Rhodamine-Based Fluorescent Probe for Al3+ through Time-Dependent PET–CHEF–FRET Processes and Its Cell Staining Application

Carbon dots/Ruthenium(III) nanocomposites for FRET fluorescence detection and removal of mercury (II) via assembling into nanofibers

The determination and removal of mercury(II) (Hg2+) are essential for human health and environmental ecosystems. Herein, an ingenious carbon dots (CDs)-based Förster resonance energy transfer (FRET) system (N, S-CDs/Ru) was fabricated employing CDs and Ru3+ units as energy-transfer doner/acceptor pairs for visual detection and efficient removal of Hg2+. The treatment of Hg2+ induced a remarkable linear enhancement of the ratiometric fluorescence (F613 nm/F478 nm) with a detection limit (LOD) of 95 nM, along with continuous fluorescence color variations from blue to red. Given that the fluorescence color recognition and processing realized the real-time and rapid quantitation of Hg2+ by paper-based smartphone sensing platform. The mechanistic study revealed that the N/S/O-rich surface of the system enabled the Hg2+-triggered self-assembly from dots to nanofibers, combing with the active FRET process. Also, the efficient removal of Hg2+ with a removal efficiency of ∼98 % and an adsorption capacity of ∼372 mg/g was obtained. Furthermore, it was found that N, S-CDs/Ru loaded commercialized SiO2 or SBA-15 could facilitate the removal of Hg2+ with a removal efficiency over 99 % and an adsorption capacity up to ∼562 mg/g. This study provides a potential strategy for environmental monitoring and remediation.

Recent developments in the creation of a single molecular sensing tool for ternary iron (III), chromium (III), aluminium (III) ionic species: A review

Rational design of a molecular sensing tool is an important topic in molecular recognition, signalling, and optoelectronics that has piqued the interest of chemists, biologists, and environmental scientists. Approximately 150 years have passed since the beginning of the fluorescent chemosensor sector. Due to the paramagnetic properties of Cr3+ and Al3+ , it is tough to prepare a photoluminescence plug-in detector. Most dye-based Al3+ sensors must be utilized in organic or mixed solvents for robust hydration of Al3+ in water. The sophisticated molecular design of sensors, conversely, allows for the detection of these metal ions in aqueous medium. The design of chemosensors using various fluorophores and their mechanisms of action have been thoroughly discussed. A literature survey covering the design of chemosensors and their mechanisms of action have been thoroughly discussed covering the period 2010-2022 and that was carried out including innovative and exemplary activities from numerous groups throughout the world that have significantly contributed to this sector. The most important advantages of these probes are their aqueous solubility and quick response with outstanding selectivity and sensitivity for temporal distribution with high fidelity of metals in living cells.

A new Fe3+-selective, sensitive, and dual-channel turn-on probe based on rhodamine carrying thiophenecarboxaldehyde: Smartphone application and imaging in living cells

A new dual-channel probe based on rhodamine B derivative (MSB) was successfully designed, synthesized, characterized by Nuclear Magnetic Resonance (NMR) Spectroscopy, Fourier Transform Infrared Spectrophotometer (FTIR), Matrix Assisted Laser Desorption Ionization Time of Flight Mass Spectrometry (MALDI-TOF MS), X-ray Photoelectron Spectroscopy (XPS), and Single Crystal X-rayDiffraction, and the sensing abilities toward Fe³⁺ cation have been demonstrated and the probe was successfully utilized for fluorescence imaging of Fe³⁺ in living cells. The probe demonstrated quite fast, sensitive, and selective response to Fe³⁺ by causing an extreme enhancement in UV-vis and fluorescence spectroscopy techniques in the buffered aqueous media which makes MSB a dual-channel probe. While the color of MSB solution was initially light yellow, it turned pink in the presence of Fe³⁺, which provided highly selective naked-eye determination among several ions as alkaline, alkaline-earth, and transition metal ions. After that, the probe was easily applied to paper strips and real samples such as drinking waters and supplementary iron tablets for sensing Fe³⁺ in an aqueous solution. The detection limit (LOD) and the response time of the probe were determined as 4.85x10^-9 M and 4 min, respectively, which are quite lower compared with other rhodamine based Fe³⁺ sensors in the literature. According to Job's plot, ¹H NMR titration, MALDI-TOF MS, XPS, and DFT study techniques, the complexation ratio between MSB and Fe³⁺ was found as 1:1. Moreover, the spectral response was reversible with alternately addition of Fe³⁺ or Na₂EDTA to the MSB solution. In addition, fluorescence imaging in NIH/3T3 mouse fibroblast cells and studies in real samples with a quite high recovery rate exhibited that the probe is qualified for detection of Fe³⁺ ion with multiple practical usages.

