Magnetic and fluorescent core-shell nanoparticles for ratiometric pH sensing

Area of Science:

• Materials Science
• Nanotechnology
• Analytical Chemistry

Background:

• Accurate pH monitoring is crucial in various scientific and medical applications.
• Developing robust and reliable pH sensors remains an active area of research.
• Nanoparticle-based sensors offer advantages in sensitivity and targeted delivery.

Purpose of the Study:

• To synthesize and characterize novel magnetic nanoparticles for ratiometric pH sensing.
• To embed two distinct fluorophores within successive silica shells for pH indication and reference.
• To evaluate the performance of these nanoparticles for pH measurements in the range of 5-8.

Main Methods:

• Preparation of iron oxide magnetic nanoparticles via coprecipitation.
• Formation of silica shells using a water-in-oil microemulsion method.
• Embedding a pH-sensitive dye (fluorescein) and a reference dye (sulforhodamine) in outer and inner silica shells, respectively.
• Characterization using techniques including DLS, TEM, VSM, XRD, and FTIR.
• Ratiometric fluorescence measurements to determine pH.

Main Results:

• Uniform nanoparticles (50-60 nm) with a magnetic core and dual silica shells were successfully prepared.
• The nanoparticles demonstrated reliable ratiometric pH measurements in the pH range of 5-8.
• A sigmoidal fit using a Boltzmann equation yielded an apparent pK(a) of 6.8.
• The reference dye exhibited minimal fluorescence change across the tested pH range.
• Statistical validation confirmed no significant difference compared to a reference method.

Conclusions:

• The developed magnetic core-silica shell nanoparticles are effective for ratiometric pH sensing.
• This system provides a stable and sensitive platform for pH monitoring in diverse media.
• The method shows high potential for applications requiring accurate pH determination.