This work presents an affordable distance-based microfluidic paper-based device (μPAD), using polydiacetylene (PDA) liposome as a chromogenic substance with a smartphone-based photo editor, for rapid and in-field analysis of quaternary ammonium compounds (QACs) (e.g., didecyldimethylammonium chloride (DDAC), benzyldimethyltetradecyl ammonium chloride (BAC), and cetylpyridinium chloride (CPC)). In-field analysis of these compounds is important to ensure their antimicrobial activity and user safety since they are widely utilized as disinfectants in households and hospitals. The μPAD featured a thermometer-like shape consisting of a sample reservoir and a microchannel as the detection zone, which was pre-deposited with PDA liposome. The color change from blue to red appeared in the presence of QACs and the color bar lengths were proportional to the QAC concentrations. Reactions of QACs with the PDA required a specific pH range (from pH 4.0 to 10.0) and a readout time of 7 min. Analytical performance characteristics of the device were tested with DDAC, BAC, and CPC showing acceptable specificity, accuracy (96.1-109.4%), and precision (%RSDs ≤ 9.3%). Limits of detection and quantitation were in the ranges of 20 to 80 and 70 to 250 μM, respectively. Feasibility of the newly developed device was demonstrated for in-field analysis of QACs in fumigation solution providing comparable results with those obtained from a colorimetric assay (P > 0.05). The proposed device shows potentials for further applications of other analytes since it offers speed, simplicity, and affordability for in-field analysis, especially in remote areas where expertise, resources, and infrastructures are limited. Graphical abstract.

Australian Centre for Research on Separation Science and School of Natural Sciences University of Tasmania Private Bag 75 Hobart 7001 Australia

Central European Institute of Technology Brno University of Technology Purkynova 123 CZ 612 00 Brno Czech Republic

Department of Chemistry and Biochemistry Mendel University in Brno Zemedelska 1 CZ 613 00 Brno Czech Republic

Department of Pharmaceutical Chemistry Faculty of Pharmacy Mahidol University 447 Sri Ayudhaya Rd Rajathevee Bangkok 10400 Thailand

Department of Pharmaceutical Chemistry Faculty of Pharmacy Srinakharinwirot University 63 Moo 7 Rangsit Nakornnayok Road Ongkharak Ongkharak Nakornnayok 26120 Thailand

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Distance-based paper microfluidic devices for rapid visual quantification of heavy metals in herbal supplements and cosmetics