Highly sensitive electrochemiluminescence biosensors for cholesterol detection based on mesoporous magnetic core-shell microspheres.

A sensitive electrochemiluminescence (ECL) biosensor for cholesterol detection based on multifunctional core-shell structured microspheres (Fe3O4@SiO2-Au@mpSiO2) is reported. This microsphere consisted of a core of silica-coated magnetite nanoparticle, an active transition layer of gold nanoparticles and a mesoporous silica shell. Scanning electron microscopy was employed to observe the morphology of the nanomaterials and transmission electron microscopy was used to further confirm the subtle structure of Fe3O4@SiO2-Au@mpSiO2. The microspheres possessed a large surface area that increased enzyme loading, and an active transition layer gold nanoparticles enhanced the ECL signal. They were used to immobilize cholesterol oxidase for cholesterol detection with a high sensitivity, low detection limit and wide linear range. The linear range was from 0.83 to 2.62 mM with a detection limit of 0.28 µM (S/N = 3). Moreover, the reproducibility, stability and selectivity of the biosensor were established.

Graphene-multiwall carbon nanotube-gold nanocluster composites modified electrode for the simultaneous determination of ascorbic acid, dopamine, and uric acid.

In this paper, graphene-multiwall carbon nanotube-gold nanocluster (GP-MWCNT-AuNC) composites were synthesized and used as modifier to fabricate a sensor for simultaneous detection of ascorbic acid (AA), dopamine (DA), and uric acid (UA). The electrochemical behavior of the sensor was investigated by electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV) and differential pulse voltammetry (DPV) techniques. The combination of GP, MWCNTs, and AuNCs endowed the electrode with a large surface area, good catalytic activity, and high selectivity and sensitivity. The linear response range for simultaneous detection of AA, DA, and UA at the sensor were 120-1,701, 2-213, and 0.7-88.3 µM, correspondingly, and the detection limits were 40, 0.67, and 0.23 µM (S/N=3), respectively. The proposed method offers a promise for simple, rapid, selective, and cost-effective analysis of small biomolecules.

An electrogenerated chemiluminescence sensor based on gold nanoparticles@C60 hybrid for the determination of phenolic compounds.

This paper described a novel strategy for the construction of an electrogenerated chemiluminescence (ECL) sensor based on gold nanoparticles@C60 (AuNPs@C60) hybrid for detecting phenolic compounds. First, C60 was functionalized with l-cysteine. Subsequently, with C60 as the core, gold nanoparticles (AuNPs) are synthesized and grown through an in situ reduction method in the presence of ascorbic acid (AA). The resulted flowerlike AuNPs@C60 nanoparticles were modified onto the glassy carbon electrode to achieve the sensor (AuNPs@C60/GCE). Here, l-cysteine not only can improve the biocompatibility and hydrophilicity of C60 but also can enhance the electrogenerated chemiluminescence (ECL) of peroxydisulfate system. Furthermore, both AuNPs and C60 are also beneficial to the ECL of the peroxydisulfate system. Due to the combination of l-cysteine, AuNPs and C60, the proposed ECL sensor exhibited an excellent analytical performance. Under an optimum condition, the ECL intensity increased linearly with phenolic compounds. The linear ranges of 6.2 × 10(-8)-1.2 × 10(-4)M, 5.0 × 10(-8)-1.1 × 10(-4)M and 5.0 × 10(-8)-1.1 × 10(-4)M were obtained for catechol (CC), hydroquinone (HQ) and p-cresol (PC), respectively, and the detection limits were 2.1 × 10(-8)M, 1.5 × 10(-8)M and 1.7 × 10(-8)M, respectively. The AuNPs@C60 hybrid might hold a new opportunity to develop an ECL sensor.

An electrogenerated chemiluminescence sensor prepared with a graphene/multiwall carbon nanotube/gold nanocluster hybrid for the determination of phenolic compounds.

A dispersible graphene/multiwall carbon nanotube/gold nanocluster (GP/MWCNTs/AuNCs) hybrid in aqueous solution was prepared in situ, and characterized by transmission electron microscopy (TEM) and ultraviolet-visible (UV-vis) spectroscopy. Based on the fact that phenolic compounds can enhance the electrogenerated chemiluminescence (ECL) signal at the GP/MWCNTs/AuNCs modified glassy carbon electrode in the presence of peroxydisulfate, an ECL sensor was proposed for the determination of phenolic compounds with high sensitivity, good repeatability and stability. Due to its fascinating features, such as good water solubility and excellent stability, the GP/MWCNTs/AuNCs hybrid would offer a suitable catalytic platform for phenolic compounds and provide potential promise for the construction of ECL sensors.

Amperometric glucose biosensor based on glucose oxidase-lectin biospecific interaction.

