A non-invasive analysis method for on-chip spectrophotometric detection using liquid-core waveguiding within a 3D...

Area of Science:

• Analytical Chemistry
• Microfluidics
• Optical Engineering

Background:

• On-chip measurement of absorbing species is limited by short sample pathlengths in miniaturized systems.
• Microfluidic devices offer small sample volumes but often struggle with sensitive detection.
• Enhancing optical pathlength is crucial for improving sensitivity in miniaturized analytical systems.

Purpose of the Study:

• To develop a microfluidic device that increases the optical pathlength for on-chip spectrophotometric measurements.
• To utilize total internal reflection for creating a liquid-core waveguide within a microfluidic channel.
• To demonstrate the feasibility of enhanced absorption measurements in a miniaturized system.

Main Methods:

• Fabrication of a microfluidic chip using Teflon fluoropolymers (PTFE, FEP, AF) as cladding for a liquid-core waveguide.
• Implementation of a 3D chip architecture for efficient light coupling and utilization.
• Demonstration of waveguiding principles and spectrophotometric analysis using crystal violet as a test analyte.

Main Results:

• Successfully created a liquid-core waveguide with a 5 mm pathlength within a < 1 µL detection volume.
• Achieved efficient coupling between the light source, microfluidic chip, and detection system.
• Obtained a linear calibration for crystal violet with high reproducibility (< 2.4% RSD) and low limits of detection (< 1.3 µM).

Conclusions:

• The developed liquid-core waveguide in a microfluidic chip effectively enhances the sampling pathlength for on-chip spectrophotometry.
• This approach provides sensitive and reproducible absorbance measurements comparable to conventional UV-Vis spectrophotometry.
• The technology offers a promising solution for miniaturized, high-sensitivity absorption-based chemical analysis.