Photoinduced Electron Transfer Sensors Research Articles

Dual-Functional Manganese-Doped ZnO-MOF Hybrid Material with Enhanced Hydrolytic Stability: A Fluorescent Photoinduced Electron Transfer Sensor for the Ultraselective Detection of Acetic Acid and Chromium (VI).

In recent years, the synthesis of metal-organic framework (MOF)─nanocomposites has received wide attention from the scientific fraternity due to the presence of a tunable hierarchical architecture and invasive versatility in applications. The present work focuses on the solvothermal synthesis of a novel hybrid MOF-nanocomposite through the impregnation of Mn-doped ZnO nanoparticles onto the matrix of a pioneer metal-organic framework that is composed of zinc metal connected with terephthalic acid linkers (MOF-5). The hierarchical arrangements of the prepared material were further assessed by Fourier-transform infrared spectroscopy (FTIR), powder X-ray diffraction (PXRD), high-resolution transmission electron microscopy (HR-TEM), UV-visible, photoluminescence (PL), and dynamic light scattering (DLS) measurements. The porosity analysis via nitrogen sorption measurements at 77 K showed that the material is porous with hierarchical micro-, wide micro-, and mesopores. The SAED pattern confirms the polycrystallinity of the material, which is in good agreement with the data obtained from PXRD analysis. Effective integration of Mn-doped ZnO onto the MOF structure was confirmed by XPS analysis, and the study further identified the oxidation state of the elements present. The synthesized analyte is an efficient fluorescent chemosensor for the detection of acetic acid, which can find further potential applications in intracellular imaging. Interestingly, the same compound also selectively detects the presence of Cr(VI) ions, thereby acting as a dual sensor, which finds applications in the sensing and removal of environmental contaminants. The material showed a sharp and intense emission at 569 nm at an excitation wavelength of 320 nm, and it exhibits high quenching efficiencies of 99.87 and 71.43% toward the sensing of μM level concentration of acetic acid and Cr2O72-, respectively. The highly efficient fluorescent sensing of pollutants, even at a shorter linear range, discarded the possibility of sensing the pollutants at higher concentration ranges. The Ksv value for the detection of acetic acid and Cr(VI) is found to be 3.7017 × 106 and 11.0324 × 106 M-1, respectively, which further confirms the higher sensing ability of the synthesized fluorophore. The mechanistic studies and density functional theory calculations of Mn-doped ZnO@MOF-5 reveal that photoinduced electron transfer plays a significant role in the turn-off response toward acetic acid and Cr2O72- ions. In the case of acetic acid, in addition to photoinduced electron transfer, hydrogen bonding interactions may also lead to fluorescence quenching. To the best of our knowledge, no precedent work has been reported for the sensing of acetic acid in the solution state. All other fluorescent sensing reports put forward the sensing and adsorption of acetic acid in the gaseous state, which makes this material a pioneer among others for the detection of acetic acid in the solution phase.

A Tool, an App and a Field: Fluorescent PET Sensors, Blood Electrolyte Analysis and Molecular Logic as Products of Supramolecular Photoscience from Northern Ireland and Sri Lanka.

The general tool of fluorescent PET (photoinduced electron transfer) sensors/switches - a molecular design principle with engineering features - is outlined, with the aid of frontier orbital energy diagrams. Fluorophores such as anthracene, 1,3-diaryl-Δ2 -pyrazolines and 4-amino-1,8-naphthalimides are employed within this system, alongside receptors such as amines, carboxylates, crown ethers and amino acids. This tool appealed to a multinational corporation for building a medical analyzer for electrolytes such as Na+ , K+ , Ca2+ and gases like CO2 , which became a commercially successful application. Finally, the tool was a springboard for chemistry to cross into computer science. The field of molecular logic can elucidate how molecules inside us handle information. Molecular examples of the simplest logic gates such as YES, NOT, OR, AND are described. A case of a human-level computation - visual edge detection - is also included.

