Two-photon fluorescence imaging of DNA in living plant turbid tissue with carbazole dicationic salt

Three carbazole dicationic salts, namely 3,6-bis(1-methyl-4-vinylpyridinium) carbazole diiodide (BMVC), 9-ethyl-3,6-bis(1-methyl-4-vinylpyridinium) carbazole diiodide (9E-BMVC) and 9-ethyl-3,6-bis(1-hydroxyethyl-4-vinylpyridinium) carbazole diiodide (9E-BHVC), were synthesized successfully. Their photophysical properties were evaluated by absorption, one-and two-photon fluorescence spectra, and their higher fluorescence intensity and larger two-photon excited fluorescence action cross-sections (Phi x delta) in the presence of DNA than those in the absence of DNA give them good DNA two-photon light-switch properties. Furthermore, their ability to image nuclei in living plant cells and turbid tissues by using two-photon excited fluorescence was carefully studied, and the experimental results indicate that these dicationic salts can exclusively label nuclei in intact living plant cells and tissues. In particular, 9E-BHVC exhibits optimized DNA labeling performance. Very importantly, compared to DAPI, 9E-BHVC can be used to carry out deeper observation using the same incident power, or can be used to obtain usable fluorescent images by using a lower incident power.