Search

The article examines enhanced sensitized near infrared (NIR) luminescence from gold nanoparticles via energy transfer from surface-bound fluorophores. The described systems showed extremely valuable features since NIR emissions, large Stoke's shifts and long lifetimes are all desirable properties for analytical applications in biology and medicine.

Abstract: Metal nanoparticles are reported to be toxic due to the generation of free radicals at their surface. Relatively inert thiol‐capped gold nanoparticles (AuNPs) have been reported to induce radical formation in the presence of hydroperoxides, which would conflict with their potential use as inert scaffolds for the design of novel nano‐antioxidants. With the aim of clarifying this aspect, we investigated the pro‐oxidant activity of dodecanethiol‐capped AuNPs (∼5 nm diameter), prepared through the Brust–Schiffrin synthesis, by oxygen‐uptake kinetic studies. The pro‐oxidant activity was found to be proportional to the impurities of the transfer agent tetraoctylammonium bromide (TOAB) left from the synthesis and decreased on repeated washing of the nanoparticles. Under identical settings similar batches of AuNP (∼9 nm diameter) prepared through the Ulman method without onium salts showed no pro‐oxidant behavior. The alternative onium phase‐transfer agents Oct4NBF4 (Oct=octyl), Hex4NBF4 (Hex=hexyl), and Hex4NPF6 were comparatively investigated and showed lower pro‐oxidant activity depending on the counterion (Br−>PF6−>BF4−). [ABSTRACT FROM AUTHOR]

Dye-doped nanoparticles (NPs) are intriguing fluorescent systems in which collective properties can arise, which are ascribable to the ensemble of dyes rather than to individual ones. Collective properties can be tailored to increase brightness and introduce photophysical versatility. In this context, self-quenching has long been regarded as the phenomenon to avoid. Here we report on the possibility to profit from a property stemming from self-quenching: nanoparticles with a high number of dyes per NP (including self-quenched dyes) display much slower photobleaching compared to nanoparticles with a lower doping degree. In this way, their emission intensity can be kept almost constant for ten times longer. This extended duration of luminescence is due to preferential photobleaching of self-quenched fluorophores. These observations can shine new light on the use of highly dye-doped nanoparticles as long-lasting, super-photostable probes under strong excitation conditions. [ABSTRACT FROM AUTHOR]

Chemosensors are molecules of abiotic origin that are able to bind selectively and reversibly the analyte of interest with a concomitant change in the property of the system. They find wide applications in lots of disciplines and our work is directed to develop new species for future applications. We present here the latest luminescent chemosensors studied in our laboratory. The chosen luminophore moieties are anthracene and dioxyxanthone derivatives that have been differently connected with receptor units such as crown ethers and thioethers. In solution a good selectivity and affinity was observed for different ions such as Na+, K+, Cs+, Ba2+, Sr2+, Ca2+ and Ag+. The binding is signaled in all cases by pronounced changes in the photophysical properties of the luminophore present in the structure of the chemosensor. [ABSTRACT FROM AUTHOR]

A more sustainable and efficient protocol for the photocatalytic α‐amino arylation promoted by fac‐Ir(ppy)3 was developed. Three noteworthy results were achieved: i) the replacement of toxic medium DMA with the greener solvents NBP and NHP, and the concurrent improvement of the process efficiency by lowering both the amine and the base amount; ii) the development of a recycling protocol for both the sustainable solvent NHP and the commercially available costly photocatalyst fac‐Ir(ppy)3, achieving environmental and economic benefits. This approach to the photocatalyst recovery avoids very demanding catalyst structural modifications; iii) the protocol in green solvents proved to be scalable up to 10 mmol of limiting reagent, maintaining excellent performance also lowering the photocatalyst loading down to 0.05 mol%. This is the first example of photocatalytic α‐arylation of amines promoted by such a low amount of catalyst. Lastly, the versatility of this approach was demonstrated by extending the use of the green solvent NBP to another photoredox process. [ABSTRACT FROM AUTHOR]

The recent burst of research on smart materials is a clear evidence of the growing interest of the scientific community, industry, and society in the field. The exploitation of the great potential of stimuli‐responsive materials for sensing, actuation, logic, and control applications is favored and supported by new manufacturing technologies, such as electrospinning, that allows to endow smart materials with micro‐ and nanostructuration, thus opening up additional and unprecedented prospects. In this wide and lively scenario, this article systematically reviews the current advances in the development of thermoactive electrospun fibers and textiles, sorting them, according to their response to the thermal stimulus. Hence, several platforms including thermoresponsive systems, shape memory polymers, thermo‐optically responsive systems, phase change materials, thermoelectric materials, and pyroelectric materials, are described and critically discussed. The difference in active species and outputs of the aforementioned categories is highlighted, evidencing the transversal nature of temperature stimulus. Moreover, the potential of novel thermoactive materials are pointed out, revealing how their development could take to utmost interesting achievements. [ABSTRACT FROM AUTHOR]

