A portable NIR fluorimeter directly quantifies singlet oxygen generated by nanostructures for Photodynamic Therapy

Area of Science:

• Biomedical Optics
• Photodynamic Therapy
• Chemical Sensing

Background:

• Photodynamic therapy (PDT) utilizes reactive oxygen species (ROS), particularly singlet oxygen (¹O₂), for treating deep-seated tumors.
• Current methods for quantifying ¹O₂ generation by nanostructures activated by penetrating radiation are limited.
• Existing sensors, like the Singlet Oxygen Sensor Green kit, can suffer from self-activation under X-ray irradiation.

Purpose of the Study:

• To develop and calibrate a portable near-infrared (NIR) fluorimeter for direct, quantitative detection of ¹O₂.
• To address the need for a reliable method to assess ROS generation by nanostructures for deep-tissue PDT.
• To overcome the limitations of existing ¹O₂ detection techniques, including self-activation issues.

Main Methods:

• Construction and calibration of a portable NIR fluorimeter utilizing a thermoelectrically-cooled InGaAs single photon avalanche photodiode (SPAD).
• Integration of the SPAD with a custom-made integrating sphere for measurements under high-energy X-ray irradiation.
• Spectroscopic detection of ¹O₂ fluorescence emission peaked at 1270nm.

Main Results:

• The developed fluorimeter achieves a detection threshold of approximately 9·10⁸ ¹O₂ molecules under realistic experimental conditions with 1-minute integration.
• The instrument was calibrated using standard photosensitizers.
• The potential of the instrument was demonstrated through the characterization of novel photosensitizing nanostructures.

Conclusions:

• The portable NIR fluorimeter provides a direct and quantitative method for ¹O₂ detection.
• This instrument offers a reliable solution for characterizing nanostructures used in deep-tissue PDT.
• The developed apparatus overcomes limitations of existing ROS detection methods, enabling accurate assessment of nanostructure performance.