Designing Multifunctional Quantum Dots For Disease Detection

Quantum dots (QDs), semiconductor nanoparticles with unique photo-physicalproperties, have become one of the dominant classes of imaging probes as well asuniversal platforms for engineering of multifunctional nanodevices. In this paper, wefirst prepared hydrophobic high quality QDs. After that, they were made surfacemodification. At last, QD barcodes and QD-based immunochromatography test stripwere prepared, and coupled with biological macromolecules, and then they were usedin the diagnosis of disease.We demonstrate a single-step synthetic method for highly luminescent and stableQDs by using the reactivity difference between Cd and Zn precursors and thatbetween Se and S precursors. A wide range of emission wavelengths (500-610nm)with a narrow fwhm (<35nm) is obtained by changing the ratios of the precursors.Under the reaction conditions selected, Cd-and Se (with a bit of S)-based cores areformed first and Zn-and S-based shells are formed successively; therefore, the QDshave a core/shell structure with composition gradients, which relieve the latticemismatch between core and shells. The QDs are characterized using the combinedtechniques of HRTEM, UV–vis, PL spectroscopy, and XRD. The QDs also haveenergy gradients depending on their compositions in a radial direction, whichenergetically confine carriers (electrons and holes) to the cores. Then ultrasoundemulsification and silica coating were used to prepare hydrophilic QDs. Ultrasoundemulsification is simple and easy to be purified with centrifugation. But the size of theas-prepared nanoparticle is big and uneven. Silica coating is a mature and good atpreparation of ultrafine particles. And the size distribution of the as-preparednanoparticle is rather narrow. But it requires a longer preparation period. As far as weconsidered, we could choose proper modification method for different biomedicalapplications.High-performance QD-encoded microbeads were prepared via gradual solventevaporation method and facile single step method. The PSEMBs and QD-encodedPSEMBs were characterized by scanning electron microscopy (SEM), laser scanningconfocal microscopy, and spectrofluorometry. For gradual solvent evaporationmethod, confocal microscope images illustrated that highly uniform bright fluorescent beads are obtained and the quantum dots (QDs) had filtrated into the entiremicrospheres with proper pore size achieved by adjusting the content of porogen.Furthermore, QD-encoded PSEMBs had been displayed to be photostable and kepttheir bright fluorescence for at least20days. For facile single step method, themonodisperse mesoporous PSEMBs are first swelled in chloroform. Afterwards, thereaction precursors, composed of Cd, Zn, Se and S, are impregnated into themicrospheres. Subsequently, the Cd1-xZnxSe1-ySyQDs are synthesized directly withinthe polymer beads by thermal decomposition. The results show that a wide range ofemission wavelengths (490nm-606nm) with a narrow full width at half maximum(FWHM)(<40nm) is obtained by changing the ratios of the precursors. Confocalmicroscopy images illustrate that highly uniform, bright fluorescent beads areobtained and the QDs have infiltrated into the entire microsphere. The resulting QDbarcodes exhibit remarkable stability against solvent induced QD leaching andchemical induced fluorescence quenching. The QD-encoded PSEMBs are found to bephotostable in phosphate buffered saline (PBS)(pH7.4) for at least3weeks.Immunoassay performances for human IgG detection indicate that the QD barcodescan be successfully applied to high-throughput multiplexed biomolecular assays.Rapid, quantitative detection of tumor markers with high sensitivity andspecificity is critical to clinical diagnosis and treatment of cancer. We describe anovel portable fluorescent biosensor that integrates QD with animmunochromatography test strip and a home-made test strip reader for detection oftumor markers in human serum. Alpha fetoprotein (AFP), which is valuable fordiagnosis of primary hepatic carcinoma and human chorionic gonadotropin (HCG),which is a reliable marker for detecting persistent gestational trophoblastic neoplasia(GTN) and reflects the clinical course of the disease, are used as model tumor markersto demonstrate the performance of the proposed immunosensor. The principle of thissensor 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 lineserved as signals was determined by the home-made test strip reader. The strongluminescence and robust photostability of QDs combined with the promisingadvantages of an ICTS and sensitive detection with the test strip reader result in goodperformance. Under optimal conditions, this biosensor is capable of detecting as lowas1ng/mL AFP standard analyte in10min with only50μL sample volume and aminimum0.85IU/L HCG standard analyte in15min with50μL sample volume. Furthermore,1000clinical human serum samples were tested by both the QD-basedICTS and a commercial electrochemiluminescence immunoassay AFP kitsimultaneously to estimate the sensitivity, specificity and concordance of the assays.Results showed high consistency except for24false positive cases (false positive rate3.92%) and17false negative cases (false negative rate4.38%); the error rate was4.10%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 testingand community screening of other tumor markers.