Crossing the divide: Experiences of taking fluorescent PET (photoinduced electron transfer) sensing/switching systems from solution to solid

The author's journey from the initial discoveries of fluorescent PET (photoinduced electron transfer) sensors and logic gates to their applications in solid-based devices is outlined. Functional molecules are immobilized on particles, films, fibres, beads and sheets for a range of purposes in analysis and identification, as well as the emulation of animal and computer behaviour.

Rare-Earth Eu3+/Gold Nanocluster Ensemble-Based Fluorescent Photoinduced Electron Transfer Sensor for Biomarker Dipicolinic Acid Detection.

The use of metal ions to bridge the fluorescent materials to target analytes has been demonstrated to be a promising way to sensor design. Herein, the effect of rare-earth ions on the fluorescence of l-methionine-stabilized gold nanoclusters (Met-AuNCs) was investigated. It was found that europium (Eu3+) can significantly suppress the emission of Met-AuNCs, while other rare-earth ions showed a negligible impact. The mechanism on the observed fluorescence quenching of Met-AuNCs triggered by Eu3+ was systematically explored, with results revealing the dominant role of photoinduced electron transfer (PET). Eu3+ can bind to the surface of Met-AuNCs by the coordination effect and accepts the electron from the excited Met-AuNCs, which results in Met-AuNC fluorescence suppression. After introducing dipicolinic acid (DPA), an excellent biomarker for spore-forming pathogens, Eu3+ was removed from the surface of Met-AuNCs owing to the higher binding affinity between Eu3+ and DPA. Consequently, an immediate fluorescence recovery occurred when DPA was present in the system. Based on the Met-AuNC/Eu3+ ensemble, we then established a simple and sensitive fluorescence strategy for turn-on determination of biomarker DPA, with a linear range of 0.2-4 μM and a low limit of detection of 110 nM. The feasibility of the proposed method was further validated by the quantitative detection of DPA in the soil samples. We believe that this study would significantly facilitate the construction of metal-ion-mediated PET sensors for the measurement of various interested analytes by applying fluorescent AuNCs as detection probes.

Rational Design of High-Performance Donor-Linker-Acceptor Hybrids Using a Schiff Base for Enabling Photoinduced Electron Transfer.

Donor-linker-acceptor (D-L-A)-based photoinduced electron transfer (PET) has been frequently used for the construction of versatile fluorescent chemo/biosensors. However, sophisticated and tedious processes are generally required for the synthesis of these probes, which leads to poor design flexibility. In this work, by exploiting a Schiff base as a linker unit, a covalently bound D-L-A system was established and subsequently utilized for the development of a PET sensor. Cysteamine (Cys) and N-acetyl-l-cysteine (NAC) costabilized gold nanoclusters (Cys/NAC-AuNCs) were synthesized and adopted as an electron acceptor, and pyridoxal phosphate (PLP) was selected as an electron donor. PLP can form a Schiff base (an aldimine) with the primary amino group of Cys/NAC-AuNC through its aldehyde group and thereby suppresses the fluorescence of Cys/NAC-AuNC. The Rehm-Weller formula results and a HOMO-LUMO orbital study revealed that a reductive PET mechanism is responsible for the observed fluorescence quenching. Since the pyridoxal (PL) produced by the acid phosphatase (ACP)-catalyzed cleavage of PLP has a weak interaction with Cys/NAC-AuNC, a novel turn-on fluorescent method for selective detection of ACP was successfully realized. To the best of our knowledge, this is the first example of the development of a covalently bound D-L-A system for fluorescent PET sensing of enzyme activity based on AuNC nanoprobes using a Schiff base.

Lighting-up protein-ligand interactions with fluorescent PET (photoinduced electron transfer) sensor designs.

The fluorescence of sensors 1 and 6, which are designed in terms of photoinduced electron transfer (PET), is switched 'on' by factors of 15 and 6 with avidin in a rather selective manner. Sensors 3 and 7, simpler derivatives of 1, are switched 'on' by factors of 16 and 7.5 with bovine serum albumin, though at 30-fold higher concentrations.

