Flow velocity detector in a microchip based on a photothermally induced grating

Area of Science:

• Microfluidics
• Photothermal techniques
• Analytical chemistry

Background:

• Microfluidic devices are essential for various chemical and biological analyses.
• Accurate measurement of flow velocity and solute concentration is critical for microchip-based assays.
• Existing methods often require separate setups for different measurements, increasing complexity.

Purpose of the Study:

• To develop a single, integrated photothermal technique for simultaneous flow velocity and solute concentration measurements in microchips.
• To demonstrate the efficacy of the technique across a broad range of flow velocities and low concentrations.
• To provide a versatile tool for microfluidic analysis.

Main Methods:

• Utilized collinear pump and probe light irradiation on a microchip with a fabricated grating pattern.
• Induced a temperature change using pump light, creating a thermal grating.
• Monitored refractive index changes via a heterodyned diffraction signal of the probe light to measure flow and concentration.

Main Results:

• Achieved a dynamic range for flow velocity measurement from 0.17 to 670 mm/s.
• Determined solute concentration with a detection limit of 2 x 10(-6) M for rhodamine B.
• Demonstrated simultaneous measurement capability using a single optical and instrumental setup.

Conclusions:

• The developed photothermal technique offers a robust and efficient method for simultaneous microfluidic analysis.
• The technique's wide dynamic range and high sensitivity are suitable for diverse chemical applications.
• This integrated approach simplifies microchip-based measurements, enhancing analytical capabilities.