ideal sensing platform for H2O2 detection.

Bio-mediated synthesis and antibacterial activity against aquatic pathogens of silver nanoparticles decorated titania nanosheets in dark and under solar-light irradiation

ABSTRACT Antibacterial nanomaterials produced by sustainable or ‘green’ synthesis methods are very important. Moreover, combination of photocatalytic antibacterial materials and antiseptic inorganic nanoparticles still remains challenging. This work reports on the two-step, green biosynthesis, characterization and antibacterial activity against aquatic pathogens of a nanocomposite formed from titanium dioxide (TiO2) nanosheets decorated with silver nanoparticles (Ag NPs), in which the grape seeds extract is used as the reducing and stabilizing agent. The as-prepared Ag/TiO2 nanocomposites were characterized by various methods. The appearance of absorption peak at about 425 nm demonstrates the formation of Ag NPs due to the typical surface plasmon resonance (SPR) effect of silver. The antibacterial activity of Ag/TiO2 nanocomposites against 6 kinds of common aquatic pathogens in the dark was tested. Furthermore, the bactericidal efficiency of the prepared nanocomposites with different contents of TiO2 nanosheets in the dark or under solar-light irradiation was compared.