Cyclodextrin supramolecular complex as a water-soluble ratiometric sensor for ferric ion sensing

Robust Inclusion Complex of Topotecan Comprised within a Rhodamine-Labeled β-Cyclodextrin: Competing Proton and Energy Transfer Processes

Monitoring the biological fate of medicaments within the environments of cancer cells is an important challenge which is nowadays the object of intensive studies. In this regard, rhodamine-based supramolecular systems are one of the most suitable probes used in drug delivery thanks to their high emission quantum yield and sensitivity to the environment which helps to track the medicament in real time. In this work, we used steady-state and time-resolved spectroscopy techniques to investigate the dynamics of the anticancer drug, topotecan (TPT), in water (pH ~6.2) in the presence of a rhodamine-labeled methylated β-cyclodextrin (RB-RM-βCD). A stable complex of 1:1 stoichiometry is formed with a K_eq value of ~4 × 10⁴ M^-1 at room temperature. The fluorescence signal of the caged TPT is reduced due to: (1) the CD confinement effect; and (2) a Förster resonance energy transfer (FRET) process from the trapped drug to the RB-RM-βCD occurring in ~43 ps with 40% efficiency. These findings provide additional knowledge about the spectroscopic and photodynamic interactions between drugs and fluorescent functionalized CDs, and may lead to the design of new fluorescent CD-based host-guest nanosystems with efficient FRET to be used in bioimaging for drug delivery monitoring.

Continuous flow synthesis of 6-monoamino-6-monodeoxy-β-cyclodextrin

The first continuous flow method was developed for the synthesis of 6-monoamino-6-monodeoxy-β-cyclodextrin starting from native β-cyclodextrin through three reaction steps, such as monotosylation, azidation and reduction. All reaction steps were studied separately and optimized under continuous flow conditions. After the optimization, the reaction steps were coupled in a semi-continuous flow system, since a solvent exchange had to be performed after the tosylation. However, the azidation and the reduction steps were compatible to be coupled in one flow system obtaining 6-monoamino-6-monodeoxy-β-cyclodextrin in a high yield. Our flow method developed is safer and faster than the batch approaches.

Preparation and Release of pH-Sensitive β-Cyclodextrin Derivative Micelles Loaded with Paclitaxel

In this paper, a new amphiphilic mono-6-β-cyclodextrin octadecylimine (6-β-CD-N-ODMA) copolymer was synthesized based on β-cyclodextrin and octadecylamine, which can self-assemble to form polymeric micelles. Drug-loaded micelles (a new drug carrier) were obtained using 6-β-CD-N-ODMA and paclitaxel (PTX) by the dialysis method. Orthogonal experiments were used to optimize the preparation method of the drug-loaded micelles. The drug-loading content of the carrier prepared by the optimized method was 1.97%. The physicochemical properties of blank micelles and drug-loaded micelles were evaluated by the fluorescence probe method, infrared spectra, dynamic light scattering, and scanning electron microscopy. The release properties of the carrier were investigated. The carrier has good pH sensitivity and the cumulative release rate after 96 h was 88% in PBS (pH = 5.0). The Ritger–Peppas equation is the optimal model for PTX released at pH 5.0, implying that the hydrolysis effect of 6-β-CD-N-ODMA is the main reason for PTX release. The results indicate that the developed carrier can increase the solubility of PTX and possess potential for increased clinical efficacy of PTX.

A Self-locked β-Cyclodextrin-rhodamine B Spirolactam with Photoswitching Properties

Supramolecular organization and self-assembly are the pillars of functionality of many nanosystems. The covalent conjugate (6-spirolactam rhodamine B-6-monodeoxy)-β-cyclodextrin (Rho-βCD) is assembled as a self-included, rigid nanostructure, identical in the crystal and in aqueous solution, as revealed by detailed X-ray and NMR analyses. Rho-βCD self-assembly is the result of an interesting reaction pathway, which partially de-aggregates Rho and disturbs the zwitterion↔spirolactone equilibrium. Rho-βCD is stable at pH 4.6, but displays controllable photoswitching between the colored, fluorescent, zwitterionic and the colorless, non-fluorescent closed structures, during several iterative cycles. After an initial drop in absorbance, the on-off process continues without further changes under our irradiation conditions, a consequence of the specific self-locked arrangement of Rho in the cavity. Rho-βCD exemplifies a water soluble photoresponsive nanosystem with improved photostability suggesting promising applications in super resolution bioimaging.

