Fluorescent probes for microdetermination of inorganic phosphates and biophosphates

Red-Emitting Polymerizable Guanidinium Dyes as Fluorescent Probes in Molecularly Imprinted Polymers for Glyphosate Detection

The development of methodologies to sense glyphosate has gained momentum due to its toxicological and ecotoxicological effects. In this work, a red-emitting and polymerizable guanidinium benzoxadiazole probe was developed for the fluorescence detection of glyphosate. The interaction of the fluorescent probe and the tetrabutylammonium salt of glyphosate was studied via UV/vis absorption and fluorescence spectroscopy in chloroform and acetonitrile. The selective recognition of glyphosate was achieved by preparing molecularly imprinted polymers, able to discriminate against other common herbicides such as 2,4-dichlorophenoxyacetic acid (2,4-D) and 3,6-dichloro-2-methoxybenzoic acid (dicamba), as thin layers on submicron silica particles. The limits of detection of 4.8 µM and 0.6 µM were obtained for the sensing of glyphosate in chloroform and acetonitrile, respectively. The reported system shows promise for future application in the sensing of glyphosate through further optimization of the dye and the implementation of a biphasic assay with water/organic solvent mixtures for sensing in aqueous environmental samples.

Colorimetric determination of acid phosphatase activity and inhibitor screening based on in situ polymerization of aniline catalyzed by gold nanoparticles

A colorimetric assay for acid phosphatase (ACP) was constructed that is based on in situ polymerization of aniline catalyzed by gold nanoparticles (AuNPs). Aniline can be polymerized by ammonium persulfate (APS) in acidic condition and form gold-polyaniline core-shell nanoparticles (Au@PANI NPs) in the presence of AuNPs with the assistance of sodium dodecyl sulfate (SDS). AuNPs were also found to accelerate the polymerization process of aniline and thus shorten the reaction time. Upon the introduction of ascorbic acid (AA), the oxidant APS was consumed via the redox reaction. That led to the suppression of the formation of PANI. Consequently, ACP activity can be supervised on the basis of hydrolysis of 2-phospho-L-ascorbic acid trisodium salt (AAP) catalyzed by ACP to release AA. With the increase of ACP activity, the intensity ratio of the absorbance at λ₇₀₅ nm (A₇₀₅) and the absorbance at λ₅₃₀ nm (A₅₃₀) gradually decreased and the color gradually changed from dark-green to light-green to blue-gray to purple and eventually to pink. This method for ACP determination worked in the range 0.40 to 2.00 U·L^-1. The detection limit is 0.043 U·L^-1. The assay was applied to determine ACP in human serum. The recovery ranged from 81.0 to 104.6%. Relative standard deviation was less than 5%. This suits the request for biological sample analysis. Graphical abstract Schematic presentation of the colorimetric determination of acid phosphatase activity and inhibitor screening based on in situ polymerization of aniline catalyzed by gold nanoparticles. : acid phosphatase (ACP); : gold nanoparticles (AuNPs); : gold-polyaniline core-shell nanoparticles (Au@PANI NPs); ascorbic acid (AA); 2-phospho-L-ascorbic acid trisodium salt (AAP).

Polydopamine coated copper nanoclusters with aggregation-induced emission for fluorometric determination of phosphate ion and acid phosphatase activity

The preparation of aggregation-induced emission-type copper nanoclusters (CuNCs) capped with polydopamine (PDA) is described. PDA was formed via in situ polymerization of dopamine in the presence of alkaline polyethylenimine. The PDA-capped CuNCs (PDA-CuNCs) exhibit orange fluorescence with maximal emission at 580 nm upon excitation at 340 nm, a storage stability of at least 2 weeks, and a quantum yield (QY) of 2.54% in aqueous solution. The QY is 28-fold higher than that of sole CuNCs. The fluorescence of the PDA-CuNCs is quenched by Fe³⁺ ion while it is recovered by PO₄^3- due to its stronger affinity for Fe³⁺. On this basis, a fluorometric phosphate assay was developed that has a 1.5 nM detection limit and a linear range over 0.003-70 μM. The method was satisfactorily applied to the determination of phosphate in local tap water and human sera, and the results agreed well with those obtained by a colorimetric method. In the presence of acid phosphatase (ACP), PO₄^3- is produced by the catalytic hydrolysis of adenosine triphosphate (ACP substrate). Thus, a fluorogenic assay for screening ACP activity was established. Response is linear over the activity range 0.0012-25 U L^-1, with a detection limit of 0.001 U L^-1 (at S/N = 3). Graphic abstract We proposed an effective polydopamine-templating strategy for the in situ synthesis of highly emissive and stable CuNCs and demonstrated its use as an ion-driven fluorescence switch for the determination of phosphate and acid phosphatase activity.

