Light-Controlled Particle Enrichment Patterns in Droplets

Abstract

Precision manipulation of particle-enrichment patterns in droplets is challenging but important in biochemical analysis and clinical diagnosis. Herein, a light strategy for precisely manipulating particle enrichment patterns is reported. Focused laser irradiation to the droplet induces a Marangoni flow owing to a localized photothermal effect, which carries in-droplet particles and concentrates them at the laser-spot-acted region. Owing to high flexibility of light, multiple particle-enriched sites are formed in a droplet, and the concentrated particles can be transported and reconstructed on demand. In addition to the island-like enrichment pattern, this optical particle manipulation strategy enables the formation of various particle-enriched patterns, such as the line-shape and circle-shape patterns. Further, light directly acts on the working fluid instead of target particles, considerably weakening dependence on particle properties. For particles whose density is similar to that of the working fluid, a portion of particles can still be concentrated. It is also found that only a small portion of submicron particles can be concentrated, while nanoparticles are hardly concentrated by this light strategy. Moreover, high reconfigurability of light enables in-parallel high-throughput operations, which is demonstrated using two laser beams to form two particle enrichment sites in a droplet simultaneously. Finally, this light strategy is also demonstrated by concentrating cells and nucleic acid molecules. This work paves the way for the applications of optofluidics in cell sorting, point-of-care analysis, and drug screening.

Efficient fabrication of bioinspired soft, ridged-slippery surfaces with large-range anisotropic wettability for droplet manipulation

“…1–6 One prevalent approach for facilitating droplet directional transport involves the design of surfaces with non-uniform wetting characteristics, incorporating gradients in either chemical composition or topography. 7–9 The natural world is a valuable source of inspiration in developing advanced materials for manipulating droplets. 10–12 As an illustration, rice leaves exhibit bidirectional anisotropic wettability, allowing water droplets to traverse along the leaf veins under self-gravity, ultimately enhancing the survival of rice plants under drought conditions.…”

Visualization of the Dynamics of Photoinduced Crawling Motion of 4-(Methylamino)Azobenzene Crystals via Diffracted X-ray Tracking

“…Microdroplet manipulation on solid surfaces holds promise for applications in surface patterning [7][8][9][10], microreactors [11][12][13][14][15], and bioassays [16][17][18][19][20]. Their motions are driven by external optical [21][22][23][24], thermal [25][26][27][28], electrical [29][30][31][32], and magnetic [33][34][35][36] stimuli. Optical stimulation has the advantage of allowing remote and directional control of motion.…”