pH fluorosensors for use in marine systems

Area of Science:

• Analytical Chemistry
• Marine Science
• Materials Science

Background:

• Accurate pH monitoring is crucial for understanding marine environments.
• Existing pH sensors may face challenges with ionic strength and calibration in marine settings.
• Development of specialized optical sensors is needed for marine applications.

Purpose of the Study:

• To develop novel optical pH sensors for marine environments.
• To synthesize and characterize lipophilic carboxyfluorescein derivatives (DHFA and DHFAE).
• To evaluate sensor performance, including pH range, ionic strength sensitivity, and optical properties.

Main Methods:

• Synthesis of DHFA and DHFAE indicators.
• Immobilization of indicators in a hydrogel matrix.
• Measurement of apparent dissociation constants (pKa).
• Assessment of cross-sensitivity to ionic strength.
• Determination of quantum yields (QY).
• Development of referenced measuring schemes (dual wavelength, dual lifetime).

Main Results:

• DHFA and DHFAE exhibit pKa values around 8.4, suitable for marine pH (7.2-9.2).
• Low cross-sensitivity to ionic strength was observed, especially with DHFAE.
• DHFA shows high quantum yield (0.94 basic), comparable to fluorescein.
• DHFAE allows for internally referenced dual wavelength measurements due to distinct emission maxima.
• Dual lifetime referenced measurements were achieved using Ru(dpp)(3) reference particles.

Conclusions:

• The developed optical pH sensors are well-suited for marine environments.
• DHFA and DHFAE offer advantages in terms of pH range, ionic strength tolerance, and referencing capabilities.
• These sensors enable advanced applications like pH imaging and phase-modulation measurements.