A terbium(III)-functionalized zinc(II)-organic framework for fluorometric determination of phosphate

A terbium(III)-functionalized zinc(II)-organic framework (Tb-MOF-Zn) is shown to be a viable fluorescent probe for phosphate. The organic ligands 4,4',4″-[((2,4,6-trimethylbenzene-1,3,5-triyl)tris(methylene))tris(oxy)]tribenzoic acid (H₃L³) contains multiple carboxyl groups that can react with zinc(II) to yield tubular MOF-Zn. The MOF-Zn was further functionalized with Tb(III) to produce a lanthanide composite of type Tb-MOF-Zn which displays strong fluorescence with excitation/emission maxima at 285/544 nm. Fluorescence is quenched by phosphate because of the specific interaction with Tb(III) in Tb-MOF-Zn. The concentration of Tb-MOF-Zn, reaction time and pH value of the solution were optimized. Fluorescence drops linearly in the 0.01 to 200.0 μM phosphate concentration range, and the detection limit is 4.0 nM. The fluorescent probe was also used to prepare a microdot array on a glass slide for visual detection of phosphate under illumination with UV light. Graphical abstractA terbium(III) functionalized zinc(II)-organic framework was synthesized and used as fluorescent probe for determination of phosphate ions.

Daphnetin: A novel blue-green photonic switch for disodium phosphates that allows monitoring of polymerase chain reactions

This paper describes the very simple and robust ratiometric photonic switching properties of daphnetin (DP) toward HPO₄^2- ions selectively in complex biological fluids, without any interference from other relevant anions under physiological conditions. The sensing ability of DP toward HPO₄^2- ions was first demonstrated using UV-Vis and fluorescence spectroscopy, dynamic light scattering (DLS), and one- and two-dimensional NMR spectroscopy. DP can detect HPO₄^2- ions at concentrations up to the sub-micromolar/nanomolar level very effectively, with a ratiometric response resulting from intramolecular charge transfer aided by aggregated-induced emission. The interactions between DP and HPO₄^2- ions resulted in new bands appearing in the UV-Vis (at 385 nm) and emission (at 535 nm) spectra. The noncovalently held HPO₄^2- ions induced pronounced specific aggregation of DP molecules, resulting in the new excimer band at 535 nm while retaining the monomer band centered at 445 nm. In contrast, reciprocal absorptivity changes were observed at 320 and 385 nm, with exponential decrements and increments, respectively. This probe could effectively monitor the consumption of dNTPs during various cycles of the polymerase chain reaction performed with relatively short oligonucleotides as well as genomic DNA from Agrobacterium tumefaciens (AcH5α strain).

On-off-on luminescent pyrophosphate probe based on the use of Mn-doped ZnS quantum dots and using Eu(III) as a mediator

