An overview on the development of different optical sensing platforms for adenosine triphosphate (ATP) recognition.

Adenosine triphosphate (ATP), one of the biological anions, plays a crucial role in several biological processes including energy transduction, cellular respiration, enzyme catalysis and signaling. ATP is a bioactive phosphate molecule, recognized as an important extracellular signaling agent. Apart from serving as a universal energy currency for various cellular events, ATP is also considered a factor responsible for numerous physiological activities. It regulates cellular metabolism by breaking phosphoanhydride bonds. Several diseases have been reported widely based on the levels and behavior of ATP. The variation of ATP concentration usually causes a foreseeable impact on mitochondrial physiological function. Mitochondrial dysfunction is responsible for the occurrence of many severe diseases such as angiocardiopathy, malignant tumors and Parkinson's disease. Therefore, there is high demand for developing a sensitive, fast-responsive, nontoxic and versatile detection platform for the detection of ATP. To this end, considerable efforts have been employed by several research groups throughout the world to develop specific and sensitive detection platforms to recognize ATP. Although a repertoire of optical chemosensors (both colorimetric and fluorescent) for ATP has been developed, many of them are not arrayed appropriately. Therefore, in this present review, we focused on the design and sensing strategy of some chemosensors including metal-free, metal-based, sequential sensors, aptamer-based sensors, nanoparticle-based sensors etc. for ATP recognition via diverse binding mechanisms.

Stationary distribution and density function analysis of SVIS epidemic model with saturated incidence and vaccination under stochastic environments.

In this article, we study the dynamical properties of susceptible-vaccinated-infected-susceptible (SVIS) epidemic system with saturated incidence rate and vaccination strategies. By constructing the suitable Lyapunov function, we examine the existence and uniqueness of the stochastic system. With the help of Khas'minskii theory, we set up a critical value [Formula: see text] with respect to the basic reproduction number [Formula: see text] of the deterministic system. A unique ergodic stationary distribution is investigated under the condition of [Formula: see text]. In the epidemiological study, the ergodic stationary distribution represents that the disease will persist for long-term behavior. We focus for developing the general three-dimensional Fokker-Planck equation using appropriate solving theories. Around the quasi-endemic equilibrium, the probability density function of the stochastic system is analyzed which is the main theme of our study. Under [Formula: see text], both the existence of ergodic stationary distribution and density function can elicit all the dynamical behavior of the disease persistence. The condition of disease extinction of the system is derived. For supporting theoretical study, we discuss the numerical results and the sensitivities of the biological parameters. Results and conclusions are highlighted.

An epidemic model through information-induced vaccination and treatment under fuzzy impreciseness.

In this work, we propose a nonlinear susceptible (S), vaccinated (V), infective (I), recovered (R), information level (U) (SVIRUS) model for the dynamical behavior of the contagious disease in human beings. We mainly consider the spread of information during the course of epidemic in the population. Different rate equations describe the dynamics of the information. We have developed the proposed model in crisp and fuzzy environments. In the fuzzy model, to describe the uncertainty prevailed in the dynamics, all the parameters are taken as triangular fuzzy numbers. Using graded mean integration value (GMIV) method, the fuzzy model is transformed into defuzzified model to represent the solutions avoiding the difficulties. The positivity and the boundedness of the crisp model are discussed elaborately and also the equilibrium analysis is accomplished. The stability analysis for both the infection free and the infected equilibrium are established for the crisp model. Application of optimal control of the crisp system is explored. Using Pontryagin's Maximum Principle, the optimal control is explained. The effect of vaccination is analyzed which leads the model to be complex in nature. The effect of saturation constant for information is described for the crisp model and also the effects of weight constants on control policy are discussed. Finally, it is concluded that the treatment is more fruitful and information related vaccination is more effective during the course of epidemic.

Preorganized Chromophores Facilitate Triplet Energy Migration, Annihilation and Upconverted Singlet Energy Collection.

Photon upconversion (UC) based on triplet-triplet annihilation (TTA) has the potential to enhance significantly photovoltaic and photocatalytic efficiencies by harnessing sub-bandgap photons, but the progress of this field is held back by the chemistry problem of how to preorganize multiple chromophores for efficient UC under weak solar irradiance. Recently, the first maximization of UC quantum yield at solar irradiance was achieved using fast triplet energy migration (TEM) in metal-organic frameworks (MOFs) with ordered acceptor arrays, but at the same time, a trade-off between fast TEM and high fluorescence efficiency was also found. Here, we provide a solution for this trade-off issue by developing a new strategy, triplet energy migration, annihilation and upconverted singlet energy collection (TEM-UPCON). The porous structure of acceptor-based MOF crystals allows triplet donor molecules to be accommodated without aggregation. The surface of donor-doped MOF nanocrystals is modified with highly fluorescent energy collectors through coordination bond formation. Thanks to the higher fluorescence quantum yield of surface-bound collectors than parent MOFs, the implementation of the energy collector greatly improves the total UC quantum yield. The UC quantum yield maximization behavior at ultralow excitation intensity was retained because the TTA events take place only in the MOF acceptors. The TEM-UPCON concept may be generalized to collectors with various functions and would lead to quantitative harvesting of upconverted energy, which is difficult to achieve in common molecular diffusion-based systems.

