A Two-Photon Fluorescent Probe for Imaging Endogenous ONOO- near NMDA Receptors in Neuronal Cells and Hippocampal Tissues

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.

A simple mitochondria-immobilized fluorescent probe for the detection of hydrogen peroxide

Hydrogen peroxide (H2O2), as one of reactive oxygen species (ROS) widely present in the human body, is involved in a variety of physiological activities. Many human diseases are associated with abnormal levels of H2O2 in the body. Mitochondria are the main organelles producing H2O2 in the human body, and monitoring the level of H2O2 in mitochondria can help to deepen the understanding of the detailed functions of H2O2 in physiological activities. However, due to the highly dynamic nature of the cells, real-time quantitative monitoring of H2O2 levels in mitochondria remains an ongoing challenge. Herein, a novel highly immobilized mitochondria-targeting fluorescent probe (QHCl) for detection of H2O2 was reasonably constructed based on quinolinium dye containing benzyl chloride moiety. Spectral experimental results demonstrated QHCl possessed outstanding selectivity toward H2O2 (λex/em = 380/513 nm). In addition, QHCl can quantitatively detect H2O2 in the concentration range of 0-20 μM with excellent sensitivity (LOD = 0.58 μM) under the PBS buffer solution (10 mM, pH = 7.4). Finally, bioimaging experiments demonstrated that the probe QHCl was able to be used for accurately detecting both endogenous and exogenous H2O2 in the mitochondria of living cells and zebrafish by its unique mitochondrial immobilization.

The development of logic gate-based fluorescent probes that respond to intracellular hydrogen peroxide and pH in tandem

Logic gate-based fluorescent probes are powerful tools for the discriminative sensing of multiple signaling molecules that are expressed in concert during the progression of many diseases such as inflammation, cancer, aging, and other disorders. To achieve logical sensing, multiple functional groups are introduced to the different substitution sites of a single fluorescent dye, which increases the complexity of chemical synthesis. Herein, we report a simple strategy that incorporates just one responsive unit into a hemicyanine dye achieving the logic gate-based sensing of two independent analytes. We introduce boronic acid to hemicyanine to quench the fluorescence, and in the presence of hydrogen peroxide (H2O2), the fluorescence is recovered due to removal of the boronate. Interestingly, the subsequent decrease in pH turned the red fluorescence of hemicyanine to green emissive because of protonation of the phenolic alcohol. This unique feature of the probe enables us to construct "INHIBIT" and "AND" logical gates for the accurate measuring of intracellular H2O2 and acidic pH in tandem. This study offers insight into the simple construction of logic-gate based fluorescent probes for the tandem sensing of multiple analytes that are correlatively produced during disease progression.

A perylenemonoimide-based fluorescent probe: ultrasensitive and selective tracing of endogenous peroxynitrite in living cells

Peroxynitrite (ONOO-), a highly reactive species, plays a key role in various physiological and pathological processes. Herein, a red-emitting fluorescent reporter perylenemonoimide-boronate ester (PMI-BE) was synthesized and utilized for ultrasensitive detection of ONOO-. The unique feature of PMI-BE is its nanomolar sensitivity with high selectivity towards ONOO-. Moreover, PMI-BE also detects endogenously generated ONOO- in live cells.

A reversible and ratiometric fluorescent probe based on rhodol derivative with an ESIPT unit for monitoring copper ion content and in situ evaluation of related drugs in cells

The amount of copper ions in the environment has an immediate effect on ecology and food safety, Menkes syndrome and Wilson's disease cause accumulation and deficiency of copper ions in the body, respectively, and neurodegenerative diseases are also closely related to copper ion levels. However, the current copper ion detection technology has a high cost, complex operation, and other disadvantages. In this study, a ratiometric fluorescent probe (RB-DH) was rationally constructed to detect copper ions by coupling benzothiazole to rhodol derivatives. It can be used to determine copper ion concentrations in water samples, agricultural products, cells, and zebrafish. Importantly, due to the reversible response of RB-DH to copper ions, the fluctuation of intracellular copper ion content during the release of copper ion-related drugs (Copper gluconate and D-penicillamine) was successfully monitored with RB-DH for the first time. This study demonstrates RB-DH's potential application in the evaluation of related drug release effects and serves as a guide for the establishment of portable detection techniques for other important substances.

Recent Progress of Spectroscopic Probes for Peroxynitrite and Their Potential Medical Diagnostic Applications

Peroxynitrite (ONOO-) is a crucial reactive oxygen species that plays a vital role in cellular signal transduction and homeostatic regulation. Determining and visualizing peroxynitrite accurately in biological systems is important for understanding its roles in physiological and pathological activity. Among the various detection methods, fluorescent probe-based spectroscopic detection offers real-time and minimally invasive detection, high sensitivity and selectivity, and easy structural and property modification. This review categorizes fluorescent probes by their fluorophore structures, highlighting their chemical structures, recognition mechanisms, and response behaviors in detail. We hope that this review could help trigger novel ideas for potential medical diagnostic applications of peroxynitrite-related molecular diseases.

