How to exploit the features of microfluidics technology.

In recent years, microfluidics technology has enabled the genesis of novel and commercially successful products ranging from portable insulin delivery devices to high speed inkjet printers. However, during this period of rapid technological evolution, it is important to recognize that microfluidics is an enabling technological tool that can potentially provide increased functionality compared to systems that utilize conventional, ‘‘macroscale’’ methods. While it may seem somewhat obvious, it is also important to realize that, like all tools, microfluidics can be particularly powerful for certain applications and not advantageous for others. For example, microfluidics may be especially well suited for applications that require handing of small amounts of samples (e.g. single cell analysis), conversely, it may be inappropriate for applications that require high volumetric throughputs (e.g. sewage treatment plants). Thus, when designing microfluidic devices, it is important not to simply scale down macroscopic processes to the microscale. Instead, it is prudent to understand and exploit the relevant physics and chemistries at the smaller length scales. Toward this end, the aim of this Focus article is to highlight a few characteristics of microfluidics technology which we think are particularly useful and provide examples of applications that exploit them. For the purposes of this article, we define microfluidics as the methodology and/or mechanism for controlled transport of measurable quantities, such as mass, energy and momentum, in a microscale environment. The word ‘‘control’’ is judiciously chosen, because we believe that it embodies the crux of microfluidics technology. In the following sections, we will focus our discussions on the effects of high surface area to volume ratio, and the utility of accurately controlling force fields within microfluidic devices. Effects of high surface area to volume ratios