A selective phosphorescent on-off-on probe with long decay lifetime has been designed for the detection of pyrophosphate ions (PPi). The detection scheme is based on the use of europium(III)-modulated Mn(II)-doped ZnS quantum dots capped with N-acetyl-L-cysteine. Both the aggregation of quantum dots and electron transfer induced by Eu(III) ions cause phosphorescence to be quenched ("off" state). Phosphorescence is, however, restored on addition of PPi to the system ("on" state). The effect is attributed to the removal of Eu(III) from the carboxy groups on the surface of the quantum dots owing to the stronger interaction between PPi and Eu(III). A linear relationship exists between phosphorescence intensity (best measured at excitation/emission wavelengths of 316/594 nm) and PPi concentration in the 400 nM to 6000 nM with a detection limit of 145 nM. An additional attractive feature is provided by the long-lived phosphorescence (1920 μs) of the quantum dots. It can be used to eliminate interference by short-lived fluorescence in biological samples by performing time resolved measurements. The probe was applied to the determination of PPi in spiked in urine samples and gave recoveries in the range from 98 to 105% with RSDs of <2.0%. Graphical abstract Schematic of a long-lived phosphorescent on-off-on probe for the sensitive and selective detection of pyrophosphate ions (PPi). It is based on the use of Eu(III)-modulated Mn(II)-doped ZnS quantum dots (QDs). Phosphorescence is quenched of QDs after the addition of Eu³⁺but restored after the addition of PPi.

Preassembly-driven ratiometric sensing of H2PO4− anions in organic and aqueous environments

The preassembly phenomenon of R1 facilitates novel ratiometric fluorescence sensing of H₂PO₄⁻ in organic and aqueous environments.

The phenanthroimidazole-based dizinc(ii) complex as a fluorescent probe for the pyrophosphate ion as generated in polymerase chain reactions and pyrosequencing

The phenanthroimidazole-based dizinc(II) complex is an efficient fluorescent probe for the pyrophosphate ion (PPi) in water with a very low detection limit, and also used to detect PPi released from DNA polymerization chain reaction.

Aggregation deaggregation influenced selective and sensitive detection of Cu2+ and ATP by histidine functionalized water-soluble fluorescent perylene diimide under physiological conditions and in living cells

A novel PDI-HIS probe detects Cu²⁺ to form aggregated nonfluorescent complex. Addition of 0.58 ppm ATP to this complex causes its rapid disaggregation thereby recovering the fluorescence by ∼99% in vitro and in A549 living cells.

Multidentate europium chelates as luminoionophores for anion recognition: impact of ligand design on sensitivity and selectivity, and applicability to enzymatic assays

The design of photoluminescent molecular probes for the selective recognition of anions is a major challenge for the development of optical chemical sensors. The reversible binding of anions to lanthanide centers is one promising option for the realization of anion sensors, because it leads in some cases to a strong luminescence increase by the replacement of quenching water molecules. Yet, it is an open problem to gain control of the sensitivity and selectivity of the luminescence response. Primarily, the selective detection of (poly)phosphate species such as nucleotides has emerged as a demanding task, because they are involved in many biological processes and enzymatic reactions. We designed a series of pyridyl-based multidentate europium complexes (seven-, six-, and five-dentate) including sensitizing chromophores and studied their luminescence intensity and lifetime responses to different (poly)phosphates (adenosine triphosphate (ATP), adenosine diphosphate (ADP), adenosine monophosphate (AMP), cyclic adenosine monophosphate (cAMP), pyrophosphate, and phosphate anions), and carboxyanions (citrate, malate, oxalacetate, succinate, α-ketoglutarate, pyruvate, oxalate, carbonate). The results reveal that the number of free coordination sites has a significant impact on the sensitivity and selectivity of the response. Because of its reversibility, the lanthanide probes can be applied to monitor the activity of ATP-consuming enzymes such ATPases and apyrases, which is demonstrated by means of the five-dentate complex.

Recent advances in H2PO4− fluorescent sensors

The recent advances in H₂PO₄⁻ fluorescent sensors were thoroughly reviewed.

