Hongmin Ma

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 immunosensor for the detection of kanamycin using Ag@Fe3O4 nanoparticles and thionine mixed graphene sheet

A highly sensitive label-free immunosensor for the detection of kanamycin had been developed using silver hybridized mesoporous ferroferric oxide nanoparticles (Ag@Fe₃O₄ NPs) and thionine mixed graphene sheet (TH-GS). TH was used as an electron transfer mediator. The electrical signal was greatly improved in the presence of GS due to its good electron-transfer ability. With the advantages of large specific surface area and excellent electrical conductivity, Ag@Fe₃O₄ NPs could immobilize more antibodies of kanamycin and promote the electron transfer. Cyclic voltammetry and square wave voltammetry were used to characterize the recognition of kanamycin. The proposed immunosensor showed good performances such as low detection limit (15 pg mL⁻¹), wide linear range (from 0.050 to 16 ng mL⁻¹), short analysis time (3 min), high stability, and good selectivity in the detection of kanamycin. The immunosensor was evaluated for pork meat sample, receiving satisfactory results.

Cathodic electrochemiluminescence immunosensor based on nanocomposites of semiconductor carboxylated g-C3N4 and graphene for the ultrasensitive detection of squamous cell carcinoma antigen

A novel label-free electrochemiluminescence (ECL) immunosensor was developed for the detection of squamous cell carcinoma antigen (SCCA) based on nanocomposites of semiconductor carboxylated graphitic carbon nitride (g-C3N4) and graphene (g-C3N4-graphene). The ECL intensity of carboxylated g-C3N4 was much enhanced after being combined with graphene which had excellent electron-transfer ability. The sensing platform was constructed by depositing g-C3N4-graphene on electrodes and immobilizing antibodies on the surface of carboxylated g-C3N4 through amidation. The specific immunoreaction between SCCA and antibody resulted in the decrease of ECL intensity and the intensity decreased linearly with the logarithm of SCCA concentration in the range of 0.025-10 ng mL(-1) with a detection limit of 8.53 pg mL(-1). The developed ECL immunosensor exhibited high sensitivity, good reproducibility and long-term stability, which possessed great potential for cancer detection in clinical laboratory diagnosis.

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.

A silver-palladium alloy nanoparticle-based electrochemical biosensor for simultaneous detection of ractopamine, clenbuterol and salbutamol.

A multiplexed electrochemical biosensor has been developed for fast and sensitive detection of ractopamine (RAC), salbutamol (SAL) and clenbuterol (CLB) based on reduced graphene oxide (rGO) and silver-palladium alloy nanoparticles (AgPd NPs). In this paper, rGO with high conductivity was used as an electrode material to immobilize artificial antigens and amplify electrochemical signal. AgPd NPs are used to label antibodies and generate a strong electrochemical signal in phosphate buffered saline (PBS) without any other substrates. Screen-printed carbon electrode (SPCE) and competition strategy were adopted to achieve simultaneous detection of RAC, SAL and CLB without cross-talk between adjacent electrodes. This method can simultaneously detect RAC, SAL and CLB ranging from 0.01 to 100 ng mL(-1) with detection limits of 1.52 pg mL(-1), 1.44 pg mL(-1) and 1.38 pg mL(-1), respectively. Satisfactory results are achieved in pork sample analysis. The designed strategy provides a promising potential in determination of other biological samples.

Label-free immunosensor based on Pd nanoplates for amperometric immunoassay of alpha-fetoprotein

In this paper, Pd nanoplates were used as a kind of electrode materials for fabrication of an electrochemical immunosensor, which was applied for detection of cancer biomarker alpha-fetoprotein (AFP). Thanks to the unique structure and properties of Pd nanoplates, the antibody of AFP (Ab) was effectively immobilized onto the surface of the Pd nanoplates modified glassy carbon electrode (GCE). Moreover, the good electrochemical properties of Pd nanoplates greatly improved the electronic transmission rate and enhanced the electrochemical signal, which led to an increase of the detection sensitivity. Based on the specific antibody-antigen interaction, a label-free immunosensor based on Pd nanoplates was developed for sensing of AFP. The current method allows us to detect AFP over a wide concentration range from 0.01 to 75.0 ng/mL with a detection limit of 4 pg/mL. The proposed immunosensor has been used to determine AFP in human serum with satisfactory results.