Designing a turn-on ultrasensitive fluorescent probe based on ICT-FRET for detection and bioimaging of Hypochlorous acid

Hypochlorous acid (HClO) plays an essential role in biological systems. The characteristics of potent oxidization and short lifetime make it challenging to detect specifically from other reactive oxygen species (ROS) at cellular levels. Therefore, its detection and imaging with high selectivity and sensitivity are of great significance. Herein a turn-on HClO fluorescent probe (named RNB-OCl) with boronate ester as the recognition site was designed and synthesized. The RNB-OCl displayed good selective and ultrasensitive to HClO with a low detection limit of 1.36 nM by the intramolecular charge transfer (ICT)-fluorescence resonance energy transfer (FRET) dual mechanism in reducing the fluorescence background and improving the sensitivity. In addition, the role of the ICT-FRET was further demonstrated by time-dependent density functional theory (TD-DFT) calculations. Furthermore, the probe RNB-OCl was successfully employed for imaging HClO in living cells.

A highly selective red-emitting fluorescent probe and its micro-nano-assembly for imaging endogenous peroxynitrite (ONOO-) in living cells

Endogenous peroxynitrite plays a very important role in the regulation of life activities. However, validated tools for ONOO^- tests are currently insufficient. We designed a fluorescent probe TPA-F-NO₂ with a low fluorescence background in water based on the D-π-A structure for the imaging of endogenous ONOO^- in living cells. TPA-F-NO₂ can realize the naked eye detection of ONOO^- due to the obvious color change. TPA-F-NO₂ has the advantages of large stokes shift, high signal-to-noise ratio, high selectivity and sensitivity. The quantitative detection can be achieved in the range of 0-14 μM ONOO^-. Due to its solvatochromic characteristics, TPA-F-NO₂ has the potential to be used in OLEDs and other fields. In addition, 4-methylumbelliferone has a wide range of anticancer effects as an inhibitor of hyaluronic acid. We prepared TPA-MU-NPs by assembling TPA-F-NO₂ and 4-methylumbelliferone. It also endows TPA-MU-NPs with ONOO^- imaging function and anti-proliferation effect on breast cancer cells and other cells. This 'probe-drug' assembly strategy provides ideas for the design and optimization of dual-functional probes.

Rational construction of a fluorescent sensor for simultaneous detection and imaging of hypochlorous acid and peroxynitrite in living cells, tissues and inflammatory rat models

Modern medical research indicates that hypochlorous acid (HClO) and peroxynitrite (ONOO^-) are important biomarkers of oxidative stress. However, the up- or down-regulation of HClO or ONOO^- has been closely associated with the occurrence and development of various diseases. In order to investigate the intrinsic entanglement relationship between HClO and ONOO^- and their relationship with the occurrence and development of inflammation, it is very valuable to develop fluorescent sensors that are capable of displaying different signals towards HClO, ONOO^- and HClO/ONOO^-. In this work, we rationally design and construct a novel robust small organic molecule fluorescent sensor (RhNp-ClO-ONOO) towards ONOO^-, HClO and HClO/ONOO^- with green, red, and green-red three different fluorescent signal outputs, respectively. RhNp-ClO-ONOO has fast responsive time for HClO (∼60 s) and ONOO^- (∼20 s). Also it has markedly low detection limits for HClO (∼25.3 nM) and ONOO^- (12.4 nM) respectively. In addition, RhNp-ClO-ONOO could be further shown to detect endogenous HClO/ONOO^- in living cells, inflammatory tissues and rat model successfully. Therefore, this novel fluorescent sensor with double responsive moiety can offer a powerful tool for studying the role of HClO and ONOO^- and the occurrence and development of inflammatory diseases.

A novel "dual-locked" fluorescent probe for ONOO- and viscosity enables serum-based rapid disease screening

Peroxynitrite (ONOO^-) plays important roles in the progression of important disease such as inflammation, cancer, and diabetes, which made it an attractable target for biosensor development. However, to detect ONOO^- solely is highly dependent on the sensitivity of the detection method and may be disturbed by unwillingly false-positive signal. Cellular viscosity is an important microenvironmental parameter and its abnormal changes are closely related to diseases such as diabetes and cancer. In this case, to construct a "dual-locked" molecular tool for both ONOO^- and viscosity sensing and to evaluate the performance of such strategy in disease diagnosis is of great importance. We herein firstly reported the construction of a novel "dual-locked" probe DCI-OV which showed capability for simultaneous measuring ONOO^- concentration and system viscosity with high sensitivity (LOD = 4.7 nM) and high specificity. Moreover, both exogenous and low level of endogenous ONOO^- in living cells could be detected using DCI-OV due to viscosity amplified signal. Furthermore, cancer cells and insulin-resistant cells could be easily distinguished using DCI-OV. By taking advantage of the "dual-locked" sensing strategy, a total of 85 samples of human serum were screened using DCI-OV based rapid disease screening method and it was capable of differentiated and subdivided patients into specific type of disease, indicating the great potential of application of DCI-OV into clinical related disease diagnosis.