The synthesis, photophysical, and anion-binding properties of a series of di-, tri-, and tetrapodal anion-binding hosts based on aminopyridinium units with pyrenyl reporter groups are described. The ditopic mesitylene-derived calix[4]arene-based host 4 binds strongly to dicarboxylates, particularly malonate, in a 2:1 anion:host ratio but is essentially nonemissive in the presence of all anions except chloride because of intramolecular quenching by the pyridinium units. Addition of chloride results in a conformational change, giving an initial increase in emission assigned to intramolecular excimer formation. Further chloride addition also results in an increase in the intensity of the pyrenyl monomer emission as chloride binding reduces the acceptor ability of the pyridinium groups. This behavior is not exhibited by control compounds 5 and 6, which lack the ditopic geometry and calixarene spacer unit; however, tripodal 6 forms 1:2 anion:host complexes with a range of anions. [ABSTRACT FROM AUTHOR]

A photoredox catalytic synthesis of functionalized 2‐aminofurans is proposed starting from α‐halo carbonyl substrates and N‐allenamides. The protocol proves to be efficient and sustainable thanks to: i) the use of visible light as green energy source, ii) the redox‐neutral nature of the transformation, allowing to avoid additives and strong oxidants, iii) the mild reaction conditions and the functional groups tolerance, iv) the low photocatalyst loading and the absence of excess reagents, v) the one‐pot formation of three new bonds in a domino sequence. According to our mechanistic hypothesis, the transformation is configured as a double radical‐polar crossover reaction, in which the photocatalyst is excited, oxidized and reduced twice for each molecule of 2‐aminofuran produced. The novelty of the designed synthetic approach also lies in the use of N‐allenamides as substrates, which, after the addition of the first electrophilic radical, preserve a further reactive π‐system, making possible the addition of a second α‐keto radical and enabling the installation of a keto functionality at a remote position. The good yields, the broad scope, and the possibility to further synthetically elaborate the obtained furans make this protocol particularly promising for the construction of useful products. [ABSTRACT FROM AUTHOR]

The growing numbers related to plastic pollution are impressive, with ca. 70 % of produced plastic (>350 tonnes/year) being indiscriminately wasted in the environment. The most dangerous forms of plastic pollution for biota and human health are micro‐ and nano‐plastics (MNPs), which are ubiquitous and more bioavailable. Their elimination is extremely difficult, but the first challenge is their detection since existing protocols are unsatisfactory for microplastics and mostly absent for nanoplastics. After a discussion of the state of the art for MNPs detection, we specifically revise the techniques based on photoluminescence that represent very promising solutions for this problem. In this context, Nile Red staining is the most used strategy and we show here its pros and limitations, but we also discuss other more recent approaches, such as the use of fluorogenic probes based on perylene‐bisimide and on fluorogenic hyaluronan nanogels, with the added values of biocompatibility and water solubility. [ABSTRACT FROM AUTHOR]

In this paper we show how it is possible to control the nature and the efficiency of collective photophysical processes in a network composed of two different fluorescent units organized on the surface of silica nanoparticles. Such a structure is obtained by covering nanoparticles with a layer of dansyl moieties (Dns) and by partially protonating them in solution. The two fluorophores Dns and Dns·H[sup +] have very different photophysical properties and can be selectively excited and detected. The interaction between the two units Dns and Dns·H[sup +] has been first investigated in a reference compound obtained by derivatizing 1,6hexanediamine with two dansyl units. The photophysical characterization of this compound (absorption spectra, fluorescence spectra, quantum yield, and lifetime) showed that the two moieties can be involved both in energy and electron-transfer processes. Dansylated nanoparticles were prepared by modifying preformed silica nanoparticles with dansylated (3-aminopropyl)trimethoxysilane. Photophysical studies indicated that protonation has a dramatic effect on the fluorescence of the nanoparticles, leading to the quenching of both the protonated units and the surrounding nonprotonated ones. This amplified response to protonation, due to charge-transfer interactions, is solvent-dependent and is less efficient in pure chloroform with respect to acetonitrile/chloroform (5/1 v/v) mixtures. The reduced efficiency of the electrontransfer processes responsible for the quenching makes energy transfer competitive to such an extent that in pure chloroform excitation energy migration takes place from Dns·H[sup +] to Dns with great efficiency. [ABSTRACT FROM AUTHOR]

