Two novel “turn on” fluorescent probes for monitoring hypochlorite in living HeLa cells

Ex Tenebris Lux: Illuminating Reactive Oxygen and Nitrogen Species with Small Molecule Probes

Reactive oxygen and nitrogen species are small reactive molecules derived from elements in the air─oxygen and nitrogen. They are produced in biological systems to mediate fundamental aspects of cellular signaling but must be very tightly balanced to prevent indiscriminate damage to biological molecules. Small molecule probes can transmute the specific nature of each reactive oxygen and nitrogen species into an observable luminescent signal (or even an acoustic wave) to offer sensitive and selective imaging in living cells and whole animals. This review focuses specifically on small molecule probes for superoxide, hydrogen peroxide, hypochlorite, nitric oxide, and peroxynitrite that provide a luminescent or photoacoustic signal. Important background information on general photophysical phenomena, common probe designs, mechanisms, and imaging modalities will be provided, and then, probes for each analyte will be thoroughly evaluated. A discussion of the successes of the field will be presented, followed by recommendations for improvement and a future outlook of emerging trends. Our objectives are to provide an informative, useful, and thorough field guide to small molecule probes for reactive oxygen and nitrogen species as well as important context to compare the ecosystem of chemistries and molecular scaffolds that has manifested within the field.

New dual-responsive fluorescent sensor for hypochlorite and cyanide sensing and its imaging application in live cells and zebrafish

Excessive levels of cyanide (CN-) and hypochlorite (ClO-) anions are the significant threats to the human health and the environment. Thus, great efforts have been to design and synthesize molecular sensors for the simple, instantaneous and efficient detecting environmentally and biologically important anions. Currently, developing a single molecular sensor for multi-analyte sensing is still a challenging task. In our present work, we developed a new molecular sensor (3TM) based on oligothiophene and Meldrum's acid units for detecting cyanide and hypochlorite anions in biological, environmental and food samples. The detecting ability of 3TM has been examined to various testing substances containing amino acids, reactive oxygen species, cations and anions, showing its high selectivity, excellent sensitivity, short response time (ClO-: 30 s, CN-: 100 s), and broad pH working range (4-10). The detection limits were calculated as 4.2 nM for ClO- in DMSO/H2O (1/8, v/v) solution and 6.5 nM for CN- in DMSO/H2O (1/99, v/v) solution. Sensor 3TM displayed sharp turn-on fluorescence increasement (555 nm, 435 nm) and sensitive fluorescence color changes caused by CN-/ClO-, which is ascribed to the nucleophilic addition and oxidation of ethylenic linkage by cyanide and hypochlorite, respectively. Moreover, sensor 3TM was applied for hypochlorite and cyanide detecting in real-world water, food samples and bio-imaging in live cells and zebrafish. To our knowledge, the developed 3TM sensor is the seventh single-molecular sensor for simultaneous and discriminative detecting hypochlorite and cyanide in food, biological and aqueous environments using two distinct sensing modes.

Monitoring of Hypochlorite Level in Fruits, Vegetables, and Dairy Products: A BODIPY-Based Fluorescent Probe for the Rapid and Highly Selective Detection of Hypochlorite

Hypochlorite/hypochlorous acid (ClO^-/HOCl), among the diverse reactive oxygen species, plays a vital role in various biological processes. Besides, ClO^- is widely known as a sanitizer for fruits, vegetables, and fresh-cut produce, killing bacteria and pathogens. However, excessive level of ClO^- can lead to the oxidation of biomolecules such as DNA, RNA, and proteins, threatening vital organs. Therefore, reliable and effective methods are of utmost importance to monitor trace amounts of ClO^-. In this work, a novel BODIPY-based fluorescent probe bearing thiophene and a malononitrile moiety (BOD-CN) was designed and constructed to efficiently detect ClO^-, which exhibited distinct features such as excellent selectivity, sensitivity (LOD = 83.3 nM), and rapid response (<30 s). Importantly, the probe successfully detected ClO^- in various spiked water, milk, vegetable, and fruit samples. In all, BOD-CN offers a clearly promising approach to describe the quality of ClO^--added dairy products, water, fresh vegetables, and fruits.

Ratiometric and colorimetric probes with large stokes shift for sensing of exogenous hypochlorite in potato sprouts and industrial effluents

Being one of the important reactive oxygen species (ROS), hypochlorite ions (ClO^-) are involved in the control of several pathological and physiological processes. However, overexpression of ClO^- may prompt several disorders including cancer. Therefore, two fluorescein functionalized compounds with catechol (probe 1) and 2-naphthyl (probe 2) as substituents were synthesized through Schiff base reaction to recognize ClO^- in food items and industrial samples. While probe 2 exhibited turn-off fluorescent response towards ClO^- with limit of detection (LOD) of 86.7 nM, structurally alike probe 1 showed excellent ratiometric response with low detection limit (36.3 nM), large Stokes shift (353 nm), and 'fast' response time (15 s). ¹H NMR titration experiments favored spiroring opening of probe 1 upon the reaction with ClO^-. Probe 1 was successfully utilized for the monitoring of exogenous ClO^- in industrial samples. Further, fabrication of probe coated fluorescent paper strips and recognition of ClO^- in sprouting potato show diverse practical applicability of our probes.

A NIR BODIPY-based ratiometric fluorescent probe for HClO detection with high selectivity and sensitivity in real water samples and living zebrafish

Hypochlorous acid (HClO) plays an important role in many physiological and pathological activities. In this work, a novel BODIPY-based Near-infrared (NIR) ratiometric fluorescent probe BODIPY-Hyp was designed for the rapid detection of HClO. The probe BODIPY-Hyp was highly selective and sensitive for HClO with a low detection limit of 16.74 nM and short response time of less than 60 s. The probe BODIPY-Hyp in response to HClO exhibited a significant blue-shifted fluorescence emission from 700 nm to 530 nm, and its fluorescence intensity ratio (I_{530 nm}/I_{700 nm}) increased about 1200 times before and after adding HClO. Moreover, the reaction mechanism of BODIPY-Hyp with HClO was verified by HRMS analysis, ¹H NMR titration and DFT calculations. Furthermore, BODIPY-Hyp was successfully processed into a portable test strip-based device for the detection of HClO. In addition, the probe BODIPY-Hyp could be used in real time to monitor the levels of HClO in living zebrafish larvae. In conclusion, BODIPY-Hyp has great application potential in the life and environmental sciences.