Construction of a pH-sensitive self-assembly in aqueous solutions based on a dansyl-modified β-cyclodextrin

Here we present a pH-responsive self-assembly based on a β-cyclodextrin (β-CD) derivative bearing a dansyl terminus (βCD-C₆-Dns). Vesicular structures were formed over the entire studied pH range (8.5-0.7); however, the molecular configuration and packing within the vesicles were different at different pH values. Intramolecular host-guest complexation occurred mainly between the dansyl group and β-CD at pH values where the dansyl group was not protonated. The alkyl chain also acted as a competitive guest to form host-guest inclusions as confirmed by 2D ¹H NMR measurements. The pH-responsive βCD-C₆-Dns vesicles have potential application prospects in pH-controlled drug release based on the low cytotoxicity of βCD-C₆-Dns.

Mono-6-Substituted Cyclodextrins-Synthesis and Applications

Cyclodextrins are well known supramolecular hosts used in a wide range of applications. Monosubstitution of native cyclodextrins in the position C-6 of a glucose unit represents the simplest method how to achieve covalent binding of a well-defined host unit into the more complicated systems. These derivatives are relatively easy to prepare; that is why the number of publications describing their preparations exceeds 1400, and the reported synthetic methods are often very similar. Nevertheless, it might be very demanding to decide which of the published methods is the best one for the intended purpose. In the review, we aim to present only the most useful and well-described methods for preparing different types of mono-6-substituted derivatives. We also discuss the common problems encountered during their syntheses and suggest their optimal solutions.

Enantioseparation on a new synthetic β-cyclodextrin chemically bonded chiral stationary phase and molecular docking study

A novel β-cyclodextrin derivative chemically bonded chiral stationary phase (EDACD) was synthesized by the reaction of mono-6-ethylenediamine-β-cyclodextrin with the active alkyl isocyanate, anchoring to silica gel. After the successful analysis and characterization using scanning electron microscopy, Fourier transform infrared spectra, solid-state nuclear magnetic resonance spectra, elemental analysis, and thermogravimetric analysis techniques, the enantioselective performance of the as-prepared EDACD column was evaluated by non-steroidal antiinflammatory drugs and flavonoids under the reversed-phase HPLC condition. The factors that affected enantioseparation including mobile phase compositions and buffers were investigated in more detail. As a result, EDACD showed a satisfactory enantioselectivity for the tested drugs. With the mobile phase of acetonitrile and 20-mM ammonium formate adjusted to pH 4.0 using formic acid (85:15, v/v) at the flow rate of 0.6 mL min^-1, the enantiomers of ibuprofen, carprofen, naproxen, indoprofen, ketoprofen, eriocitrin, naringin, and narirutin were separated with the best resolutions of 1.53, 1.64, 3.72, 2.40, 0.50, 0.61, 0.58, and 0.52. To adjust the proportion of acetonitrile to 80% (by volume), the enantiomers of pranoprofen and flurbiprofen were completely resolved with the best resolutions of 1.60 and 1.59. Additionally, by the study of the molecular docking, hydrogen bonding and inclusion complexation were believed to play an important role in chiral recognition. As a new material, EDACD will have a wider application in the analysis of chiral compounds.

Unusual Fluorescence Quenching-Based Al3+ Sensing by an Imidazolylpiperazine Derivative. β-Cyclodextrin Encapsulation-Assisted Augmented Sensing

We report in this paper an unusual β-cyclodextrin mediated-aluminum (III) ion sensing based on augmented quenching of fluorescence. The fluorescent sensing of metal ions by a new ligand prepared (L = 4-[{4-(1H-imidazol-1-yl)phenyl]imino}methyl]piperazine-1-carboxaldehyde) has been investigated as well as the effect of the supramolecular complex formation with β-CD. In aqueous solution, L shows an increase of fluorescence due to the interaction with β-cyclodextrin with a formation constant of 77 (± 12) M^-1. The ROESY NMR spectrum clearly indicates that L is encapsulated by β-CD. Theoretical calculations show the possible structure both of the L-β-CD adduct and of the coordination mode of Al³⁺ ion to L. In the presence of β-CD, the piperazine adopts a distorted conformation. It leads to an enhanced Al³⁺ sensing by the compound in its supramolecular complexed form. The lower limit of detection of Al³⁺ ions is 6.00 × 10^-8 mol L^-1. This detection limit slightly expands for L in the presence of β-CD.

