Blue-shifted Fluorescence Research Articles

An Ultrahigh Affinity DNA Aptamer for Quinine and Its Intrinsic Fluorescence Based Label-free Detection.

Measuring quinine is critical for the detection of its overdose, understanding its pharmacological and toxicological effects, and monitoring its pollution. While a previously reported aptamer named MN4 can bind quinine, it was not selected for it, leading to compromised binding affinity and specificity. In this work, a new quinine aptamer was isolated using the library immobilization capture-SELEX technique. The Q1 aptamer has a Kd value of 10 nM determined by an isothermal titration calorimetry experiment and 45 nM in a fluorescence binding assay. A 3.5 nM quinine limit of detection was obtained based on the aptamer binding-induced quenching of the intrinsic fluorescence of quinine. A large blue shift in fluorescence was observed for quinine upon binding to Q1, whereas binding to MN4 led to a very small red shift, indicating different ways of quinine binding by these two aptamers. Q1 did not bind cocaine based on NMR spectroscopy and fluorescence assays also indicated excellent selectivity against other tested molecules. This work has supplied a high affinity aptamer for quinine that can be useful for its detection and fundamental aptamer binding studies. It also highlights the advantages of using capture-SELEX to isolate aptamers for small molecules.

Designing High-Sensitivity Mechanochromic Luminescent Materials Through Friction-Induced Crystallization Strategy.

Despite recent significant breakthroughs in novel mechanochromic luminescent (ML) materials, developing a high-sensitivity ML material is still challengeable. Herein, a "friction-induced crystallization" strategy is proposed to realize highly sensitive transformations of luminescent signal, through an integration of polymeric chains and an aggregation-sensitive luminescent core, which act as mechanical sensors and fluochromic actuators, respectively. The coupling of these two components enables the material to crystallize in response to shear friction, thereby exhibiting blue-shift fluorescence due to a more restricted relaxation pathway. This study underscores a high-sensitivity ML material based on the precise regulation of molecular-scale motions, and also expands the scope and potential of ML materials toward user-friendly, interactive wearable devices.

A Turn‐On Fluorescence Probe Based on a New Salamo‐Co (II) Coordination Polymer for Tyrosine Detection and Its Application in Water Samples

ABSTRACTA novel salamo‐Co (II) coordination polymer probe CP was synthesized firstly, and its crystal structure, [Co3(L)2(PTA)(H2O)2]n·4nDMF, was determined by X‐ray diffraction analysis. The probe has a rare aggregation‐induced luminescence enhancement (AIEE) effect. When applied to amino acid detection, it was found to have a high selective recognition of tyrosine. With the increase of tyrosine, the fluorescent strength of the probe was enhanced in a short period of time. In addition, the binding ratio of probe to Tyr was determined by fluorescence titration experiment, and the detection limit LOD of probe CP for Tyr was calculated to be 2.57 × 10−9 M, and the binding constant Ka was 2.96 × 105 M−1. According to UV absorption spectrum, FT‐IR spectra, ESI mass spectrometry, and DFT calculation, it was speculated that Tyr can bind to the probe after adding Tyr into the probe solution, triggering FRET and ICT effects, resulting in increased fluorescence intensity and blue shift, and finally achieving the specific recognition of tyrosine by probe CP. Finally, the practical application of probe CP was studied. Through strip test and real water sample test, it was found that the probe can be used for qualitative and quantitative analysis of tyrosine.

Nitric oxide laser-induced fluorescence using the fifth harmonic of a broad-band Nd:YAG laser

We explore the prospects of laser-induced fluorescence diagnostics of nitric oxide (NO) using non-tunable fifth-harmonic radiation of a broad-band, ns-pulsed Nd:YAG laser at λ=213\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\lambda = 213$$\\end{document} nm. Typically, 2–5 mJ/pulse of 213-nm radiation is produced by a commercial harmonic generator in this study, with an efficiency of about 1–3% (relative to the input pulse energy). We present spectral results obtained in various environments, ranging from air-based combustion processes at room conditions up to elevated pressure and temperature environments, the latter resembling conditions typical for compression-ignition internal combustion engines. In all cases, the laser-induced fluorescence spectrum shows clear signatures of the NO spectrum, mostly on transitions in the γ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\gamma $$\\end{document}-band system (A2Σ+→X2Π\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\ ext {A}^2\\Sigma ^+ \\rightarrow X^2\\Pi $$\\end{document}). At higher fluences, multi-photon absorption also gives rise to blue-shifted fluorescence. The fluorescence yield increases with increasing pressure, allegedly due to non-resonant excitation, the efficiency of which increases with increasing pressure broadening. When applied to air-based combustion processes, interference by (hot) oxygen needs to be taken into account. We conclude that the method is a relatively straightforward option to visualize the NO distribution in a broad variety of applications.

