Yunhong Li

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.

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.

An efficient method for preparing high-performance multifunctional polymer beads simultaneously incorporated with magnetic nanoparticles and quantum dots

An efficient modified method combining conventional swelling method with high-temperature swelling method was applied to prepare high-stable multifunctional MNPs-QD-encoded polystyrene beads simultaneously with large encoding capacity and fast separation. In this paper, the results demonstrate that encapsulating QDs into pre-prepared MNPs-beads is the best sequence, which keeps high brightness and fast separation. The MNPs-QD-encoded microcarriers designed by our proposed method exhibit excellent performance for magnetic manipulation and optical encoding. What is more, they also have better physical and chemical stabilities. Compared with beads prepared via conventional swelling method, the leakage of nanoparticles from the designed MNPs-QD-encoded poly (styrene-co-ethylene glycol dimethacrylate-co-methacrylic acid) beads (PSEMBs) induced by organic solvents (e.g.cyclohexane) is less than 6%; meanwhile, fluorescence intensity of MNPs-QDs-encoded PSEMBs fluctuates slightly more in a wide range of pH 2–12 buffers. In addition, immunoassay performance for human IgG detections indicates that carboxyl groups on fluorescent microsphere surface facilitate efficient attachment of biomolecule and therefore they can be further applied to fast separation and multiplexed biomolecular assays.

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.