Shuyan Niu

Carbon nanotube-enhanced DNA biosensor for DNA hybridization detection using manganese(II)-Schiff base complex as hybridization indicator.

A Mn(II) complex, MnL (L=sodium (E)-3-((1-carboxyethylimino)methyl)-4-hydroxybenzenesulfonate), was synthesized and characterized using elemental analysis and IR spectroscopy. Cyclic voltammetry (CV) and fluorescence spectroscopy were used to investigate the interaction between MnL and salmon sperm DNA. It was revealed that MnL presented high electrochemical activity on glassy carbon electrode (GCE), and it could be intercalated into the double helices of double-stranded DNA (dsDNA). Using MnL as the hybridization indicator, a novel and sensitive electrochemical DNA biosensor based on multiwall carbon nanotubes functionalized with carboxyl groups (MWCNTs-COOH, on which DNA probes were covalently immobilized) was prepared. The target single-stranded DNA (ssDNA) could be quantified ranging from 6.7 x 10(-10)M to 8.4 x 10(-9)M with good linearity (r=0.9922). A detection limit of 1.4 x 10(-10)M (3 sigma, n=9) was achieved.

Ultrasensitive photoelectrochemical immunoassay of antibody against tumor-associated carbohydrate antigen amplified by functionalized graphene derivates and enzymatic biocatalytic precipitation.

Tumor-associated carbohydrate antigens (TACAs) are often found on the surface of cancer cells. The determination of the carbohydrate components of glycoconjugates is challenging because of the chemical complexity of glycan chains. Through monitoring corresponding antibody, we can get a good solution for clinical diagnosis. Here breast tumor-associated carbohydrate antigens Tn were used as a model and a new photoelectrochemical biosensor for ultrasensitive detection of antibody against Tn was developed. To enhance the sensitivity, both graphene oxide and graphene were used during the construction of biosensor. Through the formation of immunocomplex and the insoluble biocatalytic precipitation (BCP) product, photocurrent intensity was decreased greatly and the antibody could be detected from 0.5 to 500 pg/mL with a detection limit of 1.0×10(-13) g/mL. At the same time, the developed biosensor showed acceptable selectivity and could be used in the complex matrix. Compared with the traditional glycoarray method, this PEC method is more sensitive (5 orders of magnitude), and thus provides another platform to monitor the immune response to carbohydrate epitopes at different stages during differentiation, metastasis, or treatment.

Gold nanoparticles and polyethylene glycols functionalized conducting polyaniline nanowires for ultrasensitive and low fouling immunosensing of alpha-fetoprotein.

An ultrasensitive biosensor for alpha-fetoprotein was developed based on electrochemically synthesized polyaniline (PANI) nanowires, which were functionalized with gold nanoparticles (AuNPs) and polyethylene glycols (PEG). The prepared PEG/AuNPs/PANI composite, combining the electrical conductivity of the AuNPs/PANI with the robust antifouling ability of PEG, offered an ideal substrate for the development of low fouling electrochemical biosensors. Alpha-fetoprotein (AFP), a well-known hepatocellular carcinoma biomarker, was used as a model analyte, and its antibody was immobilized on the PEG/AuNPs/PANI for the construction of the AFP immunosensor. Using the redox current of PANI as the sensing signal, in addition to the good biocompatibility of PEG/AuNPs and the anti-biofouling property of PEG, the developed immunosensor showed improved biosensing performances, such as wide linear range and ultralow detection limit (0.007pgmL(-1)). More importantly, it is label-free, reagentless and low fouling, making it capable of assaying AFP in real serum samples without suffering from significant interference or biofouling.

Amplified electrochemiluminescence detection of cancer cells using a new bifunctional quantum dot as signal probe.

In this work, we prepared a new electrochemiluminescent signal probe using a small bifunctional composite quantum dot (QD) with intense electrochemiluminescence (ECL) and excellent magnetic property, and developed a sensitive ECL biosensor for detection of cancer cells via DNA cyclic amplification technique. The graphene oxide (GO) with unique electrical properties was used as nano-amplified platform to immobilize a large number of capture DNA (c-DNA1). The endonuclease-assisted amplification technique was applied to amplify the ECL signal change induced by target cells. Specifically, the bifunctional composite QDs with excellent magnetic property can be conveniently labeled, separated, and developed the ECL signal probe, thus an ECL method for rapid and sensitive detection of cancer cells was developed. So far, it is for the first time that the small magnetic electrochemiluminescent QDs were applied to the assays of cancer cells by using amplification strategy, which is expected to have great potential for early clinical diagnosis of cancer.