Terbium(iii)-based coordination polymer with millimeter-size single crystals and high selectivity and sensitivity for folic acid

Terbium(iii)-based coordination polymer with millimeter-size single crystals and high selectivity and sensitivity for folic acid.

Synthesis and Characterization of a Carbazole-Based Schiff Base Capable of Detection of Al3+ in Organic/Aqueous Media

A new fluorescence probe (L) selectively detecting Al³⁺ ions was synthesized via the condensation reaction, and characterized using UV-Vis, FT-IR, ¹H-NMR and ¹³C-NMR spectroscopic techniques. The limit of detection for Al³⁺ ions of this synthesized probe was found to be 9.29 × 10^-7 M, while the Ka constant value was determined to be 1.64 × 10⁴ M^-1. The stoichiometric binding ratio of L-Al³⁺ was found to be 2:1 using the Job's plot method, and this ratio was also confirmed by ¹H-NMR titration and mass spectrometry. The recyclability of the chemosensor was found by the fluorescence method through the addition of EDTA to the L-Al³⁺ solution. The obtained data showed that the carbazole-based Schiff base acted as an ideal chemosensor for Al³⁺. Carbazole-based Schiff base as a fluorescent sensor for detection of Al³⁺ was synthesized and characterized. The association constant (K_a) was calculated to be 1.64 × 10⁴ M^-1 and the limit of detection (LOD) value was determined to be 9.29 × 10^-7 M. It was determined that th Schiff base was bound to Al³⁺ ions in 2:1 stoichiometric ratio. In the presence of other competitive metal cations, the selectivity of sensor L to Al³⁺ was not significantly affected.

ZnAl2O4 Nanomaterial as a Naked-Eye Arsenate Sensor: A Combined Experimental and Computational Mechanistic Approach

Raising public awareness over the emerging health risk due to intake of arsenic-contaminated potable water is a matter of great concern. Exploration of cost-effective, self-testing kits is a substantial way to reach out to the masses and detect the presence of arsenate in water. With this agenda, a photoluminescent Mannich base Zn(II) complex (ZnMC = [Zn₂(ML)₂]·(ClO₄)₂·(H₂O); HML = Mannich base ligand) has been synthesized, and its dinuclearity was verified with single-crystal X-ray diffraction structural analysis. Among a range of anions, ZnMC was found to detect arsenate selectively by showing a turn-off emission with a color change from bright green to dark under UV light. The real-life applicability of the ZnMC probe is somewhat restricted to only sensing of arsenate, but not its removal owing to the fact of its homogeneity. Considering the efficacy of ZnMC as well as a need for its easy removal from water, slight modification has been done with chloride ions in the form of ZnMC″ (=[Zn₂(ML)₂(Cl)₂]), and finally, an interface between homogeneous and heterogeneous solid support has been explored with a strategic fabrication of ZnMC″ grafted ZnAl₂O₄, named as ZAZ nanomaterial. This not only imparts successful segregation of arsenate from drinking water but also provides naked-eye detection under ambient light as well as UV light. Thermodynamic parameters associated with the binding of arsenate to ZnMC and ZAZ have been evaluated through isothermal calorimetric (ITC) measurements. Steady-state and time-resolved fluorescence titration study, absorption titration study, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and computational calculations have been performed to get deep insights into the sensing properties. Proper justification of the sensing mechanism is the highlight of this work. ZAZ nanomaterial has been exploited to produce a self-test paper kit for arsenate detection with a limit of 9.86 ppb, which potentially enables applications in environmental monitoring.

