Jimei Zhang

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).

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.

Detection of toxoplasma gondii with a DNA molecular beacon probe

Toxoplasma gondii is a kind of microscopic parasite that may infect humans, and there are increasing concerns on the early detection of latent Toxoplasma gondii infection in recent years. This research highlights a new type of molecular beacon (MB) fluorescent probe for Toxoplasma DNA testing. We combined high-efficiency fluorescent inorganic core-shell quantum dots-CdTe/ZnS (as fluorescent energy donor) and BHQ-2 (energy acceptor) to the single-strand DNA of Toxoplasma Gondii, and a molecular beacon sensing system based on fluorescence resonance energy transfer (FRET) was achieved. Core-shell quantum dots CdTe/ZnS was firstly prepared in aqueous solution, and the influencing factor of its fluorescent properties, including CdTe/Na2S/Zn(CH3COO)2 (v/v), dependence of reaction time, temperature, and pH, is investigated systematically. The synthesized quantum dots and molecular beacon were characterized by transmission electron microscopy (TEM), ultraviolet-visible spectrophotometer (UV-vis), fluorescent spectrophotometer (FS), respectively. The TEM results showed that CdTe/ZnS core-shell quantum dots is ~11nm in size, and the quantum dots is water-soluble well. The sensing ability of target DNA of assembled MB was investigated, and results showed that the target Toxoplasma Gonddi DNA can be successfully detected by measuring the change of fluorescence intensity. The results showed that the current sensing probe will be a useful and convenient tool in Toxoplasma gondii early detection.

Preliminary Study of CdTe Quantum Dots Applied in DNA Sensors

With the development of molecular biology and genetic technology, target DNA detection and transition of genetic information are becoming increasingly significant, and electrochemical biosensor gains many concerns in direct detection of target DNA due to the advantages, i.e. simple mechanism, reliable result, low-cost process, sensitive and selective method for genetic detection. a novel biosensing system was presented and investigated based on electrochemical and DNA techniques, and the nano-scale semiconductor CdTe quantum dots (QDs) was firstly introduced to sensing system to investigated its electrochemical effect and properties, the sensing probe with structure of gold electrode (AuE)-CdTe quantum dots (CdTe QDs)-gold nanoparticles (AuNPs)-single strand sensing probe (ssDNA) was fabricated with layer-by-layer self-assembly method. The electrochemical properties and sensing ability of the probes were characterized and determined via cyclic voltammetry (CV) method. Obvious differential redox peaks current were revealed when the fabricated AuE/CdTe QDs, AuE/CdTe QDs/AuNPs, and AuE/CdTe QDs/AuNPs/ssDNA was examine by CV method, respectively. The sensing probe showed high sensitivity and specificity when the complementary target DNA and the target DNA with one-base-mismatch were determined, respectively. The current results indicated that the fabricated DNA biosensor has great potentials in detecting special DNA sequences via DNA technology.

Primary Designation and Characterization of a Molecular Beacon DNA Sensing Probe

In the current research, a fast, specific, and sensitive sensing probe was designed to detect Toxoplasma gondii DNA based on mechanism of fluorescence resonance energy transfer (FRET), and a magnetic-fluorescent CdTe/Fe3O4 quantum dots (mQDs) was utilized as energy donor, and the BHQ-2 was used as energy acceptor, respectively. The mQDs were prepared stepwisely using Fe3O4 as magnetic core and CdTe as luminescent shell at ambient temperature. The sensing probe was fabricated through labeling a stem-loop Toxoplasma gondii DNA oligonucleotide with mQDs at the 5¿¿ end and BHQ-2 at 3¿¿ end, respectively. The resulting sensing probe can be simply isolated and purified from the reactant with a common magnet in 5min. Properties of mQDs and sensing probe were investigated by transmission electron microscopy (TEM) and fluorescence spectrum (FS). The TEM data demonstrated that the size of mQDs was ~25nm. The FS data indicated twice fluorescence recovery (FR) was observed when the complete complimentary target Toxoplasma gondii DNA was introduced. Moreover, the investigation of speicificity of current sensing probe showed that only weak FR was observed when the target DNA with one-mismatch base pair was added, 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 related research.

