Metal Ion Induced FRET OFF−ON in Tren/Dansyl-Appended Rhodamine

Cascade Förster Resonance Energy Transfer Studies for Enhancement of Light Harvesting on Dye-Sensitized Solar Cells

This work reports cascade Förster resonance energy transfer (FRET)-based n-type (ZnO) and p-type (NiO) dye-sensitized solar cells (DSSCs), discussing approaches to enhance their overall performance. Although DSSCs suffer from poorer performance than other solar cells, the use of composites with carbon dot (Cdot) can enhance the power conversion efficiency (PCE) of DSSCs. However, further improvements are demanded through molecular design to stimulate DSSCs. Here, a photosensitized system based on a cascade FRET was induced alongside the conventional photosensitizer dye (N719). To N719 in a DSSC is transferred the energy cascaded through donor fluorescence materials (pyrene, 3-acetyl-7-N,N-diethyl-coumarin or coumarin and acridine orange), and this process enhances the light-harvesting properties of the sensitizers in the DSSC across a broad region of the solar spectrum. PCE values of 10.7 and 11.3% were achieved for ZnO/Cdot and NiO/Cdot DSSCs, respectively. These high PCE values result from the energy transfer among multi-photosensitizers (cascade FRET fluorophores, N719, and Cdot). Moreover, Cdot can play a role in intensifying the adsorption of dyes and discouraging charge recombination on the semiconductor. The present results raise expectations that a significant improvement in photovoltaic performance can be attained of DSSCs exploiting the cascade FRET photonics phenomenon.

A flexible tripod fluorescent probe for multiple cations detection and its application in living cells

To the flexible tripod platform tren (tris(2-aminoethyl)amine), a Rhodamine and two naphthalene fluorophores were introduced. The resulting fluorescence probe named TRN was fully characterized and employed in cell imaging. Probe TRN exhibited high selectivity and excellent sensitivity for the simultaneous fluorescence detection of Zn²⁺/Hg²⁺/Al³⁺/Cu²⁺. The significant changes in the fluorescence color make naked-eye detection possible. Furthermore, fluorescence imaging experiments of Zn²⁺/Hg²⁺/Al³⁺/Cu²⁺ in living PC3 cells demonstrated its value for practical applications in biological systems.

Sensing mechanism of a ratiometric near-infrared fluorescent chemosensor for cysteine hydropersulfide: Intramolecular charge transfer

Previous studies have shown that the cysteine hydropersulfide (Cys-SSH) as the sulfur donor is crucial to sulfur-containing cofactors synthesis. Recently, a selective and sensitive near-infrared ratiometric fluorescent chemosensor Cy-DiSe has been designed and synthesized to detect Cys-SSH spontaneously. Herein, by means of the density functional theory (DFT) and time-dependent density functional theory (TD-DFT) approaches, the sensing mechanism has been thoroughly explored. According to our calculations, the experimental data have been reproduced. The results indicate the intramolecular charge transfer (ICT) is the reason for changes in fluorescence wavelengths. Compared with the chemosensor Cy-DiSe, the larger energy gap of Cy induced by ICT mechanism leads to the blue-shift of the absorption and emission spectra, which guarantees that Cy-DiSe can become a ratiometric fluorescent chemosensor to detect Cys-SSH.

Nanoparticle-based 'turn-on' scattering and post-sample fluorescence for ultrasensitive detection of water pollution in wider window

Ultrasensitive detection of heavy metal ions in available water around us is a great challenge for scientists since long time. We developed an optical technique that combines Rayleigh scattering of UV light (365 nm) and post-sample fluorescence detection from colloidal silver (Ag) nanoparticles (NPs) having a surface plasmon resonance (SPR) band at 420 nm. The efficacy of the technique is tested by the detection of several model toxic ions, including mercury, lead, and methylmercury in aqueous media. The light scattering from the Hg-included/inflated Ag NPs at 395 nm was observed to saturate the light sensor even with ppm-order concentrations of Hg ions in the water sample. However, the pollutant is not detected at lower concentrations at this wavelength. Instead, the fluorescence of a high-pass filter (cut-off at 400 nm) at 520 nm is applied to detect pollutant concentrations of up to several hundreds of ppm in the water sample. We also detected lead and methylmercury as model pollutants in aqueous media and validated the efficacy of our strategy. Finally, we report the development of a working prototype based on the strategy developed for efficient detection of pollutants in drinking/agricultural water.

