In this communication, we demonstrate that graphene oxide (GO) greatly inhibits the peroxidatic activity of a horseradish peroxidase-mimicking DNAzyme. Combining this observation with the unique DNA/GO interactions, an ultrasensitive GO-based chemiluminescence DNA biosensing platform is developed.
High quality and facile DNA functionalized quantum dots (QDs) as efficient fluorescence nanomaterials are of great significance for bioimaging both in vitro and in vivo applications. Herein, we offer a strategy to synthesize DNA-functionalized Zn(2+) doped CdTe QDs (DNA-QDs) through a facile one-pot hydrothermal route. DNA is directly attached to the surface of QDs. The as-prepared QDs exhibit small size (3.85 ± 0.53 nm), high quantum yield (up to 80.5%), and excellent photostability. In addition, the toxicity of QDs has dropped considerably because of the Zn-doping and the existence of DNA. Furthermore, DNA has been designed as an aptamer specific for mucin 1 overexpressed in many cancer cells including lung adenocarcinoma. The aptamer-functionalized Zn(2+) doped CdTe QDs (aptamer-QDs) have been successfully applied in active tumor-targeted imaging in vitro and in vivo. A universal design of DNA for synthesis of Zn(2+) doped CdTe QDs could be extended to other target sequences. Owing to the abilities of specific recognition and the simple synthesis route, the applications of QDs will potentially be extended to biosensing and bioimaging.
Human Enterovirus 71 (EV71) and Coxsackievirus B3 (CVB3) have high risks for morbidity and mortality. A virus quantitation immunoassay has been proposed by employing two colored quantum dots (QDs), antibodies of the virus, and graphene oxide (GO). The QDs are streptavidin-conjugated quantum dots (SA-QDs), and the antibodies are biotinylated antibodies. Biotinylated EV71 antibody (Ab1) was associated with 525 nm green colored SA-QDs via biotin-streptavidin interaction forming QDs-Ab1, whereas biotinylated CVB3 antibody (Ab2) was associated with 605 nm red colored SA-QDs via biotin-streptavidin interaction forming QDs-Ab2. GO was an excellent quencher to the fluorescence of both QDs-Ab1 and QDs-Ab2. The targets of EV71 and CVB3 can break up the complex of QDs-Ab and GO, recovering the fluorescence of QDs-Ab1 and QDs-Ab2, respectively. Using these two different colored QDs-Ab fluorescence recovery intensities upon the addition of targets EV71 and CVB3, the two enteroviruses can be simultaneously quantitatively determined with a single excitation light. The detection limits of EV71 and CVB3 are 0.42 and 0.39 ng mL(-1) based on 3 times signal-to-noise ratio, respectively. More importantly, this strategy can be further used as a universal method for any protein or virus determination by changing the conjugated antibodies in disease early diagnosis, which can provide a fast and promising clinical approach for virus differentiation and determination. In a word, a simple, fast, sensitive, and highly selective assay for EV71 and CVB3 has been developed. It could be applied in clinical sample analysis with a satisfactory result. It was notable that the sensor could not only achieve rapid and precise quantitative determination of protein/virus by fluorescent intensity but also could be applied in semiquantitative protein/virus determination by digital visualization.
Optical barcoding technology based on quantum dot (QD)-encoded microparticles has attracted increasing attention in high-throughput multiplexed biological assays, which is realized by embedding different-sized QDs into polymeric matrixes at precisely controlled ratios. Considering the advantage of droplet-based microfluidics, producing monodisperse particles with precise control over the size, shape and composition, we present a proof-of-concept approach for on-demand preparation of QD-encoded microparticles based on this versatile new strategy. Combining a flow-focusing microchannel with a double T-junction in a microfluidic chip, biocompatible QD-doped microparticles were constructed by shearing sodium alginate solution into microdroplets and on-chip gelating these droplets into a hydrogel matrix to encapsulate CdSe/ZnS QDs. Size-controllable QD-doped hydrogel microparticles were produced under the optimum flow conditions, and their fluorescent properties were investigated. A novel multiplex optical encoding strategy was realized by loading different sized QDs into a single droplet (and thus a hydrogel microparticle) with different concentrations, which was triggered by tuning the flow rates of the sodium alginate solutions entrapped with different-colored QDs. A series of QD-encoded microparticles were controllably, and continuously, produced in a single step with the present approach. Their application in a model immunoassay demonstrated the potential practicability of QD-encoded hydrogel microparticles in multiplexed biomolecular detection. This simple and robust strategy should be further improved and practically used in making barcode microparticles with various polymer matrixes.
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