Fluorescence Characteristics Research Articles

Algal Classification and Chlorophyll-a Concentration Determination Using Convolutional Neural Networks and Three-Dimensional Fluorescence Data Matrices

In recent years, the frequency of harmful algal blooms has increased, leading to the release of large quantities of toxins and compounds that cause unpleasant odors and tastes, significantly compromising drinking water quality. Chlorophyll-a (Chl-a) is commonly used as a proxy for algal biomass. However, current methods for measuring Chl-a concentration face challenges in accurately quantifying algae by categories and effectively adapting to natural aquatic environments. This study combined convolutional neural networks (CNNs) and three-dimensional fluorescence data matrices to address these challenges. The algal classification model achieved over 99.5% accuracy in identifying thirteen types of algal samples, with class activation maps showing that the model primarily focused on algal pigment regions. In determining Chl-a concentrations of each algal species in mixed algae solutions (Microcystis aeruginosa, Cyclotella, and Chlorella), the models demonstrated Mean Absolute Percentage Errors (MAPEs) ranging from 6.55% to 10.56% in the ultrapure water background, 11.57% to 14.12% in the Qingcaosha Reservoir raw water background, and 21.46% to 123.37% in the Lake Taihu raw water background. After calibration, the models were significantly improved, achieving MAPEs ranging from 11.86% to 14.18% in the Lake Taihu raw water background. Discrepancies in determination performance indicated that the intensity and locations of characteristic algal pigment fluorescence peaks greatly influenced the models' accuracy. This research introduces a novel approach for algal classification and Chl-a concentration determination in water bodies, with significant potential for practical applications.

A novel cocrystal of the Zn(II) coordination molecule and the benzimidazole for efficient detection of triethylamine and antibacterial property

A new cocrystal of the Zn(II) coordination molecule and the benzimidazole (bim), [Zn(bim)(SCN)3]-[Hbim] (C10H6N5S3Zn-C7H7N2, cocrystal 1) was directly synthesized at room temperature. X-ray single crystal diffraction analysis showed that cocrystal 1 is extended into a 3D supramolecular network via hydrogen bonding and π⋅⋅⋅π stacking interactions. Information on non-covalent interactions were gathered by calculating the Hirshfeld surface and fingerprint of the crystal stacking of cocrystal 1. Photoluminescence experiments demonstrated that cocrystal 1 not only possessed good solid-state fluorescence performance but also favorable fluorescence characteristics and stability in aqueous solutions. Notably, cocrystal 1 exhibited excellent anti-interference properties, high sensitivity, high fluorescence enhancement, and low limit of detection (LOD: 59.8 μM) against triethylamine (TEA) in aqueous medium via the “Turn-On” effect. In addition, the antimicrobial properties of the cocrystal were investigated. The results of antimicrobial experiments revealed that cocrystal 1 inhibited Escherichia coli (E. coli) and Methicillin-resistant Staphylococcus aureus (MRSA). Molecular docking analysis unraveled the mode of interaction with DNA in bacteria. Cocrystal 1 is a potential multifunctional material for the preparation of TEA sensors and antimicrobial agents. Finally, the possible enhancing mechanism and potential antimicrobial mechanism were researched.

Microwave synthesis of molybdenum disulfide quantum dots and the application in bilirubin sensing

Molybdenum disulfide quantum dots (MoS2QDs) is a new type of graphite like nanomaterial, which exhibited well chemical stability, unique fluorescence characteristics, and excellent biocompatibility. The conventional hydrothermal synthesis of MoS2generally requires a long-term reaction at high temperature and high pressure. Herein, we have developed a simple and fast MoS2QDs synthesis scheme using microwave heating, and further modified the surface of MoS2QDs using 3-aminophenylboronic acid. The 3- aminophenylboronic acid modified MoS2QDs (B-MoS2QDs) were further coated by a zinc-based metal-organic backbone (ZIF-8) in a solution containing zinc ions and 2-methylimidazolium. The constructed nanohybrid B-MoS2@ZIF-8 were successfully applied to the visualization and rapid detection of bilirubin based on the ratiometric fluorescence changes. The linear range for bilirubin detection is 0.2-75 μmol·l-1, and detection limit is 0.017 μmol·l-1.