A Two-Photon Fluorescent Probe for the Visual Detection of Peroxynitrite in Living Cells and Zebrafish

Peroxynitrite (ONOO−), as an important reactive oxygen species (ROS), holds great potential to react with a variety of biologically active substances, leading to the occurrence of various diseases such as cancer and neurodegenerative diseases. In this work, we developed a novel mitochondria-localized fluorescent probe, HDBT-ONOO−, which was designed as a mitochondria-targeting two-photon fluorescence probe based on 1,8-naphthylimide fluorophore and the reactive group of 4-(bromomethyl)-benzene boronic acid pinacol ester. More importantly, the probe exhibited good biocompatibility, sensitivity, and selectivity, enabling its successful application in imaging the generation of intracellular and extracellular ONOO−. Furthermore, exogenous and endogenous ONOO− products in live zebrafish were visualized. It is greatly expected that the designed probe can serve as a useful imaging tool for clarifying the distribution and pathophysiological functions of ONOO− in cells and zebrafish.

Development and Challenge of Fluorescent Probes for Bioimaging Applications: From Visualization to Diagnosis

Fluorescent probes have been used widely in bioimaging, including biological substance detection, cell imaging, in vivo biochemical reaction process tracking, and disease biomarker monitoring, and have gradually occupied an indispensable position. Compared with traditional biological imaging technologies, such as positron emission tomography (PET) and nuclear magnetic resonance imaging (MRI), the attractive advantages of fluorescent probes, such as real-time imaging, in-depth visualization, and less damage to biological samples, have made them increasingly popular. Among them, ultraviolet-visible (UV-vis) fluorescent probes still occupy the mainstream in the field of fluorescent probes due to the advantages of available structure, simple synthesis, strong versatility, and wide application. In recent years, fluorescent probes have become an indispensable tool for bioimaging and have greatly promoted the development of diagnostics. In this review, we focus on the structure, design strategies, advantages, representative probes and latest discoveries in application fields of UV-visible fluorescent probes developed in the past 3-5 years based on several fluorophores. We look forward to future development trends of fluorescent probes from the perspective of bioimaging and diagnostics. This comprehensive review may facilitate the development of more powerful fluorescent sensors for broad and exciting applications in the future.

A New Ratiometric Design Strategy Based on Modulation of π-Conjugation Unit for Developing Fluorescent Probe and Imaging of Cellular Peroxynitrite

Ratiometric fluorescent probes could effectively offset the changes of the autofluorescence and compartmental localization. FRET, ICT, etc. are the common strategies to design probes for biosensing, but these strategies have some deficiencies. Here, we proposed a new design strategy based on π-conjugation modulation, giving two different emission bands in the absence and presence of the target. The new fluorescence probe named Rhod-DCM-B was rationally designed and synthesized, which displayed a fluorescence emission peak at 670 nm because the electron cloud focuses on the conjugated DCM unit. With the addition of ONOO^-, the fluorescence emission at 570 nm increased, accompanied by the decrease of fluorescence emission at 670 nm, showing a ratiometric signal change attributed to the opened spirane structure making the electron cloud concentrated on the xanthene core. The mechanism is well confirmed by MS and DFT calculations. Rhod-DCM-B exhibited outstanding sensitivity and excellent selectivity toward ONOO^-. Moreover, Rhod-DCM-B was effectively employed to determine endogenous and exogenous ONOO^- in living cells. As a marker for inflammation and drug-induced liver injury (DILI) process, ONOO^- in vivo was successfully monitored by Rhod-DCM-B and presented a dramatic ratiometric response.

A coumarin-based reversible two-photon fluorescence probe for imaging glutathione near N-methyl-D-aspartate (NMDA) receptors

Glutathione (GSH) is known to play a key role in the modulation of the redox environment in N-methyl-d-aspartate (NMDA) receptors. Coumarin derivative 1 bearing cyanoacrylamide and ifenprodil moieties was synthesized and reported to monitor GSH near NMDA receptors. The cyanoacrylamide moiety allows probe 1 to monitor GSH reversibly at pH 7.4 and the ifenprodil group acts as a directing group for NMDA receptors. Two-photon fluorescence microscopy allows probe 1 to successfully sense endogenous GSH in neuronal cells and hippocampal tissues with excitation at 750 nm. Furthermore, the addition of H₂O₂ and GSH induced a decrease and an increase in fluorescence emission. Probe 1 can serve as a potential practical imaging tool to get important information on GSH in the brain.

