A reversible fluorescence “off–on–off” sensor for sequential detection of aluminum and acetate/fluoride ions

Application of a surfactant-assisted dispersive liquid-liquid microextraction method along with central composite design for micro-volume based spectrophotometric determination of low level of Cr(VI) ions in aquatic samples

A fast, simple, low cost surfactant-assisted dispersive liquid-liquid microextraction method along with central composite design for the determination of low level of Cr(VI) ions in several aquatic samples has been developed. Initially, Cr(VI) ions present in the aqueous sample were readily reacted with 1,5‑diphenylcarbazide (DPC) in acidic medium through complexation. Sodium dodecyl sulfate (SDS), as an anionic surfactant, was then employed as an ion-pair agent to convert the cationic complex into the neutral one. Following on, the whole aqueous phase underwent a dispersive liquid-liquid microextraction (DLLME) leading to the transfer of the neutral complex into the fine droplet of organic extraction phase. A micro-volume spectrophotometer was used to determine Cr(VI) concentrations. Under the optimized conditions predicted by the statistical design, the limit of quantification (LOQ) obtained was reported to be 5.0 μg/L, and the calibration curve was linear over the concentration range of 5-100 μg/L. Finally, the method was successfully implemented for the determination of low levels of Cr(VI) ions in various real aquatic samples and the accuracies fell within the range of 83-102%, while the precision varied in the span of 1.7-5.2%.

Reactive Blue 4 as a Single Colorimetric Chemosensor for Sequential Determination of Multiple Analytes with Different Optical Responses in Aqueous Media: Cu2+-Cysteine Using a Metal Ion Displacement and Cu2+-Arginine Through the Host-Guest Interaction

In the current study, we reported a novel label-free and facile colorimetric approach for the sequential detection of copper ion (Cu²⁺), L-arginine (Arg), and L-cysteine (Cys) in the H₂O (10.0 mmol L^-1 HEPES buffer solution, pH 7.0) using Reactive Blue 4 (RB4). First, the presence of Cu²⁺ led to a naked-eye color and spectral changes according to the binding site-signaling subunit approach. Then, the RB4-Cu²⁺ complex was successfully applied for Cys and Arg through different recognition pathways. The optical signals for Arg were observed due to its association involving the amino group, as well as the participation of the carboxylate group in a bidentate form to the complex, while selective behavior for Cys was explained by a metal displacement mechanism. The limits of detection for Cu²⁺, Arg, and Cys were calculated to be 1.96, 1.06, and 1.33 μmol L^-1, respectively. It could also be employed for the determination of three analytes in environmental, biological, and pharmaceutical samples. Importantly, the test strips based on RB4-Cu²⁺ complex could be used as a solid-state sensor for the detection of Cys and Arg. In addition, NAND and IMPLICATION molecular logic gates were obtained by using chemical inputs and UV-Vis absorbance signal as the output. Graphical Abstract.

Azine based smart probe for optical recognition and enrichment of Mo(vi )

Single crystal X-ray structure-characterized azine derivative (L) was explored for the selective detection of molybdenum (Mo(vi)) cations through green fluorescence emission. The Mo(vi) cation assisted inhibition of photo-induced electron transfer (PET) resulted in a 37-fold fluorescence enhancement via chelation enhanced fluorescence (CHEF) that allows detection of Mo(vi) with concentration as low as 2 × 10-9 M. The chelation of Mo(vi) cations by L has been confirmed by the single crystal X-ray structure of the resulting complex. The binding constant of L for Mo(vi) is fairly high (1.33 × 106 M-1). Moreover, L is very efficient for enrichment of Mo(vi) from aqueous solution. Density functional theoretical (DFT) studies substantiate the experimental results.

New phenazine based AIE probes for selective detection of aluminium(iii) ions in presence of other trivalent metal ions in living cells

Phenazine fluorophore based imidazole derivatives (S1 and S2) were synthesized and sensor studies were carried out with various cations. Aggregation induced emission (AIE) was observed selectively for Al³⁺ among other cations under study in case of both sensors. ¹H NMR titration supported the aggregation induced emission of S2 with Al³⁺. ESI mass spectra successfully confirmed the aggregate formation. SEM images clearly showed the aggregation of receptor induced by Al³⁺ in a flower-like fashion. AIE probe was successfully applied for bio-imaging of RAW264.7 cells.

