Peng Si

Gold nanoparticle-graphite-like C3N4 nanosheet nanohybrids used for electrochemiluminescent immunosensor.

Two-dimensional graphite-like carbon nitride nanosheets (g-C3N4 NSs) were hybridized with gold nanoparticles (Au NPs) to construct an electrochemiluminescence (ECL) immunosensor. The prepared Au NP-functionalized g-C3N4 NS nanohybrids (Au-g-C3N4 NHs) exhibit strong and stable cathodic ECL activity compared to g-C3N4 NSs due to the important roles of Au NPs in trapping and storing the electrons from the conduction band of g-C3N4 NSs, as well as preventing high energy electron-induced passivation of g-C3N4 NSs. On the basis of the improved ECL stability and ECL peak intensity of the Au-g-C3N4 NHs, a novel ECL immunosensor was developed to detect carcinoembryonic antigen (CEA) as a model target analyte. The ECL immunosensor has a sensitive response to CEA in a linear range of 0.02-80 ng mL(-1) with a detection limit of 6.8 pg mL(-1). Additionally, the proposed immunosensor shows high specificity, good reproducibility, and long-term stability.

Hierarchically structured one-dimensional TiO2 for protein immobilization, direct electrochemistry, and mediator-free glucose sensing.

A novel one-dimensional hierarchically structured TiO(2) (1DHS TiO(2)) was synthesized by a solvothermal method using multiwalled carbon nanotubes (MWCNTs) as a template and evaluated for the immobilization of protein and biosensing applications. Characterization studies showed that the 1DHS TiO(2) possessed an anatase crystalline structure and a large surface area with narrow pore size distribution. Fast direct electron transfer was observed for glucose oxidase (GOx) immobilized on the 1DHS TiO(2), and excellent electrocatalytic performance for glucose detection can be obtained without a mediator. The glucose sensor based on the GOx/1DHS TiO(2)-modified electrode had a high sensitivity of 9.90 μA mM(-1) cm(-2) and a low detection limit of 1.29 μM. The fabricated biosensor displayed good selectivity and long-term stability, indicating that the novel structured TiO(2) is a promising material for the immobilization of biomolecules and the fabrication of third-generation biosensors.

Nanomaterials for electrochemical non-enzymatic glucose biosensors

This review overviews the recent development of nanomaterials for the application of electrochemical non-enzymatic glucose biosensors. The electrocatalytic mechanism and glucose sensing performance of a variety of nanostructured materials including metallic nanoparticles, metal oxides, metal complexes, alloys and carbon nanomaterials are discussed. The merits and shortfalls of each nanomaterial as electrocatalyst for non-enzymatic biosensing are evaluated and the prospects of non-enzymatic glucose biosensors are presented.

An electrochemically formed three-dimensional structure of polypyrrole / graphene nanoplatelets for high-performance supercapacitors

A novel nanoplatelet-like structure of the composites of polypyrrole (PPy) and graphene (GR) is facilely synthesized by an electrochemical method and is further employed as a supercapacitor. The nanocomposite of PPy/GR shows a porous structure with a specific surface area of as high as 136.5 m2 g−1. As a result, the composite material exhibits a high specific capacitance of 285 F g−1 at a discharge rate of 0.5 A g−1, and excellent cycling stability. Specifically, over 90% of its initial capacitance can be retained after 1000 charge/discharge cycles. With advantageous features, such as facile fabrication process, high specific capacitance and excellent cycle life, this electrochemically synthesized PPy/GR nanocomposite is quite promising for high-performance supercapacitor applications.

A hierarchically structured composite of Mn3O4/3D graphene foam for flexible nonenzymatic biosensors

We report a novel composite material of hierarchically structured Mn3O4 grown on three-dimensional graphene foam (3DGF). This hierarchical Mn3O4/3DGF composite was fabricated as a flexible and freestanding biosensor for nonenzymatic determination of glucose and H2O2, significant analytes in health care and food industry. The Mn3O4/3DGF-based biosensor achieved high sensitivity, large linear range and low detection limit for the detection of both analytes, due to the synergistic effects of the two materials, which combines the high electrocatalytic activity of the nanostructured Mn3O4 network, and high conductivity and large surface area of 3DGF. This enzymeless biosensor also exhibited excellent performance for real-time detection of glucose and H2O2 in serum and food samples.

Fluorescent pH sensor based on Ag@SiO2 core-shell nanoparticle.

We have demonstrated a novel method for the preparation of a fluorescence-based pH sensor by combining the plasmon resonance band of Ag core and pH sensitive dye (HPTS). A thickness-variable silica shell is placed between Ag core and HPTS dye to achieve the maximum fluorescence enhancement. At the shell thickness of 8 nm, the fluorescence intensity increases 4 and 9 times when the sensor is excited at 405 and 455 nm, respectively. At the same time, the fluorescence intensity shows a good sensitivity toward pH value in the range of 5-9, and the ratio of emission intensity at 513 nm excited at 455 nm to that excited at 405 nm versus the pH value in the range of 5-9 is determined. It is believed that the present pH sensor has the potential for determining pH real time in the biological sample.

