Microanalysis using surface modification and biphasic droplets

Abstract

Conventional methods for the synthesis and analysis of chemical and biological materials often utilize homogeneous bulk environments or surface immobilization on a substrate. Homogeneous bulk environments, however, require large quantities of samples and reagents as well as significant effort to functionalize materials. Liquid–substrate interfaces can also pose problems because adsorption can hinder diffusion and reagent transport during bioanalyses, and sensitive materials, such as proteins, experience denaturation, or other types of deformation. Here, we describe the construction and use of droplet microenvironments created through a combination of surface modification, water-in-oil systems, and aqueous two-phase systems (ATPSs). This integration of an immobilization-free droplet microenvironment with liquid–liquid interfaces, material compartmentalization, directional reagent transport, and small volumes enables unique material functions. Specific examples include ATPS-assisted fabrication of functional microparticles for drug delivery, microscale determination of ATPS phase diagrams, dendritic self-assembly of semiconductive nanoparticles, multiplex immunoassays, and analysis of breast cancer cell migration. Intracellular structures and function are tightly interwoven. Recapitulation of such intracellular microenvironments may enable novel biomimetic material synthesis and bioanalysis. Cell-inspired microanalysis platforms can be constructed by combined top-down microfabrication and bottom-up molecular self-assembly. Microcompartments of phase-separated aqueous solutions also play a critical role in biological processes. The biphasic microdroplets provide a unique analytical platform that conventional homogeneous bulk environments fail to achieve.