Improved sensitivity in paper-based microfluidic analytical devices using a pH-responsive valve for nitrate analysis

Area of Science:

• Microfluidics
• Analytical Chemistry
• Materials Science

Background:

• Microfluidic paper-based analytical devices (μPADs) offer portable and cost-effective diagnostics.
• Precise control of fluid flow is crucial for sequential reactions and kinetic studies in μPADs.
• Existing flow control methods can be complex or incompatible with certain analytical conditions.

Purpose of the Study:

• To develop and evaluate chitosan-based pH-responsive valves for precise lateral flow control in μPADs.
• To demonstrate the application of these valves in a nitrate determination assay.
• To assess the compatibility and impact of the valves on analytical performance.

Main Methods:

• Fabrication of μPADs using wax printing.
• Creation of pH-responsive valves using a chitosan-acetic acid solution.
• Integration of valves into μPADs for controlled flow and reaction timing.
• Nitrate determination using the Griess reaction with controlled conversion time.

Main Results:

• Chitosan valves successfully controlled lateral flow in μPADs.
• Valves opened in acidic solutions (pH > 4) without affecting flow rate or colorimetric analysis.
• Demonstrated successful nitrate determination in water samples with a linear range of 10-100 μmol L⁻¹ and a detection limit of 5.4 μmol L⁻¹.
• Valves enabled increased conversion time for nitrate to nitrite, improving assay performance.

Conclusions:

• Chitosan pH-responsive valves are a valuable tool for precise flow control in μPADs.
• This technology enables controlled kinetics for multi-step analytical procedures.
• The developed μPADs with chitosan valves show potential for diverse analytical chemistry applications, including environmental monitoring.