Microfluidic devices can perform multiple laboratory functions on a single, compact, and fully integrated chip. However, fabrication of microfluidic devices is difficult, and current methods, such as glass-etching or soft-lithography in PDMS, are either expensive or yield devices with poor chemical robustness. We introduce a simple method that combines the simple fabrication of PDMS with superior robustness and control of glass. We coat PDMS channels with a functionalized glass layer. The glass coating greatly increases the chemical robustness of the PDMS devices. As a demonstration, we produce emulsions in coated channels using organic solvents. The glass coating also enables surface properties to be spatially controlled. As a demonstration of this control, we spatially pattern the wettability of coated PDMS channels and use the devices to produce double emulsions with fluorocarbon oil.

Microfluidic devices consist of networks of micron scale channels that are engineered to perform specific functions. Miniaturization of the channels allows several functions to be integrated onto a single “lab-on-a-chip” microfluidic device (Whitesides 2006). This allows the devices to perform very sophisticated tasks, such as sorting analytes (Ahn et al. 2006; Fidalgo et al. 2008), cells (MacDonald et al. 2003), and worms (Chung et al. 2008), performing combinatorial chemistry (Pregibon et al. 2007), crystallizing proteins (Gerdts et al. 2006), detecting minute concentrations of DNA with ultra sensitive PCR (Cady et al. 2005; Beer et al. 2007), using bubbles for fluidic computing (Prakash and Gershenfeld 2007), as well as a host of other applications (Whitesides 2006). One class of microfluidics that is particularly useful for analysis of chemical and biological systems is droplet microfluidics. With microfluidics, picoliter drops can be formed, merged, and sorted at kilohertz rates (Pipper et al. 2007; Shah et al. 2008; Teh et al. 2008). The drops can serve as individual compartments for chemical reactions (Teh et al. 2008). This combination of speed and containment is very useful for highthroughput screening (Warrick et al. 2007; Guo et al. 2008), useful for the as the discovery of new drugs, the selection of high efficiency chemical catalysts, and the directed evolution of enzymes and cells (Teh et al. 2008). However, microfluidic devices can be quite complex, and their fabrication can be quite difficult. For example, fabrication of glass etched devices requires sophisticated lithographic techniques that are difficult and expensive. Fabrication of milled plastic or metal devices is simple and relatively inexpensive, but the resolution is poor and miniaturization of the fluidic components is difficult (Duffy et al. 1998; Whitesides 2006).