Controlled Growth of N-Doped and Large Mesoporous Carbon Spheres with Adjustable Litchi-Like Surface and Particle Size as a Giant Guest Molecule Carrier

N-doped mesoporous carbon nanospheres (NMCNs) with tunable particle size, pore size, surface roughness, and inner cavity are extremely important for the future development of new carriers for nanoencapsulation, high-performance giant molecule transport, and cell uptake. However, constructing such a multifunctional material via a simple method still remains a great challenge. Herein, a controlled growth technology was developed for the first time to synthesize such NMCNs based on the initial reaction temperature (IRT) and solution polarity. In this strategy, the IRT not only can adjust the micelle aggregation to obtain NMCNs with large mesopores but also can make the F127 micelle more lyophobic to prepare hollow N-doped mesoporous carbon spheres, which is a great breakthrough. Inspiringly, by varying the solution polarity to make nonuniform growth of nanoparticles, the litchi-like rough surface of NMCNs was obtained, which could significantly improve the cell uptake performance of NMCNs. The current understanding of nucleation and growth mechanism of nanospheres was further extended and realized the development of NMCNs with large mesopores and litchi-like rough surface, which provided a new and interesting fundamental principle for the synthesis of NMCNs. The mesoporous structure of NMCNs was successfully reverse-replicated by nanocasting of tetraethylorthosilicate to obtain mesoporous silica spheres (MSNs), revealing the easy transformation between NMCNs and MSNs. Insulin as a peptide drug cannot be directly administered orally. But it can be used as oral preparation after being loaded into NMCNs, which has never been reported before. Interestingly, the results of the animal experiment showed an excellent in vivo hypoglycemic activity. This finding provides a new paradigm for the fabrication of structurally well-defined NMCNs with a great promise for drug carriers.

A highly selective and sensitive fluorescent chemosensor and its application for rapid on-site detection of Al3

In this paper, a simple naphthalene-based derivative (HL) has been designed and synthesized as a Al³⁺-selective fluorescent chemosensor based on the PET mechanism. HL exhibited high selectivity and sensitivity towards Al³⁺ over other commonly coexisting metal ions in ethanol with a detection limit of 2.72nM. The 1:1 binding stoichiometry of the complex (HL-Al³⁺) was determined from the Job's plot based on fluorescence titrations and the ESI-MS spectrum data. Moreover, the binding site of HL with Al³⁺ was assured by the ¹H NMR titration experiment. The binding constant (Ka) of the complex (HL-Al³⁺) was calculated to be 5.06×10⁴M^-1 according to the Benesi-Hildebrand equation. In addition, the recognizing process of HL towards Al³⁺ was chemically reversible by adding Na₂EDTA. Importantly, HL could directly and rapidly detect aluminum ion through the filter paper without resorting to additional instrumental analysis.

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.

A turn-on chemiluminescence biosensor for selective and sensitive detection of adenosine based on HKUST-1 and QDs-luminol-aptamer conjugates

In this work, HKUST-1 and QDs-luminol-aptamer conjugates were prepared. The QDs-luminol-aptamer conjugates can be adsorbed by graphene oxide through π-π conjugation. When the adenosine was added, the QDs-luminol-aptamer conjugates were released from magnetic graphene oxide (MGO), the chemiluminescent switch was turned on. It was reported that HKUST-1 can catalyze the chemiluminescence reaction of luminol-H₂O₂ system in an alkaline medium, and improve the chemiluminescence resonance energy transfer (CRET) between chemiluminescence and QDs indirectly. Thus, the adenosine can be detected sensitively. Based on this phenomenon, the excellent platform for detection of adenosine was established. Under the optimized conditions, the linear detection range for adenosine was 1.0 × 10^-12-2.2 × 10^-10 mol/L with a detection limit of 2.1 × 10^-13 mol/L. The proposed method was successfully used for adenosine detection in biological samples.

A coumarin-derived Cu2+-fluorescent chemosensor and its direct application in aqueous media

A novel coumarin-based receptor bearing a benzohydrazide (FCBH) was developed as a fluorescent chemosensor with high selectivity toward Cu²⁺. The sensor was successfully applied to the monitoring of Cu²⁺ in aqueous solution. After the addition of Cu²⁺ to FCBH, the color of the solution changed from greenish-yellow to red, and the absorption band at 457nm red-shifted to 517nm. The fluorescent green color of FCBH disappeared and the fluorescence emission was completely quenched in the presence of Cu²⁺. Upon the addition of Cu²⁺, deprotonation of FCBH occurred, and a 1:1 metal-ligand complex formed. DFT theoretical investigation was carried out to understand the behavior of the sensing probe toward Cu²⁺. Additionally, the quenched fluorescence of the FCBH-Cu²⁺ complex was restored upon the addition of CN^- ions. The possible sensing mechanism of FCBH toward Cu²⁺ was derived from experimental and theoretical examinations.

