Ji Mei Zhang

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.

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.

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.

Synthesis and Characterization of the Core-Shell CdTe/ZnS Quantum Dots

Core-shell quantum dots are colloidal particles consisting of a semiconductor core and a shell material as an outer coating layer. It can be utilized to develop sensitive methods for the detection of specific biological entities, such as microbial species, their transcription products, and single genes etc. The goal of current research is to synthesize CdTe and core-shell CdTe/ZnS quantum dots (QDs) with an improved process, and to investigate their properties. Well-dispersed CdTe core was prepared in aqueous phase with using 3-mercaptopropionic acid (MPA) as stabilizer under conditions of pH 9.1, temperature of 100 °C, refluxing for 6h, and mol ratio of Cd2+/Te2-/MPA is 1:0.5:2.4. Average size of 8 nm CdTe core was conformed via transmission electron microscopy (TEM). Core-shell CdTe/ZnS QDs were then synthesized to improve the optical properties and biocompatibility of CdTe core. Various conditions were researched to obtain the core-shell QDs with the best optical properties, such as quantum yields, fluorescence intensity etc. The results indicated that the core-shell qualified CdTe/ZnS was prepared under conditions of pH 9.0, temperature of 45 °C, refluxing for 1h, and mol ratio of CdTe/S2-/Zn2+ is 4/1/1. CdTe/ZnS with average size of 10 nm were achieved and conformed via TEM. Moreover, red shift of a maximum emission wavelength from 547 nm of CdTe to 587 of CdTe/ZnS was observed via fluorescence spectrum (FS), which inferred the growth of QDs and formation of ZnS shells. The achieved ZnS shell make CdTe core less toxic and more biocompatible, it will be useful in biological labeling, diagnostic process and biosensing system based on fluorescence resonance energy transition (FRET).

Poly(4-vinylpyridine) Coated CdTe Core/Shell Quantum Dots

A kind of novel quantum dots (QDs) with poly(4-vinylpyridine) (PVPy) as shell and CdTe QDs as core was presented in this work. This core/shell ODs can conjugate DNA easily because the surface pyridyl exist on QDs, and which has potential application in DNA biosensors field. CdTe QDs were prepared in aqueous solution with 3-mercaptopropionic acid (MPA) as stabilizer. It was found that the fluorescent intensity of QDs was depended the reflux time. Following the increase of reflux time, the fluorescent intensity of QDs reached the maximum at 10 h with about 10 nm in diameters. And the fluorescent intensity of QDs was also increased. When the reflux time was 10 h, the diameter of QDs would increase to about 10 nm. After adjusted the pH of QDs solution system to 7.0, the MPA stabled QDs were purified by ultracentrifugation and freeze-drying respectively. The polymerization was performed in water when 4-vinylpyridine (VPy) used as monomer, N,N’-methylene-bisacrylamide (MBAAm) as crosslinker, potassium persulphate (PPS) as initiator and MPA stabled QDs as seeds. The surface carboxyl of MPA on QDs could promote the form of PVPy coated CdTe QDs. It was shown that the fluorescent intension of core/shell QDs was decreased following the polymerization and the diameter of QDs could increase to 20-30 nm.

The Core-Shell CdTe@SiO2 Particles Prepared via Reverse Microemulsion Method and their Fluorescence Properties

High-quality CdTe nanocrystals capped by mercaptopropionic acid (MPA) were prepared in aqueous solution, and core-shell CdTe@SiO2 particles were prepared via reverse microemulsion method. The core-shell CdTe@SiO2 particles were fluorescent, monodispersed, and well-separated. The obtained samples were characterized by means of transmission electron microscope (TEM), ultraviolet-visible absorption spectrometry (UV-vis) and photoluminescence (PL) emission. The influence of ionic strength on the PL emission of uncoated CdTe and CdTe/SiO2 composite nanoparticles were investigated thoroughly. Due to the presence of SiO2 shell, CdTe@SiO2 still remained a strong fluorescence at high ionic strength. Because of these advantages, it had broad applications in biological fields, such as biomarkers, cell imaging.

The Preparation of Water-Solution Mn-Doped ZnS Quantum Dots

High-Fluorescence Mn-doped ZnS quantum dots ( QDs) capped with L-Cysteine (L-Cys) were prepared in the aqueous were presented in this paper. The influences of the pH, the doped-quantity of Mn2+ and the storage time on the PL emission of quantum dots were studied. The samples were characterized by means of ultraviolet-visible absorption spectrometry (UV-vis), photoluminescence (PL) emission and infrared spectrometry (FTIR). The results showed that the fluorescence intensity reached the maximum when the pH was 10, the doped-quantity of Mn2+ was 3% and the storage time was about 7 days. The solubility of the quantum dots in the water was excellent. Because of these advantages, it can be used in biological fields, such as biomarkers, cell imaging, and sensor and so on.

DNA Electrochemical Biosensor Based on Au Nanoparticles Self-Assembled Au Electrode

A novel electrochemical DNA biosensor system based on Au nanoparticles (AuNPs) modified Au electrode and anthraquinone-2,6-disulfonic acid (AQDS) as hybridization indicator was presented in this paper. AuNPs with different particle sizes were prepared from gold chloride by reduction, and self-assembled on Au electrode (AuNPs/Au electrode) by cysteamine as linker. Then, 5’ end –SH modified DNA (HS-DNA) as nucleotide probes were self-assembled onto the surface of AuNPs modified Au electrode (HS-DNA/AuNPs/Au electrode), and the HS-DNA/AuNPs/Au electrode could detect target DNA (completely complementary with HS-DNA). Because AuNPs were on Au electrode, the surface of Au electrode was increased. Therefore, this would result in the increase of electrochemical signal and increase the sensitivity of biosensor. If a completely complementary single stranded DNA (ssDNA) as target existed in the detection system, the cathodic peak current (△Ip) of AuNPs modified Au electrode was increased about 3 times than the HS-DNA/AuNPs/Au electrode because of the hybridization between HS-DNA and complementary DNA target and the formation of double stranded DNA (dsDNA), and if the target was a mismatching base-pair with HS-DNA, the electrochemical signal of electrode would have no obviously change. These results showed that this DNA biosensor system based on AuNPs self-assembled Au electrode had an excellent sensitivity with a complete complementary DNA sequence.