FLUORESCENCE OF SOLUTIONS: A REVIEW

Alternate recognition by dengue protease: Proteolytic and binding assays provide functional evidence beyond an induced-fit

Proteases are key enzymes in viral replication, and interfering with these targets is the basis for therapeutic interventions. We previously introduced a hypothesis about conformational selection in the protease of dengue virus and related flaviviruses, based on conformational plasticity noted in X-ray structures. The present work presents the first functional evidence for alternate recognition by the dengue protease, in a mechanism based primarily on conformational selection rather than induced-fit. Recognition of distinct substrates and inhibitors in proteolytic and binding assays varies to a different extent, depending on factors reported to influence the protease structure. The pH, salinity, buffer type, and temperature cause a change in binding, proteolysis, or inhibition behavior. Using representative inhibitors with distinct structural scaffolds, we identify two contrasting binding profiles to dengue protease. Noticeable effects are observed in the binding assay upon inclusion of a non-ionic detergent in comparison to the proteolytic assay. The findings highlight the impact of the selection of testing conditions on the observed ligand affinity or inhibitory potency. From a broader scope, the dengue protease presents an example, where the induced-fit paradigm appears insufficient to explain binding events with the biological target. Furthermore, this protein reveals the complexity of comparing or combining biochemical assay data obtained under different conditions. This can be particularly critical for artificial intelligence (AI) approaches in drug discovery that rely on large datasets of compounds activity, compiled from different sources using non-identical testing procedures. In such cases, mismatched results will compromise the model quality and its predictive power.

Medicinal plant extracts interfere in gastric cancer stem cells fluorescence-based assays

Fluorescence is used in various biological assays due to its high sensitivity, versatility, and precision. In recent years, studies using medicinal plant extracts have increased. However, fluorescence-based assays could be biased by plant metabolites autofluorescence. To address this issue, this study investigated the interference caused by methanolic extracts and chloroform fractions of three medicinal plants in three fluorescence-based assays on gastric cancer stem cells(CSC): resazurin reduction, confocal microscopy, and flow cytometry. CSC were isolated based on CD44 surface marker, incubated with methanolic extracts and chloroform fractions of Buddleja incana, Dracontium spruceanum, Piper aduncum. Resazurin assay evidenced that CSC exposed to extracts and fractions from the three plants showed significant differences in relative fluorescence units (RFU) levels (p < 0.001) compared to the unexposed groups after a 3-hour incubation. In addition, DMSO-treated CSC exposed to extracts and fractions had significantly lower fluorescence levels than living ones, but higher than extracts and fractions without cells. In confocal microscopy, cancer stem cells exposed to extracts and fractions of B. incana and P. aduncum were observed in the same emission spectra of the CSC markers. In flow cytometry, CSC exposed to extracts and fractions without any fluorescent dyes were detected in the double positive quadrants for CSC markers (CD44+/CD133 + ). Among the three plants, D. spruceanum exhibited the least interference. These results show that methanolic extracts and chloroform fractions contain autofluorescent metabolites that interfere with fluorescence-based assays. These results highlight the importance of a prior evaluation for possible fluorescence interference to avoid interpretation biases in fluorescence assays.

Fluorescence of p-hydroxyazobenzocrowns - Tautomeric equilibrium effect

The spectroscopic properties of a series of para-hydroxyazobenzocrowns, including three novel compounds, were investigated using UV-Vis absorption and emission spectroscopy. This study presents, for the first time, determined quantum yield (QY) values for macrocycles of this category, ranging between 0.122 and 0.195. The highest values were obtained for crowns bearing two phenyl substituents in benzene rings. The impact of aromatic ring substituents and macroring size on the spectral characterization (1H NMR and FTIR) of p-hydroxyazobenzocrowns was examined in consideration of the azophenol ⇄ quinone-hydrazone tautomeric equilibrium. Dipole moments of p-hydroxyazobenzocrowns in the ground and excited states have been determined. The alignment between experimental findings and theoretical studies was established.

Near-Infrared Bodipy-Based Molecular Rotors for β-Amyloid Imaging In Vivo

β-amyloid (Aβ) is one of the important biomarkers for diagnosing Alzheimer's disease (AD). Many near-infrared probes based on the donor-π-acceptor structure have been developed to detect Aβ. Most reported Aβ probes are based on the N,N-dimethylamino group as the ideal donor, which is a widely accepted binding unit. As such, the development of fluorescent probes with improved binding units to detect Aβ is urgently required. Therefore, with this research three anchoring molecular rotor electron donors consisting of cyclic amines of different ring sizes are developed, namely five-membered ring (TPyr), six-membered ring (TPip), and seven-membered ring (THAI). These new anchored molecular rotors are connected to a 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY) and named TPyrBDP, TPipBDP, and THAIBDP. These probes exhibit high affinities (from 28 to 54 nm) for Aβ1-42 aggregates. The six-membered ring dye TPipBDP exhibits the highest signal-to-noise (75.5-fold) and higher affinity (28.30 ± 5.94 nm). TPipBDP can cross the blood-brain barrier and exhibits higher fluorescence enhancement with APP/PS1 (AD) double transgenic (Tg) mice than with wild-type (WT) mice.

Investigating the origin of laser-induced fluorescence in mannan-rich Phytelephas macrocarpa seeds before and after thermal aging

Natural polysaccharides, e.g., starch, cellulose and sodium alginate have been highlighted as unconventional chromophores owing to their chain structures containing clustered electron-rich groups and the rigidification imposed by inter/intramolecular interactions. On account of the abundant hydroxyl groups and dense packing of low-substituted (< 5 %) mannan chains, we have investigated the laser-induced fluorescence of mannan-rich vegetable ivory seeds (Phytelephas macrocarpa), both in the native state and after thermal aging. The untreated material emitted fluorescence at 580 nm (yellow-orange) when excited at 532 nm (green). This luminescence is intrinsic to the polysaccharide matrix abundant in crystalline homomannan, as demonstrated by lignocellulosic analyses, fluorescence microscopy, NMR, Raman, FTIR and XRD. Thermal aging at 140 °C and above intensified the yellow-orange fluorescence and caused the material to fluoresce when excited by a near-infrared laser (785 nm). In view of the clustering-triggered emission mechanism, the fluorescence of the untreated material can be attributed to hydroxyl clusters and the conformational rigidification in mannan I crystals. On the other hand, thermal aging caused dehydration and oxidative degradation of mannan chains, inducing the substitution of hydroxyl groups by carbonyls. These physicochemical changes may have affected cluster formation and increased conformational rigidification, enhancing fluorescence emission.

