Aggregation-induced emission spectral shift as a measure of local concentration of a pH-activatable rhodamine-based smart probe

Colorimetric and absorbance based sensor for sulfide and bicarbonate ions by dye doped polymer composite

We have developed a simple, rapid and cost-effective Dual-channel "colorimetric and absorbance" sensor using polyvinylpyrrolidone (PVP) capped Rhodamine6g (Rh6G) dye composite. Dye-doped polymer composite probe (PVPRH) exhibit intense, narrow absorption properties and long-term stability than the bare Rh6G. The probe's colorimetric relationship with pH was demonstrated by absorption titration. The PVPRH provides a sensitive dual channel method for the determination of sulfide and bicarbonate with colorimetric response and absorption quenching. The synthesized probe, as a two-faced, exhibited remarkable colorimetric responses from orange to pale yellow in the presence of S2- and orange to soft pink in the presence of HCO3- ion, which can be observed by the naked eye also. Under optimal conditions, the relative absorption intensity decreases with increasing ion concentration of sulfide and bicarbonate ions. This trend is observed within the probe solution concentration range of 5 mM to 50 mM. The Dye-doped polymer composite probe is easy, cost effective, rapid, and has real time detection capability for sulfide and bicarbonate ions. The composite probe is stable and optically modified and can be successfully used for detections of S2- and HCO3- ions as strip senor.

Synthesis and Optical Characterization of a Rhodamine B Spirolactam Dimer

Amide derivatives of xanthene dyes such as rhodamine B are useful in a variety of sensing applications due to their colorimetric responses to stimuli such as acidity changes and UV light. The optical properties of these molecules can be influenced by intermolecular associations into dimeric structures, but the exact impact can be hard to predict. We have designed a covalently linked intramolecular dimer of the dye rhodamine B utilizing p-phenylenediamine to link the two dyes via amide bonds. The doubly closed spirolactam version of this dimer, RSL₂, is isolated as a colorless solid. Under acidic conditions or UV exposure, RSL₂ solutions develop a pink color that is expected for the ring-opened form of the molecule. However, nuclear magnetic resonance (NMR) and single-crystal diffraction data show that the equilibrium still prefers the closed dimer state. Interestingly, the emission profile of RSL₂ shows solvatochromic blue fluorescence. Control studies of model compounds with similar structural motifs do not display similar blue fluorescence, indicating that this optical behavior is unique to the dimeric form. This behavior may lend itself to applications of such xanthene dimers to more sophisticated sensors beyond those with traditional binary on/off fluorescence profiles.

Aggregation of molecules is controlled in microdroplets

Fluorescence microscopy reveals the control of aggregation and de-aggregation of molecules in microdroplets, which is strikingly different from that in the bulk.

An "Off-On" Rhodamine 6G Hydrazide-Based Output Platform for Fluorescence and Visual Dual-Mode Detection of Lead(II)

In this study, the rhodamine 6G hydrazide (R6GH) complex was synthesized to develop an "off-on" output platform for fluorescence and visual dual-mode analysis of lead(II) (Pb2+). The prepared R6GH complex using the heat to reflux reaction of rhodamine 6G (R6G) and hydrazine hydrate was characterized through FT-IR, MS, 1H NMR, and 13C NMR and demonstrated to have good fluorescence stability and reversibility. The microenvironment for Pb2+ detection has been optimized in detail. Under the optimal conditions, the "off-on" R6GH-based fluorescence output platform showed a good response to Pb2+ in the concentration range of 0.05-6.0 μM (R2 = 0.9851) with a limit of detection (LOD) of 0.02 μM. Furthermore, at three spiked Pb2+ levels in the selected agricultural (tap water, soil) and food (fish, shrimp) samples, the developed R6GH-based fluorescence assays obtained a significant recovery range of 84.0-102.0% (RSD < 5.0%, n = 3), which had a good correlation with the results from ICP-MS (R2 = 0.9915). The developed R6GH immobilized paper-based array sensor can reach the lower LOD (2.5 μM) for Pb2+ through the naked eye. By combining with LAB analysis, a good linear response was obtained in the Pb2+ concentration range of 1.0-50.0 μM. These results indicated that the developed R6GH probe had great application potential in accurate detection of fluorescence and rapid visual and semiquantitative screening for Pb2+.

