Geometrical pH mapping of Microfluids by principal-component-analysis-based xyz-spectrum conversion method.

Area of Science:

• Analytical Chemistry
• Microfluidics
• Spectroscopy

Background:

• Accurate pH measurement in microfluidic systems is crucial for various applications.
• Conventional spectrophotometry can be limited in microscale environments.
• Developing rapid, non-invasive pH sensing methods for microfluidics is essential.

Purpose of the Study:

• To develop and validate a principal component analysis (PCA)-based method for reproducing absorption spectra of pH indicators in microfluidic devices.
• To enable geometric mapping of fluid pH values using image analysis and spectral conversion.
• To investigate pH gradients at aqueous biphasic interfaces within microfluidic channels.

Main Methods:

• Fabrication of polydimethylsiloxane (PDMS) microfluidic devices with a 1 mm channel depth.
• Hydrodynamic introduction of aqueous pH indicator solutions under varying pH conditions.
• Image analysis of the region of interest (ROI) to obtain RGB values, followed by PCA-based xyz-spectrum conversion for spectral data reproduction.

Main Results:

• High reproducibility of absorption spectra was achieved, comparable to conventional spectrophotometer methods.
• The method successfully elucidated pH gradients at aqueous biphasic interfaces, ranging from 70 to 140 μm.
• Demonstrated millisecond-order spectrophotometric information acquisition without monochromating equipment.

Conclusions:

• The PCA-based spectral reproduction method is highly effective for pH mapping in microfluidic devices.
• This technique offers a viable solution for acquiring spectrophotometric data in micro/nanospaces with high temporal resolution.
• The study highlights the applicability of this method for analyzing complex fluid interfaces and gradients.