1,721,066 research outputs found
Interplay between Cyclization and Polymerization in Ditopic Cavitand Monomers
No full textQuinoxaline kite velcrands were functionalized with a ureidopyrimidone moiety at the lower rim, in order to combine multiple hydrogen bonding and solvophobic interactions to build dual-coded supramolecular structures. The orthogonality of the selected binding motifs has been demonstrated by NMR studies, as well as the reversible nature of the obtained assemblies. At low concentration, the presence of a ring-chain equilibrium has been established by 1H NMR experiments, and confirmed by static and dynamic light scattering measurement
Fluorogenic hyaluronan nanogels for detection of micro- and nanoplastics in water
Full text linkEnvironmental pollution from plastics is exponentially increasing due to human activities. While larger microplastics can be detected with various methods, retrieving micron-sized fragments and nanoplastics remains challenging. Yet, these smaller-sized plastics have been raising considerable toxicological concern. Here, we show that a poorly emissive hyaluronan functionalized with rhodamine B (HA–RB) adheres with high affinity to various microplastic surfaces, becoming brightly emissive. Micro- and nanoplastics (MNPs) can be successfully detected with size as small as the diffraction limit of confocal microscopy (ca. 250 nm). FLIM images show that the fluorescence lifetime of the dye moieties changes according to the plastics, making possible a discrimination of the nature of MNPs based on lifetime. HA–RB, compared to previous reports, eliminates false-positive results caused by formation of dye aggregates, resulting in a higher S/N ratio which allows the unequivocal detection of nano-sized fragments
Static quenching upon adduct formation: a treatment without shortcuts and approximations
Full text linkLuminescence 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
Self-organizing core-shell nanostructures: Spontaneous accumulation of dye in the core of doped silica nanoparticles
No full textThe 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
NIR-fluorescent dye doped silica nanoparticles for in vivo imaging, sensing and theranostic
No full textThe development of nanostructures devoted to in vivo imaging and theranostic applications is one of the frontier fields of research worldwide. In this context, silica nanoparticles (SiO2-NPs) offer unquestionable positive properties: silica is intrinsically non-toxic, several versatile and accessible synthetic methods are available and many variations are possible, both in terms of porosity and functionalization for delivery and targeting purposes, respectively. Moreover, the accumulation of several dyes within a single nanostructure offers remarkable possibilities to produce very bright and photostable luminescent nanosystems. Advancements in imaging technology, bioassay, fluorescent molecular probes have boosted the efforts to develop dye doped fluorescent SiO2-NPs, but despite this, only a quite limited set of systems are applicable in vivo. Herein we discuss selected examples that appeared in the literature between 2013-17, with imaging capabilities in vivo and characterized by a significant near infrared (NIR) fluorescence emission. We present here very promising strategies to develop SiO2-NPs for diagnostic and therapeutic applications - some of which are already in clinical trials - and the possibility to develop bio-erodable SiO2-NPs. We are convinced that all these findings will be the basis for the spread of SiO2-NPs into clinical use in the near future
Collective Properties Extend Resistance to Photobleaching of Highly Doped PluS NPs
No full textDye-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
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Mapping heterogeneous polarity in multicompartment nanoparticles
No full textUnderstanding polarity gradients inside nanomaterials is essential to capture their potential as nanoreactors, catalysts or in drug delivery applications. We propose here a method to obtain detailed, quantitative information on heterogeneous polarity in multicompartment nanostructures. The method is based on a 2-steps procedure, (i) deconvolution of complex emission spectra of two solvatochromic probes followed by (ii) spectrally resolved analysis of FRET between the same solvatochromic dyes. While the first step yields a list of polarities probed in the nanomaterial suspension, the second step correlates the polarities in space. Colocalization of polarities falling within few nanometer radius is obtained via FRET, a process called here nanopolarity mapping. Here, Prodan and Nile Red are tested to map the polarity of a water-dispersable, multicompartment nanostructure, named PluS nanoparticle (NPs). PluS NPs are uniform core-shell nanoparticles with silica cores (diameter ~10 nm) and Pluronic F127 shell (thickness ~7 nm). The probes report on a wide range of nanopolarities among which the dyes efficiently exchange energy via FRET, demonstrating the coexistence of a rich variety of environments within nanometer distance. Their use as a FRET couple highlights the proximity of strongly hydrophobic sites and hydrated layers, and quantitatively accounts for the emission component related to external water, which remains unaffected by FRET processes. This method is general and applicable to map nanopolarity in a large variety of nanomaterials
pH-responsive host-guest polymerization and blending
No full textIn this work, we demonstrate - in two different settings - the potential of the recognition motif made by tetraphosphonate cavitand/N-methyl ammonium salt for the development of supramolecular polymer chemistry. In the first part a novel pH sensitive supramolecular homopolymer was assembled by proper design of the corresponding monomer, and monitoring the self-assembling process by several analytical tools, including NMR spectroscopy and light scattering techniques. These measurements provided the evidence for the formation of the homopolymer and its pH responsiveness. In the second study, the two recognition groups - tetraphosphonate cavitand (Host) and sarcosine hydrochloride (Sarc) - introduced in polystyrene (PS-Host) and poly(butyl methacrylate) (PBMA-Sarc) respectively, led to the mixing of the two otherwise immiscible polymers thanks to the energetically favourable host-guest interactions between the polymer chains. The polymer blending was verified by the presence of a single glass transition temperature (Tg) and showed its homogeneous morphology by atomic force microscopy (AFM)
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