Triplet energy migration-based photon upconversion by amphiphilic molecular assemblies in aerated water.

A molecular self-assembly approach is developed to resolve an outstanding issue in triplet energy migration-based photon upconversion (TEM-UC), that is, air-stable TEM-UC in water. Amphiphilic cationic acceptor (emitter) molecules self-assemble in water via hydrophobic and hydrogen bonding interactions, with which anionic donor (sensitizer) molecules are integrated through electrostatic interactions. Triplet energy is quantitatively transferred from the excited donor to the acceptor, which is followed by effective triplet energy migration among the pre-organized acceptors. It leads to TTA and concomitant UC emission in water. The dense acceptor chromophore arrays with extended hydrogen bonding networks show efficient barrier properties against molecular oxygen, as demonstrated by the stable UC emission even in air-saturated water.

Fast and long-range triplet exciton diffusion in metal-organic frameworks for photon upconversion at ultralow excitation power.

The conversion of low-energy light into photons of higher energy based on sensitized triplet-triplet annihilation upconversion (TTA-UC) has emerged as a promising wavelength-shifting methodology because it permits UC at excitation powers as low as the solar irradiance. However, its application has been significantly hampered by the slow diffusion of excited molecules in solid matrices. Here, we introduce metal-organic frameworks (MOFs) that promote TTA-UC by taking advantage of triplet exciton migration among fluorophores that are regularly aligned with spatially controlled chromophore orientations. We synthesized anthracene-containing MOFs with different molecular orientations, and the analysis of TTA-UC emission kinetics unveiled a high triplet diffusion rate with a micrometre-scale diffusion length. Surface modification of MOF nanocrystals with donor molecules and their encapsulation in glassy poly(methyl methacrylate) (PMMA) allowed the construction of molecular-diffusion-free solid-state upconverters, which lead to an unprecedented maximization of overall UC quantum yield at excitation powers comparable to or well below the solar irradiance.

An interrupted PET coupled TBET process for the design of a specific receptor for Hg2+ and its intracellular detection in MCF7 cells.

A new coumarin-rhodamine conjugate constitutes a unique example of the interrupted PET coupled TBET response for developing an imaging reagent for determining the intracellular distribution of Hg(2+) in MCF7 cells exposed to [Hg(2+)] as low as 2 ppb.

A taco complex derived from a bis-crown ether capable of executing molecular logic operation through reversible complexation.

As learned from natural systems, self-assembly and self-sorting help in interconnecting different molecular logic gates and thus achieve high-level logic functions. In this context, demonstration of important logic operations using changes in optical responses due to the formation of molecular assemblies is even more desirable for the construction of a molecular computer. Synthesis of an appropriate divalent as well as a luminescent crown ether based host 1 and paraquat derivatives, 2(PF(6))(2) and 3(PF(6))(2), as guests helped in demonstrating a reversible [3](taco complex) (1·{2(PF(6))(2)}(2) or 1·{3(PF(6))(2)}(2)) formation in nonpolar solvent. Detailed (1)H NMR studies revealed that two paraquat units were bound cooperatively by the two crown units in 1. Because of preorganization, the flexible host molecule 1 adopts a folded conformation, where each of two paraquat units remain sandwiched between the two aromatic units of each folded crown ether moiety in 1. Disassembly of the "taco" complex in the presence of KPF(6) and reassembly on subsequent addition of DB18C6 was initially demonstrated by (1)H NMR spectral studies, which were subsequently corroborated through luminescence spectral studies. Further, luminescence spectral responses as output signals with appropriate and two independent molecular inputs could be correlated to demonstrate basic logic operation like OR and YES gates, while the results of the three molecular inputs could be utilized to demonstrate important logic operation like an INHIBIT gate.

Ratiometric detection of Cr3+ and Hg2+ by a naphthalimide-rhodamine based fluorescent probe.

Newly synthesized rhodamine derivatives, L(1) and L(2), are found to bind specifically to Hg(2+) or Cr(3+) in presence of large excess of other competing ions with associated changes in their optical and fluorescence spectral behavior. These spectral changes are significant enough in the visible region of the spectrum and thus, allow the visual detection. For L(1), the detection limit is even lower than the permissible [Cr(3+)] or [Hg(2+)] in drinking water as per standard U.S. EPA norms; while the receptor, L2 could be used as a ratiometric sensor for detection of Cr(3+) and Hg(2+) based on the resonance energy transfer (RET) process involving the donor naphthalimide and the acceptor Cr(3+)/Hg(2+)-bound xanthene fragment. Studies reveal that these two reagents could be used for recognition and sensing of Hg(2+)/Cr(3+). Further, confocal laser microscopic studies confirmed that the reagent L(2) could also be used as an imaging probe for detection of uptake of these ions in A431 cells.

