Bingbo Zhang

Quantum dot-based immunochromatography test strip for rapid, quantitative and sensitive detection of alpha fetoprotein.

Rapid, quantitative detection of tumor markers with high sensitivity and specificity is critical to clinical diagnosis and treatment of cancer. We describe here a novel portable fluorescent biosensor that integrates quantum dot (QD) with an immunochromatography test strip (ICTS) and a home-made test strip reader for detection of tumor markers in human serum. Alpha fetoprotein (AFP), which is valuable for diagnosis of primary hepatic carcinoma, is used as a model tumor marker to demonstrate the performance of the proposed immunosensor. The principle of this sensor is on the basis of a sandwich immunoreaction that was performed on an ICTS. The fluorescence intensity of captured QD labels on the test line and control line served as signals was determined by the home-made test strip reader. The strong luminescence and robust photostability of QDs combined with the promising advantages of an ICTS and sensitive detection with the test strip reader result in good performance. Under optimal conditions, this biosensor is capable of detecting as low as 1 ng/mL AFP standard analyte in 10 min with only 50 μL sample volume. Furthermore, 1000 clinical human serum samples were tested by both the QD-based ICTS and a commercial electrochemiluminescence immunoassay AFP kit simultaneously to estimate the sensitivity, specificity and concordance of the assays. Results showed high consistency except for 24 false positive cases (false positive rate 3.92%) and 17 false negative cases (false negative rate 4.38%); the error rate was 4.10% in all. This demonstrates that the QD-based ICTS is capable of rapid, sensitive, and quantitative detection of AFP and shows a great promise for point-of-care testing of other tumor markers.

Synthesis of Zn-Cu-In-S/ZnS Core/Shell Quantum Dots with Inhibited Blue-Shift Photoluminescence and Applications for Tumor Targeted Bioimaging

A facile strategy is reported here for synthesis of Zn-Cu-In-S/ZnS (ZCIS/ZnS) core/shell QDs to address the synthetic issues that the unexpected blue-shift of CuInS2-based nanocrystals. In this strategy, Zn2+ ions are intentionally employed for the synthesis of alloyed ZCIS core QDs before ZnS shell coating, which contributes to the reduced blue-shift in photoluminescence (PL) emission. The experimental results demonstrate this elaborate facile strategy is effective for the reduction of blue-shift during shell growth. Particularly, a hypothesis is proposed and proved for explanation of this effective strategy. Namely, both cation exchange inhibition and ions accumulation are involved during the synthesis of ZCIS/ZnS QDs. Furthermore, the obtained near infrared (NIR) ZCIS/ZnS QDs are transferred into aqueous phase by a polymer coating technique and coupled with cyclic Arg-Gly-Asp peptide (cRGD) peptides. After confirmation of biocompability by cytotoxicity test on normal 3T3 cells, these QDs are injected via tail vein into nude mice bearing U87 MG tumor. The result indicates that the signals detected in the tumor region are much more distinguishing injected with ZCIS/ZnS-cRGD QDs than that injected with ZCIS/ZnS QDs.

Salt-Leached Silk Scaffolds with Tunable Mechanical Properties

Substrate mechanical properties have remarkable influences on cell behavior and tissue regeneration. Although salt-leached silk scaffolds have been used in tissue engineering, applications in softer tissue regeneration can be encumbered with excessive stiffness. In the present study, silk-bound water interactions were regulated by controlling processing to allow the preparation of salt-leached porous scaffolds with tunable mechanical properties. Increasing silk-bound water interactions resulted in reduced silk II (β-sheet crystal) formation during salt-leaching, which resulted in a modulus decrease in the scaffolds. The microstructures as well as degradation behavior were also changed, implying that this water control and salt-leaching approach can be used to achieve tunable mechanical properties. Considering the utility of silk in various fields of biomedicine, the results point to a new approach to generate silk scaffolds with controllable properties to better mimic soft tissues by combining scaffold preparation methods and silk self-assembly in aqueous solutions.

