Polypyrrole⁻Methyl Orange Raman pH Sensor

Area of Science:

• Electrochemistry
• Analytical Chemistry
• Materials Science

Background:

• Development of efficient and sensitive pH sensors is crucial for various scientific applications.
• Existing methods may require larger sample volumes or lack rapid response times.
• Polypyrrole and methyl orange are known for their electrochemical and optical properties.

Purpose of the Study:

• To develop an easy-to-prepare electrochemical pH sensor.
• To determine the pH of small sample volumes (below 1 µL) in a wide pH range (3-13).
• To utilize Raman spectroscopy for pH sensing with the developed sensor.

Main Methods:

• Electrochemical preparation of polypyrrole doped with methyl orange ions.
• Raman spectroscopy with Ar+ laser excitation (514.5 nm).
• Confocal microscopy for spectral acquisition.
• Partial least-squares (PLS) modeling for data analysis.

Main Results:

• The sensor enabled pH determination in the 3-13 range for volumes < 1 µL.
• Methyl orange Raman spectra showed noticeable changes with H+ concentration.
• PLS models achieved relative standard errors of prediction between 3.7%-3.9%.
• Sensor-based measurements yielded slightly better prediction parameters than those without the sensor.

Conclusions:

• The developed polypyrrole-based sensor offers a sensitive and efficient method for pH determination.
• The sensor is suitable for analyzing small sample volumes.
• Raman spectroscopy combined with PLS modeling provides a robust approach for pH sensing.