"Turn-on-off-on" fluorescence switching of quantum dots-cationic porphyrin nanohybrid: a sensor for DNA

In this article, we describe a new platform for probing double stranded DNA (dsDNA) by tracing the "on-off-on" fluorescence signals of quantum dots-cationic porphyrin utilizing fluorescence and synchronous fluorescence measurements. Electrostatic interaction between the negatively charged thioglycolic acid capped CdTe quantum dots (CdTe-TGA QDs) and positively charged porphyrin surfaces leads to drastic quenching (turning off) of the donor by an effective electron transfer process. Interestingly, after the addition of calf thymus DNA (CtDNA), the porphyrins peel off from the quantum dot surface and bind to dsDNA, resulting in the restoration of fluorescence intensity of quantum dots (turning on). Consequently, this can be utilized for the selective sensing of dsDNA via optical responses. Experimental results show that the increase in fluorescence intensity is proportional to the concentration of CtDNA within the range of 6.5 × 10(-9) M to 29.6 × 10(-8) M under the optimized experimental conditions. Furthermore, the peel off mechanism was confirmed by atomic force measurement.

A zinc-dipicolylethylenediamine modified near infrared fluorophore for sensing of ATP

The development of fluorescent probes for sensing of anions in biological environments is still a demanding task. Due to the structural versatility of biological active anions there are many challenges to cope with compared to fluoroionophores for the determination of metal cations. This concerns particularly the design of the recognition element, which has to provide a selective response, preferably unaffected by alterations of pH and ionic strength. Polyphosphate anions such as ATP are interesting targets in bioanalysis because they are involved in many enzymatic reactions and bear versatile biological functions. Zinc dipicolylamine complexes attached to fluorophores have been turned out to be promising candidates for ATP sensing with sufficient sensitivity and selectivity. We now report the first NIR probe that responds to ATP based on a zinc dipicolylethylenediamine receptor. It shows a "turn-on" fluorescence behavior which is selective to other polyphosphate species even at high ionic strength of the sample solution.

An ATP-selective, lanthanide complex luminescent probe

A luminescent probe based on a europium complex is developed, which effectively distinguishes adenosine-5'-triphosphate (ATP) from adenosine diphosphate (ADP) and adenosine monophosphate (AMP) in pure water at pH 6.8. With a longer lifetime (in ms range), the probe is prospectively applied to biological systems to monitor ATP levels by completely removing the background fluorescence of other molecules.

A terbium(III)-organic framework for highly selective sensing of cytidine triphosphate

Highly selective sensing of cytidine triphosphate (CTP) against other triphosphate nucleosides including ATP, GTP and UTP is successfully achieved with a luminescent terbium(III)-organic framework (TbOF) of [Tb(2)(2,3-pzdc)(2)(ox)(H(2)O)(2)](n) (2,3-pzdc(2-) = 2,3-pyrazinedicarboxylate, ox(2-) = oxalate).

Surface-functionalized fluorescent silica nanoparticles for the detection of ATP

The design of two-dyed fluorescent silica nanoparticles for ATP detection is presented. The indicator dye possesses a dipicolyl-amine (DPA) unit complexed with Zn(II) as a receptor function for ATP while a rhodamine derivative is used as the reference dye. The nanoparticles were fully characterized regarding analytical performance, morphology and cytocompatibility.

A novel method for ranitidine hydrochloride determination in aqueous solution based on fluorescence quenching of functionalised CdS QDs through photoinduced charge transfer process: spectroscopic approach

A novel method for the quantitative determination of ranitidine hydrochloride (RNH) based on the fluorescence quenching of functionalised CdS quantum dots (QDs) by RNH in aqueous solution was proposed. The method is simple, rapid, specific and highly sensitive with good precision. The thioglycolic acid (TGA)-capped CdS QDs were synthesized from cadmium nitrate and sodium sulfide in alkaline solution. Under the optimal conditions, the Stern-Volmer calibration plot of F(0)/F against concentration of RNH was linear in the range of 0.50-15.0 μg mL(-1) with a correlation coefficient of 0.996. The limit of detection (LOD) was 0.38 μg mL(-1). The method was satisfactorily applied to the direct determination of RNH in pharmaceutical formulations with no significant interference from excipients. The results were found to be in good agreement with those obtained by the reference method and the claimed value. The accuracy and reliability of the method were further ascertained by recovery studies via the standard-addition method, with percentage recoveries in the range of 98.47 to 102.30%. The possible fluorescence quenching mechanism for the reaction was also discussed.

