Dimethyl Dihydrophenazine: A Highly Conjugated Auxochrome in Fluorophores to Improve Photostability, Red-Shift Wavelength, and Enlarge Stokes Shift.

5,10-Dimethyl-5,10-dihydrophenazine (MP) is utilized as an effective auxochrome, leveraging its highly conjugated structure to enhance the photophysical and photochemical properties of fluorophores. As illustrated in the difluoride-boron complex and coumarin fluorophores, the extensive conjugation of MP auxochrome substantially red-shifts the absorption/emission wavelengths and increases Stokes shift due to the intensified intramolecular charge transfer effect; notably, MP auxochrome effectively improves fluorophores' photostability by mitigating photooxidative reactions through enhanced electron density delocalization on nitrogen atoms and increased ionization potential. Importantly, MP-based fluorophores demonstrate applicability in stimulated emission depletion nanomicroscopy, showcasing their utility in lipid droplet labeling.

Carbon Monoxide: A Second Biomarker to Couple with Viscosity for the Construction of "Dual-Locked" Near-Infrared Fluorescent Probes for Accurately Diagnosing Non-Alcoholic Fatty Liver Disease.

Nonalcoholic fatty liver disease (NAFLD) can progress to cirrhosis and liver cancer if left untreated. Therefore, it is of great importance to develop useful tools for the noninvasive and accurate diagnosis of NAFLD. Increased microenvironmental viscosity was considered as a biomarker of NAFLD, but the occurrence of increased viscosity in other liver diseases highly reduces the diagnosis accuracy of NAFLD by a single detection of viscosity. Hence, it is very necessary to seek a second biomarker of NAFLD. It has been innovatively proposed that the overexpressed heme oxygenase-1 enzyme in NAFLD would produce abnormally high concentrations of CO in hepatocytes and that CO could serve as a potential biomarker. In this work, we screened nine lactam Changsha dyes (HCO-1-HCO-9) with delicate structures to obtain near-infrared (NIR), metal-free, and "dual-locked" fluorescent probes for the simultaneous detection of CO and viscosity. Changsha dyes with a 2-pyridinyl hydrazone substituent could sense CO, and the 5-position substituents on the 2-pyridinyl moiety had a great electron effect on the reaction rate. The double bond in these dyes served as the sensing group for viscosity. Probe HCO-9 was utilized for precise diagnosis of NAFLD by simultaneous detection of CO and viscosity. Upon reacting with CO in a high-viscosity microenvironment, strong fluorescence at 745 nm of probe HCO-9 was turned on with NIR excitation at 700 nm. Probe HCO-9 was proven to be an effective tool for imaging CO and viscosity. Due to the advantages of NIR absorption and low toxicity, probe HCO-9 was successfully applied to image NAFLD in a mouse model.

Probing fluctuations in sulfur dioxide and viscosity levels during mitochondrial dysfunction using a dual-response fluorescent probe with good water solubility.

Mitochondrial dysfunction is associated with increased viscosity and reactive oxygen species (ROS) levels. As an effective antioxidant, sulfur dioxide (SO2) can actively scavenge excess ROS to regulate the redox state and protect cells from oxidative stress. However, few studies have evaluated the connection between viscosity and SO2 during mitochondrial dysfunction. Herein, a water-soluble fluorescent probe (MBI) is designed and synthesized for dual-detecting SO2 and viscosity. The probe rapidly detects SO2 within 12 s based on Michael's addition reaction. Meanwhile, increasing viscosity further inhibits the intramolecular rotation, causing the probe to show a greatly enhanced fluorescence. Probe MBI possesses mitochondria targeting capability due to its quaternary ammonium salt. More importantly, probe MBI successfully supports SO2 and viscosity imaging in living cells and can effectively monitor them during mitochondrial dysfunction and cell apoptosis.

Tackling the Selectivity Dilemma of Benzopyrylium-Coumarin Dyes in Fluorescence Sensing of HClO and SO2.

Benzopyrylium-coumarin fluorescent probes for sensing hypochlorous acid (HClO) or sulfur dioxide (SO2) are unable to distinguish between HClO and SO2 because the two compounds can react with the 4-position of benzopyrylium-coumarin dyes through the nucleophilic attack. In the current work, we introduced a phenoxazine moiety to the benzopyrylium-coumarin dye to synthesize a new fluorescent probe PBC1, which can dually sense HClO and SO2 and generate distinct fluorescence signals with rapid response time and high sensitivity and selectivity. Moreover, probe PBC1 was also successfully utilized to detect intracellular HClO and SO2 in HeLa cells and zebrafish.

