Oxidative Capacity Storage of Transient Singlet Oxygen from Photosensitization with a Redox Mediator for Improved Chemiluminescent Sensing.

Singlet oxygen, generated from type-II photosensitization, has become increasingly popular in bioassay development in recent years. However, the transient nature of singlet oxygen in water (lifetime shorter than 4 μs) as well as its high activity make it easily inactivated by solvent molecules and other coexisting species, thus deteriorating use in the analytical sensitivity. Here, we proposed the use of a simple redox mediator for storing the energy of the transient singlet oxygen. To demonstrate such an idea, singlet oxygen generated from photosensitization of the double strand DNA-SYBR Green I (dsDNA-SG) complex was explored as a redox donor that can be modulated through formation and deformation of the dsDNA structure. After screening of a series of redox mediators with luminol chemiluminescence (CL) as the probe, ferrocyanide (K4Fe(CN)6) was found to be the most efficient, resulting in ∼30-fold intensified luminol CL. By storing the oxidative capacity of singlet oxygen in ferrocyanide, the dsDNA-SG complex was evolved into a photosensitization-mediated chemiluminescence (PMCL) biosensing platform for DNA detection. Such a PMCL sensing platform allows label- and amplification-free detection of picomolar-scale DNA with a limit of detection (LOD) of 1.5 pM (0.45 fmol in absolute). The excellent sensitivity of PMCL sensing confirmed that such a facile storage approach to oxidative capacity would be appealing for singlet-oxygen-involved biosensing.