Xiaomeng Meng

Electrochemical determination of microRNA-21 based on graphene, LNA integrated molecular beacon, AuNPs and biotin multifunctional bio bar codes and enzymatic assay system

MicroRNAs (miRNAs), a kind of small, endogenous, noncoding RNAs (∼22 nucleotides), might play a crucial role in early cancer diagnose due to its abnormal expression in many solid tumors. As a result, label-free and PCR-amplification-free assay for miRNAs is of great significance. In this work, a highly sensitive biosensor for sequence specific miRNA-21 detection without miRNA-21 labeling and enrichment was constructed based on the substrate electrode of dendritic gold nanostructure (DenAu) and graphene nanosheets modified glassy carbon electrode. Sulfydryl functionalized locked nucleic acid (LNA) integrated hairpin molecule beacon (MB) probe was used as miRNA-21 capture probe. After hybridized with miRNA-21 and reported DNA loading in gold nanoparticles (AuNPs) and biotin multi-functionalized bio bar codes, streptavidin-HRP was brought to the electrode through the specific interaction with biotin to catalyze the chemical oxidation of hydroquinone by H(2)O(2) to form benzoquinone. The electrochemical reduction signal of benzoquinone was utilized to monitor the miRNA-21 hybridization event. The effect of experimental variables on the amperometric response was investigated and optimized. Based on the specific confirmation of probe and signal amplification, the biosensor showed excellent selectivity and high sensitivity with low detection limit of 0.06 pM. Successful attempts are made in miRNA-21 expression analysis of human hepatocarcinoma BEL-7402 cells and normal human hepatic L02 cells.

Electrochemical behaviour of Sudan I at Fe3O4 nanoparticles modified glassy carbon electrode and its determination in food samples

In this work, a simple and sensitive electrochemical method was developed to determine Sudan I based on magnetic Fe3O4 nanoparticles modified glassy carbon electrode using cyclic voltammetry and differential pulse voltammetry. The sensor exhibited an obviously electrocatalytic activity towards the oxidation of Sudan I, which can be confirmed by the increased oxidation peak current and the decreased oxidation peak potential when compared with the bare GCE. The determination conditions, such as pH, modifier amount, accumulation time and accumulation potential, were optimised. And some kinetic parameters were calculated. Under the optimum experimental conditions, the oxidation current of Sudan I was proportional to its concentration from 0.01 to 1μM and 1 to 20μM. The detection limit was estimated to be 0.001μM (S/N=3). The developed method was successfully applied to determine Sudan I content in food samples with satisfactory results.

One-step “green” preparation of graphene nanosheets and carbon nanospheres mixture by electrolyzing graphite rob and its application for glucose biosensing

The graphene nanosheets and carbon nanospheres mixture (GNS-CNS) was prepared by electrolyzing graphite rob in KNO(3) solution under constant current, which was characterized by TEM, AFM, SEM, FT-IR, XRD, XPS, TGA and UV-vis. The nano-mixture can keep stable in water for more than one month. Based on this kind of mixture material, a novel electrochemical biosensing platform for glucose determination was developed. Cyclic voltammetry of glucose oxidase (GOD) immobilized on GNS-CNS/GCE exhibited a pair of well-defined quasi-reversible redox peaks at -0.488 V (E(pa)) and -0.509 V (E(pc)) by direct electron transfer between the protein and the electrode. The charge-transfer coefficient (α) was 0.51, the electron transfer rate constant was 2.64 s(-1) and the surface coverage of HRP was 3.18×10(-10) mol cm(-2). The immobilized GOD could retain its bioactivity and catalyze the reduction of dissolved oxygen. The glucose biosensor has a linear range from 0.4 to 20 mM with detection limit of 0.1 mM. Moreover, the biosensor exhibits acceptable reproducibility and storage stability. The fabricated biosensor was further used to determine glucose in human plasma sample with the recoveries from 96.83% to 105.52%. Therefore, GOD/GNS-CNS/GCE could be promisingly applied to determine blood sugar concentration in the practical clinical analysis.

Amplified electrochemical microRNA biosensor using a hemin-G-quadruplex complex as the sensing element

A novel signal amplified electrochemical microRNA (miRNA) biosensor was developed here using hemin-G-quadruplex as signal unit. A hairpin structure DNA probe (43 bases) was immobilized on the gold nanoparticles (AuNPs) modified gold electrode surface with the segment at its 3′-end complementary to miRNA-21 (22 bases) and the segment at its 5′-end complementary to capture DNA (21 bases). Upon hybridization with the target miRNA-21, the hairpin structure was unfolded, which was further hybridized with capture DNA loaded on AuNPs. The AuNP contained two kinds of DNA; one was complementary to the hairpin structure DNA probe, while the other was aptamer for hemin. The electrochemical signal of hemin self-assembled in the center of G-quadruplex structure of the aptamer was measured using chronoamperometry. The miRNA-21 target was analyzed with a detection limit of 3.96 pM. Using isolated total RNA from human gastric carcinoma BGC-823 cells, human breast adenocarcinoma MCF-7 cells, human hepatocarcinoma HepG2 cells and human colon cancer HT-29 cells, the assay detected specifically miRNA-21 and over-expression of oncogene miRNA-21 was demonstrated.

