Enabling the Ultraenrichment of Colloidal Particles via Continuous Droplet Manipulation.

Concentration and uniform deposition of particles during droplet evaporation remain significant challenges in analytical systems. This natural and appropriate design of the processing steps can effectively bridge the gap between the low-concentration test substance and the accuracy of the test tool and therefore has attracted widespread academic and industrial attention. However, conventional static evaporation faces two major challenges: limited concentration efficiency and nonuniform particle deposition due to the coffee-ring effect. Here, we introduce a "dynamic enrichment" method based on a magnetically actuated droplet manipulation platform, which fundamentally alters the traditional static concentration process. This approach enables both superior enrichment and uniform particle distribution on superhydrophobic surfaces through controlled droplet movement. We systematically investigated the enrichment behavior using model particles of varying densities and sizes under different experimental conditions, including droplet volume and initial concentration. The method demonstrates consistent performance across these diverse particle properties, achieving a higher concentration efficiency and more uniform deposition compared to static enrichment. Through characterization and mechanistic statements, we show that this platform could potentially serve as a foundation for developing sensitive analytical techniques, particularly considering that the working range of particle properties aligns well with those of common biological and chemical analytes.