Development of new spectroscopic probes and specific imaging methods is of great importance for various biological studies. Prof. Ma’s research group at the Institute of Chemistry, Chinese Academy of Sciences (ICCAS), has been engaged in this area for more than 20 years, during which a series of new spectroscopic probes and sensing methods for bioactive species have been developed by using various chemical reactions. Based on their important results, Prof. Ma and his colleagues have been invited to review various design strategies on spectroscopic probes (Chem. Rev., 2014, 114, 590-659; Chem. Sci., 2016, 7, 6309-6315).
Hydroxyl radical (·OH), one of the reactive oxygen species in biosystems, is known to participate in the development of several diseases such as neurodegenerative disorders and cancer. The widely-accepted pathway for the generation of ·OH in vivo is via the iron-participated Fenton reaction (Fe2+ + H2O2). However, considering that the concentration of the dissolved O2 in cells is several orders of magnitude higher than the steady state level of H2O2, iron autoxidation process (Fe2+ + O2) may also play an important role in the generation of ·OH. Unfortunately, due to the lack of a highly sensitive method to detect trace amounts of ·OH generated during the iron autoxidation, the importance of this process is usually ignored. In order to address this issue, Prof. Ma’s research group developed the first sensitive fluorescence ·OH probe (Figure 1) that is capable of monitoring the generation of trace ·OH in iron autoxidation process. The probe was designed by utilizing both the unique aromatic hydroxylation and the electrophilicity of ·OH, and prepared by incorporating a strong electron-donating methoxy group into a cyanine fluorochrome to enhance the trapping ability for ·OH. Reaction of the probe with ·OH leads to the formation of a new product with larger π-conjugation and near-infrared fluorescence emission. The extended π-conjugation change and large emission red-shift from the probe to the product enable the probe to achieve high sensitivity in ·OH detection. The capability of the probe has been demonstrated by imaging ·OH generated in living cells under iron autoxidation as well as various stimuli. The superior analytical performance makes it useful for detecting trace ·OH in some critical physiological and pathological processes associated with iron autoxidation (Angew. Chem. Int. Ed., 2018, 57, 12830-12834).
Figure 1. New spectroscopic probe and its use in specific fluorescence imaging of ·OH.