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Superoxide anion (O2•−) is an important reactive oxygen species (ROS), and plays critical roles in biological systems. ER stress has close relation with many metabolic diseases, and could lead to the abnormal production of ROS including O2•−. Herein, we present an ER-targeting probe (ER-Tf) for the detection of O2•− in living cells. The probe ER-Tf used triflate as the response site for O2•−, and employed p-methylbenzenesulfonamide as ER-targeting moiety. In response to O2•−, the triflate of the probe ER-Tf converted to hydroxyl group, providing strong blue emission under the excitation of ultraviolet light. The probe ER-Tf exhibited high sensitivity and selectivity to O2•−. Bioimaging experiments showed that the probe ER-Tf can be applied to detect O2•− at ER, and also demonstrated that rotenone could increase the generation of O2•− in living cells, while the O2•− level at ER showed no remarkable change during ferroptosis. [ABSTRACT FROM AUTHOR]

Sulfur dioxide (SO2) plays critical biological roles in living systems, and participates in a series of physiological and pathological processes. Aspartate aminotransferase 2 (AAT-2) catalyzes L -cysteine to produce endogenous SO2, which is mainly expressed in the mitochondria of cells. Herein, we present a new mitochondria-targeting and ratiometric fluorescent probe (MNP) for the detection of SO2 in living cells. The probe MNP employed a positively charged benzopyrylium moiety as the response site for SO2, and displayed a selective ratiometric response to SO2 on the basis of a FRET mechanism. Biological experiments demonstrated that the probe MNP was mainly distributed in mitochondria and could be used for the imaging of SO2 in living cells. [ABSTRACT FROM AUTHOR]

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]

[Display omitted] • Using benzopyridine-naphthalimide as a fluorescent platform. • FRET-based response mechanism to pH. • Ratiometric imaging of SO 2 in living cells. • in situ Detection of Cys-induced SO 2 dynamic changes in living cells. Sulfur dioxide (SO 2) is an important signal molecule in living systems, and plays a wide range of physiological functions. Real-time and in situ detection of the dynamic balance of SO 2 in mitochondria is of great significance to in-depth study its biological roles. Herein, we have developed a mitochondria-targeted fluorescent probe Nap-L based on the FRET mechanism to detect SO 2 in living cells. The probe Nap-L employed naphthalimide and positively charged benzopyridine as the donor and acceptor in the FRET system, and emitted green and red fluorescence under excitation. In respond to SO 2 , the nucleophilic addition of bisulfite to benzopyridine and then interrupted the FRET process from naphthalimide to benzopyridine fluorophore, thereby triggering an obvious change in the fluorescence ratio. The probe Nap-L showed high selectivity to SO 2 over the biothiols (Hcy, GSH, Cys) and other biologically related species. Biological experiments suggested that the probe Nap-L mainly distributed in mitochondria, and can be successfully used to detect mitochondrial endogenous SO 2 in living cells. [ABSTRACT FROM AUTHOR]

ER stress has close relation with various metabolic diseases including obesity and insulin resistance, and could result in the abnormal production of ROS including O 2 - . Real-time and in situ detection of endogenous O 2 - in ER is vitally important for revealing the physiological roles of O 2 - during ER stress. Herein, we present an ER-specific two-photon probe (ER-Rs) for the detection of endogenous O 2 - in living cells and zebrafishes. The probe ER-Rs employed triflate as the response site for O 2 - , and used p -methylsulfonamide as the ER-specific moiety. In response to O 2 - , the triflate group of the probe ER-Rs was transformed to hydroxyl and the turn-on fluorescence was produced. The probe ER-Rs displayed highly sensitive and selective response to O 2 - , and c ould be employed as an ER-specific two-photon probe for the visualization of endogenous O 2 - in live cells, tissues and zebrafishes. Image 1 • An ER-specific two-photon fluorescent probe (ER-Rs) was designed and synthesized for the detection of O 2 - . • The probe ER-Rs showed highly sensitive to O 2 - with the fluorescence enhancement by 105-fold. • Two-photon imaging of endogenously produced O 2 - in ER during PMA-induced ER stress. • The probe ER-Rs could be applied for the two-photon imaging of endogenous O 2 - in living zebrafishes. [ABSTRACT FROM AUTHOR]