A novel fast-response and highly selective AIEgen fluorescent probe for visualizing peroxynitrite in living cells, C. elegans and inflammatory mice

Most of the ONOO^- fluorescent probes have restricted applications because of their aggregation-caused quenching (ACQ) effect, long response time and low fluorescence enhancement. Herein, we developed a novel AIEgen fluorescent probe (PE-XY) based on a benzothiazole and quinolin scaffold with high sensitivity and selectivity for imaging of ONOO^-. The results indicated that probe PE-XY exhibited fast response towards ONOO^- with 2000-fold enhancement of fluorescence intensity ratio in vitro. Moreover, PE-XY exhibited a relatively high sensitivity (limit of detection: 8.58 nM), rapid response (<50 s), high fluorescence quantum yield (δ = 0.81) and excellent selectivity over other analytes towards ONOO^-in vitro. Furthermore, PE-XY was successfully applied to detect endogenous ONOO^- levels in living HeLa cells, C. elegans and inflammatory mice with low cytotoxicity. Overall, this work provided a novel fast-response and highly selective AIEgen fluorescent probe for real-time monitoring ONOO^- fluctuations in living systems.

Construction of a near-infrared fluorescent probe for ratiometric imaging of peroxynitrite during tumor progression

Malignant tumors are one of the main causes for human death and are tightly associated with overexpression of reactive oxygen species (ROS) in pathological processes. Therefore, in vivo monitoring of ROS, especially ONOO-, remains of great significance for diagnosis and therapy of tumors to improve the survival rate. Herein, we designed and constructed a reliable near-infrared (NIR) ratiometric fluorescent biosensor CDMS for monitoring the fluctuations of ONOO- in the process of tumor progression. CDMS featured outstanding stability to photoirradiation, substantial quantum yields, rapid response (<5 s), high selectivity and excellent biocompatibility. Moreover, CDMS exhibited distinct ratiometric fluorescence signal changes after reacting with ONOO-. Fluorescence imaging in immune stimulated cells indicated that CDMS was competent to determine the levels of ONOO- in the cellular level. Remarkably, CDMS was further applied in monitoring the expression of ONOO- in a peritonitis mouse model and tumor-bearing mouse model. Based on the excellent properties of CDMS, the probe exhibited the potential for noninvasive in vivo visualization of ONOO- in the occurrence and process of tumor development. It is envisioned that CDMS can be employed as a promising tool for monitoring the ONOO- fluxes in tumor pathological progression, especially for tumor diagnosis and therapy.

Two-photon fluorescent probe for cellular peroxynitrite: Fluorescence detection, imaging, and identification of peroxynitrite-specific products

A new naphthalene-based boronate probe, NAB-BE, for the fluorescence-based detection of inflammatory oxidants, including peroxynitrite, hypochlorous acid, and hydrogen peroxide, is reported. The chemical reactivity and fluorescence properties of the probe and the products are described. The major, phenolic oxidation product, NAB-OH, is formed in case of all three oxidants tested. This product shows green fluorescence, with a maximum at 512 nm, and can be excited either at 340 nm or in the near infrared region (745 nm) for two-photon fluorescence imaging. Peroxynitrite is the fastest of the oxidants tested and, in addition to the phenolic product, leads to the formation of a nitrated product, NAB-NO₂, which can serve as a fingerprint for peroxynitrite. The probe was applied to detect peroxynitrite in activated macrophages using fluorimetry and two-photon fluorescence microscopy, and both NAB-OH and NAB-NO₂ products were detected in cell extracts by liquid chromatography-mass spectrometry. The combined use of fluorometric high-throughput analyses, fluorescence imaging, and liquid chromatography-mass spectrometry-based product identification and quantitation is proposed for most comprehensive and rigorous characterization of oxidants in biological systems.

N-hydroxypropyl substituted 4-hydroxynaphthalimide: Differentiation of solvents and discriminative determination of water in organic solvents

A naphthalimide-based fluorophore (HONIOH) was designed by introducing a hydroxy unit into the 4th position of the aromatic core and a hydroxypropyl unit into the N-imide site. Photophysical properties of HONIOH were highly dependent on solvents, which was ascribed to the excited state proton transfer (ESPT) coupled with intramolecular charge transfer (ICT) mechanism. Further studies demonstrated that HONIOH can be used to recognize N, N-dimethylformamide (DMF) qualitatively and differentiate methanol from ethanol. Three control compounds were synthesized, their photophysical properties were investigated in various solvents, and experimental results revealed that hydroxyl and hydroxypropyl units contribute to the solvents differentiation ability of HONIOH. In addition, HONIOH was successfully applied as a colorimetric, fluorescent probe for the discriminative detection of trace water in organic solvents, such as fluorescence turn-on response accompanied by fluorescent color changes from light yellow to purple in DMF, and fluorescence turn-off response and blue to yellow fluorescent color changes in acetonitrile, tetrahydrofuran, and acetone. We believe that N-substituted 4-hydroxynaphthalimide derivatives may find widespread applications in chemical and biochemical sensing and imaging.

