Qiuhua Yang

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.

Rapid and Quantitative Detection of Prostate Specific Antigen with a Quantum Dot Nanobeads-Based Immunochromatography Test Strip

Convenient and fast testing using an immunochromatography test strip (ICTS) enables rapid yes/no decisions regarding a disease to be made. However, the fundamental limitations of an ICTS, such as a lack of quantitative and sensitive analysis, severely hampers its application in reliable medical testing for the early detection of cancer. Herein, we overcame these limitations by integrating an ICTS with quantum dot nanobeads (QD nanobeads), which were fabricated by encapsulating QDs within modified poly(tert-butyl acrylate-co-ethyl acrylate-co-methacrylic acid) and served as a robust signal-generating reagent for the ICTS. Prostate specific antigen (PSA) was used as a model analyte to demonstrate the performance of the QD nanobeads-based ICTS platform. Under optimized conditions, the concentration of PSA could be determined within 15 min with high sensitivity and specificity using only 40 μL of sample. The detection limit was enhanced by ∼12-fold compared with that of an ICTS that used QDs encapsulated by commercial 11-mercaptoundecanoic acid (QDs@MUA) as the signal-generating reagent. At the same time, the possible clinical utility of this approach was demonstrated by measurements recorded from PSA-positive patient specimens. Our data suggest that the QD nanobeads-based ICTS platform is not only rapid and low-cost but also highly sensitive and specific for use in quantitative point-of-care diagnostics; thus, it holds promise for becoming a part of routine medical testing for the early cancer of detection.

Structural design and preparation of high-performance QD-encoded polymer beads for suspension arrays

Fluorescence-encoded polymer bead-based suspension arrays are widely used in biomolecular screening and diagnostic applications. The interior structure of polymer beads, especially the pore size, plays an important role in the preparation of fluorescent beads with a large encoding capacity and stability. Here, highly cross-linked carboxylated poly(styrene-co-ethylene glycol dimethacrylate-co-methacrylic acid) beads (PSEMBs) with optimum pore sizes were designed, fabricated, and further employed in the preparation of high-performance QD-encoded microbeads via a gradual solvent evaporation method. The PSEMBs and QD-encoded PSEMBs were characterized by scanning electron microscopy (SEM), laser scanning confocal microscopy, and spectrofluorometry. The SEM images and flow cytometry results of PSEMBs demonstrate the good sphericity and uniform particle size distribution. Confocal microscope images illustrate that highly uniform, bright fluorescent beads are obtained and the quantum dots (QDs) have filtrated into the entire microspheres, with the required pore size achieved by adjusting the content of porogen. Furthermore, QD-encoded PSEMBs were found to be photostable without leakage of QDs, and to retain their bright fluorescence for at least 20 days. Immunoassay performances for human IgG detections indicate that carboxyl groups on the fluorescent microsphere surface facilitate efficient attachment of biomacromolecules, and therefore enable high detection sensitivity (0.01 ng mL−1) in sandwich immunoreactions. These results indicate that designed optical encoding microcarriers can be successfully applied to high-throughput and multiplexed biomolecular assays. Moreover, the new porous PSEMBs designed and fabricated in this report can efficiently load other nanoparticles (e.g. magnetic nanoparticles, Au and Ag nanoparticles) for a wide range of applications.

Self-healing encapsulation strategy for preparing highly stable, functionalized quantum-dot barcodes.

Quantum dot (QD) barcodes are becoming an urgent requirement for researchers and clinicians to obtain high-density information in multiplexed suspension (bead-based) assay. However, how to improve the stability of quantum dot barcodes is a longstanding issue. Here, we present a new self-healing encapsulation strategy to generate functionalized uniform quantum dots barcodes with high physical and chemical stability. This efficient and facile strategy could make porous polymer microspheres self-heal to encapsulate QDs via the thermal motion and interaction of the molecular chains. Consequently, the new strategy solved especially the QDs leakage problem and improved the chemical stability under different pH physiological conditions as well as the longtime storage stability. In the meantime, the encoding capacity and the spatial distribution uniformity of quantum dots could be also improved. Furthermore, immunofluorescence assays for alpha fetoprotein (AFP) detections indicated that carboxyl groups on the surface of QD-encoded microspheres could facilitate efficient attachment of biomacromolecules.

An effective modified method to prepare highly luminescent, highly stable water-soluble quantum dots and its preliminary application in immunoassay

In this paper, a biocompatible poly(γ-glutamic acid) (PGA)-based polymer with numerous thiol groups grafted onto the backbone was self-synthesized. It has been successfully used to prepare water-soluble quantum dots (QDs) with high luminescence and high stability. FTIR spectroscopy, transmission electron microscopy, dynamic light scattering, spectrofluoro-photometry, fluorescence microscopy and flow cytometer were used to characterize QDs@poly(γ-glutamic acid)-grafted cysteamine (PGA-g-MEA). The results indicated that QDs@PGA-g-MEA with an identical small size were highly luminescent with a well maintained, even increased, photoluminescence (PL) intensity when compared with the tributylphosphine oxide (TOPO) coated QDs. Meanwhile, they were highly stable in aqueous solution under a wide range of pH from 2 to 12, as well as under different temperatures. The QDs@PGA-g-MEA were then applied as fluorescent probes to detect human IgGs and the results demonstrated that QDs@PGA-g-MEA had great potential for application in immunofluorescence.

