Papers by Author: Ji Mei Zhang

Abstract: A novel DNA biosensor system on silica microspheres as solid carriers which based on the fluorescence resonance energy transfer (FRET) was presented in this work when CdTe quantum dots (QDs) were as energy donors and Au nanoparticles (AuNPs) were as energy accepters. Compared with the fluorescent intensity of CdTe QDs, the fluorescent intensity of DNA biosensors decreased extremely, which indicated that the FRET occurred between CdTe QDs and AuNPs. The biosensor system would have a certain degree recovery of fluorescence when the complementary single stranded DNA was introduced into this system. The DNA detection results indicated that this novel fluorescent DNA probe system could recognize the existence of complementary target DNA or not.

Abstract: 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.

Abstract: 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.

Abstract: The core-shell CdTe/ZnS quantum dots were prepared with an improved process in aqueous phase. CdTe QDs were synthesized under conditions of pH 9.1, 96 °C, refluxing for 5h, and which was used as core material; ZnS was formed as shell material to enhance the optical properties. Optical properties were characterized with fluorescence spectrum (FS), and morphology of QDs was investigated via transmission electron microscopy (TEM) method. Moreover, composition and formation of CdTe/ZnS core-shell QDs was characterized via x-ray diffraction (XRD) method. Optimum conditions were investigated to obtain the qualified CdTe/ZnS core-shell QDs, the results indicated QDs with high quantum yields and fluorescence intensity were achieved under conditions of pH 9.0, 45 °C, refluxing for 1h, and v/v/v ratio of CdTe/Na2S/ZnSO4 is 4/1/1. The TEM data indicated that average size of 5 nm CdTe core was prepared, and CdTe/ZnS core-shell QDs with average size of 11 nm were achieved under the optimum conditions. ca 30nm of red shift of a maximum emission wavelength from ca 530 nm (CdTe) to 560 nm (CdTe/ZnS) was observed via FS under the optimum conditions, which inferred the growth of QDs and formation of ZnS shells. Furthermore, the enhanced fluorescence intensity of CdTe/ZnS core-shell QDs was detected and over two times of fluorescence intensity was increased after formation of ZnS shell. The obtained QDs will have great potential application in biological researches and biosensing system based on fluorescence resonance energy transition (FRET).

Abstract: 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.

Abstract: A novel CdTe/Ni QDs which combined both magnetism and fluorescence was successfully synthesized and its optical properties were investigated. Ni magnetic nanoparticles (MNPs) were synthesized and used as magnetic core, CdTe quantum dots (QDs) were applied as fluorescent shell material, the qualified magnetic CdTe/Ni quantum dots (mQDs) were achieved via layer-by-layer process using 1,6-hexylenediamime as linker, surface charge types of MNPs and mQDs were confirmed with a delsa nano beckman coulter. Morphology of the prepared Ni MNPs and CdTe/Ni mQDs was characterized by transmission electron microscopy (TEM), and optical properties were investigated with fluorescence spectrum (FS). Qualified CdTe/Ni mQDs with high fluorescence and narrow maximum emission peak width were obtained under the optimum conditions. Surface zeta-potential of CdTe QDs and Ni MNPs were estimated to be -36.2 and 27.97mV, respectively. TEM data indicated that ca 20nm of Ni MNPs and ca 25nm of CdTe/Ni mQDs were prepared, respectively; the size-increasing indicated the formation of CdTe shell on the Ni MNPs core. Narrow half peak width of emission peak was detected and calculated to be about 50nm via FS. High fluorescence intensity of CdTe/Ni mQDs was determined and brilliant yellow solution was observed when excited under UV360nm. The synthesized CdTe/Ni mQDs showed excellent magnetic property, and can be magnetically concentrated with a common magnet. The obtained data indicated that the prepared bi-functional CdTe/Ni mQDs possess excellent magnetic and fluorescent properties, and it can be used as a energy donor in DNA sensing based on fluorescence resonance energy transfer (FRET).