A ratiometric fluorescent probe for reversible monitoring of endogenous SO2/formaldehyde in cytoplasm and nucleoli regions and its applications in living mice

A ratiometric fluorescent probe was engineered for the reversible imaging of endogenous sulfur dioxide in the cytoplasm and nucleoli regions of living cells and in living mice.

Smart Responsive Luminescent Aptamer-Functionalized Covalent Organic Framework Hydrogel for High-Resolution Visualization and Security Protection of Latent Fingerprints

Covalent organic frameworks (COFs) have been proposed as alternative candidates for "smart" materials due to their ordered π-columnar structures. However, it remains a challenge to develop external-stimuli-responsive luminescent COFs for confidential information protection. Here, we have designed and synthesized a water-dispersible and smart responsive luminescent carboxymethyl cellulose-COF hydrogel encapsulated 5-(dimethylamino)-N,N-bis (pyridin-2-ylmethyl) napthalene-1-sulfonamide, named CMC-COF-LZU1⊃DPYNS, for latent fingerprint imaging and encryption. We show that the fluorescence of CMC-COF-LZU1⊃DPYNS is reversibly switchable upon addition of Cu²⁺/H₂O. This effect endows potential applications of tunable luminescent COFs based hydrogel as an invisible security probe for imaging, recording, storage, and security of latent fingerprint information. It is shown that the latent fingerprint information incubated by the aptamer-functionalized CMC-COF-LZU1⊃DPYNS hydrogel is invisible in the presence of Cu²⁺, but three levels of fingerprint features with high-resolution patterns could be readable upon addition of H₂O under UV light. The design strategy provides a promising platform for the development of smart responsive luminescent COFs and their detection and protection of valuable latent fingerprint information.

Ratiometric fluorescent probe based on pyrrole-modified rhodamine 6G hydrazone for the imaging of Cu2+ in lysosomes

A novel rhodamine-based Schiff base derivative was obtained via the simple condensation of substituted formyl-1H-pyrrole and rhodamine 6G hydrazone. Fluorescence resonance energy transfer enabled the subsequent use of the derivative as a naked-eye colorimetric and ratiometric fluorescent sensor for Cu²⁺ in semi-aqueous solution, and the existence of the morpholine group enabled the further application of the sensor in imaging Cu²⁺ in the lysosomes of HeLa cells.

Dansyl-appended CuII-complex-based nitroxyl (HNO) sensing with living cell imaging application and DFT studies

We introduce herein, a novel copper complex-based fluorescent probe[Cu^II(DQ₄₆₈)Cl]⁺that exhibits a significant fluorescence turn-on response towards nitroxyl with high selectivity over other biological reactive oxygen, nitrogen and sulfur species, including nitric oxide.

Potentially toxic elements and environmentally-related pollutants recognition using colorimetric and ratiometric fluorescent probes

A safer detection or sensing of toxic pollutants is one among several environmental contamination issues, across the globe. The ever-increasing industrial practices and controlled or uncontrolled release of toxic pollutants from various industrial sectors is a key source of this environmental problem. Significant research efforts have been or being made to tackle this problematic issue to fulfill the growing needs of the modern world. Despite many useful aspects, heavy metals are posing noteworthy toxicological concerns and human-health related issues at various levels of the ecosystem. In this context, notable efforts from various regulatory authorities, the increase in the concentration of these toxic heavy metals in the environment is of serious concern, so real-time monitoring is urgently required. Herein, we reviewed fluorescent sensor based models and their potentialities to address the detection fate of hazardous pollutants including chromium, manganese, cobalt, nickel, copper, and zinc as model elements. The novel aspects of turn-on/off fluorescent sensors have also been discussed from a state of the art viewpoint. In summary, comprehensive literature regarding fluorescent sensor based models and their potentialities to detect various types of toxic pollutants is reviewed.

A highly selective and sensitive fluorescent probe for Cu2+ based on a novel naphthalimide-rhodamine platform and its application in live cell imaging

Copper plays important roles in a variety of fundamental physiological processes. At the cell organelle level, aberrant copper homeostasis in lysosomes can lead to various serious diseases. Herein, a bifluorophore-based, lysosome-targetable Cu²⁺-selective ratiometric fluorescent probe (V) has been synthesized by reasonable design. The probe V shows high selectivity toward Cu²⁺ ions over other cations and exhibits high sensitivity (1.45 nM) for the detection of Cu²⁺ ions. Meanwhile, the probe is cell permeable and suitable for ratiometric visualization of lysosomal Cu²⁺ in the living cell.

