Multimodal Evaporation on Patterned Nanoparticle Arrays for Exhaled Breath Condensate Detection

Understanding droplet evaporation behavior is fundamental to a wide range of applications, including inkjet printing, microfluidics, thermal management, and biomedical sensing. Droplet evaporation typically follows a single stick-slip model on homogeneous solid substrates, while such evaporation behavior is far more complex and poorly understood because of the chemical and structural heterogeneity of substrates in practical settings. Here, we demonstrate that droplets on topographically and chemically heterogeneous substrates─engineered via patterned gold nanoparticle (AuNP) superlattice arrays─undergo multiple coexisting evaporation modes (modes 1-3), including mode 1, characterized by directional contraction toward the center of the AuNP superlattice domain; mode 2, marked by contraction away from the domain; and mode 3, featuring directional contraction with a trailing effect on the periphery. These distinct modes were demonstrated by surface-enhanced Raman scattering (SERS), exhibiting uniform analyte distributions in mode 1, which were applied in a proof-of-concept portable mask for exhaled breath condensate (EBC) collection and molecular monitoring. This mechanistic insight into multimodal droplet evaporation breaks from the classical single-model framework, offering a controllable strategy for tailoring evaporation-driven transport and localization on heterogeneous surfaces.