We develop a new strategy to prepare quantum dot (QD) barcode particles by polymerizing double emulsion droplets prepared in capillary microfluidic devices. The resultant barcode particles are composed of stable QDtagged core particles surrounded by hydrogel shells. These particles exhibit uniform spectral characteristics and excellent coding capability, as confirmed by photoluminescence analyses. By using double emulsion droplets with two inner droplets of distinct phases as templates, we have also fabricated anisotropic magnetic barcode particles with two separate cores or with a Janus core. These particles enable optical encoding and magnetic separation, thus making them excellent functional barcode particles in biomedical applications.The increasing use of high-throughput assays in biomedical applications, including drug discovery and clinical diagnostics, 1,2 demands effective strategies for multiplexing. One promising strategy is to use barcode particles, which are particles that encode information about their specific compositions and enable simple identification. Many encoding strategies have been proposed for these barcode particles; these include incorporation of segmented nanorods, 3 photo-patterning, 4-6 as well as the use of photonic crystals, 7,8 fluorescent silica colloids, 9 and semiconductor quantum dots (QDs). [10][11][12][13][14][15][16] In particular, the semiconductor QDs hold immense promise as barcode elements because of their excellent optical properties such as simultaneous excitation of multiple wavelength-and-intensity with a single light source, minimal spectral width, and remarkable photo-stability. In particular, the semiconductor QDs hold immense promise as barcode elements because of their excellent optical properties such as minimal spectral width, and remarkable photo-stability. In addition, by mixing QDs with different emission wavelengths at different concentrations, significantly larger combinations can be generated with a single excitation wavelength. To generate barcodes, QDs can be incorporated into the particles before their polymerization or during their swelling, 10,14 The QDs can also be applied as a coating on the surface of the particles. 11,12 However, QD barcodes generated by this approach often suffer from leakage of QDs; this significantly affects the performance and stability of the barcode particles. In addition, traditional processes used for generating such particles provide little control over the characteristics of the result particles, such as particle sizes and QDs number and distribution within each particles; thus the resultant QD barcodes often have high variability of fluorescence intensities. [13][14][15][16] This is exacerbated by the uncontrolled motion of these barcode particles, which reduces the sensitivity of the assay 6 and demands more complicated procedures for enriching the barcode particles during assay 17 . These, together with the debatable biocompatibility of such particles, have limited their applications. 16 Thus, novel appr...

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The deposition of PM2.5 (fine particulate matter in air with diameter smaller than 2.5 μm) in lungs is harmful to human health. However, real-time observation on the deposition of particles in the acinar area of the lung is still a challenge in experiments. Here, a fluorescent imaging method is developed to visualize the deposition process with a high temporal and spatial resolution. The observations reveal that the deposition pattern is nonuniform, and the maximum deposition rate in the acinar area differs significantly from the prediction of the widely used average deposition model. The method is also used to find single particles in the kidney and liver, though such particles are commonly believed to be too large to enter the extrapulmonary organs.

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