Single Mesenchymal Stromal Cell Migration Tracking into Glioblastoma Using Photoconvertible Vesicles.

Reliable cell labeling and tracking techniques are imperative for elucidating the intricate and ambiguous interactions between mesenchymal stromal cells (MSCs) and tumors. Here, we explore fluorescent photoconvertible nanoengineered vesicles to study mMSC migration in brain tumors. These 3 μm sized vesicles made of carbon nanoparticles, Rhodamine B (RhB), and polyelectrolytes are readily internalized by cells. The dye undergoes photoconversion under 561 nm laser exposure with a fluorescence blue shift upon demand. The optimal laser irradiation duration for photoconversion was 0.4 ms, which provided a maximal blue shift of the fluorescent signal label without excessive laser exposure on cells. Vesicles modified with an extra polymer layer demonstrated enhanced intracellular uptake without remarkable effects on cell viability, motility, or proliferation. The optimal ratio of 20 vesicles per mMSC was determined. Moreover, the migration of individual mMSCs within 2D and 3D glioblastoma cell (EPNT-5) colonies over 2 days and in vivo tumor settings over 7 days were traced. Our study provides a robust nanocomposite platform for investigating MSC-tumor dynamics and offers insights into envisaged therapeutic strategies. Photoconvertible vesicles also present an indispensable tool for studying complex fundamental processes of cell-cell interactions for a wide range of problems in biomedicine.

Vibrational-Mode-Selective Modulation of Electronic Excitation.

Vibrational-mode-selective modulation of electronic excitation is conducted with a synchronized femtosecond (fs) visible (vis) pulse and a picosecond (ps) infrared (IR) pulse. The mechanism of modulation of vibrational and vibronic relaxation behavior of excited state is investigated with ultrafast vis/IR, IR/IR, and vis-IR/IR transient spectroscopy, optical gating experiments and theoretical calculations. An organic molecule, 4'-(N,N-dimethylamino)-3-methoxyflavone (DMA3MHF) is chosen as the model system. Upon 1608 cm-1 excitation, the skeleton stretching vibration of DMA3MHF is energized, which can significantly change the shape of the absorption, facilitate the radiative decay and promote emission from vibrational excited states. As results, a remarkable enhancement and a slight blueshift in fluorescence are observed. The mode-selective modulation of electronic excitation is not limited in luminescence or photophysics. It is expected to be widely applicable in tuning many photochemical processes.

Core-Alkynylated Fluorescent Flippers: Altered Ultrafast Photophysics to Track Thick Membranes.

Fluorescent flippers have been introduced as small-molecule probes to image membrane tension in living systems. This study describes the design, synthesis, spectroscopic and imaging properties of flippers that are elongated by one and two alkynes inserted between the push and the pull dithienothiophene domains. The resulting mechanophores combine characteristics of flippers, reporting on physical compression in the ground state, and molecular rotors, reporting on torsional motion in the excited state, to take their photophysics to new level of sophistication. Intensity ratios in broadened excitation bands from differently twisted conformers of core-alkynylated flippers thus report on mechanical compression. Lifetime boosts from ultrafast excited-state planarization and lifetime drops from competitive intersystem crossing into triplet states report on viscosity. In standard lipid bilayer membranes, core-alkynylated flippers are too long for one leaflet and tilt or extend into disordered interleaflet space, which preserves rotor-like torsional disorder and thus weak, blue-shifted fluorescence. Flipper-like planarization occurs only in highly ordered membranes of matching leaflet thickness, where they light up and selectively report on these thick membranes with red-shifted, sharpened excitation maxima, high intensity and long lifetime.