Highly selective recognition of Al3+ and I- ions using a bi-functional fluorescent probe

A tripodal fluorescent probe L1 armed with Rhodamine B and 1-naphthaleneisothiocyanates was prepared in high yield. A study of the recognition properties revealed that probe L1 exhibited high sensitivity and selectivity towards Al³⁺ through a "FRET" fluorescence response and colorimetric response with low detection limits of the order of 10^-8 M. Meanwhile, probe L1 also possessed high recognition ability for I^- through fluorescence decay, which given there are comparatively few selective fluorescent probes for I^-, is significant. Furthermore, the complexation mechanisms were fully investigated by spectral titrations, ¹H NMR spectroscopic titrations and mass spectrometry. The utility of probe L1 as a biosensor in living cells (PC3 cells) towards Al³⁺ ions has also been demonstrated.

A facile strategy for achieving high selective Zn(II) fluorescence probe by regulating the solvent polarity

A simple Schiff base comprised of tris(2-aminoethyl)amine and salicylaldehyde was designed and synthesized by one-step reaction. Although this compound has poor selectivity for metal ions in acetonitrile, it shows high selectivity and sensitivity detection for Zn(II) ions through adjusting the solvent polarity (the volume ratio of CH₃CN/H₂O). In other words, this work provides a facile way to realize a transformation from poor to excellent feature for fluorescent probes. The bonding mode of this probe with Zn(II) ions was verified by ¹H NMR and MS assays. The stoichiometric ratio of the probe with Zn(II) is 1:1 (mole), which matches with the Job-plot assay. The detection limitation of the probe for Zn(II) is up to 1 × 10^-8 mol/L. The electrochemical property of the probe combined with Zn(II) was investigated by cyclic voltammetry method, and the result agreed with the theoretical calculation by the Gaussian 09 software. The probe for Zn(II) could be applied in practical samples and biological systems. The main contribution of this work lies in providing a very simple method to realize the selectivity transformation for poor selective probes. The providing way is a simple, easy and low-cost method for obtaining high selectively fluorescence probes.

FRET-based metal ion sensing by a crown-containing bisstyryl dye

A ratiometric cation FRET system containing two binding centers demonstrates distinct fluorescence changes upon interaction with alkaline, alkaline earth and heavy metal cations.

Cancer-Associated, Stimuli-Driven, Turn on Theranostics for Multimodality Imaging and Therapy

Advances in bioinformatics, genomics, proteomics, and metabolomics have facilitated the development of novel anticancer agents that have decreased side effects and increased safety. Theranostics, systems that have combined therapeutic effects and diagnostic capabilities, have garnered increasing attention recently because of their potential use in personalized medicine, including cancer-targeting treatments for patients. One interesting approach to achieving this potential involves the development of cancer-associated, stimuli-driven, turn on theranostics. Multicomponent constructs of this type would have the capability of selectively delivering therapeutic reagents into cancer cells or tumor tissues while simultaneously generating unique signals that can be readily monitored under both in vitro and in vivo conditions. Specifically, their combined anticancer activities and selective visual signal respond to cancer-associated stimuli, would make these theranostic agents more highly efficient and specific for cancer treatment and diagnosis. This article focuses on the progress of stimuli-responsive turn on theranostics that activate diagnostic signals and release therapeutic reagents in response to the cancer-associated stimuli. The present article not only provides the fundamental backgrounds of diagnostic and therapeutic tools that have been widely utilized for developing theranostic agents, but also discusses the current approaches for developing stimuli-responsive turn on theranostics.

