Absolute 3D reconstruction of thin films topography in microfluidic channels by interference reflection microscopy

Area of Science:

• Microfluidics
• Interfacial Science
• Optical Metrology

Background:

• Understanding object dynamics in microchannels requires knowledge of hydrodynamic and interfacial interactions.
• Accurate measurement of the interspace between confined objects and microchannel walls is essential for microfluidics.

Purpose of the Study:

• To develop an interferometric method for absolute topographic reconstruction of the interspace between objects and channel walls in microfluidic channels.
• To enable quantitative analysis of interfacial interactions for improved microfluidic device design and performance.

Main Methods:

• Utilized wide-field microscopic imaging in reflection interference contrast mode (RICM) at the microfluidic chip's bottom wall.
• Incorporated reflections from both lower and upper microchannel surfaces into quantitative optical signal analysis.
• Employed multiple wavelengths and illumination apertures for topographic reconstruction.

Main Results:

• Developed a method for absolute topographic reconstruction of the interspace between objects and channel walls.
• Achieved precise measurement of thin films on channel walls (0-500 nm range) with accuracy as high as 2 nm.
• Demonstrated the protocol for oil-in-water droplets in microchannels (10-400 μm height) at speeds up to 5 mm/s.

Conclusions:

• The developed interferometric method provides accurate topographic reconstruction of microchannel interspaces.
• This technique enhances the understanding of object dynamics and interfacial interactions in microfluidics.
• The method is versatile and applicable to various microfluidic applications involving confined objects.