Speaker
Description
Hypoxia is a characteristic pathophysiological property of advanced solid tumours which influences aggressiveness and resistance to treatment. Real-time measurement of tumour oxygenation is thus vital for stratifying treatment plans by hypoxic severity and monitoring variations in partial pressure of oxygen (pO$_2$) caused by high energy X-ray and other photonic therapies. Azobenzene photoswitches present a novel form of oxygen sensing predicated on their photophysical properties. Upon irradiation with light, azobenzenes undergo reversible geometric isomerization between stable trans and metastable cis isomers. The rate of cis-trans thermal relaxation is a first-order process sensitive to the molecular environment, which translates into sensor functionalities. In this work, we investigate a novel bio-inspired azobenzene photoswitch for oxygen sensitivity in solution.
A biomimetic material, FePc(PAP)$_2$ was synthesized by coordination of 4-phenylazopyridine (PAP) to iron (II) phthalocyanine (FePc). As a model system for oxygen sensing, FePc is capable of binding oxygen similarly to heme-porphyrin in blood. Solutions were purged with argon gas or flowed with oxygen gas to modulate pO$_2$. Isomerization kinetics were measured by pump-probe isomerization spectroscopy, wherein photoisomerization was initiated by irradiation with a 600 mW 365 nm LED, and then recovery of the $\pi$-$\pi^*$ absorption band was monitored as a function of time with a spectrophotometer. In addition, density functional theory (DFT) was used to theoretically calculate the activation barrier between cis and trans isomers, which can be related to isomerization rates in the presence or absence of oxygen.
To validate our experimental setup, cis-trans isomerization rates of methyl orange and methyl red photoswitches were measured to be insensitive to oxygen, as expected from literature. As a control, the isomerization lifetime of PAP was found to be several hours in ambient oxygenation. DFT calculations predict that the isomerization rate of a PAP-porphyrin system is an order of magnitude faster than PAP. As a proof-of-principle demonstration of a new molecular sensor for evaluating tumour oxygenation, the isomerization rates of PAP and FePc(PAP)$_2$ were experimentally and computationally determined as a function of oxygen concentration and will be reported in this work.
| Keyword-1 | Photoswitches |
|---|---|
| Keyword-2 | Optical sensing |
| Keyword-3 | Oxygen |
