Highly Selective Phthalocyanine−Thymine Conjugate Sensor for Hg2+ Based on Target Induced Aggregation

Recent advances in electrospinning supramolecular systems

Electrospinning is one of the simple, versatile, and convenient techniques for producing nanofibers that have found numerous applications in the fields of biomedical engineering, surface materials, and catalysis. Despite the great achievements, the electrospinning compounds are still limited to the utilization of polymers with high molar mass which are regarded as an indispensable element for the production of nanofibers. It is found that electrospinning chemicals based on supramolecular systems can avoid the use of high molecular weight polymers, and it is emerging as a powerful route to generate fibers in the nano-scale size. The presence of strong intermolecular interactions that function as chain entanglements allows for the formation of nanofibers during the process of electrospinning. This article provides recent impressive developments concerning nanofiber preparation made by the combination of electrospinning and supramolecular chemistry, which enables easy access to tailor-made nanofibers. Electrospinning supramolecular systems consisting of phospholipids, surfactants, crown ether derivatives as well as cyclodextrins will be highlighted in this review. Moreover, we will pay particular attention to the functionalities of electrospun nanofibers obtained from supramolecular systems.

Dinuclear HgII tetracarbene complex-triggered aggregation-induced emission for rapid and selective sensing of Hg2+ and organomercury species

Mercury-mediated chelate ring formation and subsequent aggregation gives strong fluorescence for rapid and selective sensing of Hg²⁺ and organomercury.

Rapid, reliable and highly selective detection of mercury species, including Hg²⁺ ions and organomercury, is of significant importance for environmental protection and human health. Herein, a new fluorescent dye 1,1,2,2-tetrakis[4-(3-methyl-1H-benzimidazol-1-yl)phenyl ethylene tetraiodide (Tmbipe) with aggregation-induced emission (AIE) potential was prepared and characterized. The presence of four positively charged methylated benzimidazole groups endows Tmbipe with excellent water solubility and almost undetectable background fluorescence. However, it can coordinate with two Hg²⁺ ions or two organomercury molecules (e.g. methylmercury and phenylmercury) to form a planar dinuclear Hg^II tetracarbene complex, which can then self-aggregate to turn on AIE fluorescence. Such a fluorescence turn-on process can be completed in 3 min. In addition, synergic rigidification of the tetraphenylethylene-bridged Tmbipe molecule by mercury-mediated chelate ring formation and subsequent aggregation results in obviously higher fluorescence enhancement than that given by the single aggregation-induced one. Low background, high fluorescence enhancement and rapid response time make Tmbipe a good fluorescent probe for reliable, sensitive and highly selective quantitation of both inorganic and organic mercury species. This probe was also demonstrated to work well for identification of mercury species accumulation in living cells.

Porphyrinoid biohybrid materials as an emerging toolbox for biomedical light management

The present article reviews the most important developing strategies in light-induced nanomedicine, based on the combination of porphyrinoid photosensitizers with a wide variety of biomolecules and biomolecular assemblies.

Fluorinated near-infrared fluorescent probes for specific detection of Hg2+ in an aqueous medium and mitochondria of living cells

A near-infrared fluorescent probe (IR-DFT) could be used for specifically and sensitively detecting Hg²⁺ in mitochondria of living cells.

Application of graphene quantum dots functionalized with thymine and thymine-appended zinc phthalocyanine as novel photoluminescent nanoprobes

Thymine Zn phthalocyanine turned off the fluorescence of graphene quantum dots, which was subsequently turned on by Hg²⁺ for its sensitive detection.

