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in vivo Detection of Singlet Oxygen Using Delayed Chemiluminescence during Photodynamic Therapy

in vivo Detection of Singlet Oxygen Using Delayed Chemiluminescence during Photodynamic Therapy Abstract: It is known that, in photodynamic therapy (PDT), singlet oxygen is the main factor mediating cytotoxicity. The effectiveness of a PDT treatment is directly linked to the singlet oxygen produced in the target. Although the luminescence from singlet oxygen can be detected and is suggested as an indicator for evaluating photodynamic therapy, the inherited disadvantages of the luminescence, namely short lifetime, long wavelength and weakness in signal strength limit its potential for in vivo applications. We have previously reported that chemiluminescence can be used to detect singlet production in PDT and linked the signal to the cytotoxicity. In the current study, we further our investigation for monitoring singlet oxygen production during PDT. The lifetime of FCLA-CL is evaluated and the results show it is much longer than that of direct luminescence of singlet oxygen. A gated measurement algorithm is thus developed to fully utilize the longer lifetime for a clean measurement of the CL without the interference from the exciting light. The results show that it is practically feasible to use the technique to monitor the singlet oxygen production by PDT in vivo. Compared to the direct singlet oxygen luminescence measurement, our new technique is highly sensitive and can be realized with conventional optical detector such as photon multiplier tube with excellent signal-to-noise ratio. It thus provides a novel means for real-time in vivo monitoring of singlet oxygen production during PDT.