Construction and investigation of a DNA sensing system based on a magnetic molecular beacon probe

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/Fe3O4magnetic core-shell quantum dots, and sensing probe were step-wisely prepared. Properties of synthesized quantum dots were investigated by transmission electron microscopy and fluorescence spectrum, respectively. Specificity and sensitivity of sensing probe was determined by measuring the recovery of fluorescence intensity. The resulting data revealed the sensing system was successfully fabricated, and which has relative high sensitivity and specificity. Moreover, a simple modeling of the current sensing system/probe was primarily created, and which was utilized to theoretically illustrate and quantitatively investigate some surface properties of the sensing probe. We expect the current modeling can profit the current research and promote the sensitivity and specificity of the sensing system.

CdTe quantum dots modified fluorescent polymer microspheres by self-assembly

Fluorescent CdTe quantum dots (QDs) modified polymer microspheres with different functional groups were prepared by self-assembly between the carboxyl of 3-mercaptopropionic acid (MPA) on the surface of QDs and basic functional groups (4-vinylpyridine (VPy), N-isopropylacrylamide (NIPAM) or acrylamide (AAM)) of the microspheres. 10 nm of CdTe QDs in diameters were prepared in aqueous solution when 3-mercaptopropionic acid (MPA) was as stabilizer, while functional polymeric microspheres were prepared by distillation-precipitation polymerization when divinylbenzene80 (DVB) was as crosslinker. The TEM results indicated that the microspheres were about 800 nm in diameters and the TEM and fluorescence spectra of QDs conjugated microspheres confirmed that the QDs were self-assembled on the surface of microspheres. The stability of QDs modified microspheres in different pH indicated that the QDs were cut off from poly(VPy-co-DVB) microspheres when the pH was 13, while the cleavage condition of poly(AAM-co-DVB) and poly(NIPAN-co-DVB) were 11 and 9–10 respectively, which indicated that the self-assembly of QDs and poly(VPy-co-DVB) microspheres had the highest stability.

Polymer microspheres carrying fluorescent DNA probes

A polymer microspheres carried DNA probe, which was based on resonance energy transfer, was presented in this paper when CdTe quantum dots(QDs) were as energy donors, Au nanoparticles were as energy accepters and poly(4- vinylpyrindine-co-ethylene glycol dimethacrylate) microspheres were as carriers. Polymer microspheres with functional group on surfaces were prepared by distillation-precipitation polymerization when ethylene glycol dimethacrylate was as crosslinker in acetonitrile. CdTe QDs were prepared when 3-mercaptopropionic acid(MPA) was as the stabilizer in aqueous solution. Because of the hydrogen-bonding between the carboxyl groups of MPA on QDs and the pyrindine groups on the microspheres, the QDs were self-assembled onto the surfaces of microspheres. Then, the other parts of DNA probe were finished according to the classic method. The DNA detection results indicated that this novel fluorescent DNA probe system could recognize the existence of complementary target DNA or not.

Preparation of P(DVB-co-MPS) inorganic-organic hybrid polymer microspheres

A novel inorganic-organic hybrid polymer microspheres were facilely synthesised by distillation-precipitation polymerization in absence of any stabilizer or surfcant. The process were conducted with [3-(Methacryloyloxy) propyl] trimethoxysilan (MPS) as monomer, divinyl benzene (DVB) as cross linking agent and azobisisobutyronitrile (AIBN) as initator in acetonitrile. A series of silica nanoparticles were prepared in accordance with the volume ratio of MPS, which was varied in the range of 10% to 50%. However, there is no microspheres obtained while the ratio up to 50%. Products were charactered by transmission electron micrograph (TEM) and fourier transform infrared spectroscopy (FTIR). We may infer it from the constructional formular and FTIR graph that there were silicon hydroxyl remained in the microsphere surface.

Short thio-multi-walled carbon nanotubes and Au nanoparticles enhanced electrochemical DNA biosensor for DNA hybridization detection

A novel and sensitive electrochemical DNA biosensor based on multi-walled carbon nanotubes functionalized with a thio group (MWNTs-SH) and gold nanoparticles (GNPs) for covalent DNA immobilization and enhanced hybridization detection is described. The key step for developing this novel DNA biosensor is to cut the pristine MWNT into short and generate lots of active sites simultaneously. With this approach, the target DNA could be quantified in a linear range from 8.5×10-10 to 1.5×10-5 mol/L, with a detection limit of 1.67×10-11 mol/L by 3σ.