Laser-induced fluorescence detection system for microfluidic chips based on an orthogonal optical arrangement

Area of Science:

• Analytical Chemistry
• Microfluidics
• Optical Detection Systems

Background:

• Microfluidic devices require sensitive detection methods for analyzing small sample volumes.
• Laser-induced fluorescence (LIF) is a powerful technique but often suffers from scattered laser light interference.
• Existing LIF systems for microfluidics can be complex and bulky.

Purpose of the Study:

• To develop a simple and highly sensitive LIF detection system for microfluidic chips.
• To minimize scattered laser light interference for improved signal-to-noise ratio.
• To demonstrate the system's performance using model fluorescent analytes.

Main Methods:

• An orthogonal optical arrangement was employed for LIF detection.
• Fluorescence emission was collected through the sidewall of the microfluidic chip.
• A crossed-channel configuration was designed to optimize light collection and reduce scatter.
• Ray-tracing simulations and systematic measurements were used to optimize the collection angle and minimize scattered light.

Main Results:

• A detection limit of 1.1 pM (S/N = 3) for fluorescein was achieved.
• Scattered laser light intensity was reduced by a factor of 38 at an optimal collection angle of 45 degrees.
• The system demonstrated high sensitivity comparable to optimized confocal LIF systems.
• Model samples including sodium fluorescein and labeled amino acids were successfully analyzed.

Conclusions:

• A simple, compact, and easily buildable LIF detection system for microfluidic chips was successfully developed.
• Collecting fluorescence through the chip sidewall effectively reduces scattered laser light, enhancing sensitivity.
• The developed system offers high detection power suitable for various microfluidic applications.