Pulsed laser fragmentation synthesis of carbon quantum dots (CQDs) as fluorescent probes in non-enzymatic glucose detection

Pulsed laser fragmentation in liquid (PLFL) is one of the synthesis routes for producing high-purity carbon quantum dots (CQDs) with less toxic by-products in a straightforward system. The limited literature regarding the application of PLFL-synthesized CQDs motivated this study to exploit them as fluorescent probes in glucose sensing. The design of a fluorescent-based non-enzymatic glucose sensor was achieved by implementing CQDs and 3-aminophenylboronic acid (APBA) as fluorescent probes and glucose receptors, respectively. The CQDs were fabricated by PLFL through an Nd:YAG nanosecond laser, starting from the carbon powder dispersion in ethanol. Then, a laser-assisted post-modification process with oxidizing acid was implemented to produce water-dispersible CQDs for easy functionalization. Functionalizing these CQDs with APBA (CQDs-APBA) resulted in a blue-shifted fluorescence emission with a 35% quantum yield and high photostability. The CQDs-APBA exhibited a turn-off response at increasing glucose concentrations. This method offers good sensitivity with a linear detection range of glucose with a concentration of 0.165 to 8 mM and a detection limit of 165 µM. The applicability of this sensor to real analytes such as saliva obtained a satisfactory result with good reproducibility. This work proves that CQDs synthesized from PLFL can also be an alternative fluorescent probe for fluorescent-based sensing applications.

Spectroscopic investigation and molecular docking analysis of an FRET probe: Trypsin from bovine pancreas@Coumarin 440 dye conjugate

Herein, a systematic investigation of energy transfer from bovine pancreas trypsin to coumarin 440 (C440) dye is presented with an aim to design a FRET probe, as trypsin is an important enzyme for absorption and digestion of nutrients in the small intestine. Conformational changes in trypsin upon interaction with C440 dye are studied by employing both spectroscopic and molecular docking techniques. Steady state and time resolved measurements validate the formation of trypsin-C440 complex via dynamic quenching, that confirms the role of C440 as an inhibitor to suppress the activity of trypsin. Spectral overlap integral, Förster's distance, rate and energy transfer efficiency are calculated from steady state measurements. The observed blue shift in fluorescence suggests conformational changes due to hydrophobicity that arises in trypsin structure on binding with C440 possibly due to their interaction through H-bond (SER195 and GLN192), hydrophobic (GLN192 and HIS57) and π-π stacking bonding (HIS57). The stability of trypsin@C440 bio-conjugate at higher temperature was established from temperature dependent PL studies and the thermodynamic parameters determined agree with second law of thermodynamics. The thermodynamic parameters such as change in enthalpy (ΔH=172.2Jmol−1), change in entropy (ΔS=15.3Jmol−1K−1) and the respective approximately same and unity values of Gibb's free energy (ΔG) and Hill coefficient (n), as well as binding affinities determined from temperature dependent fluorescence studies validate the hydrophobic, spontaneous, exothermic process engaged in trypsin@C440 bio-conjugate.

Synthesis and Characterisation of Ag-Co-Venlafaxine-Cyclodextrin Nanorods

Ag and Ag/Co nanoparticles containing venlafaxine/cyclodextrin (VF/CD) inclusion complexes were synthesized and analyzed by UV-Visible, fluorescence, computational technique, DSC, FTIR, XRD, FE-SEM, and TEM. Single emission was observed in α-CD and β-CD. A blue-shifted absorption and fluorescence maximum was seen in Ag/VF/CD and Ag/Co/VF/CD nanoparticles than VF/CD inclusion complex. TEM image exposed the existence of nanorods in Ag/VF/β-CD and Ag/Co/VF/β-CD. Pure VF drug shows more antibacterial activity than Ag/VF/β-CD and Ag/Co/VF/β-CD nanomaterials. Nano particle size is also measured by X-RD and TEM.

BODIPY phototether enables oligonucleotide cyclization and subsequent deprotection by tissue-transparent red light.

meso-methyl-BODIPY photocages release a leaving group upon visible light irradiation but often lack thermal stability. In turn, our thermally-stable, red-shifted BODIPY phototether allows oligonucleotide cyclization, preventing complementary strand hybridization. Hybridization resumes upon red-NIR irradiation, disconnecting the phototether by oxidative cleavage, which is easily monitored by a blue shift in fluorescence.