Inclusion complex vs. conjugation of hydrophobic photosensitizers with β-cyclodextrin: Improved disaggregation and photodynamic therapy efficacy against glioblastoma cells

Self-aggregation of hydrophobic porphyrin-based photosensitizers (PSs) in aqueous biological environment decreases their bioavailability and in vivo therapeutic efficacy, which hampers their clinical use in photodynamic therapy (PDT). In the current study, we explore three new supramolecular systems based of hydrophobic PSs (i.e. 5,10,15,20-tetrakis(3-hydroxyphenyl)porphyrin (mTHPP) or 5-(4-carboxyphenyl)-10,15,20-triphenylporphyrin (P1COOH)) non-covalently or covalently attached to β-CD. The two non-covalent solid inclusion complexes (β-CD)₂/mTHPP and [(β-CD)/P1COOH]₄ are prepared by a new co-precipitation@lyophilization combined method and the covalent conjugate β-CD-P1 by click chemistry. The binding type effect and effectiveness on the disaggregation in aqueous medium and in vitro PDT efficacy against glioblastoma cancer cells of PSs are investigated for the three β-CD/PS systems. The findings reveal a remarkable improvement of the disaggregation and in vitro PDT activity of these β-CD/PS systems compared to the free PSs, except for [(β-CD)/P1COOH]₄ inclusion complex caused by J-type self-aggregation of the inclusion complex in tetrameric form. β-CD-P1 conjugate shows the higher in vitro PDT efficacy compared to the other β-CD/PS systems. Overall, the results indicate that the disaggregation in aqueous medium and in vitro PDT activity of hydrophobic PSs can be improved by their binding to β-CD and the covalent binding is the best approach.

Preparation of anthracene-based tetraperimidine hexafluorophosphate and selective recognition of chromium(III) ions

A novel anthracene-based tetraperimidine hexafluorophosphate 3 was prepared, and its structure was determined through X-ray analysis, HRMS as well as ¹H and ¹³C NMR spectroscopy. In the cationic moiety of 3, two (N-ethylperimidinyl–C₂H₄)₂NCH₂– arms were attached to the 9- and 10-positions of anthracene. In addition, compound 3 was used as a chemosensor to research the ability to recognize Cr³⁺ through fluorescence and UV titrations, HRMS, as well as ¹H NMR and IR spectroscopy. The results indicate that 3 is an effective chemosensor for Cr³⁺.

Lignosulfonate: A Convenient Fluorescence Resonance Energy Transfer Platform for the Construction of a Ratiometric Fluorescence pH-Sensing Probe

Lignin is a kind of natural fluorescent polymer material. However, the application based on the fluorescent property of lignin was rarely reported. Herein, a noncovalent lignin-based fluorescence resonance energy transfer (FRET) system was readily constructed by physical blending method with spirolactam rhodamine B (SRhB) and lignosulfonate (LS) as the acceptor and donor groups, respectively. The FRET behavior, self-assembly, and energy transfer mechanism of SRhB/LS composite were systematically studied. It was demonstrated that LS could be used as a convenient aptamer as energy donor to construct water-soluble ratiometric sensors because of its inherent property of intramicelle energy transfer cascades. Our results not only present a facile and general strategy for producing lignin-based functional material but also provide a fundamental understanding about lignin fluorescence to promote the functional and high-valued applications of lignin fluorescence characteristic.

Differential Metal Ion Sensing by an Antipyrine Derivative in Aqueous and β-Cyclodextrin Media: Selectivity Tuning by β-Cyclodextrin

β-Cyclodextrin (β-CD) is a nontoxic cyclic oligosachcharide that can encapsulate all or part of organic molecules of appropriate size and specific shape through noncovalent interaction. Herein, we report the influence of β-CD complex formation of an antipyrine derivative on its metal ion sensing behavior. In aqueous solution, the antipyrine shows a turn-on fluorescence sensing of vanadyl ion, and in cyclodextrin medium it senses aluminum ion. The compound shows an unusual fluorescence quenching on binding with β-cyclodextrin (log K_SV = 2.34 ± 0.02). The differential metal ion sensing is due to the partial blocking of the chelating moiety by the cyclodextrin molecule. The structure of the antipyrine-cyclodextrin complex is optimized by two-dimensional rotating-frame Overhauser effect spectroscopy. The binding constant is determined by isothermal titration calorimetry (log K = 2.09 ± 0.004). The metal ion binding site is optimized by quanutm mechanical calculations. The lower limit of detection of vanadyl and aluminum ions, respectively, are 5 × 10^-8 and 5 × 10^-7 mol dm^-3. This is the first report of selectivity of two different cations by a chemosensor in water and in β-CD.

