Dye-Doped ZnO Microcapsules for High Throughput and Sensitive Optofluidic Micro-Thermometry

Area of Science:

• Optofluidics
• Nanotechnology
• Fluorescence Spectroscopy
• Thermometry

Background:

• Accurate temperature monitoring is crucial for understanding processes within microfluidic devices.
• Existing thermometry methods can be slow or suffer from dye diffusion and adsorption issues.
• Zinc oxide (ZnO) nanoparticles offer potential as robust fluorescent probes due to their thermal properties.

Purpose of the Study:

• To demonstrate a proof-of-concept for a high-throughput optofluidic thermometry method.
• To develop a temperature probe using ZnO microparticles doped with rhodamine dyes for millisecond-scale measurements.
• To investigate the temperature-dependent fluorescence of rhodamine B (RhB) and rhodamine 6G (Rh6G) within ZnO microparticles.

Main Methods:

• Utilized droplet microfluidics to synthesize highly monodisperse ZnO microparticles.
• Doped ZnO microparticles with RhB and/or Rh6G dyes to create fluorescent temperature probes.
• Employed fluorescence intensity measurements to quantify temperature changes at the millisecond timescale.

Main Results:

• RhB fluorescence intensity decreased linearly with temperature (-2.2%/°C), consistent with literature.
• Observed a novel, reproducible nonlinear fluorescence intensity change for Rh6G in ZnO microparticles, with a minimum at 40 °C.
• Demonstrated the feasibility of high-throughput, millisecond-scale temperature measurements in optofluidic microsystems.

Conclusions:

• The developed optofluidic method enables rapid, high-throughput temperature sensing within microsystems.
• ZnO microparticles provide an effective matrix for fluorescent dyes, preventing diffusion and enhancing heat dissipation.
• The unique nonlinear response of Rh6G in ZnO offers new possibilities for specialized thermometry applications.