A mitochondria-targeted ratiometric fluorescent nanoprobe for imaging of peroxynitrite in living cells

Peroxynitrite (ONOO^-) is a series of basic biological oxidants involved in physiological and pathological processes. The detection of ONOO^- in biological systems has been challenging due to its extremely short half-life and low steady-state concentration. In this work, a ratiometric fluorescent nanoprobe for ONOO^- was constructed by coupling covalently of graphene quantum dots (GQDs) with cyanine 5.5 (Cy5.5). This nanoprobe (GQD-Cy5.5) could selectively accumulate in mitochondrial, appears two strong fluorescence emission peaks at 520 and 694 nm. In the presence of ONOO^-, the intensity of fluorescence emission peak at 520 nm increased and the intensity of fluorescence emission peak at 694 nm decreased. The ratio (F_{520 nm}/F_{694 nm}) of fluorescence intensity at two emission peaks had a good linear relationship with the concentration of ONOO^- in the range of 0-6.0 μM, and the detection limit was 0.03 μM. The excellent properties of the nanoprobe enable its applications in the ratiometric fluorescence imaging of endogenous ONOO^- in cell mitochondria.

Gold nanoparticle integrated artificial nanochannels for label-free detection of peroxynitrite

A label-free method for rapid and highly sensitive detection of peroxynitrite (ONOO^-) was proposed by employing well-designed N-(4-aminobutyl)-N-ethylisoluminol (ABEI) capped AuNP integrated artificial nanochannels. This work paves a new pathway to develop a versatile platform for the detection of different biological small molecules and reactive species.

Nanoliposomal Ratiometric Fluorescent Probe toward ONOO- Flux

Peroxynitrite (ONOO^-), a powerful biological oxidant, is produced in the mitochondria and reacts with many biomolecular targets under various pathological conditions, leading to a range of disease states. In this work, we developed a nanoliposome-encapsulated ratiometrically fluorescent probe (NRF) based on a hemicyanine structure Cy-O obtained by facile synthesis. Upon reaction with ONOO^-, the oxidation and hydrolysis of a π-conjugation system within the nanoliposome triggers a ratiometrically fluorescent response and a large-scale emission shift (238 nm), which provides a specific and sensitive means for the ONOO^- detection. Moreover, we have performed DFT calculation at the 6-31+G(d,p) level using a suite of Gaussian 09 programs to obtain insights into the chemical structure optical properties of Cy-O. In addition, the practical applications of the nanoprobe to image exogenous and endogenous ONOO^- were achieved further in live cells and animals triumphantly.

ICT-based fluorescent ratiometric probe for monitoring mitochondrial peroxynitrite in living cells

Mitochondria-targeted near-infrared fluorescent probe for the detection of peroxynitrite and the bioimaging of peroxynitrite in cells.

Critical Evaluation of the Interaction of Reactive Oxygen and Nitrogen Species with Blood to Inform the Clinical Translation of Nonthermal Plasma Therapy

Non-thermal plasma (NTP), an ionized gas generated at ambient pressure and temperature, has been an emerging technology for medical applications. Through controlled delivery of reactive oxygen and nitrogen species (ROS/RNS), NTP can elicit hormetic cellular responses, thus stimulating broad therapeutic effects. To enable clinical translation of the promising preclinical research into NTP therapy, a deeper understanding of NTP interactions with clinical substrates is profoundly needed. Since NTP-generated ROS/RNS will inevitably interact with blood in several clinical contexts, understanding their stability in this system is crucial. In this study, two medically relevant NTP delivery modalities were used to assess the stability of NTP-generated ROS/RNS in three aqueous solutions with increasing organic complexities: phosphate-buffered saline (PBS), blood plasma (BP), and processed whole blood. NTP-generated RNS collectively (NO2 -, ONOO-), H2O2, and ONOO- exclusively were analyzed over time. We demonstrated that NTP-generated RNS and H2O2 were stable in PBS but scavenged by different components of the blood. While RNS remained stable in BP after initial scavenging effects, it was completely reduced in processed whole blood. On the other hand, H2O2 was completely scavenged in both liquids over time. Our previously developed luminescent probe europium(III) was used for precision measurement of ONOO- concentration. NTP-generated ONOO- was detected in all three liquids for up to at least 30 seconds, thus highlighting its therapeutic potential. Based on our results, we discussed the necessary considerations to choose the most optimal NTP modality for delivery of ROS/RNS to and via blood in the clinical context.