Highly stable and sensitive glucose biosensor based on covalently assembled high density Au nanostructures

We describe the development of a highly stable and sensitive glucose biosensor based on the nanohybrid materials derived from gold nanoparticles (AuNPs) and multi-walled carbon nanotubes (MWCNT). The biosensing platform was developed by using layer-by-layer (LBL) self-assembly of the nanohybrid materials and the enzyme glucose oxidase (GOx). A high density of AuNPs and MWCNT nanocomposite materials were constructed by alternate self assembly of thiol functionalized MWCNTs and AuNPs, followed by chemisoption of GOx. The surface morphology of multilayered AuNPs/MWCNT structure was characterized by field emission-scanning electron microscope (FE-SEM), and the surface coverage of AuNPs was investigated by cyclic voltammetry (CV), showing that 5 layers of assembly achieves the maximum particle density on electrode. The immobilization of GOx was monitored by electrochemical impedance spectroscopy (EIS). CV and amperometry methods were used to study the electrochemical oxidation of glucose at physiological pH 7.4. The Au electrode modified with five layers of AuNPs/MWCNT composites and GOx exhibited an excellent electrocatalytic activity towards oxidation of glucose, which presents a wide liner range from 20 μM to 10 mM, with a sensitivity of 19.27 μA mM(-1) cm(-2). The detection limit of present modified electrode was found to be 2.3 μM (S/N=3). In addition, the resulting biosensor showed a faster amperometric current response (within 3 s) and low apparent Michaelis-Menten constant (K(m)(app)). Our present study shows that the high density of AuNPs decorated MWCNT is a promising nanohybrid material for the construction of enzyme based electrochemical biosensors.

Electrodeposition of hierarchical MnO2 spheres for enzyme immobilization and glucose biosensing

Here we report the template-free growth of hierarchical MnO2 spheres on indium tin oxide by electrodeposition for the first time. The structural evolution and growth mechanism of MnO2 was carefully investigated. The hierarchical MnO2 showed mesoporous structure and good biocompatibility for the immobilization of glucose oxidase (GOx). The bioconjugate of a GOx/MnO2-modified electrode was successfully employed for the mediatorless biosensing of glucose.

In Vivo Molecular Optical Coherence Tomography of Lymphatic Vessel Endothelial Hyaluronan Receptors

Optical Coherence Tomography (OCT) imaging of living subjects offers increased depth of penetration while maintaining high spatial resolution when compared to other optical microscopy techniques. However, since most protein biomarkers do not exhibit inherent contrast detectable by OCT, exogenous contrast agents must be employed for imaging specific cellular biomarkers of interest. While a number of OCT contrast agents have been previously studied, demonstrations of molecular targeting with such agents in live animals have been historically challenging and notably limited in success. Here we demonstrate for the first time that microbeads (µBs) can be used as contrast agents to target cellular biomarkers in lymphatic vessels and can be detected by OCT using a phase variance algorithm. This molecular OCT method enables in vivo imaging of the expression profiles of lymphatic vessel endothelial hyaluronan receptor 1 (LYVE-1), a biomarker that plays crucial roles in inflammation and tumor metastasis. In vivo OCT imaging of LVYE-1 showed that the biomarker was significantly down-regulated during inflammation induced by acute contact hypersensitivity (CHS). Our work demonstrated a powerful molecular imaging tool that can be used for high resolution studies of lymphatic function and dynamics in models of inflammation, tumor development, and other lymphatic diseases.

Gold Nanoprisms as Optical Coherence Tomography Contrast Agents in the Second Near Infrared Window for Enhanced Angiography in Live Animals

Optical coherence tomography angiography (OCTA) is an important tool for investigating vascular networks and microcirculation in living tissue. Traditional OCTA detects blood vessels via intravascular dynamic scattering signals derived from the movements of red blood cells (RBCs). However, the low hematocrit and long latency between RBCs in capillaries makes these OCTA signals discontinuous, leading to incomplete mapping of the vascular networks. OCTA imaging of microvascular circulation is particularly challenging in tumors due to the abnormally slow blood flow in angiogenic tumor vessels and strong attenuation of light by tumor tissue. Here we demonstrate in vivo that gold nanoprisms (GNPRs) can be used as OCT contrast agents working in the second near infrared window, significantly enhancing the dynamic scattering signals in microvessels and improving the sensitivity of OCTA in skin tissue and melanoma tumors in live mice. This is the first demonstration that nanoparticle-based OCT contrast agent work in vivo in the second near infrared window, which allows deeper imaging depth by OCT. With GNPRs as contrast agents, the post-injection OCT angiograms showed 41% and 59% more microvasculature than pre-injection angiograms in healthy mouse skin and melanoma tumors, respectively. By enabling better characterization of microvascular circulation in vivo, GNPR-enhanced OCTA could lead to better understanding of vascular functions during pathological conditions, more accurate measurements of therapeutic response, and improved patient prognoses.