Metal-Peptide Complexes with Antimicrobial Potential for Cotton Fiber Protection

A study of the formation of copper (II) complexes with hemorphin peptide motifs in alkalic water solutions is presented. The effect of the peptide ligand on the complexing properties of the Cu (II) ion was quantified by giving the stoichiometry and stability of the complex compounds in the medium in which they are formed using voltammetric (cyclic) and spectral (UV-Vis and fluorimetric) analytical techniques. The resulting complexes were examined via IR spectroscopy to detect M-N and M-O oscillations and using the EPR approach in solution and in the solid phase to view the coordination and ligand binding regime. The possibility of the synergistic action of copper ions in the antivirus protection processes of cotton fibers coated in the same solvent with the newly obtained complex compounds was also investigated. One of the advantages is the formation of the complexes in an environment where the immobilization takes place, which contributes to increasing the efficiency of the process. The obtained results may serve as an aid for future more detailed biological studies of structure-activity relationships (SARs).

Functionalization of 7-Hydroxy-pyranoflavylium: Synthesis of New Dyes with Extended Chromatic Stability

This work reports the functionalization of pyranoflavyliums pigment using 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride coupling chemistry. Four cinnamic acids were used to establish an ester bond with the hydroxyl group of the pyranoflavylium, namely 4-dimethylamino-, 4-amino-, 4-bromo-, and trans-cinnamic acids. The experimental condition, namely the molar ratios, solvent, and reaction time, were adjusted to obtain higher reaction yields in a reduced period. Excellent reaction yields of 68%, 85%, 94%, and 99% were achieved for 4-amino, trans-, 4-bromo, and 4-dimethylamino pyranoflavylium cinnamates, respectively. The structure of the functionalized pigments was fully clarified using one-dimensional (1H) and two-dimensional (COSY, HSQC, and HMBC) NMR experiments and HRSM analysis. Regardless of the type of functionalization, the UV-Visible spectrum showed a bathochromic shift (red region) on the maximum absorption wavelength and the absence of acid-base reactions throughout a broad pH range in comparison to the pyranoflavylium precursor. This work offers a valuable environmentally friendly, quick, and straightforward alternative to flavylium compounds' challenging and labor-intensive functionalization, resulting in novel dyes with higher stability and dissimilar chromatic features.

Fabrication of succinate-alginate xerogel films for in vitro coupling of osteogenesis and neovascularization

The osseointegration of metallic implants is reliant on a cascade of molecular interactions and the delivery of macromolecules to the implant environment that occurs before substantial bone formation. Early blood vessel formation is a requisite first step in the healing timeline for osteoid formation, where vascular development can be accelerated as a result of controlled hypoxic conditioning. In this study, alginate-derived xerogel films containing varied concentrations of disodium succinate salt which has been shown to induce pseudohypoxia (short-term hypoxic effects while maintaining an oxygenated environment) were developed. Xerogels were characterized for their morphology, succinate release over time and cellular response with osteoblast-mimicking Saos-2 and human umbilical vein endothelial cells (HUVEC). Scanning electron microscopy revealed a multiscale topography that may favour osseointegration and alamarBlue assays indicated no cytotoxic effects during in vitro proliferation of Saos-2 cells. pH measurements of eluted succinate reach 95 % of peak value after 7 h of immersion for all gels containing 10 mM of succinate or less, and 60 % within the first 40 min. In vitro exposure of HUVECs to succinate-conditioned media increased the net concentration of total proteins measured by bicinchoninic acid (BCA) assay and maintains stable vascular endothelial growth factor (VEGF) and extracellular platelet-derived growth factor (PDGF) for vessel formation through comparison of enzyme-linked immunosorbent assays (ELISAs) of the culture media and cell lysate. Tube formation assays also showed a sustained increase in tube diameter across the first 48 h of HUVEC culture when succinate concentrations of 1 and 10 μM in the xerogel. Overall, the succinate-alginate films serve as a prospective organic coating for bone-interfacing implant materials which may induce temporary pseudohypoxic conditions favourable for early angiogenesis and bone regeneration in vivo at succinate concentrations of 1 or 10 μM.

Facile Conversion of the Quinone-Semicarbazone Chromophore of Naftazone into a Fluorescent Quinol-Semicarbazide: Kinetic Study and Analysis of Naftazone in Pharmaceuticals and Human Serum

Naftazone is a quinone-semi carbazone drug that possesses a strong orange color, and hence it was usually analyzed colorimetrically or by HPLC-UV. However, these methods are not sensitive enough to determine naftazone in biological samples. Naftazone lacks intrinsic fluorescence and does not possess easily derivatizable functional groups. In this contribution, we introduced the first spectrofluorimetric method for naftazone assay through reduction-elicited fluorogenic derivatization through the reduction of its quinone-semicarbazone moiety to the corresponding quinol-semicarbazide derivative by potassium borohydride as a reduction probe. The solvent-dependent fluorescence of the reaction product was studied in various protic and aprotic solvents. Eventually, the fluorescence of the reduced naftazone was measured in 2-propanol at λ_emission of 350 nm after excitation at λ_ecxitation of 295 nm. The relative fluorescence intensity was linearly correlated to the drug concentration (r = 0.9995) from 10.0 to 500 ng/mL with high sensitivity, where the lower detection limit was 2.9 ng/mL. Hence, the method was effectively applied for naftazone tablets quality control with a mean %recovery of 100.3 ± 1.5, and the results agreed with those of the comparison HPLC-UV method. Furthermore, a new salting-out assisted liquid-liquid extraction (SALLE) method was established for naftazone extraction from human serum, followed by its determination using the developed reduction-based fluorogenic method. The developed SALLE method showed excellent recovery for naftazone from human serum (92.3-106.5%) with good precision (RSD ≤ 6.8%). Additionally, the reaction of naftazone with potassium borohydride was kinetically monitored, and it was found to follow pseudo-first-order kinetics with an activation energy of 43.8 kcal/mol. The developed method's greenness was approved using three green analytical chemistry metrics.