Fluorescence characteristics of dissolved organic matter in relation to land use in the wetland waters of Poyang Lake, China

Dissolved organic matter (DOM) plays a fundamental role in regulating carbon cycling and mediating various biogeochemical processes in wetland ecosystems. In this paper, DOM absorption and fluorescence spectra, and other data from thirty representative sites of wetland waters in Poyang Lake were collected in 2021. The composition, spatial distribution, and source characteristics of DOM were analyzed by 3D fluorescence spectroscopy technique combined with parallel factor analysis (PARAFAC). The findings showed that: (1) Two humic-like constituents (C1, C2) and a tryptophan constituent (C3) were recognized in the PARAFAC model. (2) The fluorescent DOM (FDOM) constituents in the Poyang Lake wetlands showed spatial differences. The fluorescence intensity of C1 and C2 were higher in the south and north sections, and lower in the east and west sections. The fluorescent intensity of C3 in the northern wetland waters was higher than other areas. (3) DOM in the Poyang Lake wetlands was predominantly influenced by inputs from terrestrial sources. Land use type analysis showed that marshland and cultivated land have a great impact on DOM in Poyang Lake. Spatial differences of fluorescent components reveal the impacts of human-induced land use variations. The results enhance our understanding of the significant role of land use in biogeochemical processes, particularly in the export of DOM to aquatic environments. Furthermore, they provide guidance for the management and protection of water resources in the Poyang Lake wetland.

Ex Vivo Biosafety and Efficacy Assessment of Advanced Chlorin e6 Nanoemulsions as a Drug Delivery System for Photodynamic Antitumoral Application

The photosensitizer (PS) in the Photodynamic Therapy (PDT) field represents a key factor, being directly connected to the therapeutic efficacy of the process. Chlorin e6 is a second-generation photosensitizer, approved by the FDA with the most desired clinical properties for PDT applications, presenting high reactive oxygen species (ROS) generation and proven anticancer properties. However, hydrophobicity is a major limitation, leading to poor biodistribution. To overcome this condition, the present work developed an up-to-date nanoemulsion incorporating Ce6 in a new nanosystem (Ce6/NE). A comprehensive study of physicochemical properties, stability, fluorescence characteristics, the in vitro release profile, in vivo and ex vivo biocompatibility, and ex vivo efficacy was established. The nanoemulsions showed the desired particle size and stability over six months, with no spectroscopic or photophysical alterations. Uptake studies demonstrated the internalization of the Ce6/NE in monolayers, with biocompatibility at the lowest concentrations. The HET-CAM assay, however, revealed a higher biocompatibility range, also indicating Ce6/NE’s potential for cancer treatment through antiangiogenic studies. These findings highlight the use of a new promising photosensitizer for PDT modulated with nanotechnology that promotes low toxicity, higher bioavailability, and site-specific delivery.

Preferential Binding of a Long-Arm Porphyrin Ligand to Higher Order G-Quadruplex under Crowding Conditions.