Fluorescent sensing and discrimination of ATP and ADP based on a unique sandwich assembly of pyrene-adenine-pyrene

It is still a challenging task to discriminate adenosine-5'-triphosphate (ATP) from various nucleoside triphosphates, such as GTP, CTP, UTP, and TTP. The ability to distinguish ATP from adenosine diphosphate (ADP) by fluorescent signals is also urgently desired. Herein, we report two pyrene-based zinc complexes as nucleoside polyphosphate receptors with high selectivity for ATP and ADP based on fluorescence and NMR studies. A unique pyrene-adenine-pyrene sandwich assembly was observed in the case of compound 1 with ATP or ADP, resulting in the increase of monomer fluorescence intensity; whereas the other bases of nucleoside triphosphates, such as GTP, CTP, UTP, and TTP were not sandwiched, resulting in a switch in the monomer-excimer fluorescence of pyrene. The different binding patterns of various nucleobases with a pyrene-pyrene assembly make 1 a highly selective fluorescent sensor for ANP (N=di, tri). In the case of compound 2, the first 0.5 equivalents of ATP induced a strong excimer emission, whilst ADP induced a large enhancement in the monomeric fluorescent peak. This fluorescence change makes 2 an efficient sensor to discriminate ATP from ADP.

A molecular logic gate for the highly selective recognition of pyrophosphate with a hypocrellin A-Zn(II) complex

Pyrophosphate (PPi) participates in many biological and chemical processes such as energy transduction so that investigations on its role and detection have become very significant. In this contribution, we have developed a molecular logic gate for the recognition of PPi with a fluorescent hypocrellin A-zinc(II) complex (HA-Zn(2+)), and the outputs of which correspond to the fluorescence emission ratio at 604 nm and wavelength shift relative to 629 nm. The emission at 604 nm is the intrinsic fluorescence of HA, which can be effectively quenched by Zn(2+) with a new emission at 629 nm owing to the formation of the HA-Zn(2+) complex. It was found, however, that the new emission at 629 nm is highly selectively quenched with the addition of PPi, recovering the emission at 604 nm, and the recovery ratio is linearly correlated with PPi in the range of 1.8 × 10(-5) mol L(-1) to 2.4 × 10(-4) mol L(-1). ATP, UTP, CTP, GTP, GDP and GMP cannot demonstrate the same spectral actions as PPi. Since the inputs of PPi and the phosphate anions obtain different logical outputs, the designed logic gates have good selectivity and can distinguish PPi from the other anions.

An ATP fluorescent chemosensor based on a Zn(II)-complexed dipicolylamine receptor coupled with a naphthalimide chromophore

A fluorescent naphthalimide chemosensor for ATP bearing a dipicolylamine group complexed with a Zn(II) metal as a receptor moiety was synthesized and its sensing properties regarding ATP and other related phosphate species were evaluated.

Complexation of bisphosphonates with ytterbium(III): application of phosphate and ATP detection assay based on Yb(3+)-pyrocatechol violet

The coordination chemistry of bisphosphonates with Yb(3+) was investigated to evaluate the potential of the UV-vis based detection method using the Yb(3+)-pyrocatechol complexation reaction as a sensor for bisphosphonates. The complexation chemistry of Yb(3+) with phosphate and ATP analogs was previously described (E. Gaidamauskas, K. Saejueng, A.A. Holder, S. Bharuah, B.A. Kashemirov, D.C. Crans, C.E. McKenna, J. Biol. Inorg. Chem. 13 (2008) 1291-1299), and we here studied the complexation chemistry of bisphosphonates in this system. The spectrophotometric assay yields direct evidence for formation of a 4:3 metal to ligand complex at neutral pH. Direct evidence for Yb(3+):methylenebis(phosphonate) complexes with 1:1 and 1:2 stoichiometry was also obtained by potentiometry at acidic and basic pH. Direct evidence for complex formation was obtained using (1)H NMR spectroscopy although the stoichiometry was not accessed at neutral pH. Our results suggest that the spectroscopic observation of the YbPV complex can be used to conveniently measure concentrations of bisphosphonates down to 2-3 microM.