Controlling the Fluorescence Response of PET Sensors via the Metal-Ion π-Contacting Ability of the Fluorophore: Coumarin, a Weaker π Contacter.

The π-contact hypothesis, that quenching of the fluorescence of complexes of photoinduced electron transfer sensors with heavy diamagnetic metal ions may be caused by π contacts between the metal ion and the fluorophore of the sensor, is examined with a study of the fluorescent properties of the sensor 4-[[bis(2-pyridinylmethyl)amino]methyl]-6,7-dimethoxy-1-benzopyran-2-one (cdpa) and the structures of its complexes with some metal ions. The coumarin-type fluorophore of cdpa is a weaker π-contact former than the anthracenyl fluorophore of the analogue adpa (Inorg. Chem. 2014, 53, 9014): only Ag(I), the strongest π contact former, quenches the fluorescence of cdpa, apart from paramagnetic Cu(II) and Ni(II), which quench fluorescence by a redox mechanism not requiring π contacts. The structures of [Ag(cdpa)NO3] (1), [Pb(cdpa)(NO3)2] (2), [Zn(cdpa)(NO3)2] (3), [Cd(cdpa)Cl2]2 (4), [Cd(cdpa)2H2O](NO3)2 (5), and [Hg(cdpa)2H2O](NO3)2 (6) are reported. Structure 1 shows that Ag(I) is the only metal ion studied that forms π contacts with the fluorophore of cdpa in the solid state: Ag···C η(2) π contacts of 3.083 and 3.095 Å, in line with quenching of the fluorescence of the Ag(I)(cdpa) complex. In contrast, Pb(II), Zn(II), and Cd(II) show chelation-enhanced fluorescence in their cdpa complexes, and the structures of 2-4 show that the fluorophore of cdpa in each case forms no π contacts. By contrast, the adpa complexes of Pb(II) and Cd(II) show π contacts with its more strongly π-contacting fluorophore (Inorg. Chem. 2014, 53, 9014). The structures of 5 and 6 show bis-complexes of cdpa: the coordination geometries of Cd(II) and Hg(II) are discussed in relation to the number of covalently bound donor atoms present. The preferred hapticity of π-contacted metal ions is evaluated from the literature structures, suggesting that d(10) metal ions such as Ag(I) and Hg(II), and tetragonally distorted Cu(II) and Pd(II), prefer η(1) and η(2) π contacts, while more ionically bound metal ions such as K(I), Ba(II), and La(III), as well as d(10)s(2) metal ions such as Tl(I), Pb(II), and Bi(III), prefer η(6) contacts.

ChemInform Abstract: Current Developments in Fluorescent PET (Photoinduced Electron Transfer) Sensors and Switches

AbstractReview: 138 refs.

Fluorescence sensor for water based on PET (photo-induced electron transfer): Anthracene-bis(aminomethyl)phenylboronic acid ester

In order to provide a direction in molecular design toward creating a highly-sensitive fluorescence PET (photo-induced electron transfer) sensor for a trace amount of water in organic solvents, we have designed and synthesized anthracene-bis(aminomethyl)phenylboronic acid ester OA-1 and OA-2, without substituent and with cyano group, respectively, on the phenylboronic acid ester. It was found that the introduction of bis(aminomethyl)phenylboronic acid ester on the fluorophore such as anthracene activates significantly the PET compared with that of an (aminomethyl)phenylboronic acid ester. On the basis of the proposed mechanisms of fluorescence PET sensors for detection of water, a key point for creating a highly-sensitive fluorescence PET sensor based on fluorophore–phenylboronic acid ester for a trace amount of water is to effectively facilitate the formation of fluorescent ionic structure by the addition of water molecules.

Current developments in fluorescent PET (photoinduced electron transfer) sensors and switches.