Electrochemical determination of theophylline in foodstuff, tea and soft drinks based on urchin-like CdSe microparticles modified glassy carbon electrode.

A simply electrochemical method based on CdSe microparticles modified glassy carbon electrode (GCE) was developed to determine theophylline using cyclic voltammetry and differential pulse voltammetry. Theophylline showed a well-defined oxidation peak at the fabricated electrode in phosphate buffer solution and the oxidation peak current is much higher than that at the bare GCE, indicating that CdSe can effectively improve the oxidation of theophylline. Several effect factors on theophylline determination were optimised, such as CdSe amount, solution pH, scan rate and accumulation time. Under the optimal conditions, the oxidation peak current of theophylline was proportional to its concentration in the range of 1.0-40 and 40-700 μM with a correlation coefficient of 0.9974 and 0.9956, respectively. The limit of detection was estimated to be 0.4 μM (S/N=3). The developed method showed good reproducibility and excellent selectivity. The fabricated electrode was successfully used to determine theophylline in tea, carbonated cola drink, fruit juice drink, fermented milk drink and preserved fruit with acceptable recovery.

Multifunctional Fe3O4 core/Ni–Al layered double hydroxides shell nanospheres as labels for ultrasensitive electrochemical immunoassay of subgroup J of avian leukosis virus

A novel electrochemical immunosensor for ultrasensitive detection of subgroup J of avian leukosis virus (ALVs-J) was designed by using graphene sheets (GS)-layered double hydroxides (LDHs) composites modified electrode with multifunctional Fe(3)O(4) core/Ni-Al LDHs shell (LDHs@Fe(3)O(4)) nanospheres as labels. At first, the GS-LDHs were used for the immunosensor platform for improving the electronic transmission rate as well as increasing the surface area to capture a large amount of primary antibodies (Ab(1)). After that, ferrocene (Fc), secondary antibodies (Ab(2)) and horseradish peroxidase (HRP) multifunctional LDHs@Fe(3)O(4) nanospheres were used as labels with high load amount and good biological activity. Subsequently, in presence of H(2)O(2), amplified signals were obtained by an electrochemical sandwich immunoassay protocol. To embody the signal amplification property of the protocol, the analytical properties of various immunosensor platform and labels were compared in detail. Under optimal conditions, the reduction peak currents of the electrochemical immunosensor were proportional to the ALVs-J concentration over the range from 10(2.32) to 10(5.50) TCID(50)/mL with a low detection limit (180 TCID(50)/mL, S/N=3). The resulting immunosensor also displayed a good selectivity, reproducibility and stability.

Electrochemical behavior of phenacetin on CdSe microspheres modified glassy carbon electrode and its simultaneous determination with paracetamol and 4-aminophenol

A selective and sensitive electrochemistry method was developed for the determination of phenacetin on CdSe microspheres modified glassy carbon electrode (GCE). The electrode exhibited an effectively catalytic response to the oxidation of phenacetin, which was testified by the increased oxidation peak current and the decreased oxidation peak potential compared with the bare GCE. The scan rate investigation demonstrated that the electrochemical oxidation was an adsorption-controlled process in the range from 20 to 500 mV s−1. Under optimal determination conditions, the oxidation peak current of phenacetin was proportional to its concentration in the range of 0.5 to 800 μM. The limit of detection was estimated to be 0.1 μM (S/N = 3). The developed method showed good reproducibility, acceptable stability and excellent anti-interference performance. The fabricated electrode was successfully used to determine phenacetin in pharmaceutical formulation samples.

Electrochemical behavior of antipyrine at a Bi2S3 modified glassy carbon electrode and its determination in pharmaceutical formulations

A simple electrochemical method based on a Bi2S3 modified glassy carbon electrode (GCE) was developed to determine antipyrine using cyclic voltammetry and differential pulse voltammetry. Antipyrine shows a well-defined oxidation peak at the fabricated electrode in phosphate buffer solution and the oxidation peak current is much higher than that at the bare GCE, indicating that Bi2S3 can effectively improve the oxidation of antipyrine. Several effect factors on antipyrine determination were optimized, such as Bi2S3 amount, solution pH, scan rate and accumulation time. Under the optimal conditions, the oxidation peak current of antipyrine was proportional to its concentration in the range of 2.0 to 100 μM and 100 to 800 μM with a correlation coefficient of 0.9974 and 0.9956, respectively. The limit of detection was estimated to be 0.7 μM (S/N = 3). The developed method showed good reproducibility and excellent anti-interference performance. The fabricated electrode was successfully used to determine antipyrine in pharmaceutical formulations with recovery from 96% to 103.5%.