Molecular structure perspective on Temperature-Sensitive properties of rhodamine aqueous solutions

As one of the most commonly used organic fluorescent dyes, recently rhodamines have been successfully employed in temperature sensing. However, few works have been reported on their temperature-sensitive properties, which inevitably limiting their further applications. In order to solve such problem, we investigated temperature-sensitive properties of rhodamine 110, 123, 19, 6G, B and 3B focusing on their fluorescence emission spectra; and analyzed them in the molecular structure perspective. It is demonstrated that the fluorescence emission intensities of all studied rhodamines decreased with higher temperature, which inevitably enhances the probability of collisions among molecules, thus definitely leads to energy loss in fluorescence emission. While these rhodamines still have various temperature sensitivities mainly due to the substitutes: the substitute on the benzene carboxylate has little effect; the amino substituents of the three-ring xanthene enhance the temperature sensitivity due to their rotation weakening the rigidity of the three-ring xanthene; and the methyl substituents on the three-ring xanthene reduce the temperature sensitivity by enhancing the rigidity and stability of the three-ring xanthene as well as hindering the rotation of ethylamino. These findings can also be extended to other organic fluorescent dyes proved by coumarins comparable to rhodamines. The results provided by this work can be useful reference and guidance to further develop organic fluorescent dyes especially for temperature sensing.

Analyses on intracellular Fe3+ with a rhodamine probe: "turn-on" response, specific recognition and bioimaging

To overcome the existing difficulty in distinguishing ferric from ferrous ions, a rhodamine-containing probe was designed to combine with Fe³⁺ based on an opening-closing transformation of the spirolactam ring in the rhodamine moiety. Through a specific and stoichiometric fluorescence response towards Fe³⁺ by 1 : 1 binding accompanied by an obvious color change in the recognition process of Fe³⁺, a "naked-eye" detection method of Fe³⁺ in an aqueous environment is possible. Theoretical calculations gave a possible recognition mechanism of the probe-Fe³⁺ system. Further cytotoxicity and bioimaging in living L929 cells suggested the probe's future applications as a real-time analytical method for intracellular Fe³⁺ in clinical diagnosis. Besides, bioimaging applications enable the dynamic labelling and tracking of Fe³⁺ in biological systems.

Hybrid labeling system for dSTORM imaging of endoplasmic reticulum for uncovering ultrastructural transformations under stress conditions

The endoplasmic reticulum (ER) transforms its morphology to fit versatile cellular functions especially under stress conditions. Since various ER stresses are critical pathophysiological factors, the precise observations of ER can provide insights into disease diagnoses and biological researches. Live-cell super-resolution imaging is highly expected for uncovering microstructures of ER. However, to achieve this, there remains a big challenge in how to efficiently label ER with advanced fluorophores. Herein, we report a new SNAP-tag fluorescent probe, namely, CLP-TMR, for specific and high-density labeling of the newly constructed dual ER-signal (targeting and retention) peptides fused-SNAP proteins. This hybrid labeling system integrating chemical probes with genetically encoded techniques enables molecular position reconstructions of ER morphologies through direct stochastic optical reconstruction microscopy (dSTORM) imaging. The super-resolution imaging reveals several never-known ultrastructural changes responding to different ER stresses, i.e. the formation of peripheral ER sheets to restore the immunogenicity, and the long flattened ER tubules under inflammation.