Under conditions that are close to the real cellular environment, the human telomeric single-stranded overhang (∼200 nt) consisting of tens of TTAGGG repeats tends to form higher order structures of multiple G-quadruplex (G4) blocks. On account of the higher biological relevance of higher order G4 structures, ligand compounds binding to higher order G4 are significant for the drug design toward inhibiting telomerase activity. Here, we study the interaction between a cationic porphyrin derivative, 5,10,15,20-tetra{4-[2-(1-methyl-1-piperidinyl)propoxy]phenyl}porphyrin (T4), and a human telomeric G4-dimer (AG3(T2AG3)7) in the mimic intracellular molecularly crowded environment (PEG as a crowding agent) and K+ or Na+ solution (i.e., K+-PEG and Na+-PEG), by means of multiple steady-state and time-resolved spectroscopic techniques. It is revealed that the long-armed T4 selectively binds to the K+-PEG G4-dimer by intercalating into the cleft pocket between the two G4 blocks, since the two G4 monomers with parallel-stranded topology are stacked by head-to-tail arrangement and can offer π-stacking interface binding with T4. In contrast, the Na+-PEG G4-dimer with antiparallel-stranded topology adopts side-by-side arrangement of G-quartets, resulting in a lack of π-π binding sites to stabilize T4 within the cleft, and no obvious binding characteristics are observed. Interestingly, it is observed that protonation of T4 is facilitated upon binding with the K+-PEG G4-dimer, which can occur under physiological pH, due to the π-π stacking with two G-quartet planes that enhances the electron-rich character of the central porphyrin core of T4. Afterward, the protonated T4 displays dramatically different spectral characteristics (Soret band, Q-band, fluorescence band, and lifetime), which in turn serves as a spectral reporter for characterizing the DNA-binding event. These findings provide a mechanistic basis for developing targeted ligands that can specifically interact with higher order physiological G4 structures.

A Colorimetric and Fluorescent Dual-Mode Sensor Based on a Smartphone-Assisted Laccase-like Nanoenzyme for the Detection of Tetracycline Antibiotics

A copper-based nanoenzyme (Cu-BL) co-modified by L-L-lysine and 2-2-amino terephthalic acid has laccase-like activity and fluorescence characteristics. Based on this, a colorimetric and fluorescent dual-mode sensor was developed to visually and quantitatively detect tetracycline antibiotics (TCs), including tetracycline (TC), chlortetracycline (CTC), and oxytetracycline (OTC). In the colorimetric detection system, TCs can inhibit the generation of singlet oxygen (1O2) and weaken the ability of 2,4-dichlorophenol (2,4-DP) to be oxidized into pink-colored quinone substances. The linear ranges are 0.5–80 μM, 1–80 μM, and 0.25–80 μM, and the detection limits are 0.27 μM, 0.22 μM, and 0.26μM, respectively. In addition, due to the inner filter effect, tetracycline antibiotics can interact with Cu-BL, and with the increase in tetracycline antibiotic concentration, the fluorescence intensity will decrease. In addition, the smartphone sensing platform is combined with the colorimetric signal for the rapid and visual quantitative detection of tetracycline antibiotics. Generally speaking, the colorimetric/fluorescence dual-mode sensor demonstrates good stability, high specificity, and strong anti-interference capabilities, highlighting its practical application potential. This work is expected to offer novel insights for the development of multifunctional nanoenzymes and the integration of a multi-mode sensing platform.

Probing the Self-Aggregation of l-Tryptophan into Spherical Microstructures and Their Selective Interactions with Bilirubin.

The aggregation of proteins, peptides and amino acids has been a keen subject of interest owing to their implications in metabolic disorders. In this work, we investigated the self-aggregation of the unmodified aromatic amino acid l-tryptophan (Trp) into unusual spherical microstructures. Using fluorescence spectroscopy and field emission scanning electron microscopy (FE-SEM), we detail the time-dependent transformation of monomeric tryptophan into spherical aggregates with distinct fluorescence characteristics (λex = 345 nm, λem = 430 nm) compared to the monomer. Notably, the fluorescence intensity of these aggregates is selectively quenched in the presence of bilirubin, demonstrating exceptional sensitivity in the picomolar concentration range. The developed assay proved applicable and reliable for real sample analysis. Thermodynamic parameters derived from temperature-dependent fluorescence intensity measurements indicated that the aggregation process is spontaneous and driven by noncovalent interactions. Further evidence of bilirubin's strong association with the aggregates was obtained through competitive interaction studies with human serum albumin (HSA). This work offers insights into the aggregation behavior of single aromatic amino acids and their potential applications in detecting critical analytes.

