Ultra-pH-sensitive nanoprobe library with broad pH tunability and fluorescence emissions

Area of Science:

• Biomedical Engineering
• Nanotechnology
• Analytical Chemistry

Background:

• pH is a critical physiological parameter for cellular and tissue homeostasis.
• Conventional small molecule pH sensors have limitations in pH response range and fluorescence emission.
• Previous work introduced ultra-pH-sensitive (UPS) nanoprobes with sharp pH response.

Purpose of the Study:

• To expand the UPS design to a library of nanoprobes with predetermined pH transitions and wide fluorescent emissions.
• To overcome limitations of fluorophores by introducing copolymers conjugated with fluorescence quenchers (FQs).
• To create a versatile toolkit for studying pH regulation in various pathophysiological conditions.

Main Methods:

• Employed a copolymer strategy to fine-tune hydrophobicity for desired transition pH.
• Matched monomer hydrophobicity to achieve sharp pH transitions.
• Conjugated copolymers with fluorescence quenchers (FQs) to suppress emission and increase activation ratios.

Main Results:

• Developed a library of 10 nanoprobes covering the physiological pH range (4-7.4) in 0.3 pH increments.
• Achieved sharp pH transitions (on/off < 0.25 pH) and high fluorescence activation ratios (>50-fold).
• Demonstrated effective suppression of fluorophore emission by FQs, regardless of Stokes shift.

Conclusions:

• The UPS nanoprobe library offers precise, tunable pH sensing capabilities.
• These nanoprobes are valuable tools for studying pH in diseases like cancer and for developing tumor-activatable imaging systems.
• The design overcomes limitations of existing pH sensors, enabling advanced biomedical applications.