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

Area of Science:

• Analytical Chemistry
• Sensor Technology
• Materials Science

Background:

• Paper-based analytical devices (PADs) offer low-cost, portable solutions for chemical analysis.
• Contactless conductivity detection methods are desirable for preventing sensor contamination and enabling analysis of challenging samples.
• Existing methods often require sample pretreatment or specialized fluidic channels.

Purpose of the Study:

• To develop and evaluate a printed circuit board (PCB)-based capacitively coupled contactless conductivity detector (C4D) for paper-based analytical systems.
• To demonstrate the C4D's capability for direct, precise, and robust analysis of various liquid samples, including turbid soil suspensions.
• To assess the C4D's applicability in quantifying analytes like bicarbonate.

Main Methods:

• Fabrication of a C4D sensor using photolithography on a PCB to create planar copper electrodes.
• Application of a polypropylene film as an insulating and protective layer for the electrodes.
• Utilizing plain paper strips as sample reservoirs and fluidic channels for lateral flow analysis.
• Testing the sensor with standard KCl solutions, soil suspensions, and for monitoring acid-base reactions.

Main Results:

• The PCB-C4D achieved high precision (%RSD ≤1%) for KCl solutions.
• The sensor demonstrated high tolerance to soil suspensions (up to 6657 NTU), enabling direct soil salinity analysis.
• Effective monitoring of acid-base reactions and quantification of bicarbonate in water and antacid tablets were achieved.

Conclusions:

• The developed PCB-C4D is a promising, cost-effective sensor for paper-based analytical devices.
• Its contactless nature and robustness allow for direct analysis of complex samples without filtration.
• The C4D technology facilitates simple, reproducible, and precise chemical measurements in various applications.