Aggregation control of anionic pentamethine cyanine enabling excitation wavelength selective NIR-II fluorescence imaging-guided photodynamic therapy

Near-infrared (NIR)-II fluorescence imaging-guided photodynamic therapy (PDT) has shown great potential for precise diagnosis and treatment of tumors in deep tissues; however, its performance is severely limited by the undesired aggregation of photosensitizers and the competitive relationship between fluorescence emission and reactive oxygen species (ROS) generation. Herein, we report an example of an anionic pentamethine cyanine (C5T) photosensitizer for high-performance NIR-II fluorescence imaging-guided PDT. Through the counterion engineering approach, a triphenylphosphine cation (Pco) modified with oligoethylene glycol chain is synthesized and adopted as the counterion of C5T, which can effectively suppress the excessive and disordered aggregation of the resulting C5T-Pco by optimizing the dye amphipathicity and enhancing the cyanine-counterion interactions. Dynamic tuning of fluorescence characteristics and ROS generation is achieved at the aggregate level, resulting in an impressive type I ROS generation under 760 nm light irradiation, accompanied by efficient NIR-II fluorescence emission excited at 808 nm. As a result, excitation wavelength selective NIR-II fluorescence imaging-guided PDT has been successfully demonstrated for tumor diagnosis and therapeutics of female mice.

Unlocking the Photoluminescence Potential of Tabebuia Rosea Dyes: A Novel Natural Source of Broadband Visible Spectral Fluorescence for OLED Technologies.

This investigation delves into the extraction of polyphenols from the flowers of Tabebuia rosea using a basic maceration approach with acetone, ethanol, and methanol as solvents. The spectroscopic analysis of the dye obtained confirms the existence of functional groups in the polyphenol extract. The study also explores optoelectronic, fluorescence, and photometric characteristics associated with polyphenols. Micro-destructive surface techniques, such as XPS led to the acquisition of detailed information on the extracted polyphenol. The XPS analysis verified the chemical composition of the dyes, revealing that C1s, O1s, and N1s peaks are the main signals for the extracted polyphenols. Additionally, the LC-MS analysis reveals the extract contains significant amounts of active compounds in the polyphenols class, which share a common polyphenol structure. FT-IR spectroscopy confirms the presence of functional groups in the polyphenol dye extract. The optical properties showed a narrow direct bandgap (Eg= 3.08eV), indirect bandgap (Eg=2.77eV), high refractive index (n = 1.52), dielectric constant (ε = 8.982), and high optical conductivity (σ = 3.54 x103 S/m) for the polyphenols extracted in methanol solvent. Polyphenols are characterized by high quantum yield, substantial lifetime, and notable Stoke's shift. In addition, these polyphenol dyes demonstrate strong broadband visible spectra and cover a spectrum from blue to green (x = 0.32 → 0.33 and y = 0.33 → 0.38) in different solvent conditions. Such attributes make them advantageous for use in Organic-LEDs and other optoelectronic technologies, underscoring their significant potential in these domains. In addition, polyphenols are important in removing DPPH-free radicals from the environment, contributing to the production of highly antioxidant green materials.

Fluorescence Characteristics of Hoechst 33258 Complexes with Single-Stranded and Double-Stranded Polyribonucleotides in Solution at Various Solution Ionic Strengths

Fluorescence Characteristics of Hoechst 33258 Complexes with Single-Stranded and Double-Stranded Polyribonucleotides in Solution at Various Solution Ionic Strengths

Enhanced proconvulsant sensitivity, not spontaneous rapid swimming activity, is a robust correlate of scn1lab loss-of-function in stable mutant and F0 crispant hypopigmented zebrafish expressing GCaMP6s.