Near-Infrared Fluorescent Probes as Imaging and Theranostic Modalities for Amyloid-Beta and Tau Aggregates in Alzheimer's Disease

A person suspected of having Alzheimer's disease (AD) is clinically diagnosed for the presence of principal biomarkers, especially misfolded amyloid-beta (Aβ) and tau proteins in the brain regions. Existing radiotracer diagnostic tools, such as PET imaging, are expensive and have limited availability for primary patient screening and pre-clinical animal studies. To change the status quo, small-molecular near-infrared (NIR) probes have been rapidly developed, which may serve as an inexpensive, handy imaging tool to comprehend the dynamics of pathogenic progression in AD and assess therapeutic efficacy in vivo. This Perspective summarizes the biochemistry of Aβ and tau proteins and then focuses on structurally diverse NIR probes with coverages of their spectroscopic properties, binding affinity toward Aβ and tau species, and theranostic effectiveness. With the summarized information and perspective discussions, we hope that this paper may serve as a guiding tool for designing novel in vivo imaging fluoroprobes with theranostic capabilities in the future.

Wearable Smart Contact Lenses for Continual Glucose Monitoring: A Review

Diabetes mellitus is a chronic disease requiring a careful management to prevent its collateral complications, such as cardiovascular and Alzheimer's diseases, retinopathy, nephropathy, foot and hearing impairment, and neuropathy. Self-monitoring of blood glucose at point-of-care settings is an established practice for diabetic patients. However, current technologies for glucose monitoring are invasive, costly, and only provide single snapshots for a widely varying parameter. On the other hand, tears are a source of physiological information that mirror the health state of an individual by expressing different concentrations of metabolites, enzymes, vitamins, salts, and proteins. Therefore, the eyes may be exploited as a sensing site with substantial diagnostic potential. Contact lens sensors represent a viable route for targeting minimally-invasive monitoring of disease onset and progression. Particularly, glucose concentration in tears may be used as a surrogate to estimate blood glucose levels. Extensive research efforts recently have been devoted to develop smart contact lenses for continual glucose detection. The latest advances in the field are reviewed herein. Sensing technologies are described, compared, and the associated challenges are critically discussed.

Fluorene-Based Fluorometric and Colorimetric Conjugated Polymers for Sensitive Detection of 2,4,6-Trinitrophenol Explosive in Aqueous Medium

Nitroaromatic explosives are a class of compounds that are responsible for various health hazards and terrorist outrages. Among these, sensitive detection of 2,4,6-trinitrophenol (TNP) explosive has always been highly desirable considering public health and national security. In this regard, three fluorene-based conjugated polymers (CP 1, CP 2, and CP 3) were synthesized through the Suzuki-Miyaura coupling reaction and were found to be highly sensitive for fluorescence detection of TNP with detection limits of 3.2, 5.7, and 6.1 pM, respectively. Excellent selectivity of CPs toward TNP was attributed to their unique π-π interactions based on fluorescence studies and density functional theory (DFT) calculations. The high sensitivity of CPs to TNP was attributed to the static quenching mechanism based on the photoinduced electron transfer process and was evaluated by fluorescence, UV-visible absorption, dynamic light scattering, Job's plots, the Benesi-Hildebrand plots, and DFT calculations. CPs were also used for colorimetric and real-water sample analysis for the detection of TNP explosive. Meanwhile, sensor-coated test strips were fabricated for on-site detection of TNP, which makes them convenient solid-supported sensors.

Fluorescence Enhancement of Lignin-Based Carbon Quantum Dots by Concentration-Dependent and Electron-Donating Substituent Synergy and Their Cell Imaging Applications

Black liquor is an important pollutant in the pulp industry, but it also has the potential for high-value utilization. In this study, lignin extracted from black liquor was hydrothermally prepared into lignin-based carbon quantum dots (L-CQDs) using a one-pot method. Physicochemical characterization suggested that the L-CQDs exhibited a lamellar core-shell multilayered graphene structure surrounded by oxygen-containing functional groups. The fluorescence intensity of the L-CQDs was strengthened depending on their own concentration dependence and the doping of external groups. The fluorescence intensity of L-CQDs varied between 89.09 and 183.66 under different concentrations, and the most intense fluorescence (183.66) was obtained at 0.1 mg mL^-1. At hydroxyl and amino adsorption capacities of 11.08 and 0.98 mmol g^-1, the hydroxylated RL-CQDs-5 and aminated NL-CQDs-3 exhibited the highest fluorescence intensities at 689.22 and 605.39, respectively. Moreover, when pristine L-CQDs were sequentially aminated and hydroxylated, the NRL-CQDs' fluorescence intensity reached 1224.92. Cell imaging experiments proved that cells cultivated with NRL-CQDs have brighter fluorescence compared with L-CQDs. The results will render L-CQDs more suitable for practical applications.

Twisted intramolecular charge transfer (TICT) and twists beyond TICT: from mechanisms to rational designs of bright and sensitive fluorophores

The twisted intramolecular charge transfer (TICT) mechanism has guided the development of numerous bright and sensitive fluorophores. This review briefly overviews the history of establishing the TICT mechanism, and systematically summarizes the molecular design strategies in modulating the TICT tendency of various organic fluorophores towards different applications, along with key milestone studies and representative examples. Additionally, we also succinctly review the twisted intramolecular charge shuttle (TICS) and twists during photoinduced electron transfer (PET), and compare their similarities and differences with TICT, with emphasis on understanding the structure-property relationships between the twisted geometries and how they can directly affect the fluorescence of the molecules. Such structure-property relationships presented herein will greatly aid the rational development of fluorophores that involve molecular twisting in the excited state.

