Equipment-free devices with quantitative readout are of great significance to point-of-care testing (POCT), which provides real-time readout to users and is especially important in low-resource settings. Among various equipment-free approaches, distance-based visual quantitative detection methods rely on reading the visual signal length for corresponding target concentrations, thus eliminating the need for sophisticated instruments. The distance-based methods are low-cost, user-friendly and can be integrated into portable analytical devices. Moreover, such methods enable quantitative detection of various targets by naked eyes. In this review, we first introduce the concept and history of distance-based visual quantitative detection methods. Then we summarize the main methods for translation of molecular signals to distance-based readout, and different microfluidic platforms (glass, PDMS, paper and thread) are discussed in terms of applications in biomedical diagnostics, food safety monitoring, and environmental analysis. Finally, the potential and future perspectives are discussed.  

Tian, T; Li, J; Song,Y; Zhou, L; Zhu, Z ; Yang, C. Distance-based Microfluidic Quantitative Detection Methods for Point-of-Care Testing. Lab Chip, 2016, DOI: 10.1039/C5LC01562F.