Visualization of ONOO- and Viscosity in Drug-Induced Hepatotoxicity with Different Fluorescence Signals by a Sensitive Fluorescent Probe

Drug-induced liver injury (DILI) is considered gradually as a serious public health issue, and hepatotoxicity has been regarded as the main clinical problem caused by it. We suspected that both the intracellular viscosity and peroxynitrite (ONOO^-) levels in drug-induced hepatotoxicity tissue are higher than those in a healthy liver. For this reason, we have presented a fluorescent probe VO for multichannel imaging viscosity and ONOO^- simultaneously. Experimental results showed that VO has satisfactory detection performance for both viscosity and ONOO^-, and based on the advantages of its lower cytotoxicity and pH-stabilities, VO was successfully employed to image viscosity and ONOO^- in living cells and animals. More importantly, we use the probe to successfully showcase drug-induced hepatotoxicity by imaging viscosity and ONOO^- induced by acetaminophen (APAP). All the results indicate that VO has great potential for the detection of viscosity and ONOO^- and to assay drug-induced hepatotoxicity. Overall, this work offers a new detection tool/method for a deeper understanding of drug-induced organism injury.

A two-photon excited near-infrared fluorescent probe for imaging peroxynitrite during drug-induced hepatotoxicity and its remediation

Drug-induced liver injury (DILI) has been a hot issue of public health, owing to its unpredictability and serious harm to public health. Peroxynitrite (ONOO^-) is an important biomarker for the assessment and diagnosis of DILI. In this article, based on a kind of rhodamine analogue with a near-infrared (NIR) emission (610 nm-800 nm) and a two-photon absorption cross section (54 GM), a two-photon excited NIR fluorescence probe (NIR-ONOO) for ONOO^- was developed. With a high selectivity and a high sensitivity to ONOO^-, NIR-ONOO has a linear range for detection of ONOO^- from 5.0 × 10^-8 to 1.0 × 10^-5 M, a good detection limit (15 nM) and a large fluorescence enhancement (340-fold). In addition, NIR-ONOO has been used to monitor ONOO^- in cells with satisfactory results. Because of its two-photon excied NIR emission, NIR-ONOO also showed excellent performances for imaging ONOO^- including low autofluorescence, stable and persistent fluorescence, and a deep penetration (204 μm). Finally, NIR-ONOO was successfully employed to image ONOO^- in inflammatory mouse, drug-induced hepatotoxicity in cells and its remediation. All the results indicated that NIR-ONOO is a powerful chemical tool to image ONOO^- and assay drug-induced hepatotoxicity.

Real-time monitoring and accurate diagnosis of drug-induced hepatotoxicity in vivo by ratio-fluorescence and photoacoustic imaging of peroxynitrite

Because of the low tissue penetration depth and poor photostability of organic cyanine dye, in addition to environmental interference, it is a great challenge to monitor the degree of drug-induced hepatotoxicity by the in vivo detection of peroxynitrite (ONOO-). Herein, we fabricated heptamethine cyanine dye (P-cy7)-coordinated upconversion nanoparticles (UCNPs), namely UCY7, as a fluorescent nanoprobe for evaluating drug-induced hepatotoxicity. Due to the luminescence resonance energy transfer (LRET) between UCNPs and the cyanine dye (P-cy7), the irradiation changed from visible light at 660 nm to near infrared (NIR) light at 980 nm; therefore, the issues of poor photostability and severe photobleaching of cyanine dye can be effectively solved. After injecting via the tail vein, the nanoprobes are rapidly concentrated in the liver. Since the level of ONOO- is up-regulated during the drug-induced liver injury, the LRET between UCNPs and P-cy7 is disrupted to release the upconversion luminescence at 656 nm, while the upconversion luminescence at 800 nm remains constant, thus achieving the ratio-fluorescent imaging (RFLI) of ONOO- in the liver to calibrate the influence of the environment. In addition, the reduction in the absorption of nanoprobes in the presence of ONOO- allows for sensitive photoacoustic imaging (PAI). Based on the RFLI and PAI of the liver, the real-time monitoring and accurate diagnosis of different degrees of hepatotoxicity using the model of Acetaminophen (APAP) induction was achieved successfully, providing a new approach for the clinical evaluation of drug-induced hepatotoxicity.

A novel electrochemical sensor based on microporous polymeric nanospheres for measuring peroxynitrite anion released by living cells and studying the synergistic effect of antioxidants

Peroxynitrite anion (ONOO-) is a crucial reactive nitrogen species (RNS), which has aroused immense research interest in the biological and biomedical fields because aberrant expression levels of ONOO- are related to many diseases. In this work, a novel electrochemical sensor is described for the detection of peroxynitrite anion (ONOO-) released from living cells. It is constructed with a glassy carbon electrode (GCE) decorated with a nanocomposite (CTS-MPNS) synthesized from chitosan (CTS) functionalized microporous polymeric nanospheres (MPNS). The prepared CTS-MPNS/GCE sensor shows a supernormal manifestation in measuring ONOO- in a wide range of concentrations from 3.83 nM to 0.104 mM, and the detection limit is as low as 1.28 nM (S/N = 3), which makes it possible to detect trace amounts of ONOO- released from U87 cells. Significantly, the synergistic effect of different antioxidants on scavenging ONOO- in biological systems is further studied by an electrochemical method for the first time, which provides an efficient strategy for protecting cells against oxidative stress. The developed platform and the efficient strategy may pave the way for their future applications in the field of biomedicine and the treatment of cancer diseases.