Exploration of the impact of graphene oxide, acetylenic gemini, and CTAT on the photophysical and aggregation properties of dipolar coumarin 153.

Advanced spectroscopic techniques have been utilized to study the interaction between the laser dye coumarin 153 (C153) and graphene oxide (GO) nanoparticles. GO was synthesized using a modified Hummers' method and characterized by UV-vis spectroscopy, Raman laser spectroscopy, FTIR-ATR spectroscopy, FESEM, HR-TEM, and XRD techniques. The GO@C153 composite was formed by mixing two aqueous solutions of GO and C153 due to their strong interaction through stacking and hydrophobic interactions. In this case, GO acts as an effective fluorescence quencher for C153 molecules, which undergo H-type aggregation in the presence of GO. The Stern-Volmer equation and time-dependent fluorescence studies were utilized to analyse the mechanism of fluorescence quenching. According to the findings, both static and dynamic quenching processes are responsible for the reduction in fluorescence intensity. The effect of surfactants (both cetyltrimethylammonium p-toluenesulfonate (CTAT) and synthesized N,N'-dihexadecyl-N,N,N',N'-tetramethyl-N,N'-but-2-ynediyl-di-ammonium chloride (16-4-16)) on the aggregation and photophysical properties of the dye was investigated using surface tensiometry, conductometry, UV-vis absorption spectroscopy, steady-state fluorescence measurements, DLS, and time-dependent fluorescence spectroscopy. Surfactants change the microenvironment of the C153 dye, leading to spectrum shifting and a higher quantum yield, which causes a rapid rise in fluorescence intensity in the micellar medium. It has been noted that in a micellar medium rather than in an aqueous one, the luminous intramolecular charge transfer (ICT) state of C153 stabilises. Lastly, we investigated the photophysical behavior of the GO-C153-micelle ternary system and discovered that, in the presence of a micellar medium, the quenched and blue-shifted (H-type aggregation) fluorescence peak of C153 (in the presence of GO) began to intensify once more. The main goal of this work is to create an effective and fairly cost powerful fluorescence sensor. Additionally, the ternary system (GO-C153-micelle) analytical idea can be employed to identify the onset of micelle formation. In wastewater treatment analysis, the GO-C153-surfactant ternary system concept can also be used to regenerate the adsorbent (in this case, GO) from dye molecules by allowing the dye molecules to exit the adsorbent and enter the micellar medium.

Regioisomers containing triarylboron-based motifs as multi-functional photoluminescent materials: from dual-mode delayed emission to pH-switchable room-temperature phosphorescence.

Triarylboron compounds have been established as promising candidates in optoelectronic applications. However, realizing multi-functional properties in triaryl boron-based materials remains challenging. Herein, we present two regioisomers, 1 and 2, designed judiciously by connecting a dimethylamino donor and a dimesitylboryl acceptor at 1,4 and 2,6-positions of the naphthalene spacer, respectively. Both compounds 1 and 2 display simultaneous, delayed fluorescence and persistent room-temperature phosphorescence (580 nm, τ av = 168 ms, Φ = 76% for 1; 550 nm, τ av = 129 ms, Φ = 88% for 2 in 1 wt% PMMA), with the delayed fluorescence bands being sensitive to doping concentration (in PMMA). Notably, compound 1 in 1 wt% PMMA films demonstrates a reversibly switchable single-molecule phosphorescence from orange (580 nm) to green (λ Ph = 550 nm, τ av = 42 ms) in response to pH, which can be utilized for anti-counterfeiting applications. These results were further corroborated by studying the respective cationic salts 1-OTF and 2-OTF. Moreover, 1 and 2 exhibited blue-shifted fluorescence in response to mechanical pressure. Compound 2 also showed three-photon (σ3P) absorption properties which were better compared to those of compound 1.

