Semiquantitative analysis on microfluidic thread-based analytical devices by ruler

This paper describes a simple and semiquantitative method for analytical detection by measuring the length of colour change on indicator treated threads using a ruler. Thread-based analytical devices (μTADs), fabricated from two types of threads (cotton and polyester), provide an easy-to-use platform for the rapid measurement of analyte concentrations in aqueous solutions. Multiple threads were fixed to a supporting polymer film to allow capillary wicking of liquid samples, free from contact with outside surfaces. In this method, interaction between deposited reagents and analytes within samples produces coloured zones of differing lengths on the threads. The length of the coloured zones correlates with the concentrations of the analytes in the samples. The diagnostic application of the length measurement method, using μTADs, was demonstrated through the successful testing of two different bioassays, for protein and nitrite, in simulated human urine samples. Additionally, it was shown that this method can be used for the rapid analysis of environmental samples such as Ni2+ in water. Furthermore, the length measurement method can be applied to perform simultaneous assays to quantify the concentrations of different biomarkers present within the same sample. Finally, it was also compared with currently used colorimetric methods on thread, which were reported by us and others previously, and was shown to have higher accuracy and simplicity.