Ratiometric Visualization of NO/H2S Cross-Talk in Living Cells and Tissues Using a Nitroxyl-Responsive Two-Photon Fluorescence Probe

It is of scientific significance to explore the intricate relationship between two crucial gasotransmitters nitric oxide (NO) and hydrogen sulfide (H₂S) because they exert similar and interdependent biological actions within the living organisms. Nevertheless, visualization of the NO/H₂S crosstalk using effective molecular imaging tools remains challenging. To address this issue, and given that nitroxyl (HNO) has been implicated as the interdependent production of NO and H₂S via a network of cascading chemical reactions, we herein design a ratiometric two-photon fluorescent probe for HNO, termed TP-Rho-HNO, which consists of benzo[h]chromene-rhodol scaffold as two-photon energy transfer cassette with phosphine moiety as specific HNO recognition unit. The newly proposed probe has been successfully applied in ratiometric two-photon bioimaging of endogenous HNO derived from NO and H₂S interaction in the human umbilical vein cells (HUVECs) and as well as in rat brain tissues. Intriguingly, the imaging results consistently demonstrate that the mutually dependent upgeneration of H₂S and NO are present in living biosystems, indicating that this molecular probe would provide a powerful approach to elucidate the chemical foundation for the anfractuous cross-talk between the NO and H₂S signaling pathways in biology.

An unusual highly emissive water-soluble iridium lissamine-alanine complex and its use in a molecular logic gate

The interaction of iridium(iii) with a new lissamine rhodamine B sulfonyl derivative, bearing alanine as a building block, (1) with an orange emission in water results in a green highly emissive Ir@1 complex at room temperature. The new Ir@1 complex can sense the toxic Hg(2+) metal ion and cysteine. Based on such properties, a new sophisticated molecular logic gate with three inputs was designed.

An Amidochlorin-Based Colorimetric Fluorescent Probe for Selective Cu(2+) Detection

The design and synthesis of selective and sensitive chemosensors for the quantification of environmentally and biologically important ionic species has attracted widespread attention. Amidochlorin p6 (ACP); an effective colorimetric and fluorescent probe for copper ions (Cu(2+)) in aqueous solution derived from methyl pheophorbide-a (MPa) was designed and synthesized. A remarkable color change from pale yellow to blue was easily observed by the naked eye upon addition of Cu(2+); and a fluorescence quenching was also determined. The research of fluorescent quenching of ACP-Cu(2+) complexation showed the detection limit was 7.5 × 10(-8) mol/L; which suggested that ACP can act as a high sensitive probe for Cu(2+) and can be used to quantitatively detect low levels of Cu(2+) in aqueous solution. In aqueous solution the probe exhibits excellent selectivity and sensitivity toward Cu(2+) ions over other metal ions (M = Zn(2+); Ni(2+); Ba(2+); Ag⁺; Co(2+); Na⁺; K⁺; Mg(2+); Cd(2+); Pb(2+); Mn(2+); Fe(3+); and Ca(2+)). The obvious change from pale yellow to blue upon the addition of Cu(2+) could make it a suitable "naked eye" indicator for Cu(2+).

A through bond energy transfer based ratiometric probe for fluorescent imaging of Sn2+ ions in living cells

A 4-(naphthalen-1-ylethynyl) aniline appended rhodamine based fluorescent chemosensor ‘NAP-RD’ is synthesized which undergoes through bond energy transfer in the presence of Sn²⁺ ions in mixed aqueous media.

Novel triphenylamine based rhodamine derivatives: synthesis, characterization, photophysical properties and viscosity sensitivity

Five novel triphenylamine based deep red to NIR emitting rhodamine derivatives were synthesized and characterized by ¹H and ¹³C NMR spectroscopy and elemental analysis.

A mitochondria-targeted fluorescent probe for ratiometric detection of endogenous sulfur dioxide derivatives in cancer cells

A new mitochondria-targeted fluorescent probe HCy-D, constructed by dansyl and hemicyanine fluorophores, for SO₂derivatives (HSO₃⁻/SO₃²⁻) was presented.

A new type of triphenylamine based coumarin–rhodamine hybrid compound: synthesis, photophysical properties, viscosity sensitivity and energy transfer

A series of novel core modified triphenylamine coumarin–rhodamine systems (compounds MCMR, MCDR and DCMR) was designed and synthesized by incorporating a coumarin moiety on one and a rhodamine moiety on the other phenyl ring of the triphenylamine molecular skeleton.

A reaction-based fluorescent turn-on probe for Cu2+ in complete aqueous solution

FP can detect Cu²⁺ in complete aqueous solution with a rapid response time, high sensitivity, and high selectivity.

Rhodamine B-based ordered mesoporous organosilicas for the selective detection and adsorption of Al(iii)

A novel “Off–On” solid chemosensor for Al³⁺ was constructed by combining ordered mesoporous silica with a rhodamine B derivative.