Zebrafish models of genetic epilepsy benefit from the ability to assess disease-relevant knock-out alleles with numerous tools, including genetically encoded calcium indicators (GECIs) and hypopigmentation alleles to improve visualization. However, there may be unintended effects of these manipulations on the phenotypes under investigation. There is also debate regarding the use of stable loss-of-function (LoF) alleles in zebrafish, due to genetic compensation (GC). In the present study, we applied a method for combined movement and calcium fluorescence profiling to the study of a zebrafish model of SCN1A , the main gene associated with Dravet syndrome, which encodes the voltage-gated sodium channel alpha1 subunit (Nav1.1). We evaluated for spontaneous and proconvulsant-induced seizure-like activity associated with scn1lab LoF mutations in larval zebrafish expressing a neuronally-driven GECI (elavl3:GCaMP6s) and a nacre mutation causing a common pigmentation defect. In parallel studies of stable scn1lab s 552 mutant s and F0 crispant larvae generated using a CRISPR/Cas9 multi-sgRNA approach, we find that neither stable nor acute F0 larvae recapitulate the previously reported seizure-like rapid swimming phenotype nor does either group show spontaneous calcium events meeting criteria for seizure-like activity based on a logistic classifier trained on movement and fluorescence features of proconvulsant-induced seizures. This constitutes two independent lines of evidence for a suppressive effect against the scn1lab phenotype, possibly due to the GCaMP6s-derived genetic background (AB) or nacre hypopigmentation. In response to the proconvulsant pentylenetetrazole (PTZ), we see evidence of a separate suppressive effect affecting all conspecific larvae derived from the stable scn1lab s 552 line, independent of genotype, possibly related to a maternal effect of scn1lab LoF in mutant parents or the residual TL background. Nonetheless, both stable and F0 crispant fish show enhanced sensitivity to PTZ relative to conspecific larvae, suggesting that proconvulsant sensitivity provides a more robust readout of scn1lab LoF under our experimental conditions. Our study underscores the unexpected challenges associated with the combination of common zebrafish tools with disease alleles in the phenotyping of zebrafish models of genetic epilepsy. Our work further highlights the advantages of using F0 crispants and the evaluation of proconvulsant sensitivity as complementary approaches that faithfully reflect the shared gene-specific pathophysiology underlying spontaneous seizures in stable mutant lines. Future work to understand the molecular mechanisms by which scn1lab -related seizures and PTZ-related hyperexcitability are suppressed under these conditions may shed light on factors contributing to variability in preclinical models of epilepsy more generally and may identify genetic modifiers relevant to Dravet syndrome.

Microwave synthesis of molybdenum disulfide quantum dots and the application in bilirubin sensing.

Molybdenum disulfide quantum dots (MoS2 QDs) is a new type of graphite like nanomaterial, which exhibited well chemical stability, unique fluorescence characteristics, and excellent biocompatibility. The conventional hydrothermal synthesis of MoS2 generally requires a long-term reaction at high temperature and high pressure. Herein, we have developed a simple and fast MoS2 QDs synthesis scheme using microwave heating, and further modified the surface of MoS2 QDs using 3-aminophenylboronic acid. The 3- aminophenylboronic acid modified MoS2 QDs (B-MoS2 QDs) were further coated by a zinc-based metal-organic backbone (ZIF-8) in a solution containing zinc ions and 2-methylimidazolium. The constructed nanohybrid B-MoS2@ZIF-8 were successfully applied to the visualization and rapid detection of bilirubin based on the ratiometric fluorescence changes. The linear range for bilirubin detection is 0.2-75 μmol•L-1, and detection limit is 0.017 μmol•L-1.