2-Hydroxynaphthalene based acylhydrazone as a turn-on fluorescent chemosensor for Al3+ detection and its real sample applications

Developing high performance fluorescent chemosensor for Al³⁺ detection is highly desirable, due to the excess of Al³⁺ will lead to many diseases. In this paper, a simple 2-hydroxynaphthalene-based fluorescent chemosensor has been synthesized and characterized by different spectroscopic methods. The compound exhibited an "turn-on-type" fluorescent chemosensing for the detection of Al³⁺, which was ascribed to the chelation-enhanced fluorescence (CHEF). The high selectivity and sensitivity of the compound for Al³⁺ were verified by fluorescence spectra in its DMF solution, and the enhancement of fluorescent intensity could be observed by naked-eye from non-fluorescence to green light. The detection limit of the compound for Al³⁺ was found to be 4.22 × 10^-8 M and the stability constant was 4.82 × 10⁴ M^-1. The 1:1 binding stoichiometry of the compound to Al³⁺ was confirmed from the Job's plot based on fluorescence titrations. Additionally, the sensing process of the compound to Al³⁺ was chemically reversible by adding Na₂EDTA. Importantly, the probe was successfully applied to quantitative analysis of Al³⁺ in real drug and potable water samples.

A “turn-on” small molecule fluorescent sensor for the determination of Al3+ ion in real samples: theoretical calculations, and photophysical and electrochemical properties

The fluorescence sensing properties of a naphthalene-based acetohydrazide (3) were investigated. A highly selective “turn-on” response was obtained towards Al3+ ions, and this was used for real sample analysis and development of paper test strips.

FRET based ratiometric switch for selective sensing of Al3+ with bio-imaging in human peripheral blood mononuclear cells

FRET based ratiometric switch for selective sensing of Al³⁺ with bio-imaging in human peripheral blood mononuclear cells (PBMCs).

Highly selective and sensitive chemosensor for Al(III) based on isoquinoline Schiff base

As a colorimetric and fluorescent turn-on sensor to Al³⁺, N'-(2-hydroxybenzylidene)isoquinoline-3-carbohydrazide (HL) has been easily synthesized. The fluorescence intensity increases by 273 times in the presence of Al³⁺ at 458 nm. Meanwhile, the experiment data indicate that the limit of detection for Al³⁺ is 1.11 × 10^-9 M. Remarkably, the blue fluorescence signal of HL-Al³⁺ could be specially observed by the naked eye under UV light and is significantly different from those of other metal ions. Fluorescence switch based on the control of Al³⁺ and EDTA proved HL could act as a reversible chemosensor. According to ESI-MS result and the Job's plots, the 2:1 coordination complex formed by HL and Al³⁺ could be produced. Density functional theory calculations were performed to illustrate the structures of HL and complex. The cell imaging experiment indicates that HL can be applied for monitoring intracellular Al³⁺ levels in cells.

Multifunctional rhodamine B appended ROMP derived fluorescent probe detects Al3+ and selectively labels lysosomes in live cells

There a few reports of rhodamine-based fluorescent sensors for selective detection of only Al3+, due to the challenge of identifying a suitable ligand for binding Al3+ ion. The use of fluorophore moieties appended to a polymer backbone for sensing applications is far from mature. Here, we report a new fluorescent probe/monomer 4 and its ROMP derived polymer P for specific detection of Al3+ ions. Both monomer 4 and its polymer P exhibit high selectivity toward only Al3+ with no interference from other metal ions, having a limit detection of 0.5 and 2.1 µM, respectively. The reversible recognition of monomer 4 and P for Al3+ was also proved in presence of Na2EDTA by both UV-Vis and fluorometric titration. The experimental data indicates the behavior of 4 and P toward Al3+ is pH independent in medium conditions. In addition, the switch-on luminescence response of 4 at acidic pH (0 < 5.0), allowed us to specifically stain lysosomes (pH ~ 4.5-5.0) in live cells.

Study on synthesis and fluorescence property of rhodamine-naphthalene conjugate

In this study, a novel ligand (HL) consisting of 2-methyl quinoline-4-carboxylic acid, rhodamine and naphthalene moiety, was designed and synthesized, it could be developed a ratiometric fluorescent sensor for selective detection of Al³⁺ via fluorescence resonance energy transfer (FRET) from naphthalimide moiety to rhodamine moiety. The addition of Al³⁺ trigger the significant fluorescence enhancement of HL at 550 nm at the expense of the fluorescent emission of HL centered at 524 nm.