Magnetofluorescent nanohybrid comprising polyglycerol grafted carbon dots and iron oxides: Colloidal synthesis and applications in cellular imaging and magnetically enhanced drug delivery

Multifunctional nanohybrids are attracting increasing attention for potential biomedical applications such as bioimaging and drug delivery due to their combined advantages of individual components. However, challenges in the improvement of their synthesis and colloidal stability to facilitate practical biomedical applications still remain. In this work, we report an efficient synthetic approach to fabricate magnetofluorescent nanohybrid (IO-PG-CD) comprising fluorescent carbon dots (CDs) and magnetic iron oxide nanoparticles (IOs) through polyglycerol (PG) mediated covalent linkage in aqueous media. CDs and IOs are first grafted with PG layer, and then functionalized with carboxyl and amino groups, respectively. The resulting CD-PG-COOH and IO-PG-NH₂ handled as simple chemical compounds are integrated through EDC/NHS crosslinking to obtain the desired IO-PG-CD nanohybrid. The unprecedented hydrophilicity of PG layer endows IO-PG-CD nanohybrid with excellent colloidal stability in various physiological media, facilitating biomedical applications in vitro and in vivo. IO-PG-CD nanohybrid exhibits low cytotoxicity and its uptake by cells can be obviously enhanced by external magnetic attraction. The internalized IO-PG-CD nanohybrid emits multicolor fluorescence as observed by confocal fluorescence microscopy, demonstrating much better photostability than the nanoparticle labeled with organic dye. Taking advantage of enormous chelating carboxyl groups on the surface of IO-PG-CD nanohybrid, platinum-based anticancer drug was loaded on the surface (IO-PG-CD/Pt) through complexation and delivered into cancer cells in a magnetically enhanced manner, killing the cancer cells efficiently in vitro. Moreover, in vivo cancer therapy indicates that the external magnetic attraction also obviously improves the anticancer efficacy of IO-PG-CD/Pt in HeLa subcutaneous xenografts.

Reversing Redox Responsiveness of Hydrogels due to Supramolecular Interactions by Utilizing Double-Network Structures

Stimuli-responsive hydrogels have been actively researched, and some of them have been put into practical use. When we create and use stimuli-responsive hydrogel materials, controlling stimuli responsiveness of hydrogels is a very important issue. In this research, we prepared hydrogels having single-network (SN) or double-network (DN) gel structures with the host-guest interaction groups cyclodextrin and methyl viologen and evaluated their stimuli responsiveness. The results of the tensile and compression tests showed that the hydrogels with SN and DN structures exhibited opposite stimuli responsiveness in response to the redox reaction of methyl viologen through the association and dissociation of the host molecule, β-cyclodextrin, and the guest molecule, methyl viologen. Spectroscopic measurements and rheological studies all indicated that this difference in stimuli responsiveness originated from the polymer-network structures. In addition, a chemically cross-linked DN gel was prepared and its redox responsiveness was evaluated.

Chemistry and engineering of cyclodextrins for molecular imaging

Cyclodextrins (CDs) are naturally occurring cyclic oligosaccharides bearing a basket-shaped topology with an "inner-outer" amphiphilic character. The abundance of hydroxyl groups enables CDs to be functionalized with multiple targeting ligands and imaging elements. The imaging time, and the payload of different imaging elements, can be tuned by taking advantage of the commercial availability of CDs with different sizes of the cavity. This review aims to offer an outlook of the chemistry and engineering of CDs for the development of molecular probes. Complexation thermodynamics of CDs, and the corresponding implications for probe design, are also presented with examples demonstrating the structural and physiochemical roles played by CDs in the full ambit of molecular imaging. We hope that this review not only offers a synopsis of the current development of CD-based molecular probes, but can also facilitate translation of the incremental advancements from the laboratory to real biomedical applications by illuminating opportunities and challenges for future research.

