Zhao Dai

Selective and Sensitive Fluorescence Aptamer Biosensors of Adenosine Triphosphate

A fluorescence resonance energy transfer (FRET)- based aptamer biosensor (aptasensor) for sensitive determination of adenosine triphosphate (ATP) was developed. The energy donor and acceptor were 5′-carboxyfluorescein (5′-FAM) and gold nanoparticles (AuNPs), respectively. AuNPs were linked to 3′-SH-DNA by Au-S bond. This aptasensor was obtained by the hybridization between the complementary DNA strands of the 5′-FAM and AuNPs. The detecting results indicated that the FRET increase efficiency (Fr) of detecting system at 519 nm was linear when the concentration of ATP target was about 0.1–10 mmol/L. Moreover, the aptasensors showed a good stability in different buffer conditions and a low- detection limit (15.2 nmol/L) for ATP.

Toxoplasma gondii DNA Sensor Based on a Novel Ni-Magnetic Sensing Probe

we introduced a fast, specific, and sensitive sensing probe to detect Toxoplasma gondii DNA based on mechanism of fluorescence resonance energy transfer (FRET), and a multifunctional and magnetic-fluorescent CdTe/Ni quantum dots (mQDs) was prepared as energy donor, and BHQ2 was used as energy acceptor, respectively. CdTe/Ni mQDs were synthesized with a more simple method using Ni nanoparticles as core material and CdTe as shell material. The sensing probe was fabricated through labeling a stem-loop Toxoplasma gondii DNA oligonucleotide with CdTe/Ni mQDs at the 5′ end and BHQ2 at 3′ end, respectively, and the resulting sensing probe can be conveniently isolated and purified with a common magnet. Properties of mQDs and sensing probe were investigated by transmission electron microscopy (TEM), X-ray diffraction (XRD), and fluorescence spectrum (FS) methods. The TEM data demonstrated that the size of Ni nanoparticles was estimated to be ~10nm, and size of CdTe/Ni is 15nm. XRD data showed similar spectrum of CdTe and CdTe/Ni, intensity of Ni (111) typical diffraction peak was detected, which inferred the formation of CdTe on surface of Ni core. An obvious fluorescence recovery (FR) was observed when the complete complimentary target Toxoplasma gondii DNA was introduced comparing with the target DNA with one-basepair-mismatch, this result revealed the sensing probe has high sensitivity and specificity. The current sensing probe will has great potential applications in the life science and gene diagnostics.

Luminescent CdTe/CdS core-shell and CdTe/CdS/ZnS multi-layer quantum dots: synthesis and investigations for bio-application

Concerns on quantum dots (QDs) have been continuously increasing because of their advantages on photophysical properties. Water soluble CdTe/CdS core-shell and CdTe/CdS/ZnS multi-layer QDs were synthysized with mercaptopropanoic acid (MPA) as stabilizer in aqueous phase in the current research. The obtained QDs were characterized with fluorescence spectrum (FS), and quantum yields (QYs) was calculated base on the resulting data from FS. Comparing with CdTe core, red-shift of maximum emission wavelength (MEW) of CdTe/CdS was observed, which indicated the growth of QDs size. To obtain high QYs of CdTe/CdS core-shell QDs, several methods and different reaction conditions were investigated and discussed, such as dependence of Cd2+ concentration, dependence of pH, influence of S2-:Te2-, and effect of Cd2+:S2- etc. Among all of discussed methods, QYs of core-shell CdTe/CdS is generally degressive with refluxing time elapsing. The best QYs of 79.8% can be achieved when pH was set at 8.5, Cd2+:S2-=1:0.1 (mol ratio). Moreover, CdTe/CdS/ZnS multi-layer QDs was prepared, and results via FS indicated a further red-shift from 554 nm to 646 nm comparing with CdTe/CdS QDs, but QYs decreased to 14.0%. QDs currently discussed in this research are easily synthesized, and safe to organism, i.e. biocompatible. They will be useful in applications of biolabeling, imaging, and biosensing based on fluorescence resonance energy transfer (FRET).

Preparation and Characterization of the Core/Shell Structured of CdTe/Ni Fluorescent-Magnetic Particle

The niclel nanoparticles were prepared via polyol process with hydrazine hydrate as reductant, the optimum conditions were investigated and proposed to be the molar ratio of NiCl2: NaOH: Hydrazine hydrate =1: 2: 11, 60 °C, pH5.5. The qualified fluorescent-magnetic dual functional CdTe/Ni nanoparticles were synthesized via layer-by-layer (LBL) technique, Ni was designed to be magnetic core and CdTe was used as fluorescent shell material, the molar ratio of CdTe:Ni is 4.5:1. The morphology of the Ni nano particles and CdTe/Ni core shell dual functional nano particles were characterized by transmission electron microscopy (TEM), and optical properties were investigated with fluorescence spectrum (FS) and ultra violet spectrum (UV). The synthesized CdTe/Ni nanoparticles showed yellow fluorescence when excited at 365nm, CdTe/Ni magnetic core shell QDs can be simply precipitated with a common magnet. TEM data indicated that ~15nm of Ni nanoparticles were obtained and ~25nm of CdTe/Ni core shell dual functional nanoparticles were prepared. Red shift of maximum absorbance peak was detected via UV, and these results inferred the QDs growth, moreover, 40nm red shift of maximum emission wavelength from 530nm to 570nm was observed, and which showed the growth QDs and formation of CdTe shell. The prepared magnetic core shell CdTe/Ni nanoparticles showed excellent optical properties, and it is expected to be useful and helpful in DNA sensing based on fluorescence resonance energy transfer, biological separating, and DNA labeling process.