Two novel colorimetric fluorescent probes: Hg2+ and Al3+ in the visual colorimetric recognition environment

Two new dual channel Schiff base fluorescent probes, Tri-R6G and Tri-Flu, were synthesized, and can detect Hg2+ and Al3+, respectively. The two probes were characterized by FTIR, 1H NMR, 13C NMR and HRMS, and their optical properties were detected by UV and FL. Test results showed the probes' detection of Hg2+ and Al3+ compared to other metal ions (Ag+, Co2+, Cd2+, Mg2+, Cu2+, Ni2+, Ba2+, Pb2+, Cr3+, Al3+, Zn2+, Hg2+, K+, Ga2+ and Fe3+), respectively. Besides, the detection limits were determined to be 1.61 × 10-8 M and 1.15 × 10-8 M through the standard curve plot, respectively. The photoelectron transfer (PET) mechanism was guessed by the Job's plot and the infrared titration. Corresponding orbital electron distribution and molecular geometry configurations of the compounds were predicted by density functional theory (DFT). In addition, the prepared test paper changed from white to pink when the target ion was detected. The color changed from colorless to pink in a solution having a concentration of 10-5 M.

Development of Rhodamine 6G-Based Fluorescent Chemosensors for Al3+-Ion Detection: Effect of Ring Strain and Substituent in Enhancing Its Sensing Performance

Four rhodamine 6G-based chemosensors (H ₃ L1-H ₃ L4) are designed for selective detection of Al³⁺ ion. They are characterized using various spectroscopic techniques and X-ray crystallography. All absorption and emission spectral studies have been performed in 10 mM N-(2-hydroxyethyl)piperazine-N'-ethanesulfonic acid (HEPES) buffer solution at pH 7.4 in H₂O/MeOH (9:1, v/v) at 25 °C. In absorption spectra, chemosensors exhibit an intense band around 530 nm in the presence of Al³⁺ ion. Chemosensors (H ₃ L1-H ₃ L4) are nonfluorescent when excited around 490 nm. The presence of Al³⁺ ion enhances the emission intensity (555 nm) many times. The formation of complexes 1-4 is established with the aid of different spectroscopic techniques. The limit of detection value obtained in the nanomolar range confirms the high sensitivity of the probes toward Al³⁺ ion. It has been observed that the presence of aliphatic spacers in the diamine part and different halogen substituents in the salicylaldehyde part strongly influences the selectivity of the chemosensors toward Al³⁺ ion. The propensity of the chemosensors to identify intracellular Al³⁺ ions in triple-negative human breast cancer cell line MDA-MB-468 by fluorescence imaging is also examined in this study.

Low-level detection of water in polar aprotic solvents using an unusually fluorescent spirocyclic rhodamine

Detection of trace amount of water in polar aprotic solvents (acetonitrile) by novel fluorescent spirocyclic rhodamine (sDRh).

Chromogenic and fluorogenic “off–on–off” chemosensor for selective and sensitive detection of aluminum (Al3+) and bifluoride (HF2−) ions in solution and in living Hep G2 cells: synthesis, experimental and theoretical studies

A simple pyridine-dicarbohydrazide based colorimetric and fluorometric chemosensor L was designed and synthesized for Al³⁺ ion sensing in organo aqueous solution.