Following a brief introduction to the principle of fluorescent PET (photoinduced electron transfer) sensors and switches, the outputs of laboratories in various countries from the past year or two are categorized and critically discussed. Emphasis is placed on the molecular design and the experimental outcomes in terms of target-induced fluorescence enhancements and input/output wavelengths. The handling of single targets takes up a major fraction of the review, but the extension to multiple targets is also illustrated. Conceptually new channels of investigation are opened up by the latter approach, e.g.'lab-on-a-molecule' systems and molecular keypad locks. The growing trends of theoretically-fortified design and intracellular application are pointed out.

Naphthalimide-based fluorescent photoinduced electron transfer sensors for saccharides

A fluorescent probe based on PET mechanism exhibited significant fluorescence enhancement toward saccharides and was used to detect fructose in beverages with good recovery.

Significant expansion of fluorescent protein sensing ability through the genetic incorporation of superior photo-induced electron-transfer quenchers.

Photo-induced electron transfer (PET) is ubiquitous for photosynthesis and fluorescent sensor design. However, genetically coded PET sensors are underdeveloped, due to the lack of methods to site-specifically install PET probes on proteins. Here we describe a family of acid and Mn(III) turn-on fluorescent protein (FP) sensors, named iLovU, based on PET and the genetic incorporation of superior PET quenchers in the fluorescent flavoprotein iLov. Using the iLovU PET sensors, we monitored the cytoplasmic acidification process, and achieved Mn(III) fluorescence sensing for the first time. The iLovU sensors should be applicable for studying pH changes in living cells, monitoring biogentic Mn(III) in the environment, and screening for efficient manganese peroxidase, which is highly desirable for lignin degradation and biomass conversion. Our work establishes a platform for many more protein PET sensors, facilitates the de novo design of metalloenzymes harboring redox active residues, and expands our ability to probe protein conformational dynamics.

Development of highly-sensitive fluorescence PET (photo-induced electron transfer) sensor for water: anthracene–boronic acid ester

Anthracene–boronic acid ester OF-2 having a cyano group as an electron-withdrawing substituent was designed and developed as a highly-sensitive fluorescence PET sensor for detection of a trace amount of water in various solvents (polar, less polar, protic and aprotic solvents).

Fluorescent tren-based 4-amino-1,8-naphthalimide sensor for Cu(II) based on the use of the (fluorophore–spacer–receptor) photoinduced electron transfer (PET) principle

The design, synthesis and photophysical evaluation of a new chemosensor for copper [Cu(II)] is described based on the use of a functionalised 1,8-naphthlimide structure substituted at the 4-position with a tris(2-aminomethyl)amine-based (tren) ligand as a receptor for Cu(II). The sensor 1 functions as a classical photoinduced electron transfer sensor for protons, where the 4-amino-1,8-naphthalimide emission, occurring in the green part of the electromagnetic spectrum, is reversibly switched ‘ON–OFF’. A screen of various groups I and II as well as d-metal ions showed that only in the case of Cu(II), in buffered 100 mM NaCl solution, was the emission of 1 modulated, being quenched by ca. 80% upon addition of one equivalent of CuCl2 in buffered solution. The emission was, however, reversibly switched back ON, by the addition of either EDTA or glutathione. While only small changes occurred in the ground state, analysis of the changes in the emission spectra at various pH values showed that Cu(II) was detected through the formation of either a 2:1 or a 1:1 (ligand to metal) stoichiometry. The overall changes in the emission spectra of 1 as a function of H+ and Cu(II) can also be described as a molecular-level logic gate operation, corresponding to a two-input INHIBIT function.