A Zn(II) metal−organic framework with organic fluorescent ligands and hydrogen-bonding network for effectively sensing Al3+ and Ga3+ ions, and proton conduction

Energy shortage and environmental pollution become increasingly serious. Thus, there is urgent need to develop new functional materials to deal with these problems. Metal−organic frameworks (MOFs) are ideal candidates for fluorescence sensing pollutants and proton conduction. A benzothiadiazole-based three-dimensional (3D) Zn(II) MOF with the formula of {[(CH3)2NH2][Zn3(bbip)(BTDI)1.5(OH)]·DMF·MeOH·3H2O}n (JXUST-13, bbip = 2,6-bis(benzimidazol-1-yl)pyridine and H4BTDI = 5,5′-(benzo[c][1,2,5]thiadiazole-4,7-diyl)diisophthalic acid) with fluorescent ligands and rich hydrogen bond framework was used as a cation fluorescence sensor and proton conduction material. The fluorescence experiment revealed that JXUST-13 could detect Al3+ and Ga3+ ions by fluorescence blue shift and slight fluorescence enhancement. And it showed high sensitivity, good selectivity, anti-interference performance and cyclicity. The detection limits of JXUST-13 toward Al3+ and Ga3+ ions were 4.0 μM and 0.67 μM, respectively. Importantly, it could be rapidly detected by fluorescent test strips and naked eyes. The sensing mechanism may be due to the presence of electron transfer and the formation of exciplex. Proton conduction result indicated that the maximum conductivity value of JXUST-13 was 1.97 × 10−5 S·cm−1 at 80 °C and 98% RH. And the conductivity increased with humidity and temperature. The activation energy (Ea) value of JXUST-13 was 0.47 eV, which revealed the Vehicle mechanism. Therefore, JXUST-13 could be considered as a rare difunctional materials of blue-shifted fluorescence sensor for Al3+, Ga3+ ions and proton conduction.

A new hydrazone linkage-based covalent organic framework for ratiometric fluorescent probe detection of hypochlorite

A new hydrazone-linked covalent organic framework (TFTH-COF) was synthesized and characterized. TFTH-COF has porous crystalline framework structure with high thermal stability. TFTH-COF exhibited highly selective fluorescence blue-shift response towards hypochlorite (ClO−) in ethanol and accompanied by the obvious color change under both day light and UV light. TFTH-COF has the ratiometric fluorescence sensing ability for hypochlorite with high sensitivity. The ratiometric fluorescence intensity of TFTH-COF presented a linear change against hypochlorite concentration with a low detection limit of 0.417 μM. The results of XPS, FT-IR and fluorescence lifetime indicated the formation of hydrogen bond between the O and N atoms of hydroxyl and amine of TFTH-COF with hypochlorite. The DFT calculation further confirmed the formation of hydrogen bond and resulted in the change of fluorescence spectra. Its practical application ability was confirmed by good recovery rate of TFTH-COF in the quantitative detection of hypochlorite in 84 disinfectants and water samples. Moreover, TFTH-COF can also identify hypochlorite through fluorescent test strips by the naked eye. This work sheds light on the fabrication of COFs as ratiometric fluorescence probes for easily-operable, instantaneous and accurate detection and identification of different analytes.

An acetylpyrene-based fluorescent probe for selective detection of cysteine in vitro and in lipid droplets

The development of organelle-targeted probes that enable specific recognition and detection Cysteine (Cys) may provide an effective way to explore physiological processes and pathological mechanisms associated with the related diseases. In this work, an acetylpyrene-based fluorescent probe CP-1 was designed and synthesized for detecting Cys in vitro and in vivo. The probe exhibited a noticeable fluorescence blue shift upon the addition of Cys under UV light, attributed to the mechanism of the nucleophilic addition reaction. The response mechanism for Cys was studied by time-dependent density functional theory (TD-DFT) calculations and mass spectra (MS). CP-1 can not only specifically recognize Cys in the presence of other amino acids and biothiols, but also exhibit the property of targeting lipid droplets (LDs). Due to the good cell biocompatibility, CP-1 has been successfully employed for real-time tracking Cys in LDs of living cells. The ability to target LDs and the favorable biocompatibility make the probe valuable for investigating Cys-related diseases in living cell systems.