Paper based field deployable sensor for naked eye monitoring of copper (II) ions; elucidation of binding mechanism by DFT studies

The study demonstrates the fabrication of test strips made from newly synthesized ortho-Vanillin based colorimetric chemosensor (probe P) that could be employed as field deployable tool for rapid and naked eye detection of Cu²⁺. Upon addition of Cu²⁺ to the chemosensor, it exhibits rapid pink color from colorless and can be easily seen through the naked eye. This probe exhibits a remarkable colorimetric "ON" response and the absorbance intensity of the probe enhances significantly in presence of Cu²⁺. The sensing mechanism has been deduced using FTIR, XPS, LCMS and DFT studies. The binding mechanism of the probe to Cu²⁺ was substantiated by DFT studies. HOMO of the probe suggests that a high electronic density resides on O, N atoms and thus these are the favorable binding site for the metal ions. Study revealed that the P + Cu²⁺ complex is -35.64 eV more stable than individual reactants. The Cu²⁺ binds to the probe in 1:1 stoichiometry with a binding constant of 2.6 × 10⁴ M^-1 as calculated by Job's plot and Benesi-Hildebrand plot. The chemosensor shows 1.8 × 10^-8 M detection limit, which is considerably lesser than that of the WHO admissible limit of [Cu²⁺] in drinking water. Possible interfering ions namely Ca²⁺, Mg²⁺, Fe²⁺, Co²⁺, Ni²⁺, Cd²⁺, Hg²⁺, Mn²⁺, Al³⁺ and Cr³⁺ do not show any appreciable interference in the colorimetric response of the probe towards Cu²⁺. Particularly, the colorimetric "ON-OFF-ON" responses are proved to be repeated over 5 times by the sequential inclusion of Cu²⁺ and S^2-. Sensitivity of the probe in real-time water and blood samples is found at par with results with AAS and ICP-OES techniques. Further, the reversibility of the probe and the easy fabrication of deployable strips for real-field naked eye detection of Cu²⁺ suggest importance of synthesized probe.

Theoretical Design of Near-Infrared Al3+ Fluorescent Probes Based on Salicylaldehyde Acylhydrazone Schiff Base Derivatives

The aim of this paper is to design near-infrared (NIR) Al³⁺ fluorescent probes based on a Schiff base to extend their applications in biological systems. By combining benzo[h]quinoline unit and salicylaldehyde acylhydrazone, we designed two new Schiff base derivatives. According to theoretical simulations on previous experimental Al³⁺ probes, we obtained the appropriate theoretical approaches to describe the properties of these fluorescent probes. By employing such approaches on our newly designed molecules, it is found that the new molecules have high selectivity toward Al³⁺ and that their corresponding Al³⁺ complexes can emit NIR fluorescence. As a result, they are expected to be potential NIR Al³⁺ fluorescent probes.

Rhodamine-azobenzene based single molecular probe for multiple ions sensing: Cu2+, Al3+, Cr3+ and its imaging in human lymphocyte cells

A photoinduced electron transfer (PET) and chelation-enhanced fluorescence (CHEF) regulated rhodamine-azobenzene chemosensor (L) was synthesized for chemoselective detection of Al³⁺, Cr³⁺, and Cu²⁺ by UV-Visible absorption study whereas Al³⁺ and Cr³⁺ by fluorimetric study in EtOH-H₂O solvent. L showed a clear fluorescence emission enhancement of 21 and 16 fold upon addition of Al³⁺ and Cr³⁺ due to the 1:1 host-guest complexation, respectively. This is first report on rhodamine-azobenzene based Cr³⁺ chemosensor. The complex formation, restricted imine isomerization, inhibition of PET (photo-induced electron transfer) process with the concomitant opening of the spirolactam ring induced a turn-on fluorescence response. The higher binding constants 6.7 × 10³ M^-1 and 3.8 × 10³ M^-1 for Al³⁺ and Cr³⁺, respectively and lower detection limits 1 × 10^-6 M and 2 × 10^-6 M for Al³⁺ and Cr³⁺, respectively in a buffered solution with high reversible nature describes the potential of L as an effective tool for detecting Al³⁺ and Cr³⁺ in a biological system with higher intracellular resolution. Finally, L was used to map the intracellular concentration of Al³⁺ and Cr³⁺ in human lymphocyte cells (HLCs) at physiological pH very effectively. Altogether, our findings will pave the way for designing new chemosensors for multiple analytes and those chemosensors will be effective for cell imaging study.