Yellow fluorescent UV-curable epoxy acrylate/VTMS-modified GQDs coatings: study of UV-blocking and viscoelastic properties

Polymer coatings decompose in the presence of UV radiation from sunlight and beget economic and environmental losses. Hence, it is necessary to reinforce the polymer coatings with UV-blocking nanoparticles and to convert the UV light into visible light. In this research work, the surface of graphene quantum dots (GQDs) was modified by vinyltrimethoxysilane (VTMS). VTMS-modified GQDs (VmGQDs) including 0, 0.3 and 0.6 wt% were taken into account to synthesize UV-curable epoxy acrylate/VmGQDs (Ep/VmGQDs) nanocomposite coatings. Surface modification, UV-blockage, fluorescence features and viscoelastic properties of Ep/VmGQDs coatings were analyzed by various spectrometry tests. The existence of VmGQDs (0.3 wt% and 0.6 wt%) in the polymer matrix led to absorption of UV rays in UV regions and fluorescence emission in the visible area with 578 nm wavelength (yellow fluorescence). Appearance of strong absorption bands at 250, 285 and 365 nm by the coatings with VmGQDs confirmed that a large portion of UV rays was absorbed and blocked. The intensity of UV-blockage by Ep/VmGQDs 0.6 wt% was recorded >99%. Furthermore, reinforcement of the coatings with VmGQDs resulted in increase in storage modulus, cross-linking density and Tg value.

Conjugated Microporous Polymer-Based Fluorescent Probe for Selective Detection of Nitro-explosives and Metal Nitrates.

The sensitive and selective identification of nitroaromatic explosives and industrially ubiquitous nitrates, which are harmful to the environment, is crucial from the viewpoints of security and environmental remediation. New multifunctional fluorescent porous materials that can sense nitro-explosives and nitrates are under continuous development. To this end, this study synthesizes 3,10,15-/-3,10,16-tribromotrinaphtho[3.3.3]propellane (TBP) and 4,7-bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-2,1,3-benzothiadiazole (BB) and employs them as dual building blocks to prepare a porous conjugated microporous polymer (denoted as CMP-TBP-BB) via Suzuki-Miyaura borylation polycondensation. The CMP-TBP-BB synthesis strategy takes advantage of the donor and acceptor characteristics of the propeller-like trinaphtho[3.3.3]propellane moiety in TBP and the benzothiadiazole group in BB, respectively. The unusual two-dimensional conformation of the CMP with propeller-array-structured monomers helps to position the π components in the crystalline layers and establishes aligned conduction pathways. CMP-TBP-BB exhibits outstanding fluorescence characteristics. Its distinctive two-dimensional skeleton is exploited to fabricate highly aligned donor-acceptor building blocks, which is typically considered a challenging task. The porous CMP acts as a fluorescent sensor for selectively and sensitively detecting electron-deficient nitro-explosives and metal nitrates. Specifically, CMP-TBP-BB is responsive to 2,4,6-trinitrophenol and Fe(NO3)3 at parts per million levels, and the results of combined experimental and theoretical investigations of its sensing properties highlight its potential as a CMP-based fluorescence probe. Additionally, the dual-function fluorescent CMP probe exhibits remarkable temperature-sensing behavior owing to the high linearity between the fluorescence intensity and temperature, making it an excellent fluorescent thermometer.

Maturing conditions of bimetallic nanocomposites as a new factor influencing Au-Ag synergism and impact of Cu(II) and/or Fe(III) on luminescence.

Gold-silver synergism has been well documented in many scientific works dealing with luminescent nanostructures that are exploitable in biomedical and environmental application. Frequently, the ratio of Au : Ag in synthetic mixtures was varied to influence the extent of Au-Ag synergism of the resulting luminescent gold-silver nanoclusters (GSNCs). However, in our approach, a new step, maturing under differing conditions using the same Au : Ag ratio (5 : 1), has been investigated systematically for the very first time. As referent systems, monometallic gold nanoclusters (AuNCs) and protein treated by the conditions of synthesis and maturing were prepared and investigated. The selected types of maturing conditions led to distinct changes in fluorescence characteristics and, consequently, Au-Ag synergism extent (evaluated as the ratio of fluorescence quantum yields of GSNCs versus AuNCs). The best synergism was obtained for GSNCs matured at 37°C for 2.5 h. The stability of luminescent signal of these GSNCs was tested in the presence of an excess (to 20 mM) of Cu(II) and/or Fe(III) ions (crucial cofactors in living systems). The same metallic ion concentration caused different extents of GSNC luminescence quenching, for which a plausible reasoning is suggested.

