Search

Fluorescent silicon quantum dots (SiQDs) have shown a great potential as antiphotobleaching, nontoxic and biodegradable labels for various in vitro and in vivo applications. However, fabricating SiQDs with high water-solubility and high photoluminescence quantum yield (PLQY) remains a challenge. Furthermore, for targeted imaging, their surface chemistry has to be capable of conjugating to antibodies, as well as sufficiently antifouling. Herein, antibody-conjugated SiQD nanoparticles (SiQD-NPs) with antifouling coatings composed of bovine serum albumin (BSA) and polyethylene glycol (PEG) are demonstrated for immunostaining on live cancer cells. The monodisperse SiQD-NPs of diameter about 130 nm are synthesized by a novel top-down method, including electrochemical etching, photochemical hydrosilylation, high energy ball milling, and "selective-etching" in HNO3 and HF. Subsequently, the BSA and PEG are covalently grafted on to the SiQD-NP surface through presynthesized chemical linkers, resulting in a stable, hydrophilic, and antifouling organic capping layer with isothiocyanates as the terminal functional groups for facile conjugation to the antibodies. The in vitro cell viability assay reveals that the BSA-coated SiQD-NPs had exceptional biocompatibility, with minimal cytotoxicity at concentration up to 1600 μg mL(-1). Under 365 nm excitation, the SiQD-NP colloid emits bright reddish photoluminescence with PLQY = 45-55% in organic solvent and 5-10% in aqueous buffer. Finally, through confocal fluorescent imaging and flow cytometry analysis, the anti-HER2 conjugated SiQD-NPs show obvious specific binding to the HER2-overexpressing SKOV3 cells and negligible nonspecific binding to the HER2-nonexpressing CHO cells. Under similar experimental conditions, the immunofluorescence results obtained with the SiQD-NPs are comparable to those using conventional fluorescein isothiocyanate (FITC).

An improved method for the synthesis of high-performance and water-soluble quantum dots (QDs) involving the encapsulation of mercaptosuccinic acid coated QDs (MSA-QDs) with poly(diallyldimethylammonium chloride) (PDDA) followed by their direct photoactivation with fluorescent radiation near 295 K to yield PDDA-coated QDs (PDDA-QDs) has been demonstrated. The quantum yield (QY) of the PDDA-QDs was significantly improved from 0.6 (QY of MSA-QDs) to 48%. By using this synthetic strategy, highly photoluminescent PDDA-QDs of varied size were readily prepared. The surface properties of PDDA-QDs and MSA-QDs were extensively characterized. The highly luminescent and positively charged PDDA-QDs serve as a useful and convenient tool for protein adsorption. With a Δ(5)-3-ketosteroid isomerase adsorbed PDDA-QD complex, the biorecognition of steroids was demonstrated through the application of fluorescent resonance energy transfer., (Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

The quantitative detection of triglycerides is an important issue for health inspection of metabolic disorders and for food and oil-refining industries. Many methods have been designed to approach this target, in which multiple reactions catalyzed by enzymes are normally coupled consecutively. In this study, we demonstrated a simple assay system containing lipase and photoactivated luminescent CdSe/ZnS quantum dots (QDs) for the quantitative detection of triglycerides. Photoactivated CdSe/ZnS QDs function as a sensitive "indicator" to reveal the minute acidity change of the assay system resulting from the enzymatic hydrolysis of triglycerides. By controlling the initial buffer condition of the assay system at 5, 10, or 20 mM phosphate buffer at pH 8.0, respectively, the quenching ratio of the QDs fluorescence intensity monitored at the maximum photoluminescence showed a linear correlation with the concentration of the examined triglyceride in the range of 0.02-6, 0.2-10, or 2-20 mM, respectively. The assay system also provides a convenient way to estimate triglyceride concentration by visualizing the color change of the QDs fluorescence. As compared to most of the existing methods, the system reported herein possessed many advantages, including simplicity, low cost, high flexibility, and high sensitivity. Furthermore, no complicated chemical modification or enzyme immobilization is needed.

An original and novel assay system with urease as a catalyst and CdSe/ZnS quantum dots (QDs) as an indicator has been developed for quantitative analysis of urea. By mixing urease and QDs, the determination of urea can be performed in a quantitative manner. The detection is based on the enhancement of QD photoluminescence (PL) intensity, which is correlated to the enzymatic degradation of urea. By controlling the buffer concentration and pH, PL enhancement due to the degradation of urea is linear in the urea concentration ranging from 0.01 to 100mM. This property makes the urease/QDs system to be a promising urea-biosensing system. The newly developed system is a superior design and possesses many advantages, including its simple preparation, low cost, no enzyme immobilization required, high flexibility, and good sensitivity.

An improved method for the synthesis of high-performance and water-soluble quantum dots (QDs) involving the encapsulation of mercaptosuccinic acid coated QDs (MSA-QDs) with poly(diallyldimethylammonium chloride) (PDDA) followed by their direct photoactivation with fluorescent radiation near 295 K to yield PDDA-coated QDs (PDDA-QDs) has been demonstrated. The quantum yield (QY) of the PDDA-QDs was significantly improved from 0.6 (QY of MSA-QDs) to 48 %. By using this synthetic strategy, highly photoluminescent PDDA-QDs of varied size were readily prepared. The surface properties of PDDA-QDs and MSA-QDs were extensively characterized. The highly luminescent and positively charged PDDA-QDs serve as a useful and convenient tool for protein adsorption. With a Δ5-3-ketosteroid isomerase adsorbed PDDA-QD complex, the biorecognition of steroids was demonstrated through the application of fluorescent resonance energy transfer. [ABSTRACT FROM AUTHOR]

Abstract: Quantitative detection of glucose is an important issue in food industry, various biotechnological processes and medication of metabolic disorders. Many ways have been developed to approach this target. In this study, we demonstrated a simple assay system containing glucose oxidase (GOD) and CdSe/ZnS quantum dots (QDs) for specific and quantitative detection of glucose. The role of QDs functioned as an “indicator” to reveal the acidity change of the assay system resulting from the enzymatic oxidation of glucose. By controlling the initial buffer conditions of the assay system at 10mM or 30mM phosphate, pH 8.0, the quench ratio of PL intensity of QDs at 586nm was found to be linear to the tested glucose in the range of 0.2–10mM or 2–30mM, respectively. The assay system also provides a convenient way to determine the glucose concentration by visualizing the color change of QDs fluorescence. As compare to most of the existing methods, this newly developed system possesses many advantages, including simplicity, low cost, high flexibility, and good sensitivity. Furthermore, no complicated chemical modification and enzyme immobilization were needed in this system. [Copyright &y& Elsevier]