A turn-on fluorogenic chemosensor for Fe3+ and a Schottky barrier diode with frequency-switching device applications

A novel highly sensitive and selective fluorescent chemosensor L has been synthesized and characterized by various physicochemical techniques.

Fluorescence Resonance Energy Transfer Systems in Supramolecular Macrocyclic Chemistry

The fabrication of smart materials is gradually becoming a research focus in nanotechnology and materials science. An important criterion of smart materials is the capacity of stimuli-responsiveness, while another lies in selective recognition. Accordingly, supramolecular host-guest chemistry has proven a promising support for building intelligent, responsive systems; hence, synthetic macrocyclic hosts, such as calixarenes, cucurbiturils, cyclodextrins, and pillararenes, have been used as ideal building blocks. Meanwhile, manipulating and harnessing light artificially is always an intensive attempt for scientists in order to meet the urgent demands of technological developments. Fluorescence resonance energy transfer (FRET), known as a well-studied luminescent activity and also a powerful tool in spectroscopic area, has been investigated from various facets, of which the application range has been broadly expanded. In this review, the innovative collaboration between FRET and supramolecular macrocyclic chemistry will be presented and depicted with typical examples. Facilitated by the dynamic features of supramolecular macrocyclic motifs, a large variety of FRET systems have been designed and organized, resulting in promising optical materials with potential for applications in protein assembly, enzyme assays, diagnosis, drug delivery monitoring, sensing, photosynthesis mimicking and chemical encryption.

Pyrene-Phosphonate Conjugate: Aggregation-Induced Enhanced Emission, and Selective Fe3+ Ions Sensing Properties

A new pyrene-phosphonate colorimetric receptor 1 has been designed and synthesized in a one-step process via amide bond formation between pyrene butyric acid chloride and phosphonate-appended aniline. The pyrene-phosphonate receptor 1 showed aggregation-induced enhanced emission (AIEE) properties in water/acetonitrile (ACN) solutions. Dynamic light scattering (DLS) characterization revealed that the aggregates of receptor 1 at 80% water fraction have an average size of ≈142 nm. Field emission scanning electron microscopy (FE-SEM) analysis confirmed the formation of spherical aggregates upon solvent evaporation. The sensing properties of receptor 1 were investigated by UV-vis, fluorescence emission spectroscopy, and other optical methods. Among the tested metal ions, receptor 1 is capable of recognizing the Fe³⁺ ion selectively. The changes in spectral measurements were explained on the basis of complex formation. The composition of receptor 1 and Fe³⁺ ions was determined by using Job's plot and found to be 1:1. The receptor 1-Fe³⁺ complex showed a reversible UV-vis response in the presence of EDTA.

Pyridine-antipyrine appended indole derivative for selective recognition of Fe3+: Concentration dependent coloration

Combination of pyridine, antipyrine and indole in a single molecule (L2) allows selective recognition of Fe³⁺ colorimetrically in CH₃CN. The structure of L2 is confirmed from single crystal X-ray diffraction analysis. The probe displays two different visible bands at 541nm and 715nm in the presence of Fe³⁺, associated with two different colors, viz. green and pink-violet allowing determination of unknown Fe³⁺ concentration. Interestingly, removal of 2-picolyl group from indole N-center of L2 generates L3 that behaves similarly at low Fe³⁺ concentration (>0 to 1.1mM) but differently at higher Fe³⁺ concentration (>1.1mM), indicating involvement of pyridyl-N donor towards Fe³⁺, and hence different coordination environment around Fe³⁺ at higher concentration.

Two-step FRET mediated metal ion induced signalling responses in a probe appended with three fluorophores

A tri-fluorophore appended Tren receptor based probe exhibited chelation induced ratiometric fluorescence signalling through a two-step FRET process; enhancement of F_An→ F_Rhenergy transfer efficiency through an F_NBDintermediate was observed.

Novel supramolecular sensors constructed from pillar[5]arene and a naphthalimide for efficient detection of Fe3+ and F− in water

Novel water soluble supramolecular sensors for efficient detection of Fe³⁺ and F⁻ were constructed by assembling a novel naphthalimide and pillar[5]arene.