Luminescence quenching is a process exploited in transversal applications in science and technology and it has been studied for a long time. The luminescence quenching mechanisms are typically distinguished in dynamic (collisional) and static, which can require different quantitative treatments. This is particularly important – and finds broad and interdisciplinary application – when the static quenching is caused by the formation of an adduct between the luminophore – at the ground state – and the quencher. Due to its nature, this case should be treated starting from the well-known law of mass action although, in specific conditions, general equations can be conveniently reduced to simpler ones. A proper application of simplified equations, though, can be tricky, with frequent oversimplifications taking to severe errors in the interpretation of the photophysical data. This tutorial review aims to (i) identify the precise working conditions for the application of the simplified equations of static quenching and to (ii) provide general equations for broadest versatility and applicability. The latter equations can be used even beyond the sole case of pure quenching, i.e., in the cases of partial quenching and even luminescence turn-on. Finally, we illustrate different applications of the equations via a critical discussion of examples in the field of sensing, supramolecular chemistry and nanotechnology. [ABSTRACT FROM AUTHOR]

A synthetic procedure, catalysed by Ir(ppy)3 under visible‐light irradiation, for the chemodivergent synthesis of 2,3‐dihydrofurans (3) or β,γ‐unsaturated ketones (7) starting from α‐halo ketones (1) and alkenes (2) has been developed. The mild reaction conditions and the redox‐neutral nature of the process make it particularly sustainable avoiding the use of both sacrificial reactants and stoichiometric strong oxidants. Careful experimental investigations, supported by DFT calculations, allowed to disclose in details a possible mechanistic pathway and to direct the synthesis chemodivergently either toward 3 or 7, depending not only on the nature of the substrates, but also on the choice of the experimental conditions. [ABSTRACT FROM AUTHOR]

Silica nanoparticles (NPs) are versatile nanomaterials, which are safe with respect to biomedical applications, and therefore are highly investigated. The advantages of NPs include their ease of preparation, inexpensive starting materials and the possibility of functionalization or loading with various doping agents. However, the solubility of the doping agent(s) imposes constraints on the choice of the reaction system and hence limits the range of molecules that can be included in the interior of NPs. To overcome this problem, herein, we improved the current state of the art synthetic strategy based on Pluronic F127 by enabling the synthesis in the presence of large amounts of organic solvents. The new method enables the preparation of nanoparticles doped with large amounts of water-insoluble doping agents. To illustrate the applicability of the technology, we successfully incorporated a range of phosphorescent metalloporphyrins into the interior of NPs. The resulting phosphorescent nanoparticles may exhibit potential for biological oxygen sensing. [ABSTRACT FROM AUTHOR]

A nanosensor with dual‐mode fluorescence response to pH and an encoded identification signal, was developed by exploiting excitation energy transfer and tailored control of molecular organization in core–shell nanoparticles. Multiple signals were acquired in a simple single‐excitation dual‐emission channels set‐up. A nanosensor with dual‐mode fluorescence response to pH and an encoded identification signal was developed by exploiting excitation energy transfer and tailored control of molecular organization in core–shell nanoparticles. [ABSTRACT FROM AUTHOR]

We present here the development of an all-solid-state optical sensor based on phenyl-substituted diaza-18-crown-6 hydroxyquinoline (DCHQ-Ph) for the indirect selective detection of microcystin-LR (MC-LR), reaching a very low detection limit of 0.05 μg L−1, well below the World Health Organisation (WHO) guideline value (1 μg L−1) in potable water. We demonstrate the potential applicability of the developed method in fast and low-cost water toxicity estimation. [ABSTRACT FROM AUTHOR]

A new acridine-based fluorescent chemosensor,L2, featuring two sulfurated macrocyclic units has been synthesised. Proton and metal binding properties ofL2have been studied in H2O/CH3CN (1:1 v/v) by potentiometric and spectrophotometric measurements and compared with those of the analogous and previously publishedbis-macrocyclic receptor featuring two [9]aneN3units (L1). Despite a thermodynamic selectivity observed for Zn2+with bothL1andL2,L2shows a marked sensing selectivity towards Cd2+via a chelation enhancement of fluorescence (CHEF) effect both in H2O/CH3CN (1:1 v/v) and in H2O using silica core-PEG shell nanoparticles as vehiculant. On the other hand,L1shows a selective optical sensing towards Zn2+in agreement with the thermodynamic selectivity observed for the same metal ion. [ABSTRACT FROM AUTHOR]