(Pc)Eu(Pc)Eu[trans-T(COOCH3)2PP]/GO Hybrid Film-Based Nonenzymatic H2O2 Electrochemical Sensor with Excellent Performance

A facile approach was developed for preparing the multilayer hybrid films of mixed (phthalocyaninato) (porphyrinato) europium(III) triple-decker compound (Pc)Eu(Pc)Eu[trans-T(COOCH₃)₂PP] (1) and graphene oxide (GO) using the solution-processing QLS method. The combination of the nature of relatively high conductivity and great surface area for GO with the electroactive and semiconductive triple-decker compound in ITO electrode renders the hybrid film excellent sensing property for H₂O₂, due to the optimized triple-decker molecular packing in the uniform-sized nanoparticles (ca. 70 nm) formed on the GO surface. The amperometric responses are linearly proportional to the concentration of H₂O₂ in the range of 0.05-1800 μM with a fast response time of 0.03 s μM^-1, a low detection limit of 0.017 μM, and good sensitivity of 7.4 μA mM^-1. The present work represents the best result of tetrapyrrole-based nonenzymatic electrochemical sensor for H₂O₂. Nevertheless, the triple-decker/GO/ITO also shows excellent stability, reproducibility, and selectivity, indicating the great potential of electroactive tetrapyrrole rare earth sandwich compounds in combination with GO in the field of nonenzymatic electrochemical sensors.

Efficient On-Off Ratiometric Fluorescence Probe for Cyanide Ion Based on Perturbation of the Interaction between Gold Nanoclusters and a Copper(II)-Phthalocyanine Complex

A new ratiometric fluorescent sensor was developed for the sensitive and selective detection of cyanide ion (CN(-)) in aqueous media. The ratiometric sensing system is based on CN(-) modulated recovery of copper(II) phthalocyanine (Cu(PcTs)) fluorescence signal at the expense of diminished fluorescence intensity of gold nanoclusters (AuNCs). Preliminary experiments revealed that the AuNCs and Cu(PcTs) possess a turn-off effect on each other, the interaction of which being verified through studying their interactions by principle component analysis (PCA) and multivariate cure resolution-alternating least-squares (MCR-ALS) methods. In the presence of CN(-) anion, the AuNCs and Cu(PcTs) interaction was perturbed, so that the fluorescence of Cu (PcTs), already quenched by AuNCs, was found to be efficiently recovered, while the fluorescence intensity of AuNCs was quenched via the formation of a stable [Au(CN)2](-) species. The ratiometric variation of AuNCs and Cu(PcTs) fluorescence intensities leads to designing a highly sensitive probe for CN(-) ion detection. Under the optimal conditions, CN(-) anion was detected without needing any etching time, over the concentration range of 100 nM-220 μM, with a detection limit of 75 nM, which is much lower than the allowable level of CN(-) in water permitted by the World Health Organization (WHO). Moreover, the detection of CN(-) was developed based on the CN(-) effects on the blue and red florescent colors of Cu(PcTs) and AuNCs, respectively. The designed probe displays a continuous color change from red to blue by addition of CN(-), which can be clearly observed by the naked eye in the range of 7-350 μM, under UV lamp. The prepared AuNCs/Cu(PcTs) probe was successfully utilized for the selective and sensitive determination of CN(-) anion in two different types of natural water (Rodbal dam and rainwater) and also in blood serum as a biological sample.

Novel thymine-functionalized MIL-101 prepared by post-synthesis and enhanced removal of Hg(2+) from water

A novel thymine-functionalized MIL-101 (MIL-101-Thymine) material was synthesized using a post-synthesis method to remove mercury at a high efficiency. MIL-101-Thymine was successfully prepared in this work and was confirmed by several characterization methods, such as (13)C nuclear magnetic resonance, X-ray diffraction, and infrared spectroscopy. The Hg(2+) adsorption agreed well with the Langmuir model, and the maximum adsorption capacity was 51.27mg/g. The adsorption rate fit with the pseudo-second-order kinetic model. Furthermore, MIL-101-Thymine exhibited excellent selectivity towards Hg(2+) over other cations, and the maximum value of the selective coefficient reached 947.34; this result is very likely due to the highly selective interactions of T-Hg(2+)-T in MIL-101-Thymine. The result of X-ray photoelectron spectroscopy also showed that Hg(2+) was coordinated with the N of thymine in MIL-101-Thymine. Moreover, the results of the thermogravimetric analysis and adsorption experiments showed that the Hg atom was two-coordinated with the thymine group. MIL-101-Thymine was used to remove trace Hg(2+) in real water samples, and satisfactory recoveries were obtained.