Direct Coating Adherent Diamond Films on Fe-Based Alloy Substrate: The Roles of Al, Cr in Enhancing Interfacial Adhesion and Promoting Diamond Growth

Direct CVD deposition of dense, continuous, and adherent diamond films on conventional Fe-based alloys has long been considered impossible. The current study demonstrates that such a deposition can be realized on Al, Cr-modified Fe-based alloy substrate (FeAl or FeCrAl). To clarify the fundamental mechanism of Al, Cr in promoting diamond growth and enhancing interfacial adhesion, fine structure and chemical analysis around the diamond film-substrate interface have been comprehensively characterized by transmission electron microscopy. An intermediate graphite layer forms on those Al-free substrates such as pure Fe and FeCr, which significantly deteriorates the interfacial adhesion of diamond. In contrast, such a graphite layer is absent on the FeAl and FeCrAl substrates, whereas a very thin Al-rich amorphous oxide sublayer is always identified between the diamond film and substrate interface. These comparative results indicate that the Al-rich interfacial oxide layer acts as an effective barrier to prevent the formation of graphite phase and consequently enhance diamond growth and adhesion. The adhesion of diamond film formed on FeCrAl is especially superior to that formed on FeAl substrate. This can be further attributed to a synergetic effect including the reduced fraction of Al and the decreased substrate thermal-expansion coefficient on FeCrAl in comparison with FeAl, and a mechanical interlocking effect due to the formation of interfacial chromium carbides. Accordingly, a mechanism model is proposed to account for the different interfacial adhesion of diamond grown on the various Fe-based substrates.

A facile method to prepare high-performance magnetic and fluorescent bifunctional nanocomposites and their preliminary application in biomolecule detection

Magnetic and fluorescent bifunctional nanocomposites have great potential in biomolecule detection and biological imaging applications. So far, it remains a challenge to prepare bifunctional nanocomposites with high colloidal and fluorescent stability. To address this problem, we utilized a simple ring-opening reaction to conjugate Fe3O4 and CdZnSeS quantum dots (QDs). The surface amine groups of SiO2-coated Fe3O4 nanoparticles (Fe3O4@SiO2) opened the rings of the surface maleic anhydride groups of poly(styrene-co-maleic anhydride)-coated CdZnSeS QDs (QDs@PSMA), and then the resulting nanocomposite was functionalized with Jeffamine M-1000 polyetheramine (JMP) by a ring-opening reaction. The structures and properties of the bifunctional nanocomposites were fully characterized by transmission electron microscopy, dynamic light scattering, spectrofluorometry and vibrating sample magnetometry. The results indicated that the nanocomposites prepared by the conjugation method had dramatically higher quantum yields (QYs) than those prepared by the SiO2 co-encapsulation method. After introducing JMP, the nanocomposites exhibited high fluorescent and colloidal stability over a wide pH range (pH 2-13), a low level of protein adsorption in PBS with 10% fetal bovine serum at 37 °C, and a negligible level of nonspecific binding when incubated with HeLa cells. Sandwich fluoroimmunoassay results indicated that the nanocomposites can be successfully applied in a variety of diagnosis and bioimaging applications.

Highly stable quantum dots with silica–poly(EGDMA-co-MAA) synergistic protection and the preliminary application in immunoassay

For the application of biological quantitative probes, how to ameliorate chemical sensitivity and instability of quantum dots (QDs) under different environments is a longstanding issue. Here, silica and poly(EGDMA-co-MAA) as inert materials, ultrastable QD/SiO2/poly(EGDMA-co-MAA) fluorescent nanoprobes with a tri-layer core-shell structure were successfully prepared by distillation precipitation polymerization. The QD/SiO2/poly(EGDMA-co-MAA) demonstrated ultra-high chemical stability due to the synergistic combination of silica and cross-linked polymer stabilizing the fluorescence intensity of QDs under harsh chemical environments, including strong acidic solutions, which is unavailable for any of the current encapsulation technologies used alone. Immunochromatography test strips (ICTS) for the detection of human chorionic gonadotrophin (HCG) antigen was developed by using QD/SiO2/poly(EGDMA-co-MAA) as fluorescent nanoprobes. The results showed admirable reliability and sensitivity in antigen detection. Whats more, reliable quantitative detection based on QD/SiO2/poly(EGDMA-co-MAA) was realized. We expect the ultrastable QDs will open up exciting opportunities in accurate quantitative analysis and imaging.

Facile single step preparation of high-performance quantum dot barcodes

We demonstrate the facile preparation of highly luminescent Cd1−xZnxSe1−ySy quantum dot (QD)-encoded poly(styrene-co-ethylene glycol dimethacrylate-co-methacrylic acid) beads (PSEMBs) in a straightforward and reproducible manner. The monodisperse mesoporous PSEMBs are first swelled in chloroform. Afterwards, the reaction precursors, composed of Cd, Zn, Se and S, are impregnated into the microspheres. Subsequently, the Cd1−xZnxSe1−ySy QDs are synthesized directly within the polymer beads by thermal decomposition. The results show that a wide range of emission wavelengths (490 nm–606 nm) with a narrow full width at half maximum (FWHM) (<40 nm) is obtained by changing the ratios of the precursors. Confocal microscopy images illustrate that highly uniform, bright fluorescent beads are obtained and the QDs have infiltrated into the entire microsphere. The resulting QD barcodes exhibit remarkable stability against solvent induced QD leaching and chemical induced fluorescence quenching. The QD-encoded PSEMBs are found to be photostable in phosphate buffered saline (PBS) (pH 7.4) for at least 3 weeks. Immunoassay performances for human IgG detection indicate that the QD barcodes can be successfully applied to high-throughput multiplexed biomolecular assays.