Wen-You Li

Composite of CdTe quantum dots and molecularly imprinted polymer as a sensing material for cytochrome c.

A newly designed molecularly imprinted polymer (MIP) material was fabricated and successfully utilized as recognition element to develop a quantum dots (QDs) based MIP-coated composite for selective recognition of the template cytochrome c (Cyt). The composites were synthesized by sol-gel reaction (imprinting process). The imprinting process resulted in an increased affinity of the composites toward the corresponding template. The fluorescence of MIP-coated QDs was stronger quenched by the template versus that of non-imprinted polymer (NIP)-coated QDs, which indicated the composites could recognize the corresponding template. The results of specific experiments further exhibited the recognition ability of the composites. Under optimum conditions, the linear range for Cyt is from 0.97 μM to 24 μM, and the detection limit is 0.41 μM. The new composites integrated the high selectivity of molecular imprinting technology and fluorescence property of QDs and could convert the specific interactions between imprinted cavities and corresponding template to the obvious changes of fluorescence signal. Therefore, a simple and selective sensing system for protein recognition has been realized.

Macroporous Thermosensitive Imprinted Hydrogel for Recognition of Protein by Metal Coordinate Interaction

A thermosensitive macroporous hydrogel showing selectivity for the lysozyme was developed by an imprinting procedure that is based on metal coordinate interaction. A metal chelate monomer [N-(4-vinyl)-benzyl iminodiacetic acid] forming coordination complex with the template protein in the presence of Cu ions co-polymerized with N-isopropylacrylamide and acrylamide, using N,N-methylenebisacrylamide as the cross-linker to prepare the thermosensitive protein-imprinted hydrogel. The synergetic combination of the smart property of the macroporous thermosensitive hydrogel with the merits of the coordinate interaction improved the selectivity and adsorption capacity, with respect to template lysozyme. The macropores were created by the frozen polymerization, and the influences of frozen polymerization and the chelate monomer content on the hydrogel affinity were investigated. The imprinted hydrogel can respond not only to external stimuli, but also to the template protein with a certain degree of shrinking. In recognition of the protein, the interaction of the imprinted thermosensitive hydrogel to the protein can be switched between the coordinate effect and the electrostatic effect by adding or not adding Cu ions. Finally, this imprinted hydrogel was used to purify the template lysozyme from the mixture of proteins and the real sample, which demonstrated its high selectivity.

Novel surface modified molecularly imprinted polymer using acryloyl-β-cyclodextrin and acrylamide as monomers for selective recognition of lysozyme in aqueous solution

A novel protein imprinted polymer for selective recognition of lysozyme was obtained. Acryloyl-beta-cyclodextrin, which offered hydrophilic exterior and hydrophobic cavity that were allowed to self-assemble with the template protein through hydrogen interaction and hydrophobic interaction, was synthesized and used as the functional monomer. Polymerization was carried out in the presence of acrylamide as an assistant monomer, which resulted in a new type of protein imprinted polymer. Langmuir adsorption model was employed to describe the isotherms, and maximum adsorption capacity was evaluated. The performance of such imprinted polymer was further demonstrated by high-performance liquid chromatography, and the results showed that the column packed with the lysozyme imprinted silica beads could effectively separate lysozyme from the mixture of lysozyme-cytochrome c, lysozyme-bovine serum albumin, lysozyme-avidin or lysozyme-methylated bovine serum albumin, which showed its high selectivity.

Molecularly imprinted polymer prepared with bonded β-cyclodextrin and acrylamide on functionalized silica gel for selective recognition of tryptophan in aqueous media

A novel molecularly imprinted polymer (MIP) selective for tryptophan (Trp) was described where polymerization was performed in aqueous media. Three kinds of molecularly imprinted polymers were prepared with surface molecular imprinting technique on functionalized silica gel (F-silica gel). MIPs prepared using bonded beta-cyclodextrin (beta-CD) and acrylamide (AA), either separately or in combination have shown various recognition properties. The results of adsorption experiments indicated that the selectivity of MIP, which was synthesized with bonded beta-CD and AA [MIP(1)], was superior to those obtained with AA [MIP(2)] or bonded beta-CD [MIP(3)]. In addition, the high-performance liquid chromatography (HPLC) column packed with MIP(1) could not only separate Trp from other aromatic amino acids, but also separate the template from its enantiomer in aqueous mobile phase. This study developed a new method for chiral amino acid separation and purification.

