Singlet oxygen luminescence detection

The detection of a single photon at 1270 nm wavelength allows the direct monitoring of Singlet Oxygen (1O2), making Singlet Oxygen Luminescence Detection (SOLD) a powerful dosimetry technique for photodynamic therapy in the treatment of cancer. However, the direct detection of 1O2 emission at 1270 nm wavelength is extremely challenging as the 1O2 → 3O2 transition in biological media has very low probability and short lifetime due to the high reactivity of singlet oxygen with biomolecules. Recent advances in single photon detection providing high detection efficiency, low noise single-photon detectors are an important innovation in the development of a practical SOLD system for eventual clinical use. In this thesis I present a compact fibre coupled SOLD system, using a supercontinuum pump source to precisely target exact photosensitizer absorption peak wavelengths and single-photon detectors for near-infrared detection by benchmarking a superconducting and a semiconductor photon counting detector. Both pump laser and detector are intrinsically fibre-coupled making them ideally suited for the development of practical singlet oxygen sensor head. The SOLD system was used to carry out a series of singlet oxygen time-resolved measurements in solution and in live cells. These measurements offer information on the photosensitized generation and deactivation of singlet oxygen generated by different photosensitizers and microenvironments at the 1270 nm wavelength and a first investigation of the 1590 nm singlet oxygen luminescence signal is presented

Enhanced optics for time-resolved singlet oxygen luminescence detection

Singlet oxygen luminescence dosimetry (SOLD) is a highly promising direct monitoring method for photodynamic therapy (PDT) in the treatment of cancer. Early SOLD systems have been hampered by inefficient excitation, poor optical collection and immature infrared single photon detection technology. We report carefully engineered improvements addressing all of these deficiencies. We use a supercontinuum source with a tunable filter to precisely target the peak absorption wavelength of the chosen photosensitizer; we have designed a compact and versatile optical package for precise alignment; we have successfully employed state-of-the-art superconducting photon counting technologies. Through these improvements, we can achieve real-time histogram acquisition from a photosensitizer in solution test sample. This setup opens the pathway to physiological SOLD studies for PDT dosimetry

A miniaturized 4 K platform for superconducting infrared photon counting detectors

We report on a miniaturized platform for superconducting infrared photon counting detectors. We have implemented a fibre-coupled superconducting nanowire single photon detector in a Stirling/Joule–Thomson platform with a base temperature of 4.2 K. We have verified a cooling power of 4 mW at 4.7 K. We report 20% system detection efficiency at 1310 nm wavelength at a dark count rate of 1 kHz. We have carried out compelling application demonstrations in single photon depth metrology and singlet oxygen luminescence detection

Laser-Induced Erasable and Re-Writable Waveguides within Silver Phosphate Glasses

Femtosecond direct laser writing is a well-established and robust technique for the fabrication of photonic structures. Herein, we report on the fabrication of buried waveguides in AgPO3 silver metaphosphate glasses, as well as, on the erase and re-writing of those structures, by means of a single femtosecond laser source. Based on the fabrication procedure, the developed waveguides can be erased and readily re-inscribed upon further femtosecond irradiation under controlled conditions. Namely, for the initial waveguide writing the employed laser irradiation power was 2 J/cm2 with a scanning speed of 5 mm/s and a repetition rate of 200 kHz. Upon enhancing the power to 16 J/cm2 while keeping constant the scanning speed and reducing the repetition rate to 25 kHz, the so formed patterns were readily erased. Then, upon using a laser power of 2 J/cm2 with a scanning speed of 1 mm/s and a repetition rate of 200 kHz the waveguide patterns were re-written inside the glass. Scanning electron microscopy (SEM) images at the cross-section of the processed glasses, combined with spatial Raman analysis revealed that the developed write/erase/re-write cycle, does not cause any structural modification to the phosphate network, rendering the fabrication process feasible for reversible optoelectronic applications. Namely, it is proposed that this non-ablative phenomenon lies on the local relaxation of the glass network caused by the heat deposited upon pulsed laser irradiation. The resulted waveguide patterns Our findings pave the way towards new photonic applications involving infinite cycles of write/erase/re-write processes without the need of intermediate steps of typical thermal annealing treatments