Self-assembly of nitrogen-doped carbon nanoparticles: a new ratiometric UV-vis optical sensor for the highly sensitive and selective detection of Hg2+ in aqueous solution

A novel ratiometric UV-vis optical sensor for Hg²⁺ was developed based on the self-assembly of nitrogen-doped carbon nanoparticles.

Barbituric acid–triphenylamine adduct as an AIEE-type molecule and optical probe for mercury(ii)

A barbituric acid–triphenylamine adduct displayed interesting aggregation-induced emission enhancement (AIEE) features in a THF–water co-solvent system and can act as a fluorescence turn-on probe for Hg²⁺.

DNA-functionalized upconversion nanoparticles as biosensors for rapid, sensitive, and selective detection of Hg2+ in complex matrices

DNA-functionalizable upconversion biosensors for the sensitive and selective determination of Hg²⁺ ions in complex matrices.

Fluorescent and colorimetric sensors for environmental mercury detection

The development of fluorescent and colorimetric sensing strategies for environmental mercury is described.

Ultrasensitive, rapid, and selective detection of mercury using graphene assisted laser desorption/ionization mass spectrometry

We report an extremely sensitive and specific detection of mercuric ions (Hg²⁺) based on graphene assisted laser desorption/ionization mass spectrometry (GALDI-MS). Combining the highly selective coordination interactions between thymine (T) and Hg²⁺, we present a simple, effective, and novel approach, based on π-π interactions of the T-Hg²⁺-T complex and G that can serve as a platform and matrix for GALDI-MS. The present sensor not only exhibits high selectivity and sensitivity (picomolar) to Hg²⁺ in aqueous solution, but also can elucidate the chemical structures of the metal complexes. The significant advantage in the current approach is that there is no need for a sophisticated instrument, and no sample pretreatment is required to detect the Hg²⁺ ions.

The role of "disaggregation" in optical probe development

"Aggregation-caused signal change" is a well-established mechanism by now and has been widely used as the basis for optical probe and sensor development. Compared to aggregation, its reverse process, disaggregation, has received much less attention and is not properly discussed in the literature so far. With the less established paradigm or mechanism, although some of the reported sensors and probes seem to work through disaggregation phenomena, the proper interpretation of the results and applying the concept to novel probe development is seriously hampered. The process from aggregation to disaggregation generally causes a recovery or enhancement of fluorescence signals, and thus provides an interesting new path to design "turn-on" probes. This tutorial review will provide the balanced comparison between aggregation and disaggregation mechanism, and focuses on the less explored advantages of "disaggregation" as a novel sensing mechanism and its recent applications in probe development.

Sensitive naked-eye detection of Hg2+based on the aggregation and filtration of thymine functionalized vesicles caused by selective interaction between thymine and Hg2+

A sensitive and low-cost method based on rapid interaction between functionalized PDA vesicles and Hg²⁺for the naked-eye detection of Hg²⁺.

Effects of structures of HgX2 complexes (X = CF3SO3 and Cl) with chiral bidentate ligands on circular dichroism spectra