An amperometric glucose biosensor based on high electrocatalytic activity of gold/platinum hybrid functionalized zinc oxide nanorods (Pt-Au@ZnONRs) and glucose oxidase (GOx)-lectin biospecific interaction was proposed. The Pt-Au@ZnONRs, which were prepared through a multiple-step chemosynthesis, were modified onto the surface of glassy carbon electrode (GCE) by a simple casting method due to the excellent film forming ability of the Pt-Au@ZnONRs suspension. Subsequently, a layer of porous gold nanocrystals (pAu) film was assembled onto the Pt-Au@ZnONRs film by immersing the electrode in HAuCl(4) solution to perform the electrochemical deposition at a constant potential of -0.2V. Following that, Concanavalin A (ConA) was immobilized onto the surface of pAu film through physical adsorption and covalent binding interactions between gold nanomaterials and the amino groups or thiol groups of ConA protein. Finally, the GOx was easily immobilized on the ConA/pAu/Pt-Au@ZnONRs/GCE by the biospecific interaction between GOx and ConA. The Pt-Au@ZnONRs composites were characterized using transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). Cyclic voltammetry (CV) was used to characterize the assembly process of the modified electrode. Proposed biosensor showed a high electrocatalytic activity to the glucose with a wide linear range covering from 1.8 µM to 5.15 mM, a low detection limit of 0.6 µM and a low apparent Michaelis-Menten constant (K(M)(app)) of 0.41 mM. Furthermore, the biosensor exhibited good reproducibility and long-term stability, as well as high selectivity. The integration of Pt-Au@ZnONRs and GOx-lectin biospecific interaction would offer potential promise for the fabrication of biosensors and biocatalysts.

Facile synthesis of graphene hybrid tube-like structure for simultaneous detection of ascorbic acid, dopamine, uric acid and tryptophan.

In the present work, a tube-like structure of graphene hybrid as modifier to fabricate electrode for simultaneous detection of ascorbic acid (AA), dopamine (DA), uric acid (UA) and tryptophan (Trp) was reported. The hybrid was synthesized by a simple method based on graphene sheets (GS) and 3,4,9,10-perylenetetracarboxylic acid (PTCA) via π-π stacking interaction under ultrasonic condition. The combination of GS and PTCA could effectively improve the dispersion of GS, owing to PTCA with the carboxylic-functionalized interface. Comparing with pure GS or PTCA modified electrode, GS-PTCA displayed high catalytic activity and selectivity toward the oxidation of AA, DA, UA, and Trp. Moreover, cyclic voltammetry, different pulse voltammetry and scanning electron microscopy were employed to characterize the sensors. The experiment results showed that the linear response range for simultaneous detection of AA, DA, UA, and Trp were 20-420 µM, 0.40-374 µM, 4-544 µM and 0.40-138 µM, respectively, and the detection limits were 5.60 µM, 0.13 µM, 0.92 µM and 0.06 µM (S/N=3). Importantly, the proposed method offers promise for simple, rapid, selective and cost-effective analysis of small biomolecules.

Highly-sensitive cholesterol biosensor based on platinum-gold hybrid functionalized ZnO nanorods.

A novel scheme for the fabrication of gold/platinum hybrid functionalized ZnO nanorods (Pt-Au@ZnONRs) and multiwalled carbon nanotubes (MWCNTs) modified electrode is presented and its application for cholesterol biosensor is investigated. Firstly, Pt-Au@ZnONRs was prepared by the method of chemical synthesis. Then, the Pt-Au@ZnONRs suspension was dropped on the MWCNTs modified glass carbon electrode, and followed with cholesterol oxidase (ChOx) immobilization by the adsorbing interaction between the nano-material and ChOx as well as the electrostatic interaction between ZnONRs and ChOx molecules. The combination of MWCNTs and Pt-Au@ZnONRs provided a favorable environment for ChOx and resulted in the enhanced analytical response of the biosensor. The resulted biosensor exhibited a linear response to cholesterol in the wide range of 0.1-759.3 µM with a low detection limit of 0.03 µM and a high sensitivity of 26.8 µA mM(-1). The calculated apparent Michaelis constant K(M)(app) was 1.84 mM, indicating a high affinity between ChOx and cholesterol.

Study on the application of reduced graphene oxide and multiwall carbon nanotubes hybrid materials for simultaneous determination of catechol, hydroquinone, p-cresol and nitrite.

In this paper, the reduced graphene oxide and multiwall carbon nanotubes hybrid materials (RGO-MWNTs) were prepared and a strategy for detecting environmental contaminations was proposed on the basis of RGO-MWNTs modified electrode. The hybrid materials were characterized by the scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS) and N(2) sorption-desorption isotherms. Due to the excellent catalytic activity, enhanced electrical conductivity and high surface area of the RGO-MWNTs, the simultaneous measurement of hydroquinone (HQ), catechol (CC), p-cresol (PC) and nitrite (NO(2)(-)) with four well-separate peaks was achieved at the RGO-MWNTs modified electrode. The linear response ranges for HQ, CC, PC and NO(2)(-) were 8.0-391.0 µM, 5.5-540.0 µM, 5.0-430.0 µM and 75.0-6060.0 µM, correspondingly, and the detection limits (S/N=3) were 2.6 µM, 1.8 µM, 1.6 µM and 25.0 µM, respectively. The outstanding film forming ability of RGO-MWNTs hybrid materials endowed the modified electrode enhanced stability. Furthermore, the fabricated sensor was applied for the simultaneous determination of HQ, CC, PC and NO(2)(-) in the river water sample.