A Ratiometric, Fast-Responsive, and Single-Wavelength Excited Fluorescent Probe for the Discrimination of Cys and Hcy.

The ratiometric detection of cysteine (Cys) and homocysteine (Hcy) is very challenging because of their highly similar chemical structures and properties. By introducing the phenylethynyl group into a coumarin dye as the sensing group, the ratiometric fluorescent probe CP was developed to selectively and rapidly discriminate between Cys and Hcy. With a single-wavelength excitation, the presence of Cys or Hcy induced the probe to produce distinct ratiometric fluorescence changes: from red (λmaxem = 608 nm) to blue (λmaxem = 485 nm) toward Cys and from red to mixed red/blue toward Hcy. Moreover, the probe was capable of visualizing and discriminating between intracellular Cys and Hcy in HeLa cells and zebrafish by exhibiting different ratiometric fluorescence signals.

Rational Development of Dual-Ratiometric Fluorescent Probes for Distinguishing between H2S and SO2 in Living Organisms.

For better investigating the complicated relationships between H2S and SO2, simultaneously detecting and visualizing them with good selectivity is crucial. However, most sensing mechanisms for H2S and SO2 probes are based on the addition reactions with the double bonds, which have no selectivity. In this work, by introducing an active triple bond into 4-dicyanovinyl-7-diethylamino-coumarin, we construct two unique sensors for not only distinguishing between H2S and SO2 but also sensing H2S and SO2 in a dual-ratiometric manner. Moreover, the modified sensor was successfully applied in living cells and zebrafish for discriminating H2S and SO2.

Investigation of the Relationship Between H2O2 and HClO in Living Cells by a Bifunctional, Dual-ratiometric Responsive Fluorescent Probe.

As two important reactive oxygen species, hydrogen peroxide (H2O2) and hypochlorous acid (HClO) play vital roles in many physiological and pathological processes. However, the relationship between these two species is seldom investigated, in part, because of the lack of robust molecular tools that can simultaneously visualize HClO and H2O2 in biosystems. In this work, we present a design strategy to construct a single fluorescent probe that can detect H2O2 and HClO by simultaneously monitoring two distinct detection channels. In the design, one phenothiazine-based coumarin serves as a chromophore and sensor for HClO, while a second coumarin precursor containing a boronate ester acts as a sensor for H2O2. After a head-to-head screening of three candidates differing in their coumarin precursor moieties, probe CSU1 was found to have the optimal characteristics. As shown experimentally, it is able to detect them selectively and sensitively to generate distinct fluorescence signals and patterns in living cells. Furthermore, the endogenous generation of HClO from H2O2 and Cl- catalyzed by myeloperoxidase enzyme in living cells can be clearly monitored by the probe. These studies demonstrate the potential of the probe as a powerful tool to investigate the interplay of HClO and H2O2 in oxidative stress.

Fluorescent Detection of Dynamic H2O2/H2S Redox Event in Living Cells and Organisms.

The elusive mechanism of action between signaling molecules H2O2 and H2S in oxidative stress demands a fluorescent probe, capable of their detection in a discriminative and dynamic manner. Herein we report the design and study of a probe TCAB. As demonstrated, it responds to H2O2 and H2S selectively and sensitively to generate distinct fluorescence signals and patterns. Cyan imaging for H2O2 in a ratiometric fashion and two-colored, enhanced blue and newly produced red for H2S are observed. When both are present, the sequential reaction of H2O2 and H2S with the probe gives cyan then red signal, while the reverse sequence produces an inverse red-cyan signal. The unrivaled discriminative multicolor imaging capacity of the probe enables us to monitor dynamic H2O2 and H2S redox processes in living cells and organisms. It is expected that the probe could serve as a powerful tool to investigate the correlation and distinction of biologically significant H2S- and H2O2-engaged redox processes.

Rational Design of a Two-Photon Ratiometric Fluorescent Probe for Hypochlorous Acid with a Large Stokes Shift.

By introducing the tetrahydroquinoxaline group as the electron donor to enhance intramolecular charge transfer effect, we deliberately designed a coumarin derivative, TQC-HClO, to serve as a two-photon ratiometric fluorescent probe for imaging hypochlorous acid in cells and zebra fish with good sensitivity and high selectivity. TQC-HClO displayed an obvious two-photon absorbance cross-section (over 100 GM in 800-840 nm), large Stokes shifts (159 to 173 nm), and a ratiometric fluorescence change from orange (λmaxem = 583 nm) to red (λmaxem = 650 nm) in response to hypochlorous acid.