Novel Hybrid Structure Silica/CdTe/Molecularly Imprinted Polymer: Synthesis, Specific Recognition, and Quantitative Fluorescence Detection of Bovine Hemoglobin

This work presented a novel strategy for the synthesis of the hybrid structure silica/CdTe/molecularly imprinted polymer (Si-NP/CdTe/MIP) to recognize and detect the template bovine hemoglobin (BHb). First, amino-functionalized silica nanoparticles (Si-NP) and carboxyl-terminated CdTe quantum dots (QDs) were assembled into composite nanoparticles (Si-NP/CdTe) using the EDC (1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride) chemistry. Next, Si-NP/CdTe/MIP was synthesized by anchoring molecularly imprinted polymer (MIP) layer on the surface of Si-NP/CdTe through the sol-gel technique and surface imprinting technique. The hybrid structure possessed the selectivity of molecular imprinting technique and the sensitivity of CdTe QDs as well as well-defined morphology. The binding experiment and fluorescence method demonstrated its special recognition performance toward the template BHb. Under the optimized conditions, the fluorescence intensity of the Si-NP/CdTe/MIP decreased linearly with the increase of BHb in the concentration range 0.02-2.1 μM, and the detection limit was 9.4 nM. Moreover, the reusability and reproducibility and the successful applications in practical samples indicated the synthesis of Si-NP/CdTe/MIP provided an alternative solution for special recognition and determination of protein from real samples.

Molecularly imprinted polymer anchored on the surface of denatured bovine serum albumin modified CdTe quantum dots as fluorescent artificial receptor for recognition of target protein

A new type of molecularly imprinted polymer (MIP)-based fluorescent artificial receptor was developed by anchoring MIP on the surface of denatured bovine serum albumin (dBSA) modified CdTe quantum dots (QDs) using the surface molecular imprinting process. The approach combined the merits of molecular imprinting technology and the fluorescent property of the CdTe QDs. The dBSA was used not only to modify the surface defects of the CdTe QDs, but also as assistant monomer to create effective recognition sites. Three different proteins, namely lysozyme (Lyz), cytochrome c (Cyt) and methylated bovine serum albumin (mBSA), were tested as the template molecules and then the receptors were synthesized by sol-gel reaction (imprinting process). The results of fluorescence and binding experiments demonstrated the recognition performance of the receptors toward the corresponding template. Under optimum conditions, the linear range for Lyz was from 1.4×10(-8) to 8.5×10(-6) M, and the detection limit was 6.8 nM. Moreover, the new artificial receptors were applied to separate and detect Lyz in real samples. This fluorescent artificial receptor may serve as a starting point in the design of highly effective synthetic fluorescent receptor for recognition of target protein.

Epitope imprinted polymer coating CdTe quantum dots for specific recognition and direct fluorescent quantification of the target protein bovine serum albumin

A novel epitope molecularly imprinted polymer (EMIP) for specific recognition and direct fluorescent quantification of the target protein bovine serum albumin (BSA) was demonstrated where polymerization was performed on the surface of silica nanospheres embedded CdTe quantum dots (QDs). The synthetic peptide derived from the surface-exposed C-terminus of bovine serum albumin (BSA, residues 599-607) was selected as the template molecule. The resulting EMIP film was able to selectively capture the template peptide and the corresponding target protein BSA via the recognition cavities. Based on the fluorescence quenching, the EMIP-coated QDs (molecular imprinted polymer coating CdTe QDs using epitope as the template) nanospheres were successfully applied to the direct fluorescence quantification of BSA. Compared with BMIP-coated QDs (molecular imprinted polymer coating CdTe QDs using BSA as the template), the imprinting factor and adsorption capacity of EMIP-coated QDs were greatly increased. The prepared EMIP-coated QDs can also discriminate even one mismatched sequences from the original sequences of the epitope of the BSA. The practical analytical performance of the EMIP-coated QDs was examined by evaluating the detection of BSA in the bovine calf serum sample with satisfactory results. In addition, the resulting EMIP-coated QDs nanospheres were also successfully applied to separating BSA from the bovine blood sample.

