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Peroxynitrite (ONOO-) could deplete ER-associated Ca2+ and cause ER stress, and thereby precise and in situ detection of ONOO- at ER is highly important for the study of its biological roles. Herein, we present a ratiometric two-photon ER-targeting fluorescent probe (NAB) for the detection of ONOO- in living cells and brain tissues. NAB utilized 4-bromomethylphenyl borate as a recognition site for ONOO-, and utilized p -toluenesulfonamide as ER-targeting group. After the response of NAB to ONOO-, the 4-bromomethylphenyl borate converted to hydroxyl, resulting in the change of the fluorescence color from blue to yellow. The probe NAB could show highly sensitive response to ONOO- within 6 s, and exhibited excellent selectivity to ONOO-. The probe NAB mainly located at ER and showed excellent ER-targeting property. Ratiometric two-photon imaging demonstrated that the probe NAB could selectively detect exogenous ONOO- at ER, and also could be applied to image metformin-induced ONOO- in living HepG2 cells. Furthermore, NAB can effectively detect the changes of ONOO- level in brain tissues, and revealed that the endogenous ONOO- level at ER showed increase in hippocampus of the depressive mouse. [Display omitted] • A ratiometric two-photon and ER-targeting probe for ONOO- was developed. • The fluctuation of endogenous ONOO- at ER was imaged in a ratiometric two-photon manner. • ONOO- level at ER showed an increase in hippocampus of the depressive mouse. [ABSTRACT FROM AUTHOR]

Peroxynitrite (ONOO-) plays crucial roles in a variety of physiological and pathological processes in living systems, and therefore, real-time and in situ imaging of ONOO- is of great significance to in-depth study its biological roles. Herein, we have developed PET-ESIPT-based fluorescent probes (BCN and BCN-A) for the detection of ONOO- in living cells, zebrafishes and brain tissues. BCN was a highly sensitive ONOO- probe in which the fluorescence property of the fluorophore was simultaneously controlled by PET and ESIPT mechanisms, and transformed to BCN-A via acetylation. Especially, BCN showed large Stokes shift in response to ONOO-, and displayed high selectivity to ONOO-. BCN-A employed the acetate group to switch off ESIPT process of the fluorophore and improve the membrane permeability. In living cells, BCN-A released an ONOO--responsive probe (BCN) by the hydrolysis of esterase, and then detected ONOO-. Biological imaging demonstrated that although both metformin and rotenone are mitochondrial complex I inhibitors, metformin can increase the generation of ONOO- while rotenone had no significant influence on the generation of ONOO- in living cells and zebrafishes. Moreover, the amygdala and perirhinal/entorhinal cortex in the brain of depressive mouse both showed increasing fluorescence intensity relative to those of normal mouse, which suggested that the LPS-induced depressive disorder could result in the generation of ONOO- in the two brain areas of mouse. We expect that the probes (BCN and BCN-A) could extensively serve as the powerful molecular tools to investigate the biological roles of ONOO- for the in-depth study of drug mechanism and depressive disorder. [Display omitted] • Using cyanobenzene dicarbonyl unit as response site for ONOO-. • PET-ESIPT-based response mechanism to ONOO-. • Imaging of metformin-induced ONOO- in living cells and zebrafishes. • Detection of ONOO- level changes in brain depressive mice. [ABSTRACT FROM AUTHOR]

Cell death can destroy homeostasis and is a hallmark of many pathological conditions. Discrimination of live and dead cells is a crucial task for the biological, medical and pharmaceutical studies. Herein, we constructed an ESIPT-based fluorescent probe (BTE) on the basis of the different esterase activity in live and dead cells. Under excitation, the probe BTE showed the blue emission peaked at 465 nm, while it mainly displayed green emission peaked at 543 nm after it was hydrolyzed by esterase. Imaging of the cells treated by H 2 O 2 and ultraviolet (UV) radiation demonstrated that the probe BTE is effective in the detection of the health of cells, could help us to better understand cell death and its effects in a range of diseases and treatments. Unlabelled Image • Discrimination of live and dead cells in a ratiometric mode. • Response of the probe to esterase on the basis of ESIPT • Image the unhealthy status the cells treated with H 2 O 2 • Analysis the damage of ultraviolet UV radiation to live cells [ABSTRACT FROM AUTHOR]