A new strategy to fabricate multifunctional luminescent MOFs, extending their application range from pH sensing to amino acid information coding

Herein, we propose a new strategy for designing new types of wide range pH-sensitive metal-organic frameworks (MOFs) with double luminescent centers on UiO-66-2OH. The UiO-66-2OH has a ligands-based emission at 530 nm. To introduce another luminescent center, PMA (1,2,4,5-benzenetetracarboxylic acid), as the functional site, is used to substitute the initial ligand, BDC-2OH (2,5-dihydroxyterephthalic acid), of UiO-66-2OH. Eu³⁺ ions, another luminescent center at 613 nm, are coordinated to the free carboxyl group on PMA. Finally, TTA (2-Thenoyltrifluoroacetone) is coordinated with Eu³⁺ ions to balance the emission at 613 nm (Eu³⁺ ions) and 530 nm (BDC-2OH). For the sake of both strong emissions, we explored the loading levels of PMA. The optimized structure is Eu(TTA)@MUM5 ("MUM" is the abbreviation of "Mixed ligand UiO-66-2OH MOFs" and "5" represents the molar percentage of PMA is 50%), which exhibits strong emission at 530 nm (alkaline solution) and 613 nm (neutral solution). Remarkably, the synthesized material has an exponential relationship (R² = 0.9973) over the pH range of 1.87 to 9.65 and a linear relationship (R² = 0.9987) when pH = 11.01-13.35. Further experiments have proved that Eu(TTA)@MUM5 could distinguish different amino acids. Based on that, we build an information transferring circle with two coding modes on Eu(TTA)@MUM5 using aseptic acid and arginine as coding factors.

A GLUT1 inhibitor-based fluorogenic probe for Warburg effect-targeted drug screening and diagnostic imaging of hyperglycolytic cancers

Increased expression of glucose transporters, especially GLUT1 has been proven to be involved in the Warburg effect. Therefore, GLUT1-targeted oncological approaches are being successfully employed for clinical tumor diagnostic imaging (e.g. the ¹⁸F-FDG/PET), drug delivery and novel anticancer drug development. Despite the long history of the Warburg effect-targeted cancer diagnosis, other than antibody labeling, there have been no imaging tools developed for direct detection of the GLUT1 expression. Herein, we report the new strategy of using a non-antibody GLUT1 binding probe for Warburg effect-based tumor detection and diagnostic imaging. By specifically inhibits the transport function of GLUT1, the newly designed fluorescent probe, CUM-5, was found to be a useful tool not only for sensitive GLUT1-mediated cancer cell detection, but also for cell-based high-throughput GLUT inhibitor screening. In in vivo studies, CUM-5 shows clear advantages including desirable tumor-to-normal tissue contrast and excellent tumor selectivity (Tm/Bkg and Tm/Torg), as well as high fluorescence stability (long response time) and ideal physiological biocompatibility. In particular, the GLUT1 inhibitor probe offers the potential use for glycolysis-based diagnostic imaging in triple-negative breast cancer which is claimed to have unsatisfactory results with FDG/PET diagnosis, thus remaining a highly metastatic and lethal disease with a need for sensitive and precise identification.

A review on recent advances in amino acid and peptide-based fluorescence and its potential applications

Fluorescence is widely used to detect functional groups and ions, and peptides are used in various fields due to their excellent biological activity.

Fluorescent Chromophores Containing the Nitro Group: Relatively Unexplored Emissive Properties

Apart from numerous applications, for example in azo dye precursors, explosives, and industrial processes, the nitro group (-NO₂ ) appears on countless molecules in photochemical research owing to its unique characteristics such as a strong electron-withdrawing ability and facile conversion to the reduced substituent. Although it is well known as a fluorescence quencher, fluorescent chromophores that contain the nitro group have also emerged, with 3-nitrophenothiazine being recently reported to have 100 % emission quantum yield in nonpolar solvents. The diverse characters of nitro-containing chromophores motivated us to systematically review those chromophores with nitro substituents, their associated photophysical properties, and applications. In this Review, we succinctly elaborate the advance of the fluorescent nitro chromophores in fields of intramolecular charge transfer, fluorescent probes and nonlinear properties. Special attention is paid to the rationalization of the associated emission spectroscopy, so that the readers can gain insights into the structure-photophysics relationship and hence gain insights for the strategic design of nitro chromophores.

Computational study of the intermolecular interactions and their effect on the UV-visible spectra of the ternary liquid mixture of benzene, ethanol and propylene glycol

Quantum chemical calculations are well-equipped to provide answers to the questions regarding the different aspects of intermolecular interactions. We investigate the benzene, ethanol and 1,2 propanediol ternary mixture with theoretical as well as experimental UV-Vis spectroscopy. An extensive theoretical study on the molecular structure and UV-Vis spectral analysis was undertaken using density functional theory (DFT) method. Structural parameter analysis and the HOMO-LUMO (highest occupied molecular orbital-lowest unoccupied molecular orbital) energy gap help to describe the possible interaction between molecules in dimer and in combination. Interaction energy has been calculated from topological study. Time-dependent density functional theory (TDDFT) calculations on dimer/cluster in gas phase help to understand the effect of the molecular interaction on the overall spectral shift and related intensity variation. Our results show that in the ternary mixture, the interaction energies of the interactions are π-π interaction: 0.52-2.57 kcal/mol, Hp-π interaction: 1.15 kcal/mol and H-bonding: 2.49 to 4.46 kcal/mol. The π-π interaction and H-bonding cause red shift in absorption spectra while Hp-π interaction causes blue shift. In the ternary mixture, the strength of different kinds of interaction depends on the concentration, and as each interaction has its own effect on spectral shift, the overall experimental spectra get broader and distorted from the Gaussian shape.

PDMPO: a specific silicon or silica, pH sensitive fluorescent probe?

In order to understand Si behavior and biodisponibility in soils and plants, we evaluated the use of PDMPO (2-(4-pyridyl)-5-((4-(2-dimethylaminoethylaminocarbamoyl)methoxy)phenyl)oxazole) that was supposed to be a Si-specific fluorescence marker and to have a pH-dependent fluorescence. We studied the interactions between PDMPO and water-dissolved Si, Al and natural organic matter (humic acids, HA). Six systems with different HA, Si and Al concentrations were studied by fluorescence spectroscopy at pH 4, 7 and 9. The Al–PDMPO complex was characterized by infrared spectroscopy and the particle size distribution in solution was characterized by nano tracking analysis. We found that when usual pH buffers are not present, the PDMPO fluorescence was not pH dependent and was not Si-specific. In the PDMPO–Si–HA system, the PDMPO fluorescence signals were greatly enhanced, suggesting the formation of highly fluorescent ternary HA–PDMPO–Si groups. When Al was added to the system, the fluorescence was strongly quenched, suggesting the formation of low-fluorescence quaternary HA–PDMPO–Si–Al groups. The PDMPO fluorescence is therefore greatly sensitive to complexable metals and to natural organic matter and is therefore difficult to be applied for the quantification of Si or pH in a complex medium.