Detection of Mycobacterium tuberculosis based on H37Rv binding peptides using surface functionalized magnetic microspheres coupled with quantum dots – a nano detection method for Mycobacterium tuberculosis

Despite suffering from the major disadvantage of low sensitivity, microscopy of direct smear with the Ziehl–Neelsen stain is still broadly used for detection of acid-fast bacilli and diagnosis of tuberculosis. Here, we present a unique detection method of Mycobacterium tuberculosis (MTB) using surface functionalized magnetic microspheres (MMSs) coupled with quantum dots (QDs), conjugated with various antibodies and phage display-derived peptides. The principle is based upon the conformation of the sandwich complex composed of bacterial cells, MMSs, and QDs. The complex system is tagged with QDs for providing the fluorescent signal as part of the detection while magnetic separation is achieved by MMSs. The peptide ligand H8 derived from the phage display library Ph.D.-7 is developed for MTB cells. Using the combinations of MMS-polyclonal antibody+QD-H8 and MMS-H8+QD-H8, a strong signal of 103 colony forming units (CFU)/mL H37Rv was obtained with improved specificity. MS-H8+QD-H8 combination was further optimized by adjusting the concentrations of MMSs, QDs, and incubation time for the maximum detection signal. The limit of detection for MTB was found to reach 103 CFU/mL even for the sputum matrices. Positive sputum samples could be distinguished from control. Thus, this novel method is shown to improve the detection limit and specificity of MTB from the sputum samples, and to reduce the testing time for accurate diagnosis of tuberculosis, which needs further confirmation of more clinical samples.

Effective Reduction of Nonspecific Binding by Surface Engineering of Quantum Dots with Bovine Serum Albumin for Cell-Targeted Imaging

Quantum dots (QDs) have been widely used as fluorescent probes in cell-targeted imaging. However, nonspecific binding to cellular membranes has been a major challenge. In this study, a new approach is developed for effective reduction of nonspecific binding by bovine serum albumin (BSA)-coated QDs in cell targeting. The experimental results show efficient transfer of hydrophobic QDs from organic to aqueous phase in the presence of BSA aqueous solution under ultrasonication. This ultrasonication-based approach is facile, rapid, and efficient. Stabilization of QDs is mainly achieved by multiple mercapto groups in BSA macromolecules as multidentate ligands and partially by hydrophobic interaction between BSA and pending fatty ligands on QDs. The water solubility of QDs is enhanced by the surface amino and carboxyl groups, which also provide reaction sites for conjugation of targeting ligands. The BSA-coated QDs, with an overwhelming majority of hydrodynamic diameter size of ca. 18 nm, are colloidally stable under both acidic and basic conditions and found to exhibit strong fluorescent intensities. The nonspecific cellular binding is effectively reduced by BSA-coated QDs, compared with the mercaptopropionic acid (MPA)-coated CdTe QDs. BSA-coated QDs are further functionalized with cyclic Arg-Gly-Asp (cRGD) peptide. The cell assays indicate their high target-selectivity in integrin α(v)β(3)-expressed cell imaging.

Gold nanoclusters as contrast agents for fluorescent and X-ray dual-modality imaging.

Multimodal imaging technique is an alternative approach to improve sensitivity of early cancer diagnosis. In this study, highly fluorescent and strong X-ray absorption coefficient gold nanoclusters (Au NCs) are synthesized as dual-modality imaging contrast agents (CAs) for fluorescent and X-ray dual-modality imaging. The experimental results show that the as-prepared Au NCs are well constructed with ultrasmall sizes, reliable fluorescent emission, high computed tomography (CT) value and fine biocompatibility. In vivo imaging results indicate that the obtained Au NCs are capable of fluorescent and X-ray enhanced imaging.