Rhodamine-alginate conjugate as self indicating gel beads for efficient detection and scavenging of Hg2+ and Cr3+ in aqueous media.

Effective extraction of Hg(2+) and Cr(3+) ions from aqueous media by novel rhodamine-alginate polymer-based highly fluorogenic, as well as colorimetric, chemosensor beads.

Recognition of Hg2+ and Cr3+ in physiological conditions by a rhodamine derivative and its application as a reagent for cell-imaging studies.

A new rhodamine-based receptor, derivatized with an additional fluorophore (quinoline), was synthesized for selective recognition of Hg(2+) and Cr(3+) in an acetonitrile/HEPES buffer medium of pH 7.3. This reagent could be used as a dual probe and allowed detection of these two ions by monitoring changes in absorption and the fluorescence spectral pattern. In both instances, the extent of the changes was significant enough to allow visual detection. More importantly, the receptor molecule could be used as an imaging reagent for detection of Hg(2+) and Cr(3+) uptake in live human cancer cells (MCF7) using laser confocal microscopic studies. Unlike Hg(ClO(4))(2) or Hg(NO(3))(2) salts, HgCl(2) or HgI(2) failed to induce any visually detectable change in color or fluorescence upon interaction with L(1) under identical experimental conditions. Presumably, the higher covalent nature of Hg(II) in HgCl(2) or HgI(2) accounts for its lower acidity and its inability to open up the spirolactam ring of the reagent L(1). The issue has been addressed on the basis of the single-crystal X-ray structures of L(1)·HgX(2) (X(-) = Cl(-) or I(-)) and results from other spectral studies.

Solvent-dependent aggregation behavior of a new Ru(II)-polypyridyl based metallosurfactant.

Variation of the solvent polarity leads to the formation of vesicles and reverse vesicles of a newly synthesized amphiphilic Ru(II)-polypyridyl complex.

Zn(II)-cyclam based chromogenic sensors for recognition of ATP in aqueous solution under physiological conditions and their application as viable staining agents for microorganism.

Two chromogenic complexes, L.Zn (where L is (E)-4-((4-(1,4,8,11-tetraazacyclotetradecan-1-ylsulfonyl)phenyl)diazenyl)-N,N-dimethylaniline) and its [2]pseudorotaxane form (α-CD.L.Zn), were found to bind preferentially to adenosine triphosphate (ATP), among all other common anions and biologically important phosphate (AMP, ADP, pyrophosphate, and phosphate) ions in aqueous HEPES buffer medium of pH 7.2. Studies with live cell cultures of prokaryotic microbes revealed that binding of these two reagents to intercellular ATP, produced in situ, could be used in delineating the gram-positive and the gram-negative bacteria. More importantly, these dyes were found to be nontoxic to living microbes (eukaryotes and prokaryotes) and could be used for studying the cell growth dynamics. Binding to these two viable staining agents to intercellular ATP was also confirmed by spectroscopic studies on cell growth in the presence of different respiratory inhibitors that influence the intercellular ATP generation.

Recognition of Hg(2+) using diametrically disubstituted cyclam unit.

A newly synthesized 1,4,8,11-tetraazacyclotetradecane derivative (L), functionalized with a diazo moiety as the reporter functionality, is found to bind specifically to Hg(2+) with an associated change in color that could be visually detected. With biologically benign ß-CD, it forms an inclusion complex (L·2ß-CD), which shows a much higher solubility in water, and this helps in developing a more intense color on binding to Hg(2+) in a CH(3)CN-HEPES buffer medium. The nontoxic nature of L was checked with the living cells of a Gram negative bacterium, Pseudomonas putida . Further, experiments revealed that these two reagents could be used as staining agents for the detection of Hg(2+) present in this microorganism.

Zn(II) based colorimetric sensor for ATP and its use as a viable staining agent in pure aqueous media of pH 7.2.

Selective colorimetric detection of ATP in physiological conditions by a Zn(II)-based receptor is reported. This reagent was found to be non-toxic to the living cells and could be used for studying the growth of the yeast cells.

Specific recognition and sensing of CN- in sodium cyanide solution.

Specific recognition of CN(-) in sodium cyanide solution was achieved using two imidazole-based receptors (A and B). Visually detectable color changes were associated with the formation of hydrogen bonded adducts, A.CN(-) and B.CN(-). Ratiometric fluorescence response was achieved for receptor A on binding to CN(-), and this reagent was used for imaging bacterial cells pre-exposed to 1.42 microM CN(-) solution.