Sensor Array Based Determination of Edman Degradated Amino Acids Using Poly(p-phenyleneethynylene)s.

A cross-reactive optical sensor array based on poly(p-phenyleneethynylene)s (PPEs) determines Edman degraded amino acids. We report a sensor array composed of three anionic PPEs P1-P3, and their electrostatic complexes with metal ions (Fe2+ , Cu2+ , Co2+ ). We recorded distinct fluorescence intensity response patterns as "fingerprints" of this chemical tongue toward standard phenylthiohydantoin (PTH) amino acids-degradation products of the Edman process. These "fingerprints" were converted into canonical scores by linear discrimination analysis (LDA), which differentiates all of the PTH-amino acids. This array discriminates PTH-amino acid residues degraded from an oligopeptide through Edman sequencing. This approach is complementary to chromatography approaches which rely on mass spectrometry; our array offers the advantage of simplicity.

A ratiometric fluorescent probe for simultaneous detection of Cys/Hcy and GSH.

GSH, Cys and Hcy are the main intracellular thiols to play crucial roles in human pathologies. It is a great challenge to differentiate these three biothiols using single molecular fluorescent probes due to their close similarities in chemical structure and reactivity. In this work, based on the fluorescence resonance energy transfer (FRET) mechanism, a fluorescent probe CPR was constructed to simultaneously distinguish GSH and Cys/Hcy by means of ratiometric fluorescence changes: from red (584 nm) to green (542 nm) for GSH and from red (584 nm) to blue (472 nm) for Cys/Hcy. This probe showed high sensitivity and selectivity with low limits of detection (LOD = 12 nm, 13 nm and 30 nm for Cys, Hcy and GSH, respectively) and was capable of imaging GSH and Cys/Hcy in cells and zebrafish in a ratiometric manner with low toxicity.

Detecting Counterfeit Brandies.

A hypothesis-free sensor array (optoelectronic tongue) composed of an anionic, a cationic and two neutral poly(para-aryleneethynylene)s (PAE) at pH 3, 7 and 13 discriminate more than 30 spirits (including brandy, Branntwein, Cognac, Spirituose, and Weinbrand). Counterfeits (made by mixing of low-quality spirits and caramel colour) and different batches of identical brands of brandies are discriminated. The sensor array works without sample preparation or great instrumental cost, and is superior to conventional methods with respect to sample need (10-20 µL), time and effort. The discrimination stems from differential fluorescence quenching of the PAE-array by the complex mixture of the beverages' colourants, from the oak barrels or added caramel colour. The collected quenching data were analysed by linear discriminant analysis (LDA) and principal component analysis (PCA) to achieve successful discrimination.

A Simple Optoelectronic Tongue Discriminates Amino Acids.

A self-assembled nine-element optoelectronic tongue consisting of a positively charged water-soluble poly(para-phenyleneethynylene) and three metal ions (Fe2+ , Co2+ , and Cu2+ ) at three different pH values (7, 10, and 13) discriminates all of the 20 natural amino acids in water. Unknown identification was not ideal. Addition of a highly positively charged green fluorescent protein in the presence of Fe2+ , Co2+ , and Cu2+ increased the unknown identification to above 86 %. Linear discriminant analysis (LDA) orders the responses according to the amino acid type, that is, hydrophobic, polar, anionic, or cationic.

Poly(p-phenyleneethynylene)-based tongues discriminate fruit juices.

We describe a simple optoelectronic tongue, consisting of a positively charged, fluorescent poly(para-phenyleneethynylene), P2, that reacts to fruit juices, when employed at three different pH-values (pH 3, 7, 13). This minimal tongue identifies and discriminates 14 different commercially available apple juices, 6 different grape juices and 5 different black currant juices from each other. A similar, negatively charged fluorescent polymer, P1, also achieved discrimination, but the analyte concentration had to be increased by a factor of 50. A mixture of black currant juice and red grape juice is identified as red grape juice, for specific combinations of grape and black currant juices. A mixture of red and green grape juice passes as red grape juice in our sensing system when it contains more than 70% of red grape juice. The data were obtained by fluorescence quenching of the conjugated polymers and processed by linear discriminant analysis of the collected data.

A Polymer/Peptide Complex-Based Sensor Array That Discriminates Bacteria in Urine.