To understand Si behavior in soils and plants, we evaluated the use of PDMPO that was supposed to be a Si-specific, pH-dependent fluorescence marker. We found that the PDMPO fluorescence is neither Si-specific nor pH dependent.

Polyglycerol-Based Thermoresponsive Nanocapsules Induce Skin Hydration and Serve as a Skin Penetration Enhancer

The use of penetration enhancers (chemical or physical) has been proven to dramatically improve the penetration of therapeutics. Nevertheless, their use poses great risks, as they can lead to permanent damage of the skin, reduce its barrier efficiency, and result in the intrusion of harmful substances. Among the most used skin penetration enhancers, water is greatly accepted because skin quickly recovers from its exposure. Nanocapsules (NCs) represent a promising combination of the carrier system and penetration enhancer because their water-containing void combined with their polymer-based shell can be used to induce high local skin hydration, while simultaneously aiding the transport of drugs across the skin barrier. In this study, NCs were synthesized with a void core of 100 nm in diameter, a thermoresponsive shell based on different ratios of poly(N-isopropylacrylamide) and poly(N-isopropylmethacrylamide) as thermoresponsive polymers, and dendritic polyglycerol as a macromolecular cross-linker. These NCs can shrink or swell upon a thermal trigger, which was used to induce the release of the entrapped water in a controlled fashion. The interactions and effects of thermoresponsive NCs on the stratum corneum of excised human skin were investigated using fluorescence microscopy, high-resolution optical microscopy, and stimulated Raman spectromicroscopy. It could be observed that the thermoresponsive NCs increase the amount of deuterated water that penetrated into the viable epidermis. Moreover, NCs increased the skin penetration of a high-molecular weight dye (Atto Oxa12 NHS ester, MW = 835 g/mol) with respect to formulations in water or 30% DMSO, emphasizing the features of the NCs as a skin penetration enhancer.

Visualising electrochemical reaction layers: mediated vs. direct oxidation

Electrochemical treatments are widely used for 'clean up' in which toxic metals and organic compounds are removed using direct or mediated electrolysis. Herein we report novel studies offering proof of concept that spectrofluorometric electrochemistry can provide important mechanistic detail into these processes. A thin layer opto-electrochemical cell, with a carbon fibre (radius 3.5 μm) working electrode, is used to visualise the optical responses of the oxidative destruction of a fluorophore either directly, on an electrode, or via the indirect reaction of the analyte with an electrochemically formed species which 'mediates' the destruction. The optical responses of these two reaction mechanisms are first predicted by numerical simulation followed by experimental validation of each using two fluorescent probes, a redox inactive (in the electrochemical window) 1,3,6,8-pyrenetetrasulfonic acid and the redox-active derivative 8-hydroxypyrene-1,3,6-trisulfonic acid. In the vicinity of a carbon electrode held at different oxidative potentials, the contrast between indirect electro-destruction, chlorination, and direct oxidation is very obvious. Excellent agreement is seen between the numerically predicted fluorescence intensity profiles and experiment.

Exploring the Effects of Various Polymeric Backbones on the Performance of a Hydroxyaromatic 1,2,3-Triazole Anion Sensor

Polymeric chemosensors are vital sensing tools because of higher sensitivity compared to their monomeric counterparts and tunable mechanical properties. This study focuses on the incorporation of a hydroxyaromatic 1,2,3-triazole sensor, 2-(4-phenyl 1H-1,2,3-triazol-1-yl)phenol (PTP), into polymers. By itself, the triazole has a selective, fluorometric response to the fluoride, acetate, and dihydrogen phosphate anions, and is most responsive to fluoride. Current investigations probe the suitability of various polymeric backbones for the retention and enhancement of the triazole’s sensing capabilities. Backbones derived from acrylic acid, methyl methacrylate, divinylbenzene, and styrene were explored. UV-illumination, Nuclear Magnetic Resonance (NMR) titration, and ultraviolet-visible (UV-Vis) absorption and fluorescence spectroscopy studies are used to investigate the performance of newly synthesized polymers and the derivatives of PTP that serve as the polymers’ precursors. Among the polymers investigated, copolymers with styrene proved best; these systems retained the sensing capabilities and were amenable to tuning for sensitivity.

A versatile depigmentation, clearing, and labeling method for exploring nervous system diversity

Tissue clearing combined with deep imaging has emerged as a powerful alternative to classical histological techniques. Whereas current techniques have been optimized for imaging selected nonpigmented organs such as the mammalian brain, natural pigmentation remains challenging for most other biological specimens of larger volume. We have developed a fast DEpigmEntation-Plus-Clearing method (DEEP-Clear) that is easily incorporated in existing workflows and combines whole system labeling with a spectrum of detection techniques, ranging from immunohistochemistry to RNA in situ hybridization, labeling of proliferative cells (EdU labeling) and visualization of transgenic markers. With light-sheet imaging of whole animals and detailed confocal studies on pigmented organs, we provide unprecedented insight into eyes, whole nervous systems, and subcellular structures in animal models ranging from worms and squids to axolotls and zebrafish. DEEP-Clear thus paves the way for the exploration of species-rich clades and developmental stages that are largely inaccessible by regular imaging approaches.

Activatable Formation of Emissive Excimers for Highly Selective Detection of β-Galactosidase

Small-molecular fluorescence sensors have become promising detection tools in many fields attributing to their high sensitivity, excellent temporal and spatial resolution, and low cytotoxicity. However, high concentration or aggregation-induced fluorescence quenching effect has usually hindered the development of traditional fluorescence dyes. Herein, a new fluorophore cyanovinylene dye BMZ with excimer emission property has been constructed. It shows an obvious enhanced and red-shift emission upon aggregation in aqueous solution, which overmatches the conventional pyrene with longer absorption and emission wavelengths. Using this unique optical property, a new fluorescence probe BMZ-Gal has been developed for trapping of β-galactosidase (β-Gal) activity with high selectivity, low limit of detection of 0.17 U, and rapid recognition, which is based on the β-Gal-induced formation of red-shift emitting excimer. β-Gal has a strong affinity for BMZ-Gal, which is verified through the Michaelis-Menten constants (K_m, 1.87 μM) and the hydrolysis efficiencies (K_cat/K_m, 1.78 × 10³ M^-1 s^-1). Furthermore, the assay system has been successfully used for detecting endogenous β-Gal in living ovarian cancer cells and can passively targeted to identify β-Gal in organelle level and determine its subcellular location with satisfactory accuracy. We anticipate that the new fluorophore cyanovinylene dye herein may inaugurate new opportunities for the development of excimer emission sensors.