A novel pyridinium-based fluorescent probe for ratiometric detection of peroxynitrite in mitochondria

Peroxynitrite (ONOO^-) is a primary kind of reactive oxygen species. Excessive ONOO^- can induce oxidative damage to biomolecules and further results in various diseases. So, quantitative monitoring ONOO^- with excellent selectivity and sensitivity is imperative for elucidating its role in biological processes. In this study, a novel pyridinium fluorescent ONOO^- probe (CPC) has been constructed base on ICT-modulated by combining coumarin fluorophore and diphenylphosphinate recognition group. The fluorescence response of CPC for ONOO^- is realized via the removal of diphenylphosphinate group. The probe CPC shows prominent features for detection of ONOO^- including fast response rate (within 3 min), excellent selectivity and sensitivity, distinct colorimetric (red to green), and a large emission wavelength shift (105 nm). The emission intensity ration (I₅₃₈/I₆₄₃) exhibits 153-fold enhancement along with the increasing ONOO^- and the detection limit is as low as 1.60 × 10^-8 M. These good response properties make CPC possible to quantitative detection of ONOO^- concentration. By using the strategy, the ratiometric CPC has been employed to detection of mitochondrial ONOO^- in live cell successfully.

Ultrafast Detection of Peroxynitrite in Parkinson's Disease Models Using a Near-Infrared Fluorescent Probe

Parkinson's disease (PD) is a neurodegenerative disease that devastatingly affects people's lives. Numerous research studies have shown that peroxynitrite (ONOO^-) plays a pivotal role in the pathogenesis of PD. However, a suitable tool that could quickly and sensitively detect ONOO^- in various PD models is still lacking. To this end, we designed and synthesized a series of near-infrared probes that could detect ONOO^- within seconds by near-infrared fluorescent imaging in an ultrafast and highly selective manner. It is noteworthy that one of those developed probes, NIR-PN1, showed excellent sensing performance and blood-brain barrier penetrating ability. NIR-PN1 was successfully applied for imaging of ONOO^- fluxes in multiple PD models including PC12 cell, Drosophila, C. elegans, and mouse brain, indicating its great potential application not only for understanding the biological roles that ONOO^- played in PD but also for early PD diagnosis and treatment.

Series of Mitochondria/Lysosomes Self-Targetable Near-Infrared Hemicyanine Dyes for Viscosity Detection

Six mitochondria/lysosomes self-targetable and viscosity-sensitive dyes (1a-1f) were developed via simple structure modification on cyanine-derived dyes. They all showed remarkable OFF-ON fluorescent response to viscosity in the near-infrared region (652-690 nm) and exhibited good linear relationship with solution viscosity. The transient absorption spectra were used to evaluate the excited-state lifetime of dye 1a in different viscosity environments. Furthermore, cellular imaging assays indicated that different derivatives (1a-1f) with the same chromophore core exhibited different organelle-targeting abilities. Among them, dyes 1a-1c could sense lysosomal viscosity fluctuations while dyes 1d-1f could be applied in mitochondrial viscosity detections.

Observation of peroxynitrite overproduction in cells during 5-fluorouracil treatment via a ratiometric fluorescent probe

We describe a colorimetric and fluorescent probe 3a to detect cellular peroxynitrite with high selectivity and sensitivity. 3a was successfully applied in the bioimaging of exogenous and endogenous peroxynitrite in living cells. The up-regulation of peroxynitrite in cancer cells and normal cells during 5-fluorouracil treatment was finally monitored.

Synthesis of Small Fluorescent Molecules and Evaluation of Photophysical Properties

A series of aniline-based fluorophores were newly synthesized. To increase their fluorescence quantum yields, it was particularly important to substitute 3,3,3-trifluoroprop-1-enyl (TFPE) groups next to the amino group to benefit from an extended π-electron delocalization. Among these, 5-CN-2-TFPE-aniline was found to behave as an excellent fluorophore with a reasonable fluorescence quantum yield of 0.89 even in aqueous solution. l-Alanine peptide, a nonfluorescent analogue of 5-CN-2-TFPE-aniline, was synthesized and successfully employed as an enzyme probe to detect aminopeptidase N activity.

FRET-based sensor for visualizing pH variation with colorimetric/ratiometric strategy and application for bioimaging in living cells, bacteria and zebrafish

Acid–base balance plays a key role in regulating biological processes, and the cells must stabilize the pH within a certain range, and pH instability will cause a series of diseases.

Product-boosted fluorescence signal: a new approach for designing small-molecule probes for detection of peroxynitrite

In situ self-assembled boronate ester comprising commercially available 2-formylphenylboronic acid and 2-(2′,3′-bihydroxyphenyl)benzothiazole (BHBT) is explored for the detection of ONOO⁻ with product-boosted fluorescence.

