Quasi-intrinsic fluorescent probes for detecting the DNA adduct ( ABP dG) based on an excited-state intermolecular charge transfer mechanism.

N'-(2'-Deoxyguanosin-8-yl)-4-aminobiphenyl ( ABP dG) is one of the most representative carcinogenic DNA adducts formed by human exposure to 4-aminobiphenyl (4-ABP) during dye production, rubber-manufacturing processes and cigarette smoke. Accordingly, the ultrasensitive detection of ABP-derived adducts in DNA with minimal interference to the native structures becomes key for elucidating carcinogenesis mechanisms and mitigating the risk of cancer. In view of the lack of efficient optical emission in ABP G, we report a theoretical study on the photophysical properties of a set of quasi-intrinsic fluorescent C-analogues, which can form stable W-C base pairs with ABP G. It is found that fluorophore replacement and ring-expansion can bring a red-shifted absorption and bright photoluminescence due to additional π-conjugation. In particular, because the tricyclic cytosine analogue 1,3-diaza-2-oxophenoxazine (tC O ) possesses distinct optical properties, it is proposed as a biosensor to identify ABP G. The TDDFT-calculated absorption maximum of tC O is red-shifted by 97 nm in comparison with that of the native C base, which contributes to selective excitation after incorporating into the nucleic acids. Although the fluorescence is insensitive to base pairing with natural guanine, the excited state intermolecular charge transfer (ESICT)-governed "OFF-ON" signal can be observed in the presence and absence of ABP G. Moreover, to evaluate the direct availability of the bright C-analogues with high selectivity for the deoxyguanosine adduct ABP G in DNA, we further investigated thoroughly the effects of its linking to deoxyribose on its absorption and emission, which shows little difference from that of experiment.