A rhodamine based turn-on chemosensor for Fe3+ in aqueous medium and interactions of its Fe3+ complex with HSA

A novel hexa-coordinating rhodamine-based chemosensor, HL6, selectively and rapidly recognizes Fe³⁺ in the presence of a number of metal cations, numerous anions and amino acids in purely aqueous medium with live cell imaging applications.

Action-FRET of β-cyclodextrin inclusion complexes

Action-FRET is introduced as an original method to probe the structure of gaseous non-covalent complexes.

A new fluorescent PET sensor probe for Co2+ ion detection: computational, logic device and living cell imaging applications

A new probe, 2 exhibit quenching with Co²⁺ (∼80% at 634 nm) while 2·Co²⁺ ensemble exhibit enhancement with NO₃⁻ (∼82% at 632.5 nm). On–Off–On behavior of 2 (Co²⁺ and NO₃⁻ ions) the function of a sequential XNOR gate and can be utilized in live cell imaging.

Fluorescent pH-Sensing Probe Based on Biorefinery Wood Lignosulfonate and Its Application in Human Cancer Cell Bioimaging

A water-soluble, ratiometric fluorescent pH probe, L-SRhB, was synthesized via grafting spirolactam Rhodamine B (SRhB) to lignosulfonate (LS). As the ring-opening product of L-SRhB, FL-SRhB was also prepared. The pH-response experiment indicated that L-SRhB showed a rapid response to pH changes from 4.60 to 6.20 with a pK_a of 5.35, which indicated that L-SRhB has the potential for pH detection of acidic organelle. In addition, the two probes were internalized successfully by living cells through the endocytosis pathway and could distinguish normal cells from cancer cells by different cell staining rates. In addition, L-SRhB showed obvious cytotoxicity to cancer cells, whereas it was nontoxic to normal cells in the same condition. L-SRhB might have potential in cancer therapy. L-SRhB might be a promising ratiometric fluorescent pH sensor and bioimaging dye for the recognition of cancer cells. The results also provided a new perspective to the high-value utilization of lignin.

Competition between self-inclusion and drug binding explains the pH dependence of the cyclodextrin drug carrier - molecular modelling and electrochemistry studies

A non-toxic lipoic acid derivative of β cyclodextrin (βCDLip) with an electron-rich aromatic linker was studied as a carrier for the drug doxorubicin with the aim of decreasing the toxic side effects of this drug. The modified cyclodextrin strengthened the drug binding and differentiated the complex-forming ability with dependence on pH. The stability constants of the complexes were evaluated by voltammetry and spectrofluorometry. Molecular modelling provided deeper insight into the nature of the ligand structure itself and the drug-ligand interactions, showing the different contributions of the self-inclusion of the ligand substituent at different pH values. As a result, the modes of interaction of βCDLip with the drug and factors affecting the stabilities of the complex under the pH conditions of healthy and tumour cells could be discovered and explained.

Nanomolar colorimetric quantitative detection of Fe³⁺ and PPi with high selectivity

A novel rhodamine and 8-hydroxyquinoline-based derivative was synthesized, which is shown to act as a colorimetric chemosensor for Fe(3+) in aqueous solution with high selectivity over various environmentally and biologically relevant metal ions and anions with a distinct color change from colorless to pink in very fast response time (<1 min). Fe(3+) can be detected quantitatively in the concentration range from 6.7 to 16 μM and the detection limit (LOD) on UV-vis response of the sensor can be as low as 15 nM. The 'in situ' prepared Fe(3+) complex (1⋅Fe) showed high selectivity toward PPi against many common anions, and sensitivity (the LOD can be as low as 71 nM). In addition, both the chemosensor and the 'in situ' prepared Fe(3+) complex are reusable for the detection of Fe(3+) and PPi respectively.

Highly selective fluorescent chemosensor for detection of Fe(3+) based on Fe3O4@ZnO

The combination of fluorescent nanoparticles and specific molecular probes appears to be a promising strategy for developing fluorescent nanoprobes. In this work, L-cysteine (L-Cys) capped Fe₃O₄@ZnO core-shell nanoparticles were synthesized for the highly selective detection of Fe³⁺. The proposed nanoprobe shows excellent fluorescent property and high selectivity for Fe³⁺ due to the binding affinity of L-Cys with Fe³⁺. The binding of Fe³⁺ to the nanoprobe induces an apparent decrease of the fluorescence. Thus a highly selective fluorescent chemosensor for Fe³⁺ was proposed based on Fe₃O₄@ZnO nanoprobe. The magnetism of the nanoprobe enables the facile separation of bound Fe³⁺ from the sample solution with an external magnetic field, which effectively reduces the interference of matrix. The detection limit was 3 nmol L⁻¹ with a rapid response time of less than 1 min. The proposed method was applied to detect Fe³⁺ in both serum and wastewater samples with acceptable performance. All above features indicated that the proposed fluorescent probe as sensing platform held great potential in applications of biological and analytical field.