The effects of the structures of HgX2 complexes (X = CF3SO3 and Cl) with chiral bidentate ligands [(R)-(−)-1-(1-naphthyl)-N,N-bis(pyridin-4-ylmethyl)ethanamine, (R)-(+)-1-phenyl-N,N-bis(pyridin-4-ylmethyl)ethanamine, (R)-(−)-1-(1-naphthyl)-N,N-bis(pyridin-3-ylmethyl)ethanamine, and (R)-(+)-1-phenyl-N,N-bis(pyridin-4-ylmethyl)ethanamine] on circular dichroism (CD) spectra are reported. The CD spectra of free (R)-(−)-1a and (R)-(+)-1b, which have 4-pyridyl groups, are similar to those of (R)-(−)-2a and (R)-(+)-2b, which have 3-pyridyl groups. When equimolar amounts of Hg(CF3SO3)2 are added to these ligands, a decrease in the CD intensity of (R)-(−)-2a is observed, and significant spectral changes (intensity and shape) are observed in (R)-(−)-1a, (R)-(+)-1b, and (R)-(+)-2b. X-ray crystal structures suggest that the (R)-(−)-2a/Hg(CF3SO3)2 complex is a coordination polymer with no bridging CF3SO3 anions, whereas the (R)-(−)-1a/Hg(CF3SO3)2 and (R)-(+)-1b/Hg(CF3SO3)2 complexes are coordination polymers with CF3SO3 anion bridges, and the (R)-(+)-2b/Hg(CF3SO3)2 complex has a tricyclic structure bridged by CF3SO3 anions. Two different conformers, which have clockwise and counter-clockwise screw senses between the naphthalene axis and the pyridine axis, are observed in the ligand components of the (R)-(−)-2a/Hg(CF3SO3)2 complex. In contrast, the X-ray structures of the (R)-(−)-2a/HgCl2 and (R)-(+)-2b/HgCl2 complexes are one-dimensional coordination polymers without bridging Cl anions. The significant CD spectral changes in the HgX2 complexes with different chiral bidentate ligands require formation of rigid structures and a single-directional screw sense between chromophores.

A phthalocyanine-based fluorescent sensor for Zn2+ ion

This paper describes the preparation and spectral properties of a near-infrared fluorophore in which two bis(2-picolyl)amino moieties are axially linked to a silicon(IV) phthalocyanine core. The effects of various metal ions on its absorption and fluorescence spectra have been examined. The results indicate that this compound shows a high sensitivity and moderate selectivity toward Zn2+ ion.

Highly sensitive and selective spectroscopic detection of mercury(II) in water by using pyridylporphyrin-DNA conjugates

Single-labeled pyridylporphyrin-DNA conjugates are reported as highly sensitive and selective spectroscopic sensors for mercury(II) ions in water. The effects of chemical structure (thymine versus adenine), number of nucleotides (monomer versus octamer), and porphyrin metalation (Zn versus free base) on the sensitivity and selectivity of mercury(II) detection are explored. The results indicated that pyridylporphyrin rather than the nucleobase plays a crucial role in mercury(II) sensing, because porphyrin conjugates with both adenosine and thymidine exhibited excellent mercury(II) detection. Mercury(II) recognition was shown in emission quenching, as well as in a redshift of the porphyrin Soret band absorption. The limit of detection (LOD, 3σ/slope) of zinc(II) pyridylporphyrin-5'-oligodeoxythymidine (ZnPorT8) obtained by fluorescence quenching was calculated to be 21.14 nM. Other metal cations (Zn(2+), Cd(2+), Pb(2+), Mn(2+), Ca(2+), Ni(2+), Mg(2+), Fe(2+), Cu(2+), and Na(+)) did not interfere with the emission and absorption sensing of mercury(II). Free-base porphyrin-oligothymine conjugate 2HPorT8 displayed similar sensitivity to ZnPorT8 but different selectivity. The results also implied that the sensing properties of porphyrin-deoxythymidine conjugates could potentially be tuned by porphyrin metalation.

Through bond energy transfer: a convenient and universal strategy toward efficient ratiometric fluorescent probe for bioimaging applications

Fluorescence resonance energy transfer (FRET) strategy has been widely applied in designing ratiometric probes for bioimaging applications. Unfortunately, for FRET systems, sufficiently large spectral overlap is necessary between the donor emission and the acceptor absorption, which would limit the resolution of double-channel images. The through-bond energy transfer (TBET) system does not need spectral overlap between donor and acceptor and could afford large wavelength difference between the two emissions with improved imaging resolution and higher energy transfer efficiency than that of the classical FRET system. It seems to be more favorable for designing ratiometric probes for bioimaging applications. In this paper, we have designed and synthesized a coumarin-rhodamine (CR) TBET system and demonstrated that TBET is a convenient strategy to design an efficient ratiometric fluorescent bioimaging probe for metal ions. Such TBET strategy is also universal, since no spectral overlap between the donor and the acceptor is necessary, and many more dye pairs than that of FRET could be chosen for probe design. As a proof-of-concept, Hg(2+) was chosen as a model metal ion. By combining TBET strategy with dual-switch design, the proposed sensing platform shows two well-separated emission peaks with a wavelength difference of 110 nm, high energy transfer efficiency, and a large signal-to-background ratio, which affords a high sensitivity for the probe with a detection limit of 7 nM for Hg(2+). Moreover, by employing an Hg(2+)-promoted desulfurization reaction as recognition unit, the probe also shows a high selectivity to Hg(2+). All these unique features make it particularly favorable for ratiometric Hg(2+) sensing and bioimaging applications. It has been preliminarily used for a ratiometric image of Hg(2+) in living cells and practical detection of Hg(2+) in river water samples with satisfying results.

