The floating microfluidic probe: Distance control between probe and sample using hydrodynamic levitation

Abstract

Microfluidic probes (MFPs) are an emerging class of non-contact scanning devices used to perform local chemical reactions on surfaces covered with liquid. Typically, the probe is scanned at a distance between 10 μm and 50 μm over the surface. For proper functioning, the distance between the probe and the surface needs to be kept stable. Here, we present a self-regulating distance control for a microfluidic probe based on hydrodynamic levitation, and we call the device the "floating MFP." By injecting a liquid between the probe head and the surface (flow rates: 5-500 μl min-1), we were able to achieve levitation heights up to 15 μm without perturbation of the probe function. We provide an analytical solution describing the levitation, which fits well with the experimental data. This work helps in the design and implementation of distance control in MFPs for a broad range of applications. © 2014 AIP Publishing LLC.