Danyi Wei

Electrochemiluminescence immunosensor based on graphene-CdS quantum dots-agarose composite for the ultrasensitive detection of alpha fetoprotein

A novel strategy for the enhancement of electrochemiluminescence (ECL) was developed by combining CdS quantum dots (QDs), graphene (G) and agarose. This enhanced ECL was exploited to develop a label-free ECL immunosensor for the ultrasensitive detection of alpha fetoprotein (AFP). The novel G-CdS QDs-agarose composite was first coated on the glass carbon electrode surface to form a robust film, which exhibited high ECL intensity, good biocompatibility and high stability. After that 3-aminopropyl-triethoxysilane (APS), as a binding linker, was conjugated to the G-CdS QDs-agarose composite film on the electrode, the ECL signal was significantly enhanced. The fabrication of ECL immunosensor was successfully completed by immobilizing the AFP-antibody (Ab) onto the electrode through glutaric dialdehyde (GLD). The specific immunoreaction between AFP and antibody resulted in the decrease in ECL intensity and the intensity decreased linearly with the logarithm of AFP concentration in the range of 0.0005-50 pg mL(-1) with a detection limit of 0.2 fg mL(-1). The immunosensor exhibits high sensitivity, specificity, stability, reproducibility and good regeneration, thus has the potential to be used in clinical application. Besides, the highly enhanced ECL from the G-CdS QDs-agarose composite film opened new avenues to apply graphene and QDs ECL in analytical systems and ECL biosensors.

A test strip platform based on DNA-functionalized gold nanoparticles for on-site detection of mercury (II) ions

A test strip, based on DNA-functionalized gold nanoparticles for Hg(2+) detection, has been developed, optimized and validated. The developed colorimetric mercury sensor system exhibited a highly sensitive and selective response to mercury. The measurement principle is based on thymine-Hg(2+)-thymine (T-Hg(2+)-T) coordination chemistry and streptavidin-biotin interaction. A biotin-labeled and thiolated DNA was immobilized on the gold nanoparticles (AuNPs) surface through a self-assembling method. Another thymine-rich DNA, which was introduced to form DNA duplexes on the AuNPs surface with thymine-Hg(2+)-thymine (T-Hg(2+)-T) coordination in the presence of Hg(2+), was immobilized on the nitrocellulose membrane as the test zone. When Hg(2+) ions were introduced into this system, they induced the two strands of DNA to intertwist by forming T-Hg(2+)-T bonds resulting in a red line at the test zone. The biotin-labeled and thiolated DNA-functionalized AuNPs could be captured by streptavidin which was immobilized on the nitrocellulose membrane as the control zone. Under optimized conditions, the detection limit for Hg(2+) was 3 nM, which is lower than the 10nM, maximum contaminant limit defined by the US Environmental Protection Agency (EPA) for drinking water. A parallel analysis of Hg(2+) in pool water samples using cold vapor atomic absorption spectrometry showed comparable results to those obtained from the strip test. Therefore, the results obtained in this study could be used as basic research for the development of Hg(2+) detection, and the method developed could be a potential on-site screening tool for the rapid detection of Hg(2+) in different water samples without special instrumentation. All experimental variables that influence the test strip response were optimized and reported.

Determination of melamine in dairy products by an electrochemiluminescent method combined with solid-phase extraction

An electrochemiluminescence (ECL) enhancement method combined with solid-phase extraction has been developed for the determination of melamine in dairy products. It was found that melamine in a strong base solution is able to enhance the ECL of Ru(bpy)(3)(2+) at glass carbon electrode. The optimum experimental conditions for the determination of trace melamine by ECL, such as scan mode and scan rate of the applied potential, the type of buffer solutions and their pH conditions, were investigated. Under optimized conditions, the enhanced ECL intensity was linearly proportional to the logarithm of melamine concentration in the range of 0.01-1.0 ppb, and the detection limit was 0.003 ppb. The method has been successfully demonstrated to determine melamine in dairy products including liquid milk, yogurt and milk powder samples. The relative standard deviations ranging from 5.3% to 11.2% and the recoveries from 95.2% to 102.4% were acquired by this method. A possible mechanism for the ECL enhancement effect was also proposed.

