How to Minimize Light-Organic Matter Interactions for All-Optical Sub-Cutaneous Temperature Sensing

Area of Science:

• Biomedical Optics
• Materials Science
• Chemical Sensing

Background:

• Light penetration into biological tissues is limited by scattering and absorption, particularly by hemoglobin and adipose tissue.
• Minimally invasive optical sensing in tissues is challenging due to significant optical losses.
• A narrow optical window (630-900 nm) exists for light transmission in tissues, offering potential for optical sensing.

Purpose of the Study:

• To develop the first all-optical temperature sensing system operating within the narrow biological optical window.
• To utilize triplet-triplet annihilation photon energy upconversion (TTA-UC) for sensitive and minimally invasive temperature measurements.
• To demonstrate a stable and oxygen-resistant TTA-UC sensing system for biological applications.

Main Methods:

• Employed an asymmetrical benzo-fused BODIPY dye as the emitter and palladium benzo-naphtho-porphyrins as the sensitizer for TTA-UC.
• Excited the TTA-UC system at 658 nm with low light intensity (1 mW/cm²).
• Embedded the sensing dyes within a biocompatible, FDA-approved natural wax/matrix for stability and safety.

Main Results:

• Achieved stable TTA-UC temperature sensing for over 100 seconds in an oxygen-rich environment.
• Demonstrated high temperature sensitivity exceeding 200 mK around physiological temperature (36 °C).
• The system is protected against oxygen-stimulated damage, ensuring consistent performance.

Conclusions:

• All-optical temperature sensing is feasible within the narrow biological optical window using TTA-UC.
• The developed TTA-UC system offers a promising tool for minimally invasive, highly sensitive temperature monitoring in biological tissues.
• The use of biocompatible materials and oxygen-resistant properties enhances the applicability of this sensing technology in physiological conditions.