Electrolytes are key components of Li/O 2 batteries. The ionic liquid-like structure and good electrochemical and thermal stability of solvent-in-salt electrolytes make them of great interest for lithium batteries. Solutions of lithium bis(trifluoromethanesulfonyl)imide in tetraethylene glycol dimethyl-ether with molar ratios ranging from 1:9 to 1:0.9 are here investigated. A voltammetric study of oxygen redox reaction in presence of different concentrations of salt, from salt-in-solvent to solvent-in-salt solutions, is reported here for the first time along with a novel luminescence method for the evaluation of O 2 solubility. The results indicate that superconcentrated solutions favor the solution formation mechanism of Li 2 O 2 during discharge which in turn is beneficial for battery cycling stability. Despite the higher viscosity of solvent-in-salt solutions than conventional electrolytes, O 2 solubility is improved at the highest salt concentrations. These findings contribute to understand electrochemical processes in solvent-in-salt solutions for Li/O 2 and next generation metal-based batteries. [ABSTRACT FROM AUTHOR]

Alzheimer’s disease (AD) has been defined as a multi-factorial disorder resulting from a complex array of networked cellular and molecular mechanisms. In particular, elevated levels of Aβ protein and its aggregation products in the presence of metal ions proved to be highly neurotoxic and therapeutic strategies aimed at preventing Aβ generation and oxidative stress may represent an effective approach for AD treatment. A recent paradigm for the treatment of complex diseases such as AD suggests the employment of multifunctional compounds, single chemical entities capable of simultaneously modulating different targets involved in the pathology. In this paper, the “pharmacophores combination” strategy was applied, connecting the main scaffold of the BACE-1 ligand 1 to that of the chalcone 2, as metal chelating pharmacophore, to obtain a small library of compounds. Conjugate 5 emerged as the most interesting derivative, proving to inhibit BACE-1 with low-micromolar potency, and showing neuroprotective effects. In particular, 5 proved to be able to protect from metal-associated oxidative stress by hampering intracellular Cu2+-induced ROS formation without any direct neurotoxic effect. [ABSTRACT FROM AUTHOR]

Abstract: Novel highly ethynylated materials carrying aminoacidic side arms on poly(aryleneethynylene) (PAE) conjugated backbones have been prepared and fully characterized. The luminescent sensing properties of these materials toward metal ions were investigated. All compounds showed high selectivity toward Hg(II) ions, and a signal amplification in Hg(II) detection was observed for the polymeric compound in comparison with other molecular ligands. [Copyright &y& Elsevier]

Abstract: This review aims to give an overview on the state of the art in the precise context of metal complexes-based ECL dyes directly adsorbed on, included in or interacting with nanoparticles of various nature. Electrogenerated chemiluminescence, or electrochemiluminescence (ECL), is the process through which species generated at electrodes undergo homogeneous high-energy electron transfer reactions to give excited states that emit light. When stable ECL probes such as ruthenium coordination complexes are used, this process can be performed several times, free of the interferences typical of photoluminescence such as the excitation light, providing a clear and stable signal suitable for highly sensitive assays. The ECL emission is initiated and controlled by the electrode potential and immobilization of the ECL probes on the electrode surface allows one to reduce the consumption of expensive reagents, simplifies the experimental design, and creates regenerable sensing devices. The organization of the electrode surface is thus the key point to optimize the device performance. Nanoparticles have proved their potential as tools to organize the ECL probes, to increase the active area and to improve the electrochemical properties of the interface. There is an extended research devoted on one hand to optimize the materials, and on the other hand to explore the wide horizon of possibilities that arise from the combination of nanoparticles and ECL probes, co-reagents, (bio)markers and other functional moieties. The results discussed in this review clearly show that the use of nanoparticles aimed to obtain signal enhancement represents one of the most interesting research lines for the development of the ECL technique. The activity in this field is so dynamic that outstanding results could reasonably be expected in the near future. [Copyright &y& Elsevier]