Novel Hg2+-imprinted polymers based on thymine-Hg2+-thymine interaction for highly selective preconcentration of Hg2+ in water samples

A novel functional monomer T-IPTS, 3-isocyanatopropyltriethoxysilane (IPTS) bearing thymine (T) bases, was synthesized for imprinting Hg(2+). Then a novel Hg(2+) ionic imprinted polymers (IIPs) based on thymine-Hg(2+)-thymine (T-Hg(2+)-T) interactions, i.e. Hg-IIPs-T, were prepared by sol-gel process for the first time in this work. The Hg-IIPs-T exhibited excellent selectivity towards Hg(2+) over Cd(2+), Zn(2+) Pb(2+), Co(2+), Mn(2+), Mg(2+) and Ca(2+), due to the specific T-Hg(2+)-T interactions with high selectivity and high affinity. Accordingly, Hg-IIPs-T were used as solid-phase extraction (SPE) sorbents for preconcentration of trace Hg(2+) in water samples, and satisfactory recoveries ranging from 95.2 to 116.3% were obtained. Also, under optimized conditions, preconcentration factor and detection limit were achieved of 200 and 0.03 μg L(-1), respectively. The IIPs-T-SPE proved to be a rapid and high-effective cleanup and enrichment method for trace Hg(2+) in water samples. More importantly, these results indicated that devising and synthesizing new functional monomers tailor-made for template would become a general promising way to improve the selectivity and stability of IIPs.

Specific binding of anionic porphyrin and phthalocyanine to the G-quadruplex with a variety of in vitro and in vivo applications

The G-quadruplex, a four-stranded DNA structure with stacked guanine tetrads (G-quartets), has recently been attracting attention because of its critical roles in vitro and in vivo. In particular, the G-quadruplex functions as ligands for metal ions and aptamers for various molecules. Interestingly, the G-quadruplex can show peroxidase-like activity with an anionic porphyrin, iron (III) protoporphyrin IX (hemin). Importantly, hemin binds to G-quadruplexes with high selectivity over single-stranded DNA (ssDNA) and double-stranded DNA (dsDNA), which is attributable to an electrostatic repulsion of phosphate groups in ssDNA and dsDNA. The G-quadruplex and hemin-G-quadruplex complex allow development of sensing techniques to detect DNA, metal ions and proteins. In addition to hemin, anionic phthalocyanines also bind to the G-quadruplex formed by human telomere DNA, specifically over ssDNA and dsDNA. Since the binding of anionic phthalocyanines to the G-quadruplex causes an inhibition of telomerase activity, which plays a role in the immortal growth of cancer cells, anionic phthalocyanines are promising as novel anticancer drug candidates. This review focuses on the specific binding of hemin and anionic phthalocyanines to G-quadruplexes and the applications in vitro and in vivo of this binding property.

Hg2+-sensing system based on structures of complexes

The first example of a new Hg(2+)-sensing system based on the structures of complexes is reported. The system uses a combination of a new chiral bidentate ligand and CD spectroscopy. Significant CD spectral changes are observed when Hg(2+) is added, whereas no CD spectral changes are observed in the cases of Li(+), Na(+), K(+), Mg(2+), Ca(2+), Mn(2+), Fe(2+), Co(2+), Ni(2+), Cu(2+), Zn(2+), Rb(+), Ag(+), Cd(2+), La(3+), Gd(3+), and Pb(2+).