Development and application of a method for analysis of phthalates in ham sausages by solid-phase extraction and gas chromatography-mass spectrometry.

A gas chromatography-mass spectrometry assay was developed and successfully applied for the determination of phthalates in ham sausage migrated from packaging film. The phthalates studied were dimethyl phthalate (DMP), diethyl phthalate (DEP), dibutyl phthalate (DBP), benzylbutyl phthalate (BBP), bis(2-ethylhexyl) phthalate (DEHP) and di-n-octyl phthalate (DNOP), with dibutyl adipate (DBA) as internal standard. The sample pre-treatments included extraction with n-hexane, solvent evaporation and reconstitution with acetonitrile before and after solid-phase extraction (SPE). The extraction and cleaning up procedure was carried out with cartridges containing dimethyl butylamine groups, which showed extraction efficiencies over 87.3%. The calibration curves obtained were linear with correlation coefficients greater than 0.99. The method proved to be accurate and precise for the six phthalates used. It was successfully applied to a study on the migration of phthalates from packaging PVC film into ham sausage.

Simultaneous determination of phthalates and adipates in human serum using gas chromatography-mass spectrometry with solid-phase extraction.

A gas chromatography-mass spectrometry assay was developed and validated for the simultaneous determination of phthalates and adipates in human serum. The phthalates and adipates studied were dimethyl phthalate, diethyl phthalate, dibutyl phthalate, benzylbutyl phthalate, di-2-ethylhexyl phthalate, di-n-octyl phthalate, diethyl adipate, dibutyl adipate, diisobutyl adipate, bis(2-butoxyethyl) adipate and di-2-ethylhexyl adipate, with diisooctyl phthalate as internal standard. The extraction and cleaning up procedure was carried out with solid-phase extraction cartridges containing dimethyl butylamine groups, which showed extraction efficiencies over 88% for each analyte and the internal standard. The calibration curves obtained were linear with correlation coefficients greater than 0.98. For all analytes, the assay gave CV% values for intra-day precision from 4.9 to 13.3% and mean accuracy values from 91.4 to 108.4%, while inter-day precision was 5.2-13.4% and mean accuracy 91.0-110.2%. The limits of detection for the assay of phthalates and adipates were in the range 0.7-4.5 ng/mL. The method is simple, sensitive and accurate, and allows for simultaneous determination of nanogram levels of phthalates and adipates in human serum. It was successfully applied to an investigation on the level of phthalates and adipates in a non-occupationally exposed population.

GC/MS method for the determination of adipate plasticizers in ham sausage and its application to kinetic and penetration studies.

A GC/MS method was developed and successfully validated for the determination of adipate plasticizers in ham sausage migrated from polyvinylidene chloride (PVDC) packaging film. The sample pretreatment includes liquid extraction, solvent evaporation, and reconstitution before and after solid phase extraction (SPE). For the 5 adipate plasticizers studied, the SPE process with Oasis MAX cartridge showed an extraction efficiency from 85.7% to 106%, and the calibration curves are all linear in the range of 5 to 1000 ng/g with correlation coefficients greater than 0.998. The method proved to be accurate and precise; the average intraday recovery ranges from 85.4% to 114.6% with a %CV value from 2.5 to 11.3, and the average interday recovery from 83.6% to 118.5% with a %CV value from 2.8 to 15.6, respectively, for the adipate plasticizers. The method is sensitive and was effectively applied in the kinetic and penetration studies of the adipate plasticizers migrating from food-grade PVDC packaging film into ham sausage. The experimental data showed that approximately 6.8% of dibutyl adipate (DBA) in the packaging film migrated into the ham sausage in 4 mo and the migration reached the innermost portion of the sausage in 6 mo.