PEGylated Polyaniline Nanofibers: Antifouling and Conducting Biomaterial for Electrochemical DNA Sensing

Biofouling arising from nonspecific adsorption is a substantial outstanding challenge in diagnostics and disease monitoring, and antifouling sensing interfaces capable of reducing the nonspecific adsorption of proteins from biological complex samples are highly desirable. We present herein the preparation of novel composite nanofibers through the grafting of polyethylene glycol (PEG) polymer onto polyaniline (PANI) nanofibers and their application in the development of antifouling electrochemical biosensors. The PEGylated PANI (PANI/PEG) nanofibers possessed large surface area and remained conductive and at the same time demonstrated excellent antifouling performances in single protein solutions as well as complex human serum samples. Sensitive and low fouling electrochemical biosensors for the breast cancer susceptibility gene (BRCA1) can be easily fabricated through the attachment of DNA probes to the PANI/PEG nanofibers. The biosensor showed a very high sensitivity to target BRCA1 with a linear range from 0.01 pM to 1 nM and was also efficient enough to detect DNA mismatches with satisfactory selectivity. Moreover, the DNA biosensor based on the PEGylated PANI nanofibers supported the quantification of BRCA1 in complex human serum, indicating great potential of this novel biomaterial for application in biosensors and bioelectronics.

DNA/SINGLE-WALLED CARBON NANOTUBES BASED FLUORESCENCE DETECTION OF Hg2+

A new, highly selective, and sensitive technique has been developed for the detection of Hg2+ using singled-wall carbon nanotubes (SWNTs) and two kinds of oligonucleotides. The fluorescence of the thymine-rich single stranded DNA labeled with dye (the probe ssDNA) was effectively quenched by the SWNTs. In the presence of a target DNA (rich T-T mismatched with probe), the tightness of the DNA wrapping around the SWNTs was loosened. Since binding of Hg2+ turned the T-T mismatches to stable T-Hg2+-T base pairs, and the binding rate of DNA and the nanotube was lower than that of DNA hybridization, it induced the release of DNA molecules from the SWNTs, and this resulted in a remarkable increase of fluorescence compared to that of the DNA-SWNTs. The assay exhibited a dynamic response range for Hg2+ from 4.52 × 10−8 M to 7.21 × 10−7 M with a detection limit of 10 nM.

A Novel Fluorescence Sensor for Cocaine with Signal Amplification through Cycling Exo-Cleaving with a Hairpin Probe

A novel fluorescence assay, based on the signal amplification through cycling reactions of aptameric recognition and nucleic acid exo-cleaving, was established for the sensitive detection of cocaine. In this assay, a new single fluorophore-labeled DNA-hairpin probe was used. This smart probe was established based on the significant nucleobase quenching between the nucleobases and the fluorophore. In the presence of cocaine and its aptamer, the structure of the smart probe changed to recover the fluorescence. In order to enhance the sensitivity of this assay, exonuclease III was introduced to enable the inputted cocaine to react with multiple probes in a recycling manner. Under the optimal conditions, a linear range for cocaine from 4.0 × 10−9 to 8.0 × 10−8 M with a detection limit of 1.76 × 10−9 M (3σ, n = 11) was obtained.

A Fluorescence Assay Based on GoldMag-CS Nanoparticles for Hepatitis B Virus DNA

A sensitive fluorescence assay for hepatitis B virus (HBV) DNA was developed based on the dissociation of bio-bar-code DNA probes from GoldMag-CS nanoparticles (NPs) and magnetic separation. In this method, the target sequence (HBV DNA) was recognized through sandwich hybridization by the catching probes and the detection probes. Catching probes were modified with biotins, and were specifically bound on streptavidin-coated 96-well microplates; detection probes were all attached on the GoldMag-CS nanoparticles, which also bound bio-bar-code strands with fluorescent tags. Bio-bar-codes were dissociated from the NPs by dithiothreitol (DTT) after DNA target recognition and magnetic separation, and then quantified. Streptavidin-coated 96-well microplates diminished the nonspecific binding of DNA-conjugated GoldMag-CS nanoparticles, thus lowering the background; and GoldMag-CS nanoparticles provided easy separation and significant signal amplification. Together, these two effects brought about the detection limit as low as 7.52 fM.