Fluorescence-profile pre-definable quantum-dot barcodes in liquid-core microcapsules
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Microparticles incorporated with quantum-dot (QD) barcodes for multiplexed bioassays attract a great attention due to their potential applications in drug discovery, gene profiling and clinic diagnostics. However, the existing QD barcodes lack a necessary optical stability to ambient fluids or a repeatability of fluorescent profiles. We developed a new QD barcode by loading an aqueous QD mixture as a liquid core into a monodispersed polymer microcapsule by a microfluidic method to avoid those problems. We found that the QDs in the liquid cores were able to maintain their original characteristics, especially the linear relation between photoluminescence intensity and concentration. In addition, we found that the fluorescent profiles of the QD-loaded liquid cores were the same as those of the QD mixtures before being loaded inside the microcapsules. With these two properties, the QD barcodes can be predefined directly by multiplexing the emission peaks and concentrations of the QDs in the liquid cores. Furthermore, the graphical information from fluorescent images of the microcapsules, such as the sizes and numbers of the QD-loaded liquid cores, offers another dimension for barcoding to increase the coding capacity. We also presented a microfluidic method to manufacture the QD-barcoded microcapsules of size ~30 μm. These pre-definable QD barcodes with stable fluorescent profiles can be used as a platform for various high-throughput screening applications in different bioassay buffers.