Fluorescence enhancement of quinolines by protonation

A study of the fluorescence enhancement of isoquinoline, acridine (benzo[b]quinoline) and benzo[h]quinoline is reported with six organic acids of different pK_a values. Protonation was found to be an effective tool in the fluorescence enhancement of quinolines. A significant increase in the fluorescence intensity is observed only when strong acids are used, resulting in an over 50-fold increase in fluorescence with trifluoroacetic or benzenesulfonic acid and isoquinoline in a 1.5 : 1 ratio. The benzenesulfonic acid was found to be the most effective in the protonation of the bases despite its higher pK_a value compared to trifluoro- and trichloroacetic acid. The X-ray crystal structures of 14 salts reveal the charge-assisted hydrogen bond O⋯N distances to vary very little, from 2.560(2)–2.714(3) Å, with the exception of the isoquinolinium benzenesulfonate where the O⋯N distance of 2.862(7) Å is caused by additional intermolecular interactions in the solid-state.

The acid–base interactions of quinolines are studied in both liquid and solid-state to explore efficient tools for fluorescence enhancement.

Photophysical Properties of New Pyrazolone Based Azo- Compounds

New 5-pyrazolone based azo- dyes (2-5) and a bisazo- dye (6) were synthesized via diazo- coupling reaction with substituted aryl amines. All azo-5-pyrazolone compounds were characterized with the aid of FTIR, UV-Vis., ¹H NMR, ¹³C NMR-APT and, GC-MS or ESI⁽⁺⁾-MS spectroscopic techniques. NMR studies showed that all azo- and bisazo- compounds, are in hydrazo-keto form except compound 5 which is in enol-azo form in solution. FTIR(ATR) studies indicated that compounds 2 and 4 are in azo-keto form, compounds 3 and 6 are in hydrazo-keto form and compound 5 is in enol-azo form in the solid state. All newly synthesized compounds were investigated for their absorption and emission characteristics. Photophysical properties of the solvent polarity effect and acid/base effect on the absorption and emission spectra were evaluated for an azo- (2) and a bisazo- compound (6). All azo-5-pyrazolone compounds showed fluorescence properties and the solvents with different polarities gave rise to shifts in the absorption and emission spectra of 2 and 6. The base addition did not affect the emission spectra while changing the absorption properties of the azo- and bisazo- compounds. Thermal work of 2 and 6 were carried out with TG/DTG technique and the results showed that compound 2 had adequate stability for industrial applications as a fluorescent material.

Combined effects of salinity, temperature, hypoxia, and Deepwater Horizon oil on Fundulus grandis larvae

Oil spills have polluted the marine environment for decades and continue to be a major source of polycyclic aromatic hydrocarbons (PAHs) to marine ecosystems around the globe, for example during the 2010 Deepwater Horizon spill. Although the toxicity of PAHs to fish has been well studied, their effects combined with abiotic stressors are poorly understood. The goal of this study was to describe the combined impacts of crude oil and environmental stressors on fish larvae, a sensitive life stage. Gulf killifish (Fundulus grandis) larvae (<24 h post-hatch) were exposed for 48 h to high energy water accommodated fractions (HEWAF; total PAHs 0-125 ppb) of Macondo oil from the Deepwater Horizon spill under different combinations of environmental conditions (dissolved oxygen 2, 6 ppm; temperature 20, 25, 30 °C; salinity 3, 10, 30 ppt). Even under optimal environmental conditions (25 °C, 10 ppt, 6 ppm) larval survival and development were negatively affected by PAHs, starting with the lowest concentration tested (∼15 ppb). Hypoxia and high temperature each increased the adverse effects of HEWAF on development and mortality. In contrast, salinity had little effect on any of the endpoints measured. Importantly, expression of the detoxifying gene cyp1a was highly induced in PAH-exposed larvae under normoxic conditions, but not under hypoxic conditions, potentially explaining the enhanced toxicity observed under hypoxia. This work highlights the importance of considering how suboptimal environmental conditions can exacerbate the effects of pollution on fish early life stages.

Activity-based ratiometric FRET probe reveals oncogene-driven changes in labile copper pools induced by altered glutathione metabolism

Copper is essential for life, and beyond its well-established ability to serve as a tightly bound, redox-active active site cofactor for enzyme function, emerging data suggest that cellular copper also exists in labile pools, defined as loosely bound to low-molecular-weight ligands, which can regulate diverse transition metal signaling processes spanning neural communication and olfaction, lipolysis, rest-activity cycles, and kinase pathways critical for oncogenic signaling. To help decipher this growing biology, we report a first-generation ratiometric fluorescence resonance energy transfer (FRET) copper probe, FCP-1, for activity-based sensing of labile Cu(I) pools in live cells. FCP-1 links fluorescein and rhodamine dyes through a Tris[(2-pyridyl)methyl]amine bridge. Bioinspired Cu(I)-induced oxidative cleavage decreases FRET between fluorescein donor and rhodamine acceptor. FCP-1 responds to Cu(I) with high metal selectivity and oxidation-state specificity and facilitates ratiometric measurements that minimize potential interferences arising from variations in sample thickness, dye concentration, and light intensity. FCP-1 enables imaging of dynamic changes in labile Cu(I) pools in live cells in response to copper supplementation/depletion, differential expression of the copper importer CTR1, and redox stress induced by manipulating intracellular glutathione levels and reduced/oxidized glutathione (GSH/GSSG) ratios. FCP-1 imaging reveals a labile Cu(I) deficiency induced by oncogene-driven cellular transformation that promotes fluctuations in glutathione metabolism, where lower GSH/GSSG ratios decrease labile Cu(I) availability without affecting total copper levels. By connecting copper dysregulation and glutathione stress in cancer, this work provides a valuable starting point to study broader cross-talk between metal and redox pathways in health and disease with activity-based probes.

