Kexia Mao

Electrochemical bisphenol A sensor based on N-doped graphene sheets.

Bisphenol A (BPA), which could disrupt endocrine system and cause cancer, has been considered as an endocrine disruptor. Therefore, it is very important and necessary to develop a sensitive and selective method for detection of BPA. Herein, nitrogen-doped graphene sheets (N-GS) and chitosan (CS) were used to prepare electrochemical BPA sensor. Compared with graphene, N-GS has favorable electron transfer ability and electrocatalytic property, which could enhance the response signal towards BPA. CS also exhibits excellent film forming ability and improves the electrochemical behavior of N-GS modified electrode. The sensor exhibits a sensitive response to BPA in the range of 1.0×10(-8)-1.3×10(-6) mol L(-1) with a low detection limit of 5.0×10(-9) mol L(-1) under the optimal conditions. Finally, this proposed sensor was successfully employed to determine BPA in water samples with satisfactory results.

Label-free electrochemical immunosensor based on graphene/methylene blue nanocomposite

For the specificity of prostate cancer markers, prostate specific antigen (PSA) has been widely used in prostate cancer screening, diagnosis, and treatment after monitoring. In normal male serum, PSA can only be detected in traces of 0-4 ng mL(-1). In this paper, we constructed an electrochemical immunosensor for PSA detection using a nanocomposite film of graphene sheets-methylene blue-chitosan (GS-MB-CS) as electrode material. The nanocomposite film showed high binding affinity to the electrode and was used to immobilize the antibody of PSA. The modification procedure was monitored by cyclic voltammetry (CV). An amperometric biosensor was easily developed based on the response of peak current to the capture of PSA induced by specific antigen-antibody reactions. Under optimum conditions, the amperometric signal decreased linearly with PSA concentration (0.05-5.00 ng mL(-1)). A low limit of detection (13 pg mL(-1)) and a high selectivity are obtained. Moreover, the prepared immunosensor was applied for the analysis of PSA in serum samples with satisfactory results. The proposed method may have a promising future in biochemical assays for high selectivity, good reproducibility, and stability.

Electrochemical immunosensor for α-fetoprotein detection using ferroferric oxide and horseradish peroxidase as signal amplification labels

An electrochemical immunosensor for quantitative detection of α-fetoprotein (AFP) in human serum was developed using graphene sheets (GS) and thionine (TH) as electrode materials and mesoporous silica nanoparticles (MSNs) loaded with ferroferric oxide (Fe3O4) nanoparticles and horseradish peroxidase (HRP) as labels for signal amplification. In this study, the compound of GS and TH (GS-TH) was used as a substrate for promoting electron transfer and immobilization of primary antibody of AFP (Ab1). MSNs were used as a carrier for immobilization of secondary antibody of AFP (Ab2), Fe3O4, and HRP. The synergistic effect occurred between Fe3O4 and HRP and greatly improved the sensitivity of the immunosensor. This method could detect AFP over a wide concentration range from 0.01 to 25 ng ml(-1) with a detection limit of 4 pg ml(-1). This strategy may find wide potential application in clinical analysis or detection of other tumor markers.

A novel chemiluminescent flow-injection analysis of transferrin by its reduction of the luminol--hydrogen peroxide reaction catalysed by meso-tetra-(3-methoxyl-4-hydroxyl) phenyl manganese porphyrin.

Based on the inhibition effect of transferrin (Tf) on the reaction of the luminol-hydrogen peroxide (H(2)O(2)) chemiluminescence (CL) system, catalysed by meso-tetra-(3-methoxyl-4-hydroxyl) phenyl manganese porphyrin (MnP) as a mimetic enzyme of peroxides, a sensitive flow-injection CL method has been developed for the determination of Tf in an alkaline medium. The CL reaction was carefully investigated by examining the variations of reaction conditions. Under optimum conditions, the linear range for the determination of transferrin was 0.04-20.0 μg/mL and the detection limit was 1.62 ng/mL. This proposed method was sensitive, convenient and simple, and has been successfully applied to the determination of transferrin in a serum sample.

Ultrasensitive multiplexed immunosensors for the simultaneous determination of endocrine disrupting compounds using Pt@SBA-15 as a non-enzymatic label

The simultaneous determination of different analytes based on multiplexed immunosensors is attractive and promising in bioassays and environmental analysis. In this paper, a novel ultrasensitive multiplexed immunoassay method was developed for the determination of endocrine disrupting compounds (EDCs) based on disposable screen-printed carbon electrodes. Different capture antibodies were separately immobilized on the carbon electrodes to form an immunosensor array. Platinum nanoparticle-functionalized mesoporous silica nanoparticles (Pt@SBA-15) was used as catalytic labels of secondary antibodies. Due to the catalytic activities of the platinum nanoparticles and the large surface area of SBA-15, a strong electrical response towards the analytical antigens was achieved. The multiplexed immunoassay array enables the simultaneous determination of different analytes. Using diethylstilbestrol and estradiol as model analytes, this multiplexed immunoassay method showed wide linear ranges with detection limits down to 0.28 and 1.2 pg mL-1 for diethylstilbestrol and estradiol, respectively. The proposed sensing strategy enriches electrochemical immunoassays and has a promising application in bioassays and environmental analysis.

Studies of Catalytic Kinetic Spectrophotometric Determination of Trace Manganese (II) Sensitized by Microemulsion Medium

A new catalytic kinetic spectrophotometric method for the determination of trace amount of manganese (II) (Mn (II)) in microemulsion medium has been developed. The method is based on the catalytic effect of Mn (II) on the oxidation of nuclear fast red by potassium periodate with Nitrilotriacetic Acid (NTA) as an activitor in the presence of Tween-80/n-butanol/n-heptane microemulsion and HAc-NaAc buffer solution (pH = 5.80). The linear ranges are in the range of 0.800 ~ 4.00 ng/mL of Mn(II) at 520 nm and the detection limit is 1.80 times 10 -10 g/mL. This method can be used in the determination of trace Mn(II) in nutriment, food and different water samples with satisfying results.