FRET-based fluorescence ratiometric and colorimetric sensor to discriminate Fe3+ from Fe2+

A new benzothiazole–quinoline–rhodamine-6G-based probe was synthesised. The probe can exclusively detect Fe³⁺ through a ratiometric manner in a mixed aqueous system with a detection limit in the 10⁻⁸ M range.

Rhodamine-Functionalized Graphene Quantum Dots for Detection of Fe(3+) in Cancer Stem Cells

A turn-on orange-red fluorescent nanosensor based on rhodamine B derivative-functionalized graphene quantum dots (RBD-GQDs) has been successfully synthesized for Fe(3+) detection with high sensitivity and selectivity. By connecting with GQDs, the water solubility, sensitivity, photostability, and biocompatibility of RBD are drastically improved. The most distinctive feature of the RBD-GQDs, which sets them apart from other previously reported fluorophores or GQDs, is that they with the detection limits as low as 0.02 μM are demonstrated as a Fe(3+) turn-on fluorescent nanosensor in cancer stem cells. Fe(3+) binding to such GQDs (RBD-GQDs-Fe(3+)) with orange-red fluorescence of 43% quantum yield were demonstrated to be the biomarkers for cancer stem cell imaging.

Novel highly selective and reversible chemosensors based on dual-ratiometric fluorescent electrospun nanofibers with pH- and Fe(3+)-modulated multicolor fluorescence emission

Novel dual-ratiometric fluorescent electrospun (ES) nanofibers featuring high sensitivity for pH and ferric ion (Fe(3+)) were prepared using binary blends of poly(2-hydroxyethyl methacrylate-co-N-methylolacrylamide-co-nitrobenzoxadiazolyl derivative) (poly(HEMA-co-NMA-co-NBD)) and a spirolactam rhodamine derivative (SRhBOH) by employing a single-capillary spinneret. The HEMA, NMA, and NBD moieties were designed to exhibit hydrophilic properties, chemical cross-linking, and fluorescence (fluorescence resonance energy transfer (FRET) donor), respectively. The fluorescence emission of SRhBOH was highly selective for pH and Fe(3+); when SRhBOH detected acidic media and Fe(3+), the spirocyclic form of SRhBOH, which is nonfluorescent, was transformed into the opened cyclic form and exhibited strong fluorescence emission. The emission colors of ES nanofibers in acidic or Fe(3+) aqueous solutions changed from green to red because of FRET from NBD (donor) to SRhBOH (acceptor). The off/on switching of the FRET process was modulated by adjusting the SRhBOH blending ratio, pH, and Fe(3+) concentration. Poly(HEMA-co-NMA-co-NBD) ES fibers blended with 20% SRhBOH showed high sensitivity in sensing Fe(3+) and pH because of the substantial 57 nm red shift in emission as well as substantial reversible dual photoluminescence. The prepared FRET-based dual-ratiometric fluorescent ES nanofibrous membranes can be used as "naked eye" sensors and have potential for application in multifunctional environment sensing devices.

Optical sensor: a promising strategy for environmental and biomedical monitoring of ionic species

In this review, we cover the recent developments in fluorogenic and chromogenic sensors for Cu²⁺, Fe²⁺/Fe³⁺, Zn²⁺and Hg²⁺.

An ultrafast molecular rotor based ternary complex in a nanocavity: a potential “turn on” fluorescence sensor for the hydrocarbon chain

Formation of a ternary complex by an ultrafast molecular rotor (UMR) with a macrocyclic cavitand has been investigated for the sensitive detection of the alkyl chain of a surfactant.

Rhodamine appended hexaphenylbenzene derivative: through bond energy transfer for sensing of picric acid

A rhodamine appended hexaphenylbenzene based derivative 5 has been designed and synthesized, which displays through bond energy transfer in the presence of picric acid in MeOH and serves as a "turn on" sensor for picric acid.