Exosomes, the smallest sized extracellular vesicles (30 ~ 150 nm) packaged with lipids, proteins, functional messenger RNAs and microRNAs, and double-stranded DNA from their cells of origin, have emerged as key players in intercellular communication. Their presence in bodily fluids, where they protect their cargo from degradation, makes them attractive candidates for clinical application as innovative diagnostic and therapeutic tools. But routine isolation and analysis of high purity exosomes in clinical settings is challenging, with conventional methods facing a number of drawbacks including low yield and/or purity, long processing times, high cost, and difficulties in standardization. Here we review a promising solution, microfluidic-based technologies that have incorporated a host of separation and sensing capabilities for exosome isolation, detection, and analysis, with emphasis on point of care and clinical applications. These new capabilities promise to advance fundamental research while paving the way toward routine exosome-based liquid biopsy for personalized medicine.

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Interferometric techniques have proven useful to infer proximity and local surface profiles of microscopic objects near surfaces. But a critical trade-off emerges between accuracy and mathematical complexity when these methods are applied outside the vicinity of closest approach. Here we introduce a significant advancement that enables reflection interference contrast microscopy to provide nearly instantaneous reconstruction of an arbitrary convex object’s contour next to a bounding surface with nanometre resolution, making it possible to interrogate microparticle/surface interaction phenomena at radii of curvature 1,000 times smaller than those accessible by the conventional surface force apparatus. The unique view-from-below perspective of reflection interference contrast microscopy also reveals previously unseen deformations and allows the first direct observation of femtolitre-scale capillary condensation dynamics underneath micron-sized particles. Our implementation of reflection interference contrast microscopy provides a generally applicable nanometre-scale resolution tool that can be potentially exploited to dynamically probe ensembles of objects near surfaces so that statistical/probabilistic behaviour can be realistically captured.

Current accurate applications of reflection interference contrast microscopy (RICM) are limited to known geometries; when the geometry of the object is unknown, an approximated fringe spacing analysis is usually performed. To complete an accurate RICM analysis in more general situations, we review and improve the formulation for intensity calculation based on nonplanar interface image formation theory and develop a method for its practical implementation in wedges and convex surfaces. In addition, a suitable RICM model for an arbitrary convex surface, with or without a uniform layer such as a membrane or ultrathin coating, is presented. Experimental work with polymer vesicles shows that the coupling of the improved RICM image formation theory, the calculation method, and the surface model allow an accurate reconstruction of the convex bottom shape of an object close to the substrate by fitting its experimental intensity pattern.