Automated Microfluidic Droplet-Based Sample Chopper for Detection of Small Fluorescence Differences Using Lock-In...

Area of Science:

• Biotechnology
• Analytical Chemistry
• Microfluidics

Background:

• Fluorescence detection is crucial for microfluidic devices but often requires complex optics and expertise for ultrasensitive measurements.
• Existing methods face challenges with signal drift (1/f noise) and require specialized equipment for high sensitivity.

Purpose of the Study:

• To extend the microfluidic analog to an optical beam chopper (μChopper) for fluorescence detection using standard wide-field microscopy.
• To improve precision and enable phase-locked measurements in droplet microfluidics.
• To achieve ultrasensitive detection limits for various analytes and biological processes.

Main Methods:

• Automated pneumatic valves were integrated into the μChopper for precise droplet control.
• Fluorescence measurements were phase-locked to droplet generation at a 0.04 Hz bandwidth.
• The system was applied to quantify free fatty acid uptake in adipocytes and perform homogeneous immunoassays.

Main Results:

• Achieved a detection limit of 12 pM fluorescein and detected as little as 310 zeptomoles in single droplets.
• Quantified single-cell free fatty acid uptake rates at 3.5 ± 0.2 × 10^-15 mol cell^-1.
• Demonstrated insulin detection limits of 9.3 nM (190 amol) in homogeneous immunoassays.

Conclusions:

• The automated μChopper, combined with lock-in detection, offers a high-performance, accessible platform for sensitive fluorescence measurements in limited sample volumes.
• This technique simplifies implementation in various droplet microfluidic systems.
• Enables precise quantification of cellular processes and analytes previously challenging to measure.