Development of a Ruthenium(II) Complex Based Luminescent Probe for Imaging Nitric Oxide Production in Living Cells

A unique ruthenium(II) complex, bis(2,2′‐bipyridine)(4‐(3,4‐diaminophenoxy)‐2,2′‐bipyridine)ruthenium(II) hexafluorophosphate ([(Ru(bpy)₂(dabpy)][PF₆]₂), has been designed and synthesized as a highly sensitive and selective luminescence probe for the imaging of nitric oxide (NO) production in living cells. The complex can specifically react with NO in aqueous buffers under aerobic conditions to yield its triazole derivative with a high reaction rate constant at the 10¹⁰ M ^?1 s^?1 level; this reaction is accompanied by a remarkable increase of the luminescence quantum yield from 0.13 to 2.2 %. Compared with organic probes, the new Ru^II complex probe shows the advantages of a large Stokes shift (>150 nm), water solubility, and a wide pH‐availability range (pH independent at pH>5). In addition, it was found that the new probe could be easily transferred into both living animal cells and plant cells by the coincubation method, whereas the triazole derivative was cell‐membrane impermeable. The probe was successfully used for luminescence‐imaging detection of the exogenous NO in mouse macrophage cells and endogenous NO in gardenia cells. The results demonstrated the efficacy and advantages of the new probe for NO detection in living cells.     

A Ratiometric Fluorescent Probe Based on a Through‐Bond Energy Transfer (TBET) System for Imaging HOCl in Living Cells

A simple ratiometric probe (Naph‐Rh) has been designed and synthesized based on a through‐bond energy transfer (TBET) system for sensing HOCl. In this probe, rhodamine thiohydrazide and naphthalene formyl were connected by simple synthesis methods to construct a structure of monothio‐bishydrazide. Free probe Naph‐Rh showed only the emission of naphthalene. When probe Naph‐Rh reacted with HOCl, monothio‐bishydrazide could be converted into 1,2,4‐oxadiazole, which not only ensured that the donor and the acceptor were connected with electronically conjugated bonds, but also resulted in the spiro‐ring opening and the emission of rhodamine. Therefore, a typical TBET process took place. The probe possessed high‐energy transfer efficiency and large pseudo‐Stokes shifts. As the first TBET probe for HOCl, Naph‐Rh showed excellent selectivity and sensitivity toward HOCl over other reactive oxygen species (ROS)/reactive nitrogen species (RNS), and could respond fast to a low concentration of HOCl in the real sample. In addition, the probe was suitable for imaging HOCl in living cells due to its real‐time response, excellent resolution, and reduced cytotoxicity.     

Environment‐sensitive Fluorescent Turn‐on Chemical Probe for the Specific Detection of O‐Methylguanine‐DNA Methyltransferase (MGMT) in Living Cells

MGMT protein, which has been associated with resistance to antitumor alkylation drugs for many patients, is a very useful prognostic marker to provide a guide for therapeutic decisions. Considering the large number of cellular samples that have to be handled daily at the hospitals, it is thus important to develop a rapid and simple analytical method to distinguish MGMT activity in different types of cells. In this paper, we describe a MGMT‐activated fluorescence turn‐on probe for the rapid no‐wash imaging of MGMT in living cells. The probe consists of a specific MGMT suicide pseudosubstrate, O⁶‐benzyl‐guanine and an environment‐sensitive fluorophore, SBD. In the presence of MGMT, the enzyme transfers SBD to the protein active site where the hydrophobic surrounding causes the fluorophore to exhibit more than 50‐fold fluorescence enhancement. With this probe, bright fluorescence was observed for MGMT‐positive, Hela S3 and MCF‐7 cells, while MGMT‐deficient CHO cells displayed no fluorescence. We believe that this fluorescence activation probe design can also be extended to detect other transferases, for which there are still no effective methods to image them in living cells.