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[Display omitted] • A new quinoxaline-based turn-on fluorescent probe for biothiols was developed. • Detecting biothiols with at least 69-fold fluorescence enhancement. • The probe exhibited outstanding sensitivity and selectivity towards biothiols. • A promising tool for detecting endogenous and exogenous biothiols in living cells. Maintaining biothiols homeostasis is extremely important for the health of organisms. In this work, a pair of fluorescent probes (Acr-QX8A and Acr-QX9A) was designed and synthesized to monitor biothiols. The two probes applied the same fused four ring quinoxaline as the skeleton, benzyl carbamate as the linker and acryloyl group as the recognition site, whose only difference was the amino group's position on the skeleton. By comparing the optical properties, Acr-QX9A exhibited superior performances than Acr-QX8A and chosen for further studies. Probe Acr-QX9A displayed 180-fold, 135-fold and 69-fold fluorescence intensity enhancements upon interactions with Cys, Hcy and GSH respectively, owing to the release of fluorophore QX9A and the restoration of intramolecular charge transfer (ICT) process. Acr-QX9A showed good selectivity and excellent anti-interference, which could be served as the naked-eye colorimetric probe for biothiols detection. More importantly, the probe exhibited high sensitivity towards biothiols with outstanding detection of limits (75.2 nM for Cys, 92.7 nM for Hcy and 370 nM for GSH). Encouraged by the appreciable results in solutions, probe Acr-QX9A was then successfully applied as a promising tool for monitoring both endogenous and exogenous biothiols in living cells. [ABSTRACT FROM AUTHOR]

[Display omitted] • A novel Near-infrared Turn-on Fluorescent probe has been synthesized. • Fast response to Selenocysteine with a large turn-on Near-infrared fluorescence signal. • Low detection limit, high selectivity and sensitivity. • Capability for identification of Sec in living cells and mice. Selenocysteine (Sec) plays critical roles in many physiological and pathological processes of human beings, thus it is of great significance to develop accurate methods for detecting and visualizing Sec. Herein, a new anthracene derivative (YZ-M5) as a near-infrared (NIR) fluorescent probe for sensing Sec was designed. Based on the target-induced modulation of the intramolecular charge transfer (ICT) process of the probe, YZ-M5 can display a rapid strong NIR fluorescence enhancement at 660 nm for Sec within 5 min. The quantitative detection range for Sec is 0–40 μM with a low detection limit of 18.5 nM. YZ-M5 also showed high selectivity and sensitivity, as well as the capability for identification of Sec in living cells and mice. [ABSTRACT FROM AUTHOR]

• An ultra-sensitive fluorescent probe TC-gal with high affinity to β-galactosidase was developed. • The detection of β-galactosidase with low background fluorescence and high signal-to-noise ratio was realized by the response of "turn-on" fluorescence of probe TC-gal. • The visualization of endogenous β-galactosidase in ovarian cancer cells and senescent cells was achieved. • The sensing mechanism based on a competition of TICT with ICT provided a novel idea for design of fluorescent biosensor. The detection of β-galactosidase is significant for identifying the occurrence of ovarian cancer and cellular senescence. Since the complexity and diversity of biological systems, fluorescent probes for biological detection are required to own good selectivity, high selectivity and strong anti-interference ability. To meet this challenge, we designed a "turn-on" fluorescent probe TC-gal by adjusting the effect of twisted intramolecular charge transfer (TICT) between intramolecular charge transfer (ICT) of the fluorophore for ultra-sensitive detecting of β-galactosidase. The β-galactosidase can specifically trigger an enhanced (more than 800 folds) light-up fluorescence of TC-gal due to attenuated TICT effect of tetraphenylethylene part and increased ICT effect induced by electron donating effect of generated hydroxyl. Such "turn-on" fluorescence selectively triggered by β-galactosidase endows probe TC-gal with low background fluorescence and high signal-to-noise ratio. It is demonstrated that designed TC-gal exhibits high selectivity, ultra-high sensitivity (LOD = 8.4 × 10−5 U/mL) and strong affinity (Km = 18.4 μM) to β-galactosidase in buffer solution with good anti-interference ability to other biological analytes. Furthermore, biocompatible probe TC-gal is successfully applied to detect endogenous β-galactosidase in ovarian cancer cells and distinguish senescent cells. We anticipate this work can inspire the generation of superior fluorescent biosensors for biological and medical application. [ABSTRACT FROM AUTHOR]

• A simple near-infrared fluorescence probe based on dicyanoisophorone was synthesized. • This probe exhibited excellent specificity in the detection of N 2 H 4 over other amino compounds. • This probe showed excellent response performance to N 2 H 4 through distinct fluorescence enhancement. • This probe was applicable for N 2 H 4 detection in living cells and real water samples. With the widespread use of N 2 H 4 , it brings potential risks to human health. In order to determine N 2 H 4 effectively in both environment and living systems, a simple near-infrared fluorescence probe was prepared for the specific response of N 2 H 4 based on the intramolecular charge transfer (ICT) mechanism. This probe provided a "turn on" fluorescence response to N 2 H 4 with characteristics including high selectivity, rapid response (within 1 min), low cytotoxicity, and low detection limit (0.022 μM). In addition, it can be used to expediently trace N 2 H 4 in HepG2 cells and water samples. Thus, Probe 1 is a promising tool to identify the level of N 2 H 4. [ABSTRACT FROM AUTHOR]