N,N'-Bis-((8-hydroxy-7-quinolinyl)methyl)- 1,1 0-diaza-18-crown-6 ether 1a and its analogue 1c are known as fluorescent sensors of magnesium in living cells. With the aim to investigate the effects of the substitution pattern on the photophysical properties of ligands 1 and their metal complexes, we developed an efficient microwaves enhanced one-pot Mannich reaction so double-armed diaza-crown ligands I carrying a variety of substituents. This new protocol is characterized by shorter reaction times, enhanced yields, and improved product purities with respect to the use of conventional conductive heating. [ABSTRACT FROM AUTHOR]

Keywords: dye staining; luminescence; microplastics and nanoplastics; plastic pollution; sensors EN dye staining luminescence microplastics and nanoplastics plastic pollution sensors 1 1 1 12/22/21 20211215 NES 211215 B Environmental pollution especially b by micro- and nanoplastics is highly topical our days. Dye staining, luminescence, microplastics and nanoplastics, plastic pollution, sensors Different detection methods are discussed in the Review by L. Prodi et al. on page 17529 ff. GLO:OLD/15dec21:chem202187062-toc-0001.jpg PHOTO (COLOR): . gl GLO:OLD/15dec21:chem202187062-toc-0001.jpg PHOTO (COLOR): . gl. [Extracted from the article]

Abstract: The metal ion binding properties of three photoactive poly-(arylene ethynylene) co-polymers with potentially complexing units have been described. Upon protonation or complexation, the intensity of the luminescence typical of these conjugated polymers is completely quenched, due to the extended electronic conjugation of the polymer backbones. In the case of the formation of complexes with Yb3+ and Er3+, one of the studied polymers gives rise to an efficient sensitization of their typical metal centred NIR emission. This feature is of particular interest for the preparation of new materials that are the subject of active research for their possible applications in optical imaging and in optical amplification for telecommunication purposes. [Copyright &y& Elsevier]

The process of formation of silica nanoparticles doped with a newly synthesized pyrene derivative has been investigated by means of fluorescence steady-state and time-resolved spectroscopy. The changes in the photophysical properties of the fluorophore were correlated to the increase of the nanoparticles hydrodynamic volume measured via dynamic light scattering (DLS) allowing us to determine the radial profile of the concentration of the dye. Experiments performed at a "low" degree of doping show that the fluorophore is almost completely included considerably before the end of the nanoparticles growth, allowing us to identify a self-organizing core-shell substructure. A strong enhancement of the fluorescence of the dye and a corresponding increase of its excited-state lifetime was observed upon its inclusion as a result of the shielding effect from molecular oxygen due to the silica matrix, a situation confirmed by the absence of the oxygen singlet emission in the near-infrared luminescence spectra. In the case of "high" loading, on the other hand, a heavily doped core showing an excimeric-like emission is first formed. Further growth leads to the formation of layers where the concentration of dye gradually decreases and the monomeric emission becomes relevant. The effect of the degree of doping on the kinetics of growth is also reported. At both concentration regimes, ultrafiltration experiments revealed the complete inclusion of the dye molecules. The average number of dye molecule per nanoparticles was also determined. [ABSTRACT FROM AUTHOR]

Abstract: Films based on TiO2 nanoparticles (NPs) have been successfully used as sensing elements in chemical sensors. TiO2 colloidal suspensions can be obtained by spontaneous hydrolysis in acidic solutions of Ti(IV) compounds. The obtained TiO2 NPs can be employed to build up nanostructured films. With the purpose of preparing TiO2-based nanostructured, imprinted materials as sensing elements for piezoelectric sensors, we obtained TiO2 NP dispersions by hydrolyzing potassium titanyl oxalate in the presence of a target analyte (tyrosine). Since morphological properties of the synthesized NPs are known to influence the nanostructured film characteristics, an analytical strategy to characterize such colloidal systems can combine a size-based separation method with spectroscopic analysis to correlate the particle size distribution (PSD) with the particle-target interaction properties able to determine the sensing efficiency. In this work, we present the characterization of colloidal tyrosine-TiO2 NP systems by flow field-flow fractionation (FlFFF) with online, UV/Vis absorption detection and offline fluorescence analysis. FlFFF eliminates the possible contribution of free tyrosine to the absorption and fluorescence properties of the NPs. FlFFF also fractionates NPs on a size basis. Particle size distribution (PSD) profiles of the fractionated NPs are then obtained by conversion of the multi-wavelength UV/Vis fractograms. Size of the fractionated NPs is finally related to fluorescence properties of the collected NPs fractions. Good correlation between the fluorescence intensity, which is proportional to the tyrosine uptake, and the FlFFF-based, NP mass-size frequency distribution finally confirms the existence of tyrosine-TiO2 NP interaction. [Copyright &y& Elsevier]