Novel DNA Electrochemical Biosensor Using Anthraquinone-2-Sulfonic Acid Sodium Salt as Hybridization Indicator

A novel DNA biosensor based on layer-by-layer self-assembled multi-walled carbon nanotubes (MWNTs) functionalized with a mercapto group (SH-MWNTs) and gold nano-particles (GNPs) was presented, where anthraquinone-2-sulfonic acid sodium salt (AQMS) was used as hybridization indicator. The differential pulse voltammetry responses demonstrated that this DNA/GNPs/SH-MWCNTs/Au biosensor was enabled to specifically detect the single-base mismatch DNA sequence in phosphate buffer solution with pH 7.4 containing 0.3 mol/L Na+ and 1.0 mmol/L AQMS. The result showed that when the target DNA concentration was 1.0×10-10 to 1.6×10-5 mol/L, the cathodic peak current of Au electrode system with AQMS as indicator was linearly related to complementary NDA concentration, and the detection limit was about 3.82×10-11 mol/L and had good stability and specificity.

Graphene Oxide Modified DNA Electrochemical Biosensors

One approach had been developed for the covalent modification of graphene sheets: amidation and esterification of graphene oxide (GO). Graphene oxide was synthesized by oxidizing graphite in strong acid and lots of oxygen-containing groups, such as hydroxyl and carboxyl processed in the carbon layers, made GO strongly hydrophilic activity as well as certain of chemical activity. This work researched a novel DNA biosensor which fabricated by immobilizing GO on Au electrode modified with mercaptoethylamine(MEA), was investigated by cyclic voltammetry. The results showed that graphite oxide was an excellent material and had a promising prospect in biosensor construction.

DNA Biosensors Based on Layer-by-Layer Self-Assembled Multilayer Films of Carbon Nanotubes and Gold Nanoparticles

The paper has been withdrawn do to double publication. The original was published by SPIE Proceedings of SPIE, vol 7493, 74935A in 2009 (DOI:10.1117/12.840316)

Fabrication and Characterization of a Toxoplasma gondii DNA Sensing System

We presented a fast, specific, and sensitive DNA sensing system, which composed of a CdTe/Fe3O4 magnetic core-shell quantum dots (energy donor), a commercial quencher (BHQ2; energy acceptor), and a designed single strand Toxoplasma gondii DNA. The designed single strand Toxoplasma gondii DNA was applied to link the energy donor and acceptor, and target DNA was detected based on mechanism of fluorescence resonance energy transfer. The CdTe quantum dots, Fe3O4 magnetic nanoparticles, CdTe/Fe3O4 magnetic core-shell quantum dots, and sensing probe were step-wisely prepared. Properties of synthesized quantum dots were investigated by transmission electron microscopy, fluorescence spectrum, nano zeta potential and submicron particle size analyzer, and X-ray diffraction, respectively. Specificity and sensitivity of sensing probe was determined by measuring the recovery of fluorescence intensity. The obtained sensing probe with magnetic properties can be simply separated or concentrated from the hybridized solution with a common magnet. The resulting data revealed the sensing system was successfully fabricated, and which has high sensitivity and specificity.

Fluorescence Enhanced Quantum Dots: Its Synthesis, Optical Properties, and Ecotoxicity Research

Quantum dots (QDs) are normally based on the semiconductor materials and widely used in biosensing, bioimaging, biolabeling, and biotreatment for their excellent properties. The ecotoxicity research of QDs correspondingly kept in rising in recent years. CdTe and CdTe/ZnS QDs were prepared via an improved process in aqueous phase, morphology of QDs was characterized with transmission electron microscopy, and optical properties were investigated via fluorescence spectrum. Ecotoxicity of CdTe and CdTe/ZnS were assayed by measuring the inhibitory growth of Rhodococcus sp. strain C1 when QDs existed in broth culture, which was screened from sewage, and its morphology was characterized with optical microscope and scanning electron microscope. CdTe QDs showed strong inhibitory effect against growth of Rhodococcus sp. strain C1, and little growth was observed after 72h cultivation. CdTe/ZnS QDs showed prophasic inhibition before 36h, and growth recovery was observed after 48h of cultivation. Enhanced optical properties and decreasing ecotoxicity were validated after ZnS shell formation, these results indicated that CdTe/ZnS QDs with core-shell structure has great potential in bio-applications.

DNA biosensors based on layer-by-layer self-assembled multilayer films of carbon nanotubes and gold nanoparticles

A novel DNA biosensor based on layer-by-layer self-assembled multi-walled carbon nanotubes (MWNTs) and gold nano-particles (GNPs) was presented in this paper, in which the probe HS-ssDNA oligonucleotides, MWNTs and GNPs were all covalently immobilized by chemical Au-Sulphide bonding. Firstly, the super short MWNTs were prepared and modified with thio groups which could be self-assembled onto the surface of Au elcetrode by Au-sulphide bonding, then the GNPs were chemically adhered to the surfaces of MWNTs by forming Au-sulphide bonding again, at last the selfassamble of probe DNA oligonucleotides were also covalently immobilized via Au-sulphide bonding between thio groups at the ends of the DNA oligonucleotides and GNPs. Hybridization between the probe HS-ssDNA oligonucleotides and target DNA oligonucleotides was confirmed by the changes in the voltammetric peak of an anionic intercalator, anthraquinone-2,6-disulfonic acid (AQDS) as a hybridization indicator. The cyclic voltammetric and differential pulse voltammetry responses demonstrated that the DNA biosensors based on Layer-by-layer self-assembled multilayer films of MWNTs and NGPs offer a higher hybridization efficiency and selectivity compared to those based on only random MWNTs or GNPs.