Spectroscopic studies on the interaction between CdTe nanoparticles and lysozyme.

Nanoparticles of cadmium telluride (CdTe) coated with thioglycolic acid (TGA) were prepared in the water phase. The interaction between CdTe nanoparticles (NPs) and lysozyme (Lyz) was investigated by fluorescence and circular dichroism (CD) spectroscopy at pH 7.40. It was proved that the fluorescence quenching of Lyz by CdTe NPs was mainly a result of the formation of CdTe-Lyz complex. By the fluorescence quenching results, the Stern-Volmer quenching constant (K(SV)), binding constant (Ka) and binding sites (n) were calculated. The binding distance (r) between Lyz (the donor) and CdTe NPs (the acceptor) was obtained according to fluorescence resonance energy transfer (FRET). Gradual addition of CdTe NPs to the solution of Lyz led to a marked increase in fluorescence polarization (P) of Lyz, which indicated that CdTe NPs were located in a restricted environment of Lyz. The effect of CdTe NPs on the conformation of Lyz has been analyzed by means of synchronous fluorescence spectra and CD spectra, which provided the evidence that the secondary structure of Lyz has been changed by the interaction of CdTe NPs with Lyz.

A new hydrothermal refluxing route to strong fluorescent carbon dots and its application as fluorescent imaging agent.

Due to their unique optical and biochemical properties, the water-soluble fluorescent carbon dots (CDs) have attracted a lot of attention recently. Here, strong fluorescent carbon dots with excellent quality have been synthesized by the hydrothermal refluxing method using lactose as carbon source and tris(hydroxymethyl) aminomethane (i.e. Tris) as surface passivation reagent. This facile approach was simple, efficient, economical, green without pollution, and allows large-scale production of CDs without any post-treatment. TEM measurements showed that the resulting particles exhibited an average diameter of 1.5 nm. The obtained CDs possess small particle sizes, good stability in a wide range of pH values (pH 3.5-9.5), high tolerance of salt concentration, strong resistibility to photobleaching, and a fluorescent quantum yield up to 12.5%. The CDs were applied to optical bioimaging of HeLa cells, showing low cytotoxicity and excellent biocompatibility.

Highly sensitive synchronous fluorescence determination of mercury (II) based on the denatured ovalbumin coated CdTe QDs

Chemically denatured ovalbumin (dOB) was used to modify the surface of 3-mercaptopropionic acid (MPA) stabilized CdTe quantum dots (QDs), which resulted in a great enhancement of the synchronous fluorescence intensity. Moreover, dOB shell layer can effectively prevent the binding of other cations onto the QDs core and enhance the selective binding ability of Hg(2+) to dOB coated CdTe QDs (CdTe-dOB QDs). A simple method with high sensitivity and selectivity was developed for the determination of Hg(2+) with the CdTe-dOB QDs as fluorescence probe based on the merits of synchronous fluorescence spectroscopy (SFS). When scanning with excitation and emission wavelengths of 250 nm and 470 nm (Δλ=λ(em)-λ(ex)=220 nm), respectively, the maximum synchronous fluorescence peak of the CdTe-dOB QDs was located at 328 nm. Under optimal conditions, the change of the synchronous fluorescence intensity was in good linear relationship with the Hg(2+) concentration in the range of 0.08×10(-7) to 30.0×10(-7) mol L(-1) and the detection limit was 4.2×10(-9) mol L(-1) (S/N=3). The relative standard deviation of seven replicate measurements for the concentration of 2.0×10(-7) mol L(-1) and 20.0×10(-7) mol L(-1) were 2.8% and 2.3%, respectively. Compared with general fluorescence methods, the proposed method, which combined the advantages of high sensitivity of synchronous fluorescence and specific response of Hg(2+) to CdTe-dOB, had a wider linear range and higher sensitivity. Furthermore, the proposed method was applied to the determination of trace Hg(2+) in water samples with satisfactory results.