Longwei He

Fluorescent chemosensors manipulated by dual/triple interplaying sensing mechanisms

Fluorescence imaging is a powerful approach for noninvasive and real-time visualization and tracking of biomolecules and biological processes in living systems. The fluorescent chemosensors with dual/triple interplaying sensing mechanisms tend to provide diverse fluorescence signals or amplify the response signals, which are propitious to simultaneously track multiple analytes or to improve the selectivity and sensitivity of the chemosensors. Thus, the development of dual/triple sensing mechanism-based chemosensors has attracted great interest recently. This review highlights the representative cases of the fluorescent chemosensors with dual/triple interplaying sensing mechanisms published since 2010, and these chemosensors are classified according to the types of the interplaying sensing mechanisms, including ICT-FRET, PET-FRET, PET-ICT-ESIPT, etc.

A fast responsive two-photon fluorescent probe for imaging H2O2 in lysosomes with a large turn-on fluorescence signal

Hydrogen peroxide (H2O2) plays a crucial role in many biological processes in the human body. As our understanding of the complexity of physiological H2O2 in lysosome, investigative tools are required to make sense of this interconnectivity. Toward this goal, we have developed a new example of a fast responsive and lysosome-targeted two-photon H2O2 fluorescent probe (Lyso-HP) with a large turn-on fluorescence signal (80-fold fluorescence enhancement). The addition of H2O2 to Lyso-HP results a dramatic fluorescence enhancement around 550 nm. The probe could image exogenous and endogenous H2O2 in living cells and the probe was located in lysosomes with high colocalization coefficient (0.96) compared with LysoTracker. The large fluorescence enhancement of the two-photon probe Lyso-HP renders it attractive for imaging H2O2 in living tissues with deep tissue penetration. Significantly, the probe is feasible for fluorescently monitoring H2O2 level changes in lysosomes and suitable for fluorescence imaging of H2O2 in living tissues with deep penetration by using two-photon microscopy.

Colorimetric and ratiometric fluorescent probe for hydrogen sulfide using a coumarin–pyronine FRET dyad with a large emission shift

Ratiometric fluorescent probes with two well-resolved emission bands have attracted considerable attention, as they can be employed to carry out ratiometric measurements. The ratiometric measurements can alleviate to some extent the shortcomings of intensity-based probes induced by the probe concentration effects, influence of probe environment, and instrumental limitations. Herein, a colorimetric and ratiometric fluorescent probe (CP-H2S) based on a coumarin–pyronine FRET dyad was developed for the detection of H2S in vitro and in vivo. In an aqueous solution, the probe exhibits an inherent red emission of the pyronine unit excited from the coumarin unit by FRET process, whereas an encounter of CP-H2S and H2S suppresses the FRET process and elicits a new blue emission of the coumarin moiety with a concomitant decrease in the red emission. The spectral shift of these two distinct emission bands is up to 119 nm. Moreover, there was a 252.7-fold enhancement in the ratiometric fluorescence intensity signal, and the energy-transfer efficiency was found to be 96.7%. These desirable results suggest that the CP-H2S probe can significantly reduce the crosstalk signals and improve the accuracy of ratiometric measurements. Remarkable ratio of signals of the CP-H2S probe upon responding to H2S was also obtained in living cells imaging.

Mitochondria and lysosome-targetable fluorescent probes for HOCl: recent advances and perspectives

Hypochlorous acid (HOCl), as one of the reactive oxygen species (ROS), plays an important role in the destruction of pathogens in the immune system. However, abnormal concentration of biogenic HOCl can also damage host tissues, and it has been shown to be associated with many diseases. Accordingly, detection of HOCl at the subcellular level is important for understanding inflammation and cellular apoptosis. Toward this end, in the past few years, a wide variety of fluorescent HOCl probes have been engineered and applied for imaging of HOCl in subcellular organelles. In this review, we highlight the representative cases of the fluorescent HOCl probes with mitochondria and lysosome-targetable ability. The discussion includes their design strategies, sensing mechanisms, and applications in bio-imaging of HOCl in mitochondria and lysosomes.

Improved Aromatic Substitution–Rearrangement-Based Ratiometric Fluorescent Cysteine-Specific Probe and Its Application of Real-Time Imaging under Oxidative Stress in Living Zebrafish

Biothiols, including cysteine (Cys), homocysteine (Hcy), and glutathione (GSH), play a crucial role in many physiological processes. Cys production and metabolism is closely connected with Hcy and GSH; meanwhile, the dynamic antioxidant defenses network by Cys is independent of the GSH system, and Cys can serve as a more effective biomarker of oxidative stress. Hence, it is significant and urgent to develop an efficient method for specific detection of Cys over other biothiols (Hcy/GSH). However, most of the present Cys-specific fluorescent probes distinguished Cys from Hcy through response time, which would suffer from an unavoidable interference from Hcy in long-time detection. In this work, in order to improve the selectivity, we employed an improved aromatic substitution-rearrangement strategy to develop a ratiometric Cys-specific fluorescent probe (Cou-SBD-Cl) based on a new fluorescence resonance energy transfer (FRET) coumarin-sulfonyl benzoxadiazole (Cou-SBD) platform for discrimination of Hcy and GSH. Response of Cou-SBD-Cl to Cys would switch FRET on and generate a new yellow fluorescence emission with a 56.1-fold enhancement of ratio signal and a 99 nm emission shift. The desirable dual-color ratiometric imaging was achieved in living cells and normal zebrafish. In addition, probe Cou-SBD-Cl was also applied to real-time monitor Cys fluctuation in lipopolysaccharide-mediated oxidative stress in zebrafish.

The development of an ICT-based formaldehyde-responsive fluorescence turn-on probe with a high signal-to-noise ratio

An illuminating ICT-based formaldehyde-responsive fluorescent probe (PBD-FA) with long wavelength emission was judiciously designed and synthesized, which is suitable for detecting FA in aqueous solution and living cells, both with significant fluorescence signal-to-noise ratios.

A turn-on fluorescent formaldehyde probe regulated by combinational PET and ICT mechanisms for bioimaging applications

An illuminating formaldehyde-responsive fluorescence probe (Naph-FA) with a turn-on emission signal was rationally designed and synthesized. The reaction-based probe undergoes successive condensation, 2-aza-Cope rearrangement and hydrolysis processes in response to formaldehyde, and the fluorescence signal was regulated by combinational PET and ICT mechanisms.