Point-of-care diagnostic (POC) test devices provide rapid results on an ever expanding range of medical tests. One rationale for POC testing is that it may streamline healthcare and improve clinical outcomes. Another advantage is that rapid testing will lead in turn to rapid intervention. For example, the finding of a high blood glucose by a diabetic patient can be acted upon immediately by administration of the appropriate therapy.
A consensus is emerging that much of the future growth in POC diagnostics - which will likely require assays of increasing technical complexity - will involve microfluidics, a versatile technology that makes possible the miniaturization of complex fluid handling and integrated detection. As such, research on microfluidics for POC applications has increased markedly in recent years, fueled by an interest in constructing field-deployable analytical instruments. Compared to conventional microfluidics, however, there is one distinguishing requirement of POC diagnostics: extreme simplicity of use, which usually translates to minimal or no ancillary equipment. This feature has proven to be the downfall of many otherwise promising integrated lab-on-a-chip systems, in terms of their ability to be used at the POC.
The interest in POC microfluidic-based devices has been intense and has cut across all major disciplines in lab-on-a-chip research, including engineering (biomedical, chemical, electrical, and mechanical), chemistry, and physics. This research is just starting to bear fruit in terms of translation into new clinical capabilities.

This themed issue features articles covering a range of topics in microfluidics and POC testing:

• Basic science and tools for controlling surface chemistry (Ho), controlling liquid flow (Pamula), integrating optics with microfluidics (a critical review by L. Lee), and optimizing assay parameters (Sia)
• Applications in nucleic acid-based molecular diagnostics, including integrated systems involving nucleic acid amplification such as RT-PCR (S.H. Lee) and NABSA (L. Lee), visualization for electrophoresis (Ugaz), and fluorescence in situ hybridization (Backhouse) 
• Applications in immunoassays (Singh), clinical chemistry (Do) and cell analysis (Toner, Irimia, McDevitt, and a perspective by Kitamori)
• Applications in global health (an area with high clinical impact but laden with special design constraints), including techniques for stable storage of samples (Yager) and centrifugation of samples in the field (Whitesides), paper-based microfluidics (Whitesides, and a focus article by Zhao & van den Berg), and microfluidics using minimal instruments (critical review by Weigl)