Contactless conductivity detector from printed circuit board for paper-based analytical systems

Nattapong Chantipmanee; Thitaporn Sonsa-Ard; Nutnaree Fukana; Kamolchanok Kotakanok; Thitirat Mantim; Prapin Wilairat; Peter C Hauser; Duangjai Nacapricha

doi:10.1016/j.talanta.2019.120227

Contactless conductivity detector from printed circuit board for paper-based analytical systems

Talanta. 2020 Jan 1:206:120227. doi: 10.1016/j.talanta.2019.120227. Epub 2019 Aug 5.

Authors

Nattapong Chantipmanee¹, Thitaporn Sonsa-Ard¹, Nutnaree Fukana¹, Kamolchanok Kotakanok², Thitirat Mantim³, Prapin Wilairat⁴, Peter C Hauser⁵, Duangjai Nacapricha⁶

Affiliations

¹ Flow Innovation-Research for Science and Technology Laboratories (Firstlabs), Thailand; Department of Chemistry and Center of Excellence for Innovation in Chemistry, Faculty of Science, Mahidol University, Rama 6 Road, Bangkok, 10400, Thailand.
² Flow Innovation-Research for Science and Technology Laboratories (Firstlabs), Thailand.
³ Department of Chemistry, Faculty of Science, Srinakharinwirot University, Sukhumvit 23, Bangkok, 10110, Thailand.
⁴ Flow Innovation-Research for Science and Technology Laboratories (Firstlabs), Thailand; National Doping Control Centre, Mahidol University, Rama 6 Road, Bangkok, 10400, Thailand.
⁵ Department of Chemistry, University of Basel, Klingelbergstrasse 80, CH-4056, Basel, Switzerland.
⁶ Flow Innovation-Research for Science and Technology Laboratories (Firstlabs), Thailand; Department of Chemistry and Center of Excellence for Innovation in Chemistry, Faculty of Science, Mahidol University, Rama 6 Road, Bangkok, 10400, Thailand. Electronic address: dnacapricha@gmail.com.

PMID: 31514895
DOI: 10.1016/j.talanta.2019.120227

Abstract

This work presents a capacitively coupled contactless conductivity detector (C⁴D) etched out from a printed circuit board (PCB) as potential sensor for paper-based analytical systems. Two lines of any desirable pattern forming 35-μm thick planar copper electrodes were produced on a PCB plate (40 mm × 60 mm) by photolithography. The final PCB plate was covered with polypropylene film to serve as the insulating layer for the C⁴D detector. The film also protected the copper electrodes from corrosion. Electrodes made in this planar geometry make the PCB-C⁴D suitable as sensor for flat devices such as paper-based analytical devices. For this work, plain paper strips were employed as sample reservoir and as fluidic channel without hydrophobic pattern. A dried paper strip was first placed over the sensor, followed by dispensing a fixed volume of the liquid sample onto the paper. Entrapment of the liquid sample in the paper strip leads to reproducible size and position of the detection zone of the sample liquid for the capacitive coupling effect. High precision was obtained with %RSD ≤1% (n = 18) for standard solutions of KCl. Soil suspensions could be analyzed without prior filtration by placing a drop onto the paper strip extending away from the detector zone. The paper strip filtered out soil particles at the surface of the paper. Therefore, only soil filtrate moved towards the detection zone by lateral flow. The C⁴D detection using paper strip showed high tolerance to soil suspension with turbidity up to 6657 NTU, offering direct analysis of soil salinity. Cleaning with moist tissue paper between samples is adequate even for dirty samples such as soil suspension. We also monitored conductivity of acid-base reaction in the microfluidic paper channels, which was later applied to the quantification of bicarbonate in water and in antacid tablet ("Soda Mint Tablet").

Keywords: Carbonate; Contactless conductivity detector; Paper-based; Printed circuit board; Sensor; Soil salinity.