Ultrasound-Triggered BSA/SPION Hybrid Nanoclusters for Liver-Specific Magnetic Resonance Imaging

Nanoclusters of superparamagnetic iron oxide nanoparticles (SPION) are developed for liver-specific magnetic resonance imaging (MRI) by a unique synthesis route. The process is efficient, environmentally benign, and straight forward within five minutes. The clustering effect is triggered in the presence of bovine serum albumin (BSA) aqueous phase under ultrasonication condition. The hydrophobic SPION are densely self-assembled into BSA/SPION hybrid nanoclusters with a uniform size of ~86 nm. The as-prepared BSA/SPION hybrid nanoclusters are found to be biocompatible and stable. They exhibit high transverse relaxivity and longitudinal relaxivity in water (r(2) and r(1) values are 600.8 and 4.3 s(-1) per mM of Fe(3+), respectively). In vivo T(2)-weighted MRI shows excellent enhancement in liver with an imaging time-window up to 48 h. In vivo biodistribution study indicates a gradual excretion of the nanoclusters via hepatobiliary (HB) processing. No toxicity is observed in the in vivo and ex vivo experiments. The BSA/SPION hybrid nanoclusters present great potential in MRI as the liver-specific contrast agents (CAs).

In Vivo Cancer Targeting and Imaging-Guided Surgery with Near Infrared-Emitting Quantum Dot Bioconjugates

Early detection and subsequent complete surgical resection are among the most efficient methods for treating cancer. However, low detection sensitivity and incomplete tumor resection are two challenging issues. Nanoparticle-based imaging-guided surgery has proven promising for cancer-targeted imaging and subsequent debulking surgery. Particularly, the use of near infrared (NIR) fluorescent probes such as NIR quantum dots (QDs) allows deep penetration and high sensitivity for tumor detection. In this study, NIR-emitting CdTe QDs (maximum fluorescence emission peak at 728 nm) were synthesized with a high quantum yield (QY) of 38%. The tumor-specific QD bioconjugates were obtained by attaching cyclic Arg-Gly-Asp peptide (cRGD) to the surface of synthesized QDs, and then injected into U87 MG tumor-bearing mice via tail veins for tumor-targeted imaging. The tumor and its margins were visualized and distinguished by NIR QD bioconjugates, and tumor resection was successfully accomplished via NIR guidance using a Fluobeam-700 NIR imaging system. Our work indicates that the synthesized tumor-specific NIR QDs hold great promise as a potential fluorescent indicator for intraoperative tumor imaging.

Bioinspired synthesis of gadolinium-based hybrid nanoparticles as MRI blood pool contrast agents with high relaxivity

A unique biomineralization approach was developed to synthesize gadolinium-based hybrid (GH) nanoparticles for effective blood pool contrast agents. This approach is bioinspired, environmentally benign, and straightforward. As-prepared GH nanoparticles are biocompatible and well stable in serum. They exhibit much higher longitudinal relaxivity and transverse relaxivity in water (r1 and r2 values of 15.0 and 19.7 s−1 per mM of Gd3+, respectively) than those measured for Gd–DTPA solution (r1 and r2 values of 3.7 and 4.6 s−1 per mM of Gd3+, respectively). In vivo T1-weighted magnetic resonance imaging (MRI) in living mice shows that the GH nanoparticles have an intravascular half-life up to 1 h, much longer than that of Gd–DTPA (about 10 min). As the GH nanoparticles were found to be cleared gradually via hepatobiliary (HB) processing, they can also serve as ideal candidates for liver specific MR contrast agents. In particular, these GH nanoparticles are bioinspired and environmentally benign, therefore promising for medical imaging applications.

Quantum dots/particle-based immunofluorescence assay: synthesis, characterization and application.

Recently, it has been proved that quantum dots (QDs) hold the potential to be used in the bioanalysis as fluorescent probes for their many unique optical properties. In this paper, immunofluorescence assay, an integration of particle-based immunoassays and fluorescent QD-probes, was constructed. Firstly, high quality CdSe/ZnS QDs were prepared. Then after being water-solubilized by amphiphilic polymer based on self-assembling, the QDs were labeled by immunoglobulin G (IgG) antibody. At the same time, both carboxyl-polystyrene (PS) and magnetic carboxyl-PS microspheres were prepared and coated by antigens. The antigen sensitized PS microspheres were specifically captured by the QD-IgG bioconjugates based on the antibody-antigen reaction, which was confirmed by the immunofluorescence test in vitro. The sensitivity of current assay was tested by sandwich immunofluorescence assay using human alpha fetoprotein (AFP) as antigen model. The detection limit of AFP antigen is 4.9 ng/mL.