Acylhydrazone as a novel “Off–On–Off” fluorescence probe for the sequential detection of Al3+and F−

An acylhydrazone,SPBH,acts as a sequential fluorescence “Off–On–Off” probe for Al³⁺/F⁻, and the phenomenon was detectable by the naked eye.

A novel off-on fluorescent chemosensor for Al3+derived from a 4,5-diazafluorene Schiff base derivative

The performance of a chemosensor is closely related to its structure. A new Schiff bass (DFSB) based on 4,5-diazafluorene units has been synthesized in this work. The interaction of DFSB with different metal ions has been studied using UV-vis absorption spectra and fluorescent spectra. The results show that DFSB is a highly selective and sensitive probe for Al³⁺ ions over other commonly coexisting metal ions in ethanol. A very obvious fluorescence enhancement effect was observed, and a turn-on ratio over 1312-fold was triggered with the addition of 10 equiv. of Al³⁺ ions. What is more, such fluorescent responses could be detected by the naked eye under a UV-lamp. The lowest detection limit for Al³⁺ was determined as 3.7 × 10⁻⁸ M. The complex solution (DFSB–Al³⁺) exhibited reversibility with EDTA. These results may be caused by the unique molecular structure.

A highly selective and sensitive“turn-on” fluorescent sensor for detecting Al³⁺ derivated from 4,5-diazafluorene.

A new fluorescent probe for quick and highly selective detection of hydrogen sulfide and its application in living cells

Hydrogen sulfide (H₂S) is one of the endogenous regulators of many physiological processes.

Construction and comparison of BSA-stabilized functionalized GQD composite fluorescent probes for selective trypsin detection

BSA-stabilized amino-functionalized GQDs are the best sensors for trypsin with a low limit of detection.

Development of a fluorescent capillary biosensor based on self-assembled AuNP/LDH for micro-volume intracellular pyruvate

A highly sensitive fluorescent capillary biosensor based on self-assembled AuNPs/LDH for micro-volume intracellular pyruvate.

A novel chemosensor based on rhodamine and azobenzene moieties for selective detection of Al3+ ions

Both rhodamine and azobenzene moieties have been conjugated to prepare a novel chemosensor for the detection of Al³⁺ through CHEF-PET and the spirolactam ring opening mechanism.

A new fluorescence turn-on chemosensor for nanomolar detection of Al3+ constructed from a pyridine–pyrazole system

A pyridine–pyrazole based fluorescence turn-on chemosensor provides access to selective detection of Al³⁺ in solution as well as in HepG2 living cells.

Development of an Fe3O4@Cu silicate based sensing platform for the electrochemical sensing of dopamine

Abnormal levels of dopamine (DA) in body fluids is an indication of serious health issues, hence development of highly sensitive platforms for the precise detection of DA is highly essential. Herein, we demonstrate an Fe₃O₄@Cu silicate based electrochemical sensing platform for the detection of DA. Morphology and BET analysis shows the formation of ∼320 nm sized sea urchin-like Fe₃O₄@Cu silicate core–shell nanostructures with a 174.5 m² g⁻¹ surface area. Compared to Fe₃O₄ and Fe₃O₄@SiO₂, the Fe₃O₄@Cu silicate urchins delivered enhanced performance towards the electrochemical sensing of DA in neutral pH. The Fe₃O₄@Cu silicate sensor has a 1.37 μA μM⁻¹ cm⁻² sensitivity, 100–700 μM linear range and 3.2 μM limit of detection (LOD). In addition, the proposed Fe₃O₄@Cu silicate DA sensor also has good stability, selectivity, reproducibility and repeatability. The presence of Cu in Fe₃O₄@Cu silicate and the negatively charged surface of the Cu silicate shell play a vital role in achieving high selectivity and sensitivity during DA sensing. The current investigation not only represents the development of a highly selective DA sensor but also directs towards the possibility for the fabrication of other Cu silicate based core–shell nanostructures for the precise detection of DA.

Abnormal levels of dopamine (DA) in body fluids is an indication of serious health issues, hence development of highly sensitive platforms for the precise detection of DA is highly essential.