(Invited) Exciton Generation in C60 Fullerene Clusters

Carbon-based nanometric-size species have been proposed as valuable key nanomaterials in biomedicine, photocatalysis, photovoltaics and optoelectronics. A common strategy for the development of applications is the design of multi-adduct derivatives. Based on C60 fullerene, it depends on the desired purpose to put the appropriate substituents imparting good solubility and/or intra-/intermolecular interactions. Very promising applications are expected for giant molecules based on hexakis-adducts of C60.1-4 Recently, Martín and co-workers synthesized and characterized the structural and photophysical properties of a series of three tridecafullerenes bearing different glycodendrons and spacers to the C60 units.5 These globular multifullerene systems exhibit rather long-lived triplet excited states and, in particular, one of them, compound 13, showed an exceptional ultra-long-lived triplet state with a mean lifetime of 93 ms in an aqueous phase at room temperature, which is well apart from other organic molecules or coordination compounds reported so far. It is known that molecular systems displaying triplet excited states with ultra-long lifetimes are of particular interest in applications like biomedicine, photovoltaics, nonlinear optics, or photocatalysis. For example, compound 13 might be a good choice for applications of the photodynamic treatment of hypoxic tumors.5 The structural implications were studied in reference 5, but computational studies of the photophysical properties for these tridecafullerene systems have not been unrevealed yet. In reference [5], Martín and co-workers reported the UV/Vis absorption spectra of these tridecafullerenes and compared them with their respective hexakis-adduct precursors. They also collected the fluorescence emission maxima and the lifetimes of the singlet and triplet excited states for all these systems, highlighting the long lifetimes displayed for the tridecafullerenes. It is worth noting the extraordinarily long triplet mean lifetime detected for compound 13, which also showed the highest hypochromic shift in the UV/Vis absorption spectrum, the largest blue-shifted fluorescence and the shortest-lived singlet. In this work, the experimental emission spectrum is provided for each tridecafullerene and precursor, and we emphasize the rarely appearance of the two simultaneously experimental emission peaks at around 2 eV (~620 nm) and 2.8 eV (~443 nm). The emission peak at 2 eV is usual for C60 and derivatives, but not the one at 2.8 eV. Although this abnormal peak is more intense in the precursors, it is also significantly present in the tridecafullerenes. We performed a computationally study about the photophysical properties of these tridecafullerenes compounds as well as for the C60 fullerene. 1 Ramos-Soriano, J.; Reina, J. J.; Illescas, B. M.; de la Cruz, N.; Rodríguez-Pérez, L.; Lasala, F.; Rojo, J.; Delgado, R.; Martín, N. J. Am. Chem. Soc. 2019, 141, 15403–15412. 2 Rodríguez-Pérez, L.; Ramos-Soriano, J.; Pérez-Sánchez, A.; Illescas, B. M.; Muñoz, A.; Luczkowiak, J.; Lasala, F.; Rojo, J.; Delgado, R.; Martín, N. J. Am. Chem. Soc. 2018, 140, 9891–9898. 3 Nierengarten, J. F. Chem. Commun. 2017, 53, 11855 –11868. 4 Muñoz, A.; Sigwalt, D.; Illescas, B. M.; Luczkowiak, J.; Rodríguez-Pérez, L. Nierengarten, I.; Holler, M.; Remy, J. S.; Buffet, K.; Vincent, S. P.; Rojo, J.; Delgado, R.; Nierengarten, J. F.; Martín, N. Nat. Chem. 2016, 8, 50 –57. 5 Ramos-Soriano, J.; Pérez-Sánchez, A.; Ramírez-Barroso, S.; Illescas, B. M.; Azmani, K.; Rodríguez-Fortea, A.; Poblet, J.M.; Hally, C.; Nonell, S.; García-Fresnadillo, D.; Rojo, J.; Martín. N. Angew. Chem. Int. Ed. 2021, 60, 16109–16118. Figure 1

Dual-Responsive Carbon Quantum Dots for the Simultaneous Detection of Cytosine and 5-Methylcytosine Interpreted by a Machine Learning-Assisted Smartphone.