Self-Targeting of Carbon Dots into the Cell Nucleus: Diverse Mechanisms of Toxicity in NIH/3T3 and L929 Cells

It is important to understand the nanomaterials intracellular trafficking and distribution and investigate their targeting into the nuclear area in the living cells. In our previous study, we firstly observed penetration of nonmodified positively charged carbon dots decorated with quaternary ammonium groups (QCDs) into the nucleus of mouse NIH/3T3 fibroblasts. Thus, in this work, we focused on deeper study of QCDs distribution inside two healthy mouse NIH/3T3 and L929 cell lines by fluorescence microspectroscopy and performed a comprehensive cytotoxic and DNA damage measurements. Real-time penetration of QCDs across the plasma cell membrane was recorded, concentration dependent uptake was determined and endocytic pathways were characterized. We found out that the QCDs concentration of 200 µg/mL is close to saturation and subsequently, NIH/3T3 had a different cell cycle profile, however, no significant changes in viability (not even in the case with QCDs in the nuclei) and DNA damage. In the case of L929, the presence of QCDs in the nucleus evoked a cellular death. Intranuclear environment of NIH/3T3 cells affected fluorescent properties of QCDs and evoked fluorescence blue shifts. Studying the intracellular interactions with CDs is essential for development of future applications such as DNA sensing, because CDs as DNA probes have not yet been developed.

Study of the effect of the introduction of Tris(bipyridine)ruthenium(II) chloride into silicon dioxide particles by spectrofluorometry methods

The Stoeber reaction was used to grow silica microparticles in the presence of the fluorescent dye Tris(bipyridine)ruthenium (II) chloride. The diameter of the obtained particles varies from about 150 to 280 nm depending on the dye concentration. Using spectrofluorometry methods, concentration quenching of fluorescence of dye solutions was studied before and after growing the microparticles. It was found out that the concentration quenching of fluorescence decreases significantly after its incorporation into the silicon dioxide microparticles upon excitation in the short-wavelength region of the spectrum.

J-dimer emission in interwoven metal-organic frameworks

J-dimer emission is an emergent property that occurs when pairs of ground state fluorophores associate, typically in a dilute solution medium. The resulting fluorescence is shifted with respect to the monomer. J-dimer emission, however, has never been observed in concentrated dispersions or in the solid state. We posited that multivariate (MTV) MOFs with double interwoven structures would help to isolate these dimers within their crystalline matrix. Using this strategy, J-aggregate density was controlled during crystallization by following a substitutional solid solution approach. Here, we identified the presence of J-dimers over the entire composition range for interwoven PIZOF-2/NNU-28 structures with variable amounts of a diethynyl-anthracene aggregate-forming link. We produced bulk crystals that systematically shifted their fluorescence from green to red with lifetimes (up to 13 ns) and quantum yields (up to 76%) characteristic of π–π stacked aggregates. Photophysical studies also revealed an equilibrium constant of dimerization, K_D = 1.5 ± 0.3 M⁻¹, enabling the first thermodynamic quantification of link–link interactions that occur during MOF assembly. Our findings elucidate the role that supramolecular effects play during crystallization of MTV MOFs, opening pathways for the preparation of solid-state materials with solution-like properties by design.

J-dimer emission is an emergent property that occurs when pairs of ground-state fluorophores associate within multivariate MOFs producing tunable red shifted emission.

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).

Nanoparticles Can Wrap Epithelial Cell Membranes and Relocate Them Across the Epithelial Cell Layer

Although the link between the inhalation of nanoparticles and cardiovascular disease is well established, the causal pathway between nanoparticle exposure and increased activity of blood coagulation factors remains unexplained. To initiate coagulation tissue factor bearing epithelial cell membranes should be exposed to blood, on the other side of the less than a micrometre thin air-blood barrier. For the inhaled nanoparticles to promote coagulation, they need to bind lung epithelial-cell membrane parts and relocate them into the blood. To assess this hypothesis, we use advanced microscopy and spectroscopy techniques to show that the nanoparticles wrap themselves with epithelial-cell membranes, leading to the membrane's disruption. The membrane-wrapped nanoparticles are then observed to freely diffuse across the damaged epithelial cell layer relocating epithelial cell membrane parts over the epithelial layer. Proteomic analysis of the protein content in the nanoparticles wraps/corona finally reveals the presence of the coagulation-initiating factors, supporting the proposed causal link between the inhalation of nanoparticles and cardiovascular disease.