Single sensor for multiple analytes in different optical channel: Applying for multi-ion response modulation

A Schiff-base, (2,4-di-tert-butyl-6-((2-hydroxyphenyl-imino)-methyl)phenol) (L), has been improved to function as a simultaneous multi-ion probe in different optical channel. The probe changes from colorless to orangish upon being deprotonated by F^-, while the presence of Al³⁺ significantly enhances the fluorescence of the probe due to the inhibition of CN isomerization, cation-induced inhibition of excited-state intramolecular proton transfer (ESIPT), and chelation enhanced fluorescence (CHEF). Dual-channel "off-on" switching behavior resulted from the sequential input of F^- and Al³⁺, reflecting the balance of independent reactions of Al³⁺ and F^- with L and with one another. This sensing phenomenon realizes transformation between multiple states and beautifully mimics a "Write-Read-Erase-Read" logic circuit with two feedback loops.

Optical and electrochemical dual channel sensing of Cu2+ using functionalized furo[2,3-d]pyrimidines-2,4[1H,3H]-diones

Owing to their easy accessibility and high degree of structural and functional diversity, many multicomponent reactions (MCRs) have been a rich source of conjugate π-systems, functionalised chromophores (or fluorophore) and redox active molecules. Despite their high explorative potential and practical benefits, only a few MCR products have been so far investigated for their metal sensing abilities. In the present report, two furopyrimidinones (FPys) based molecular systems have been synthesized by [4+1] cycloaddition based MCR sequence. Designed chemosensors displayed optic (absorption spectra) as well as electroanalytical (ion selective electrode) response toward Cu²⁺ ion in solution and membrane phase respectively (dual channel sensing). Different aspects of both the sensing phenomena such as selectivity, association constants, detection limit, membrane composition etc. were studied in detail using UV-Vis spectroscopy, NMR titration and cell assembly. Both the compounds showed excellent performance characteristics such as high selectivity, acceptable affinity and low detection limits (10^-7M) in both sensing assays with potential utility in the area of sample monitoring.

A highly selective and sensitive rhodamine-derived fluorescent probe for detection of Cu2

A novel water-soluble and reversible fluorescent probe was designed and synthesized based on a rhodamine B derivative. It was used for detection of Cu²⁺ in drinking water and in living cells with high sensitivity and excellent selectivity. The tested concentration range and the limit of detection (LOD) of the probe were 0-15.00μmolL^-1 and 0.085μmolL^-1, respectively. In addition, the mode of binding and mechanism of interaction between the probe and Cu²⁺ were analyzed by density functional theory (DFT) calculations.

Fluorimetric detection of Sn(2+) ion in aqueous medium using Salicylaldehyde based nanoparticles and application to natural samples analysis

The fluorescent 2-[(E)-(2-phenylhydrazinylidene)methyl]phenol nanoparticles (PHPNPs) were prepared by a simple reprecipitation method. The prepared PHPNPs examined by Dynamic Light Scattering show narrower particle size distribution having an average particle size of 93.3nm. The Scanning Electron Microphotograph shows distinct spherical shaped morphology of nanoparticles. The blue shift in UV-absorption and fluorescence spectra of PHPNPs with respect to corresponding spectra of PHP in acetone solution indicates H- aggregates and Aggregation Induced Enhanced Emission (AIEE) for nanoparticles. The nanoparticles show selective tendency towards the recognition of Sn(2+) ions by enhancing the fluorescence intensity preference to Cu(2+), Fe(3+), Fe(2+), Ni(2+), NH4(+), Ca(2+), Pb(2+), Hg(2+) and Zn(2+) ions, which actually seem to quench the fluorescence of nanoparticles. The studies on Langmuir adsorption plot, fluorescence lifetime of PHPNPs, DLS-Zeta sizer, UV-visible and fluorescence titration with and without Sn(2+) helped to propose a suitable mechanism of fluorescence enhancement of nanoparticles by Sn(2+) and their binding ability during complexation. The fluorescence enhancement effect of PHPNPs induced by Sn(2+) is further used to develop an analytical method for detection of Sn(2+) from aqueous medium in environmental samples.

Xanthine sensor development based on ZnO–CNT, ZnO–CB, ZnO–GO and ZnO nanoparticles: an electrochemical approach

The wet-chemical method was used to prepare the various ZnO–CNT, ZnO–CB, ZnO–GO nanocomposites, and ZnO nanoparticles in higher pH medium, which were finally utilized with 5% nafion to produce a thin film of NCs/Nafion/GCE sensor that has a faster response towards selected xanthine with higher sensitivity, lower detection limit, and large linear dynamic range by electrochemical approach.

Pyrene–antipyrine based highly selective and sensitive turn-on fluorescent sensor for Th(iv)

Herein, a turn-on flruorescent sensor for thorium(iv) based on pyrene–antipyrine unit is described.