Molecular design and synthesis of fluorescence PET (photo-induced electron transfer) sensors for detection of water in organic solvents

A series of anthracene–boronic acid ester OM-1, OM-2, OU-1, and OU-2 have been designed and synthesized as a new class of fluorescence PET (photo-induced electron transfer) sensors for detection and quantification of a trace amount of water in organic solvents. OM-1 and OM-2 have a boronic acid ester and bisboronic acid ester, respectively, located in the proximity of a tertiary amino group as an electron donor via a methylene spacer at the 9-position on the anthracene fluorophore. In OU-1, on the other hand, a boronic acid ester is directly connected to the 10-position of the anthracene fluorophore. OU-2 has bisboronic acid esters, which are located at the same positions as those of OM-1 and OU-1. It was found that OM-1 and OM-2 show enhancement of fluorescence with the increase in water content for various solvents (polar, less polar, protic and aprotic solvents), which can be attributed to the suppression of PET due to the formation of fluorescent ionic structures OM-1a or OM-2a by hydrolysis. For OU-1 and OU-2, on the other hand, there is no appreciable change in fluorescence intensity upon addition of water to the solution. We propose that a key point for creating a highly-sensitive fluorescence PET sensor for detection of a trace amount of water is to design molecular structures capable of forming a stable fluorescent ionic structure between the protonated tertiary amino group and the hydroxylated boronic acid ester by hydrolysis.

Fluorescent Polymer Nanoparticle for Selective Sensing of Intracellular Hydrogen Peroxide

Fluorescent boronate-modified polyacrylonitrile (BPAN) nanoparticles of 50 nm diameter were fabricated for use as a selective H(2)O(2) sensor. The fluorescence intensity changed and an emission peak shifted when BPAN nanoparticles selectively interacted with H(2)O(2), relative to other reactive oxygen species (ROS). The BPAN nanoparticles undergo photoinduced electron transfer (PET) between a Schiff base moiety and boronate, which enhances the fluorescence and makes the nanoparticles suitable for selective ROS recognition. We demonstrate the use of these nanoparticles as a detector of endogenous H(2)O(2) produced in living cells. The representative features of the fluorescent BPAN nanoparticles that make them particularly attractive for H(2)O(2) and ROS detection are the following: they are easily synthesized as PET sensors; they exhibit a characteristic emission peak and peak shift that distinguishes reaction with H(2)O(2) from other ROS; and compared to organic compounds, the sensing moiety on BPAN polymer nanoparticles is more thermally stable and has superior mechanical properties, enabling their use in various biomedical applications.

Highly sensitive fluorescence PET (photo-induced electron transfer) sensor for water based on anthracene–bisboronic acid ester

Anthracene–bisboronic acid ester was designed and developed as a highly sensitive fluorescence PET sensor for the detection of trace amounts of water in various solvents (polar, less polar, protic and aprotic solvents).

Fluorescence PET (photo-induced electron transfer) sensor for water based on anthracene-amino acid

An anthracene-amino acid system with two carboxyl groups has been designed and synthesized as a new class of fluorescence PET (photo-induced electron transfer) sensor for detection of water in organic solvents. An enhancement in fluorescence is observed with increasing water content in 1,4-dioxane, THF, acetonitrile and ethanol, which is attributable to the suppression of PET by the intramolecular proton transfer of the carboxyl proton to the amino group. The detection limit and quantitation limit are, respectively, 0.1 and 0.3 wt% for 1,4-dioxane, 0.4 and 1.2 wt% for THF, 0.1 and 0.3 wt% for acetonitrile and 0.1 and 0.3 wt% for ethanol.

Fluorescence PET (photo-induced electron transfer) sensors for water based on anthracene–boronic acid ester

Anthracene-boronic acid ester as a new class of fluorescence PET sensors for detection of a trace amount of water in organic solvents has been designed and developed.

ChemInform Abstract: Luminescence and Charge Transfer. Part 2. Aminomethyl Anthracene Derivatives as Fluorescent PET (Photoinduced Electron Transfer) Sensors for Protons.

ChemInform Abstract: Luminescence and Charge Transfer. Part 2. Aminomethyl Anthracene Derivatives as Fluorescent PET (Photoinduced Electron Transfer) Sensors for Protons.