Azulene-Derived Fluorescent Probe for Bioimaging: Detection of Reactive Oxygen and Nitrogen Species by Two-Photon Microscopy

Two-photon fluorescence microscopy has become an indispensable technique for cellular imaging. Whereas most two-photon fluorescent probes rely on well-known fluorophores, here we report a new fluorophore for bioimaging, namely azulene. A chemodosimeter, comprising a boronate ester receptor motif conjugated to an appropriately substituted azulene, is shown to be an effective two-photon fluorescent probe for reactive oxygen species, showing good cell penetration, high selectivity for peroxynitrite, no cytotoxicity, and excellent photostability.

A time-resolved near-infrared phosphorescent iridium(iii) complex for fast and highly specific peroxynitrite detection and bioimaging applications

Peroxynitrite (ONOO^-), one of the reactive oxygen/nitrogen species (ROS/RNS) found in vivo, plays crucial roles in many physiological and pathological processes. The ability to selectively and sensitively determine ONOO^-in vivo is important for the understanding of its biological roles. Thus, by utilizing the excellent chemical stability and photostability, high luminescence efficiency, and long luminescence lifetime of iridium complexes, we developed a novel near-infrared (NIR) phosphorescent iridium(iii) complex (FNO2) probe to detect ONOO^- within seconds. The probe FNO2 showed better selectivity towards ONOO^- over other interfering biomolecules, including O₂^- and ClO^-. Moreover, it possessed a long luminescence lifetime, which enabled successful elimination of the interference from background fluorescence in vitro (simulated by Rhodamine B) in time-resolved emission spectra. Finally, in addition to its low cytotoxicity, the probe FNO2 showed emission wavelength in the NIR region and was able to specifically sense ONOO^- induced in living cells and inflamed mouse models.

A highly selective and sensitive red-emitting fluorescent probe for visualization of endogenous peroxynitrite in living cells and zebrafish

Peroxynitrite (ONOO-) has been proven to participate in various physiological and pathological processes, and may also be a contributing factor in many diseases. In view of this, there is a need to develop detection tools for unambiguously tracking a small amount of endogenous ONOO- to reveal its exact mechanisms. In this paper, a colorimetric and red-emitting fluorescent probe Red-PN, based on a rhodamine-type fluorophore and hydrazide reactive site is described. The probe Red-PN possesses the advantages of rapid response (within 5 s), visual color change (from colorless to pink), preeminent sensitivity (detection limit = 4.3 nM) and selectivity. Because of these outstanding performances, it was possible to accurately detect endogenous ONOO-. It was encouraging that the probe Red-PN could be used effectively for tracking the relatively low levels of endogenous and exogenous ONOO- in living cells and zebrafish. Thus, it is envisioned that the probe Red-PN would have promising prospects in applications for imaging ONOO- in a variety of biological settings.

Novel Dimethylhydrazine-Derived Spirolactam Fluorescent Chemodosimeter for Tracing Basal Peroxynitrite in Live Cells and Zebrafish

The precise cellular function of peroxynitrite (ONOO^-) in biosystems remains elusive, primarily owing to being short of ultrasensitive techniques for monitoring its intracellular distribution. In this work, a novel rhodamine B cyclic 1,2-dimethylhydrazine fluorescent chemodosimeter RDMH-PN for highly specific and ultrasensitive monitoring of basal ONOO^- in biosystems was rationally designed. The fluorescence titration experiments demonstrated that RDMH-PN was capable of quantitatively detecting 0-100 nM ONOO^- (limit of detection = 0.68 nM). In addition, RDMH-PN has outstanding performances of ultrafast measurement, naked-eye detection, and preeminent selectivity toward ONOO^- to accurately detect intracellular basal ONOO^-. Finally, it has been confirmed that RDMH-PN could not only map the intracellular basal ONOO^- level by inhibition tests but also trace the fluctuations of endogenous and exogenous ONOO^- levels with diverse stimulations in live cells and zebrafish.

Two-Photon Probes for Golgi Apparatus: Detection of Golgi Apparatus in Live Tissue by Two-Photon Microscopy

We have developed blue- and yellow-emitting two-photon probes (BGolgi-blue and PGolgi-yellow) from 6-(benzo[ d]oxazol-2-yl)-2-naphthalylamine and 2,5-bis(benzo[ d]oxazol-2-yl)pyrazine derivatives as the fluorophores and trans-Golgi-network peptide (SDYQRL) as the Golgi-apparatus-targeting moiety. HeLa cells labeled with BGolgi-blue and PGolgi-yellow emitted two-photon-excited fluorescence at 462 and 560 nm, respectively, with effective two-photon-action cross-section values of 1860 and 1600 × 10^-50 cm⁴·s/photon, respectively. The probes can detect the Golgi apparatus in live cells and deep inside live tissue via two-photon microscopy at widely separated wavelength regions with high selectivity and minimal pH interference, and they are photostable and have low cytotoxicity.