DNA methylation is an epigenetic alteration that results in 5-methylcytosine (5-mC) through the addition of a methyl group to the fifth carbon of a cytosine (C) residue. The methylation level, the ratio of 5-mC to C, in urine might be related to the whole-body epigenetic status and the occurrence of common cancers. To date, never before have any nanomaterials been developed to simultaneously determine C and 5-mC in urine samples. Herein, a dual-responsive fluorescent sensor for the urinary detection of C and 5-mC has been developed. This assay relied on changes in the optical properties of nitrogen-doped carbon quantum dots (CQDs) prepared by microwave-assisted pyrolysis. In the presence of C, the blue-shifted fluorescence intensity of the CQDs increased. However, fluorescence quenching was observed upon the addition of 5-mC. This was primarily due to photoinduced electron transfer as confirmed by the density functional theory calculation. In urine samples, our sensitive fluorescent sensor had detection limits for C and 5-mC of 43.4 and 74.4 μM, respectively, and achieved satisfactory recoveries ranging from 103.5 to 115.8%. The simultaneous detection of C and 5-mC leads to effective methylation level detection, achieving recoveries in the range of 104.6-109.5%. Besides, a machine learning-enabled smartphone was also developed, which can be effectively applied to the determination of methylation levels (0-100%). These results demonstrate a simple but very effective approach for detecting the methylation level in urine, which could have significant implications for predicting the clinical prognosis.

Turn on the luminescence channel by the suppression of conical intersection process for the sulfur-containing hydrogen-bonded molecules

The sulfur-containing hydrogen bonds exhibit notable potential in gene and protein engineering. As an important research direction of sulfur-containing hydrogen bonding dynamics, the excited-state intramolecular proton transfer (ESIPT) reaction of the thiol proton has garnered significant interest. Recently, Chou et al. synthesized a series of sulfur-containing H-bonded molecules, inclusive of 3-thiolflavone (3 TF), its trifluoromethyl derivative (3FTF), and its diethylamino derivative (3NTF), thereby inaugurating a new chapter in the ESIPT reaction of the thiol proton. Nevertheless, many open issues cannot be answered solely by experimental means and call for a detailed theoretical investigation, especially the relationship between the molecular excited-state properties and different luminescence properties of the three molecules. Herein, we validate that the molecules undergo the ESIPT reaction of the thiol proton and identify the time scale through the time-dependent density functional theory (TDDFT) calculation. Moreover, employing the spin-flip TDDFT approach, the analysis of the non-radiative transition process reveals that difference in Gibbs free energy of activation (ΔG⧧) for the transition from Frank-Condon point to minimum energy conical intersection (MECI) point primarily accounts for the different luminescence properties of the three molecules. Besides, we also reveal the reason for the abnormal blue-shifted fluorescence of the 3NTF in the aggregated state by the ONIOM (TDDFT: UFF) strategy. These findings are favorable to understanding the luminescence mechanism of sulfur-containing H-bonded molecules and provide a reference for the synthesis and design of the luminescent materials based on the molecules with thiol proton transfer properties.

A butterfly-shaped AIEgen with excited-state intramolecular proton transfer effect for colorimetric and fluorescent detection of copper and zinc ions

Multipurpose aggregation-induced emission (AIE) fluorescence probes for metal ion detection have drawn extensive interest in recent years. Here, a butterfly-shaped AIE luminogen (TOPD) was synthesized from 2-hydroxy-5-(1,2,2-triphenylethenyl)-benzaldehyde and o-phenylenediamine via a one-step Schiff-base condensation for flexibly detecting copper and zinc ions. The aggregated state of TOPD revealed a large Stokes shift of 263 nm due to the excited-state intramolecular proton transfer (ESIPT) effect benefiting from the planar cis-configuration and enol-keto tautomerization of TOPD molecules confirmed by the modeling investigation. TOPD showed remarkable colorimetric and high selective fluorescence turn-off response to Cu2+ in phosphate buffer saline/tetrahydrofuran (PBS/THF, 9:1, v/v) with a low detection limit (0.14 μM) and quick response time (<30 s). TOPD realized the Zn2+ sensing via turn-on and blue-shifted fluorescence in PBS/THF (8:2, v/v) with a detection limit of 0.93 μM. The significant color changes can be directly discriminated by the “naked eye”. Experiments and DFT theoretical calculations strongly suggested that sensing mechanisms were via 1:1 TOPD-metal complexes. The strategy of tunable AIE fluorescence could provide new ideas for potential applications in the detection of multiple ions in environmental fields.