Ruthenium-catalyzed C-H bond activation and annulation of phenothiazine-3-carbaldehydes: facile access to dual-emission materials.

Reported herein is the first example of a ruthenium-catalyzed C-H activation/annulation of phenothiazine-3-carbaldehydes to construct structurally diverse pyrido[3,4-c]phenothiazin-3-iums with dual-emission characteristics. Novel organic single-molecule white-light materials based on pyrido[3,4-c]phenothiazin-3-iums with dual-emission and thermally activated delayed fluorescence (TADF) characteristics have been developed for the first time herein. Furthermore, the dual-emission molecule could be fabricated as water-dispersed NPs, which could be applied in two-channel emission intensity ratio imaging to observe the intercellular structure and can specifically target the cell membrane.

Identifying sources of dissolved organic matter in sediments of a shallow lake by fluorescence and ultraviolet spectral characteristics of water and alkali extractable organic matter (WEOM and AEOM)

Identifying sources of dissolved organic matter in sediments of a shallow lake by fluorescence and ultraviolet spectral characteristics of water and alkali extractable organic matter (WEOM and AEOM)

Archaerhodopsin 3 is an ideal template for the engineering of highly fluorescent optogenetic reporters.

Archaerhodopsin-3 (AR-3) variants stand out among other rhodopsins in that they display a weak, but voltage-sensitive, near-infrared fluorescence emission. This has led to their application in optogenetics both in cell cultures and small animals. However, in the context of improving the fluorescence characteristics of the next generation of AR-3 reporters, an understanding of their ultrafast light-response in light-adapted conditions, is mandatory. To this end, we present a combined experimental and computational investigation of the excited state dynamics and quantum yields of AR-3 and its DETC and Arch-5 variants. The latter always display a mixture of all-trans/15-anti and 13-cis/15-syn isomers, which leads to a bi-exponential excited state decay. The isomerisation quantum yield is reduced more than 20 times as compared to WT AR-3 and proves that the steady-state fluorescence is induced by a single absorption photon event. In wild-type AR-3, we show that a 300 fs, barrier-less and vibrationally coherent isomerization is driven by an unusual covalent electronic character of its all-trans retinal chromophore leading to a metastable twisted diradical (TIDIR), in clear contrast to the standard charge-transfer scenario established for other microbial rhodopsins. We discuss how the presence of TIDIR makes AR-3 an ideal candidate for the design of variants with a one-photon induced fluorescence possibly reaching the emission quantum yield of the top natural emitter neorhodopsin (NeoR).

A novel ratiometric fluorescent probe based on an internal reference of lanthanide/nucleotide for alkaline phosphatase detection.

Based on the specific hydrolytic ability of alkaline phosphatase (ALP), a novel biocompatible ratiometric lanthanide fluorescent probe based on an internal reference (CIP@SiO2-Ce/ATP-Tris) was constructed with Ce3+ as the central ion, adenosine triphosphate (ATP) as the ligand, Tris as the auxiliary ligand and ciprofloxacin (CIP) encapsulated into SiO2 nanoparticles as the reference signal. The fluorescent probe emits characteristic fluorescence at 363 nm belonging to Ce3+ as the working signal and at 435 nm belonging to CIP as the reference signal. Dephosphorylation disrupted the coordination of Ce/ATP-Tris with the enzymatic reaction of ALP, which resulted in fluorescence quenching of Ce3+. The reference fluorescence was kept stable because of the protective effect of encapsulation by SiO2. The biosensor analysis method was achieved by comparing the relationship between I435/I363 and ALP concentration. The detection limit is 0.0025 U L-1, and the linear range of detection is 0.1-20 U L-1. It was subsequently used to detect ALP in samples of fetal bovine serum and human serum, and promising results were obtained.