A negatively charged poly(para-phenyleneethynylene) (PPE) forms electrostatic complexes with four positively charged antimicrobial peptides (AMP). The AMPs partially quench the fluorescence of the PPE and discriminate fourteen different bacteria in water and in human urine by pattern-based fluorescence recognition; the AMP-PPE complexes bind differentially to the components of bacterial surfaces. The bacterial species and strains form clusters according to staining properties (Gram-positive and Gram-negative) or genetic similarity (genus, species, and strain). The identification and data treatment is performed by pattern evaluation with linear discriminant analysis (LDA) of the collected fluorescence intensity data.

Fluorescent, MRI, and colorimetric chemical sensors for the first-row d-block metal ions.

Transition metals (d-blocks) are recognized as playing critical roles in biology, and they most often act as cofactors in diverse enzymes; however, improper regulation of transition metal stores is also connected to serious disorders. Therefore, the monitoring and imaging of transition metals are significant for biological research as well as clinical diagnosis. In this article, efforts have been made to review the chemical sensors that have been developed for the detection of the first-row d-block metals (except Cu and Zn): Cr, Mn, Fe, Co, and Ni. We focus on the development of fluorescent sensors (fall into three classes: "turn-off", "turn-on", and ratiometric), colorimetric sensors, and responsive MRI contrast agents for these transition metals (242 references). Future work will be likely to fill in the blanks: (1) sensors for Sc, Ti, and V; (2) MRI sensors for Cr, Mn, Co, Ni; (3) ratiometric fluorescent sensors for Cr(6+), Mn(2+), and Ni(2+), explore new ways of sensing Fe(3+) or Cr(3+) without the proton interference, as well as extend applications of MRI sensors to living systems.

Biotin-tagged fluorescent probe for in situ visualization of γ-glutamyl transpeptidase in cancerous cells and tissues.

γ-Glutamyl transpeptidase (GGT), a cell-surface enzyme, is strongly implicated in mammalian malignancy growth and migration processes including human hepatocarcinogens. However, simply and conveniently detect of GGT on the cell membrane remains highly challenging. In this study, a biotin-tagged fluorescent probe Nap-biotin-glu was developed using glutamic acid, naphthalimide, and biotin as the reaction site, fluorescent reporter, and membrane-targeting group, which required only three steps. Colocalization fluorescence imaging and immunofluorescence analysis indicated that probe Nap-biotin-glu was successfully realized in situ visualizing of GGT on the cell membrane.Owing to the significant over-expressed GGT level in tumor, the probe was successfully applied to distinguish cancer tissues from adjacent normal tissues.

Calcium-enriched carbon nanoparticles loaded with indocyanine green for near-infrared fluorescence imaging-guided synergistic calcium overload, photothermal therapy, and glutathione-depletion-enhanced photodynamic therapy.

Combining phototherapy with other treatments has significantly advanced cancer therapy. Here, we designed and fabricated calcium-enriched carbon nanoparticles (Ca-CNPs) that could effectively deplete glutathione (GSH) and release calcium ions in tumors, thereby enhancing the efficacy of photodynamic therapy (PDT) and the calcium overload effect that leads to mitochondrial dysfunction. Due to the electrostatic interaction, π-π stacking interaction, multiple hydrogen bonds, and microporous structures, indocyanine green (ICG) was loaded onto the surface of Ca-CNPs with a high loading efficiency of 44.7 wt%. The obtained Ca-CNPs@ICG can effectively improve the photostability of ICG while retaining its ability to generate singlet oxygen (1O2) and undergo photothermal conversion (Ca-CNPs@ICG vs. ICG, 45.1% vs. 39.5%). In vitro and in vivo experiments demonstrated that Ca-CNPs@ICG could be used for near-infrared fluorescence imaging-guided synergistic calcium overload, photothermal therapy, and GSH depletion-enhanced PDT. This study sheds light on the improvement of 1O2 utilization efficiency and calcium overload-induced mitochondrial membrane potential imbalance in tumor cells.

An estradiol-functionalized red-emissive photosensitizer for enhanced and precise photodynamic therapy of breast cancers.

In this work, we developed a red-absorbing photosensitizer (NBS-ER) with specific targeting ability toward estrogen receptors (ER). NBS-ER could specifically bind the overexpressed ER in breast cancers to increase its accumulation, thereby amplifying the photodynamic therapeutic effect. With the aid of red fluorescence from NBS-ER, imaging-guided therapy could be achieved.

Correction: Copper coordination-based conjugated polymer nanoparticles for synergistic photodynamic and chemodynamic therapy.

Correction for 'Copper coordination-based conjugated polymer nanoparticles for synergistic photodynamic and chemodynamic therapy' by Qiang Cheng et al., Chem. Commun., 2023, https://doi.org/10.1039/d3cc01107k.