Specific Ion Effects on Protein Thermal Aggregation from Dilute Solutions to Crowded Environments

We have investigated specific ion effects on protein thermal aggregation from dilute solutions to crowded environments. Ovalbumin and poly(ethylene glycol) have been employed as the model protein and crowding agent, respectively. Our studies demonstrate that the rate-limiting step of ovalbumin thermal aggregation is changed from the aggregation of unfolded protein molecules to the unfolding of the protein molecules, when the solution conditions are varied from a dilute solution to a crowded environment. The specific ion effects acting on the thermal aggregation of ovalbumin generated by kosmotropic and chaotropic ions are different. The thermal aggregation of ovalbumin molecules is promoted by kosmotropic anions in dilute solutions via an increase in protein hydrophobic interactions. In contrast, ovalbumin thermal aggregation is facilitated by chaotropic ions in crowded environments through accelerated unfolding of protein molecules. Therefore, there are distinct mechanisms causing the ion specificities of protein thermal aggregation between dilute solutions and crowded environments. The ion specificities are dominated by ion-specific hydrophobic interactions between protein molecules and ion-specific unfolding of protein molecules in dilute solutions and crowded environments, respectively.

Characterization and photocatalytic behavior of 2,9-di(aryl)-1,10-phenanthroline copper(i) complexes

The synthesis, characterization, photophysical properties, theoretical calculations, and catalytic applications of 2,9-di(aryl)-1,10-phenanthroline copper(i) complexes are described. Specifically, this study made use of di(aryl)-1,10-phenanthroline ligands including 2,9-di(4-methoxyphenyl)-1,10-phenanthroline (1), 2,9-di(4-hydroxyphenyl)-1,10-phenanthroline (2), 2,9-di(4-methoxy-3-methylphenyl)-1,10-phenanthroline (3), and 2,9-di(4-hydroxy-3-methylphenyl)-1,10-phenanthroline (4). The 2 : 1 ligand-to-metal complexes, as PF₆^- salts, i.e., ([Cu·(1)₂]PF₆, [Cu·(2)₂]PF₆, [Cu·(3)₂]PF₆, and [Cu·(4)₂]PF₆) have been isolated and characterized. The structures of ligands 1 and 2 and complexes [Cu·(1)₂]PF₆ and [Cu·(3)₂]PF₆ have been determined by single-crystal X-ray analysis. The photoredox catalytic activity of these copper(i) complexes was investigated in an atom-transfer radical-addition (ATRA) reaction and the results showed fairly efficient activity, with a strong wavelength dependence. In order to better understand the observed catalytic activity, photophysical emission and absorption studies, and DFT calculations were also performed. It was determined that when the excitation wavelength was appropriate for exciting into the LUMO+1 or LUMO+2, catalysis would occur. On the contrary, excitations into the LUMO resulted in no observable catalysis. In light of these results, a mechanism for the ATRA photoredox catalytic cycle has been proposed.

Organic cation rhodamines for screening organic cation transporters in early stages of drug development

The aim of this study was to investigate the suitability of rhodamine-123, rhodamine-6G and rhodamine B as non-radioactive probes for characterizing organic cation transporters in respiratory cells. Fluorescent characteristics of the compounds were validated under standard in vitro drug transport conditions (buffers, pH, and light). Uptake/transport kinetics and intracellular accumulation of the compounds were investigated. Uptake/transport mechanisms were investigated by comparing the effect of pH, temperature, concentration, polarity, OCTs/OCTNs inhibitors/substrates, and metabolic inhibitors on the cationic dyes uptake in Calu-3 cells. Fluorescence stability and intensity of the compounds were altered by buffer composition, light, and pH. Uptake of the dyes was concentration-, temperature- and pH-dependent. OCTs/OCTNs inhibitors significantly reduced intracellular accumulation of the compounds. Whereas rhodamine-B uptake was sodium-dependent, pH had no effect on rhodamine-123 and rhodamine-6G uptake. Transport of the dyes across the cells was polarized: (AP→BL>BL→AP transport) and saturable: {V_max=14.08±2.074, K_m=1821±380.4 (rhodamine-B); V_max=6.555±0.4106, K_m=1353±130.4 (rhodamine-123) and V_max=0.3056±0.01402, K_m=702.9±60.97 (rhodamine-6G)}. The dyes were co-localized with MitoTracker®, the mitochondrial marker. Cationic rhodamines, especially rhodamine-B and rhodamine- 6G can be used as organic cation transporter substrates in respiratory cells. During such studies, buffer selection, pH and light exposure should be taken into consideration.

Overview of fluorescence glucose sensing: a technology with a bright future

Fluorescence represents a promising alternative technology to electrochemistry and spectroscopy for accurate analysis of glucose in diabetes; however, no implanted fluorescence glucose assay is currently commercially available. The method depends on the principle of fluorescence, which is the emission of light by a substance after absorbing light. A fluorophore is a molecule that will absorb energy of a specific wavelength and reemit energy at a different wavelength. A fluorescence glucose-sensing molecule can be constructed to increase or decrease in fluorescence from baseline according to the ambient concentration of glucose. A quantum dot is a semiconductor crystal that can serve as a sensor by fluorescing at a desired wavelength or color, depending on the crystal size and materials used. If receptor molecules for glucose can be adsorbed to single-wall carbon nanotubules, then the resulting binding of glucose to these receptors will alter the nanotubes' fluorescence. Fluorescence glucose sensors can provide a continuous glucose reading by being embedded into removable wire-shaped subcutaneous or intravenous catheters as well as other types of implanted structures, such as capsules, microcapsules, microbeads, nano-optodes, or capillary tubes. Fluorescence glucose-sensing methods, which are under development, offer four potential advantages over commercially used continuous glucose monitoring technologies: (1) greater sensitivity to low concentrations of glucose, (2) the possibility of constructing sensors that operate most accurately in the hypoglycemic range by using binding proteins with disassociation constants in this range, (3) less need to recalibrate in response to local tissue reactions around the sensor, and (4) no need to implant either a transmitter or a power source for wireless communication of glucose data. Fluorescence glucose sensors also have four significant disadvantages compared with commercially used continuous glucose monitoring technologies: (1) a damaging foreign body response; (2) a sensitivity to local pH and/or oxygen, which can affect the dye response; (3) potential toxicity of implanted dyes, especially if the implanted fluorophore cannot be fully removed; and (4) the necessity of always carrying a dedicated light source to interrogate the implanted sensor. Fluorescence sensing is a promising method for measuring glucose continuously, especially in the hypoglycemic range. If currently vexing technical and engineering and biocompatibility problems can be overcome, then this approach could lead to a new family of continuous glucose monitors.