Label-free electrochemical immunosensor for prostate-specific antigen based on silver hybridized mesoporous silica nanoparticles

Due to high sensitivity and good selectivity, electrochemical immunosensor is often used to detect tumor markers. Prostate-specific antigen (PSA) is the most validated tumor marker for prostate cancer. In this work, mesoporous silica nanoparticles (MSNs) were used to increase the fixation capacity of primary antibody, and silver nanoparticles (Ag NPs) were used to enhance the electron transfer rates. Silver hybridized mesoporous silica nanoparticles (Ag@MSNs) were synthesized and used as electrode material. Hydroquinone (HQ) generated a stable electrochemical signal and was used as a mediator. Based on the specific antibody-antigen interaction, a label-free immunosensor was developed for the sensing of PSA. The current method allows us to detect PSA over a wide concentration range from 0.05 to 50.0 ng ml(-1) with a detection limit of 15 pg ml(-1). The proposed immunosensor was used to determine PSA in human serum with satisfactory results.

A novel ECL biosensor for the detection of concanavalin A based on glucose functionalized NiCo2S4 nanoparticles-grown on carboxylic graphene as quenching probe

An electrochemiluminescence (ECL) biosensor was developed for detection of Concanavalin A (Con A). Chitosan/Ru(bpy)32+/silica/Fe3O4 nanomaterials (CRuSi-Fe3O4) were synthesized through W/O microemulsion route. The added Fe3O4 nanoparticles can simplify the prepared process and enhance the conductivity of nanomaterials which can increase the ECL intensity of luminophor CRuSi-Fe3O4. In addition, the layered structure of CRuSi-Fe3O4 can immobilize lots of Con A using glutaraldehyde as the coupling agent which can improve the sensitivity of the biosensor. Then the quenching probe glucose functionalized NiCo2S4 nanoparticles-grown on carboxylic graphene (NiCo2S4-COOH-rGO@Glu) was anchored on the modified-electrode via the specific carbohydrate-Con A interaction. Here, NiCo2S4 was used to quench the ECL of CRuSi-Fe3O4, graphene was used to grow NiCo2S4 nanoparticles as carrier materials and glucose was served as the recognition element for bounding Con A. Therefore, a desirable quenching ECL signal was measured with S2O82- as the coreactant of CRuSi-Fe3O4. Under the optimization of determination conditions, a linear response range for Con A from 0.5pgmL-1 to 100ngmL-1 was obtained, and the detection limit was calculated to be 0.18pgmL-1 (S/N=3).

Graphene-Based Optical and Electrochemical Biosensors: A Review

The unexpected discovery of graphene and especially the follow-up explosion of interest in its properties and applications marked the beginning of a new carbon era. Graphene is a real two-dimensional crystal (one-atom-thick) with high crystal quality and quite unusual electronic properties, and has shown great promise in a variety of applications, such as field-effect transistors, photovoltaic devices, and biosensors. In addition to the properties that make graphene an excellent transducer material in biosensors, such as high electron transfer ability and specific surface area, several advantages of graphene over carbon nanotubes, one of its well-studied allotropes, are becoming apparent. Graphene shows super-quenching capability toward various organic dyes and quantum dots due to the long-range nanoscale resonance energy transfer. Graphene-based hybrid materials, especially nanoparticle-decorated graphene nanocomposites, have been widely used as electrode materials for the development of electrochemical biosensors. In this review, we outline the recent advances about the application of graphene-based materials in biosensors, with focus on fluorescence and electrochemical biosensors.

Metal ions-based immunosensor for simultaneous determination of estradiol and diethylstilbestrol

Environmental estrogens (EEs) can cause various endocrine diseases. Herein, we designed an ultrasensitive electrochemical immunosensor for simultaneous detection of two typical EEs, estradiol and diethylstilbestrol. These two analytes were immobilized on graphene sheet (GS) modified glassy carbon electrode (GCE). Amino-group functionalized mesoporous Fe3O4 (Fe3O4-NH2) was loaded with Pb(2+) or Cd(2+), and then incubated with estradiol and diethylstilbestrol antibodies, respectively. Using an electrochemical analysis technique, two well-separated peaks were generated by the redox reaction of Pb(2+) or Cd(2+), making the simultaneous detection of two analytes on the electrode possible. Subsequently, square wave anodic stripping voltammetry (SWASV) and electrochemical impedance spectroscopy (EIS) were used to investigate the electrochemical behaviors of the immunosensor. Under optimized conditions, the SWASV peak currents were proportional to the concentrations of estradiol and diethylstilbestrol in the range from 0.050 pg mL(-1) to 100 ng mL(-1) and 1.0 pg mL(-1) to 100 ng mL(-1), respectively. The immunosensor exhibited highly sensitive response to estradiol with a detection limit of 0.015 pg mL(-1) and diethylstilbestrol with a detection limit of 0.38 pg mL(-1). Furthermore, the immunosensor was satisfactorily employed to detect estradiol and diethylstilbestrol simultaneously in water samples.