Rhodamine probes for Fe3+: theoretical calculation for specific recognition and instant fluorescent bioimaging

Aim: To overcome the existing difficulty in distinguishing Fe(III) from Fe(II), rhodamine-containing Fe3+ probes, giving off different fluorescence responses to ferric and ferrous ions, were synthesized. Materials & methods: Color change in Fe3+ recognition, accompanying spirolactam opening–closing, could be used for ‘naked-eye’ detection. Theoretical calculations revealed the possible Fe3+-probe combination mechanism. Results: Apart from the probes’ specific response toward Fe3+, the Fe3+-probe demonstrated highly quantitative relationships in fluorescence titration, instant labeling and dynamic tracking of intracellular Fe3+ in bioimaging. Conclusion: Cytotoxity and bioimaging in living L929 suggested the probes’ future applications as real-time detection methods for Fe3+ in clinical diagnosis. Instant and time-lapse imagings, based on fluorescence-time stability of Fe3+-probe, enables the dynamic labeling and tracking of Fe3+ in living systems.

Turn-On Fluorescent Sensors for the Selective Detection of Al3+ (and Ga3+) and PPi Ions

Rationally designed multiple hydroxyl-group-based chemosensors L1-L4 containing arene-based fluorophores are presented for the selective detection of Al³⁺ and Ga³⁺ ions. Changes in the absorption and emission spectra of L1-L4 in ethanol were easily observable upon the addition of Al³⁺ and Ga³⁺ ions. Competitive binding studies, detection limits, and binding constants illustrate significant sensing abilities of these chemosensors with L4, showing the best results. The interaction of Al³⁺/Ga³⁺ ions with chemosensor L4 was investigated by fluorescence lifetime measurements, whereas Job's plot, high-resolution mass spectrometry, and ¹H NMR spectral titrations substantiated the stoichiometry between L4 and Al³⁺/Ga³⁺ ions. The solution-generated [L-M³⁺] species further detected pyrophosphate ion (PPi) by exhibiting emission enhancement and a visible color change. The binding of Al³⁺/Ga³⁺ ions with chemosensor L4 was further supported by density functional theory studies. Reversibility for the detection of Al³⁺/Ga³⁺ ions was achieved by utilizing a suitable proton source. The multiionic response, reversibility, and optical visualization of the present chemosensors make them ideal for practical applications for real samples, which have been illustrated by paper-strip as well as polystyrene film-based detection.

A feedback-controlling digital microfluidic fluorimetric sensor device for simple and rapid detection of mercury (II) in costal seawater

By combination of miniaturization potential of digital microfluidics (DMF) and sensitivity of fluorescence probe, an integrated sensor device has been initially constructed for mercury detection in coastal waters. The actuation feature of the detecting target, seawater droplet, which remains unclear, was basically explored. To overcome a potential risk of driven failure, induced by diversity ion ingredients in seawater, a feedback control loop was included into control system. Analyzing method for coastal waters was well established on DMF, which showed satisfied stability and selectivity in Hg sensing under high salinity condition, with the sensitivity of Hg²⁺ at the parts per billion level and total testing time less than 20s. With the advantages of being fast, amenable to automation and low cost, this device is promising for the formation of simple and rapid sensor device, especially for a routine monitoring and emergency detection of Hg/or other metals in coastal waters.

Photoswitchable probe with distinctive characteristics for selective fluorescence imaging and long-term tracing

A photo-switchable and high-contrast bio-imaging indicator 4,4'-(1E,1'E)-(4,4'-(cyclopentene-1,2-diyl)bis(5-methylthiophene-4,2-diyl))bis(methan-1-yl-1-ylidene)bis(azan-1-yl-1-ylidene)bis(2-(benzo[d]thiazol-2-yl)phenol) (BMBT) has been demonstrated, by integrating photochromophore with excited-state intramolecular proton transfer (ESIPT) moiety. The ability of reversible emission switching enables arbitrarily selective labeling or concealing of cells simply by controlling light irradiation. Besides, when the emission was switched on, BMBT is demonstrated to exhibit unique characteristics of aggregation induced emission (AIE), providing a high on-off ratio for favorable bio-imaging. Thus, the non-labeling and easily-controlled selective imaging, as well as good biocompatibility indicates BMBT to be a favorable cell probe with great potentials for functional bio-imaging fluorophore.