Toxicity of crude oil chemically dispersed in a wave tank to embryos of Atlantic herring (Clupea harengus)

Tests of crude oil toxicity to fish are often chronic, exposing embryos from fertilization to hatch to oil solutions prepared using standard mixing procedures. However, during oil spills, fish are not often exposed for long periods and the dynamic nature of the ocean is not easily replicated in the lab. Our objective was to determine if brief exposures of Atlantic herring (Clupea harengus) embryos to dispersed oil prepared by standard mixing procedures was as toxic as oil dispersed in a more realistic model system. Embryos were first exposed to chemically dispersed Alaska North Slope crude and Arabian light crude oil for 2.4 h to 14 d from fertilization to determine if exposure time affected toxicity. Toxicity increased with exposure time, but 2.4-h exposures at realistic concentrations of oil induced blue-sac disease and reduced the percentage of normal embryos at hatch; there was little difference in toxicity between the two oils. Secondly, oil was chemically dispersed in a wave tank to determine if the resultant oil solutions were as toxic to herring embryos as laboratory-derived dispersed oil using a single exposure period of 24 h. Samples taken 15 min postdispersion were more toxic than laboratory-prepared solutions, but samples taken at 5, 30, and 60 min postdispersion were less toxic. Overall, the laboratory- and wave tank-derived solutions of dispersed oil provided similar estimates of toxicity despite differences in the methods for preparing test solutions, suggesting that laboratory and wave tank data are a reliable basis for ecological risk assessments of spilled oil.

High-resolution, noninvasive, two-photon fluorescence measurement of molecular concentrations in corneal tissue

PURPOSE

To perform high-resolution, noninvasive, calibrated measurements of the concentrations and diffusion profiles of fluorescent molecules in the live cornea after topical application to the ocular surface.

METHODS

An 800-nm femtosecond laser was used to perform two-photon fluorescence (TPF) axial scanning measurements. Calibration solutions consisting of sodium fluorescein (Na-Fl; concentration range, 0.01%-2.5%) and riboflavin (concentration range, 0.0125%-0.1%) were tested in well slides, and TPF signals were assessed. Excised feline eyeballs preserved in corneal storage medium and with either intact or removed corneal epithelia were then treated with Na-Fl, riboflavin, or fluorescein dextran (Fl-d) of different molecular weight (MW) for 30 minutes. Calibrated TPF was then used immediately to measure the concentration of these molecules across the central corneal depth.

RESULTS

The axial resolution of our TPF system was 6 μm, and a linear relationship was observed between TPF signal and low concentrations of most fluorophores. Intact corneas treated with Na-Fl or riboflavin exhibited a detectable penetration depth of only approximately 20 μm, compared with approximately 400 to 600 μm when the epithelium was removed before fluorophore application. Peak concentrations for intact corneas were half those attained with epithelial removal. Debrided corneas treated with 2,000,000 MW Fl-d showed a half-maximum penetration depth of 156.7 μm compared with 384 μm for the 3,000 MW dextran. The peak concentration of the high MW dextran was one quarter that of the lower MW dextran.

CONCLUSIONS

TPF is an effective, high-resolution, noninvasive method of quantifying the diffusion and concentration of fluorescent molecules across the cornea.

Fluorescein punctate staining traced to superficial corneal epithelial cells by impression cytology and confocal microscopy

PURPOSE

The basis of fluorescein-associated superficial punctate staining in dry eyes is controversial. Prior explanations include fluorescein pooling in surface erosive defects, intercellular trapping of fluorescein, and intracellular staining in dead cells. In this study, the hypothesis that punctate erosions are individual cells with enhanced fluorescence was tested.

METHODS

Ten impression cytology membrane materials were compared, to optimize cellular yield in buccal mucosa and cornea. Clinicocytologic correlation of punctate fluorescent spots was performed in four dry eye patients. Individual punctate spots were localized by fiducial marks in photographs, before and after removal with impression membranes, and were traced in fluorescence microscopy and cytologic staining. Two-way contingency table analysis was used to determine the correlation of punctate spots with cells removed by the membrane. Clinicopathologic correlation of punctate spots was performed in 10 corneas removed in dry eye patients by transplantation for concurrent diseases. Punctate fluorescence was tracked in specimens by fiducial marks and epifluorescence. The distribution of fluorescent spots in specific cell layers of the cornea was determined by confocal microscopy.

RESULTS

Cellular yield was greatest with impressions from polytetrafluoroethylene (PTFE [Teflon]; BioPore; Millipore, Billerica, MA) membrane compared with its closest rival (P = 0.019). Punctate fluorescent spots, most of which disappeared after impression cytology (71%), correlated with cells on the membranes (P = 0.009). The punctate spots were more frequent in the superficial cell layers of the cornea (80%) compared with the deepest two layers (0%) (P < 0.00049).

CONCLUSIONS

Punctate epithelial erosions correspond to enhanced fluorescence in epithelial cells predominantly in superficial layers of the cornea and would be more aptly named fluorescent epithelial cells (FLECs).

Synthesis, characterization and fluorescence studies of 3,5-diaryl substituted 2-pyrazolines

A series of 2-pyrazolines have been synthesized from α, β unsaturated ketones and hydrazine hydrate with acetic/formic acid in ethanol/DMSO. The structures of 2-pyrazolines have been established by spectroscopic techniques i.e. UV, IR, (1)H NMR, (13)C NMR and micro element analysis. Fluorescence spectra were recorded in the solution at fixed concentration and same excitation wavelength at 290 nm. The absorption band positions of all the compounds broadly lie between 280 and 336 nm and fluorescence band positions in the range between 300 and 370 nm, the near ultraviolet region.