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Distance vs. capillary flow dynamics-based detection methods on microfluidic paper-based analytic device (µPAD).

In recent years, there has been a high interest in paper-based microfluidic sensors or microfluidic paper-based analytic devices (µPADs) towards low-cost, portable and easy-to-use sensing for chemical and biological targets. µPAD allows spontaneous liquid flow without any external or internal pumping as well as innate filtration capability. While both optical (colorimetric and fluorescent) and electrochemical detection have been demonstrated on µPADs, several limitations still remain such as the need for additional equipment, vulnerability to ambient lighting perturbation, and inferior sensitivity. In this minireview, alternative detection methods on µPADs are covered to resolve these issues, including the relatively well studied distance-based measurements as well as the newer capillary flow dynamics-based method. Detection principles, assay performance, strengths, and weaknesses are explained for these methods, along with their potential future applications towards point-of-care medical diagnostics and other field-based applications.