A Highly Selective and Sensitive Fluorescent Chemosensor for Detecting Al3+ Ion in Aqueous Solution and Plant Systems

The solubilized form of aluminum, Al³⁺, is present under acid soil conditions and toxic to both animals and plants. Detecting and quantifying Al³⁺ is vital for both chemistry and biology. A new Schiff-based fluorescent turn-on sensor (probe L) for the selective detection of the Al³⁺ ion was synthesized by coupling 2-hydroxy-1-naphthaldehyde and 2-aminoisoindoline-1,3-dione, and the structure was characterized by nuclear magnetic resonance spectra. The probe L exhibited an excellent selective and sensitive response to the Al³⁺ ion over other metal ions in DMSO-H₂O (1:9 v/v). Fluorescence quantification revealed that probe L was promising for the detection and accumulation of Al³⁺. Treating rice seedlings with Al³⁺ at 25–200 μM inhibited their growth. Al³⁺ treatment produced reactive oxygen species in rice roots. Practical applications of the fluorescent probe for the quantification of Al³⁺ in water samples and rice seedlings are demonstrated. Detecting the Al³⁺ ion with the probe L is easy and a potential alternative to existing analytical methods. The method can be used for detecting the Al³⁺ content of aqueous solution and plant systems. The novel fluorescent probe L has good potential for monitoring Al³⁺ content in the environment and biological systems.

Novel thiophene-based colorimetric and fluorescent turn-on sensor for highly sensitive and selective simultaneous detection of Al3+ and Zn2+ in water and food samples and its application in bioimaging

A novel bifunctional thiophene-based Schiff base TS as a colorimetric and fluorescent turn-on sensor for rapid and simultaneous detection of Al³⁺ and Zn²⁺ ions with high selectivity and sensitivity has been developed. The sensor shows remarkable fluorescence enhancement response for Al³⁺ and Zn²⁺ over a broad pH range with good anti-interference capability, which accompanied with an obvious color change easily detected by naked eyes. Sensor TS can detect as low as 3.7 × 10^-9 M for Al³⁺ and 3.0 × 10^-8 M for Zn²⁺, whereas respective association constants are 1.16 × 10⁴ M^-1 and 2.08 × 10⁴ M^-1. With the help of fluorescence titration and Job's plot, the stoichiometric ratio of TS with Al³⁺/Zn²⁺ was determined to be 1:1. The sensing mechanism of sensor TS with Al³⁺/Zn²⁺ based on the chelation-enhanced fluorescence (CHEF) was analyzed in detail through ¹H NMR titration, FTIR, HRMS and DFT studies. Moreover, sensor TS has been applied to the detection of Al³⁺ and Zn²⁺ in real environmental water and food samples as well as the filter paper-based test strips. Furthermore, sensor TS has good cell-permeability and can be used to selectively sense intracellular Al³⁺ and Zn²⁺ by bioimaging.

Design and Synthesis of Nanosensor Based on CdSe Quantum Dots Functionalized with 8-Hydroxyquinoline: a Fluorescent Sensor for Detection of Al3+ in Aqueous Solution

A novel nanosensor based on CdSe quantum dots (QDs) capped with 8-hydroxyqunoline (HQ) was developed for Al³⁺ ions determination in aqueous solutions. The method is based on the fluorescence enhancement of the HQ functionalized QDs in the presence of Al³⁺ ions, due to the strong interaction between Al³⁺ and HQ. Prepared nanosensor exhibited an acceptable selectivity and sensitivity for Al³⁺ ions in the presence of other metal ions. Plot of Log(I/I₀) against Log[Al³⁺] shows a good linearity in the range of 0.02-3.0 mM, and the method could be used for detection of Al³⁺ ions concentration in aqueous solutions.