Fluorescence Spectral Changes Research Articles

A turn-off fluorescent sensor based on Schiff base incorporating diformyl phenol moiety for the detection of Cu2+ in aqueous solution at nanomolar level and its application in living cells

Given the critical role of trace copper ion in human health, its sensitive detection in environmental and biological samples is crucial. We, herein, designed and synthesized a diformyl phenol-based turn-off fluorescent sensor ((5-(tert-butyl)-2-hydroxy-1,3-phenylene)bis (methanylylidene)) bis (azanylylidene)) bis(4-hydroxy-2H-chromen-2-one) (MH-4)) for the spectrofluorometric detection of Cu2+ ion, which has sensitive and selective fluorescence quenching over other competitive metal ions. The efficiency and fast response of the sensor were confirmed by UV–Visible, fluorescence spectral changes, which may be due to the formation of coordination bond between MH-4 and Cu2+ ions. The binding stoichiometry of MH-4 with Cu2+ was examined with the help of UV–Vis and fluorescence titrations, and Job’s plot, which gives a 1:1 coordination stoichiometry; this is further confirmed through MS studies. The binding constant of the complex was found to be 9.4 x 107 M−1. Then, the absorbance and fluorescence-based detection limits were calculated to define the sensitivity range of the proposed sensor and were found to be 69.30 nM and 37.40 nM, respectively. Finally, a live cell image study of MH-4 in L929 (murine aneuploid fibrosarcoma) cells was also performed to test the cell permeability of MH-4 and its effectiveness for selective detection of Cu2+ in living cells.

Thermodynamics of oligomerization and Helix-to-sheet structural transition of amyloid β-protein on anionic phospholipid vesicles

Understanding oligomerization and aggregation of the amyloid-β protein is important to elucidate the pathological mechanisms of Alzheimer's disease, and lipid membranes play critical roles in this process. In addition to studies reported by other groups, our group has also reported that the negatively-charged lipid bilayers with a high positive curvature induced α-helix-to-β-sheet conformational transitions of amyloid-β-(1–40) upon increase in protein density on the membrane surface and promoted amyloid fibril formation of the protein. Herein, we investigated detailed mechanisms of the conformational transition and oligomer formation of the amyloid-β protein on the membrane surface. Changes in the fractions of the three protein conformers (free monomer, membrane-bound α-helix-rich conformation, and β-sheet-rich conformation) were determined from the fluorescent spectral changes of the tryptophan probe in the protein. The helix-to-sheet structural transition on the surface was described by a thermodynamic model of octamer formation driven by entropic forces including hydrophobic interactions. These findings provide useful information for understanding the self-assembly of amyloidogenic proteins on lipid membrane surfaces.

Constructing [2.2]Paracyclophane‐Based Ultrasensitive Optical Fluorescent‐Phosphorescent Thermometer with Cucurbit[8]uril Supramolecular Assembly

AbstractThe pursuit of developing novel approaches to fully organic and efficient phosphorescent materials is in high demand. The optical activity of such functional, organic phosphorescent/fluorescent materials may exhibit great temperature dependence, allowing their application as advanced, highly sensitive molecular thermometers. In this study, a rational strategy involving host–guest complexation and polymerization of [2.2]paracyclophane (PCP) based molecules with cucurbit[8]uril (CB8) to suppress the molecular motion and promote temperature‐dependent phosphorescence is presented. The rigid cavity of CB8 provides an ideal microenvironment to host PCP molecules 1 and 2, significantly enhancing the photophysical performance after complexation. Co‐polymerizing phosphors 1 and 2 with acrylamide is an efficient method for improving phosphorescence. Incorporating CB8 into the resulting P‐1 and P‐2 polymers enhances phosphorescence performance. Importantly, the obtained materials exhibit a big structure‐dependent spectral shift and change of phosphorescence lifetimes with temperature, allowing novel, phosphorescence‐based, and purely organic optical thermometers to be developed. The practical applications of PCP‐based luminescent materials in temperature sensing via a multi‐parameter approach are showcased, i.e., using fluorescence spectral shift and changes in bandwidth, as well as phosphorescence lifetimes, exhibiting thermal sensitivity of ≈17.7 cm−1 °C−1, 47.8 cm−1 °C, and 5.2% °C−1, respectively.

Spectroscopic Investigation of Coumarin Based Novel Fluorescent TURN OFF Sensor for the Selective Detection of Fe3+: In-vitro Live Cell Imaging Application.

The novel TURN-OFF fluorescent sensors 4-(Benzo[1,3]dioxol-5-yloxymethyl)-7-hydroxy-chromen-2-one (4BHC) and 4-(6-Bromo-benzo[1,3]dioxol-5-yloxymethyl)-7-hydroxy-chromen-2-one (4BBHC) are designed and synthesized for the spectrofluorometric detection of the biologically important Fe3+ ions, which has sensitive and selective fluorescence quenching over other competitive metal ions. The effectiveness of the sensors and rapid response are validated through UV-Visible, and fluorescence spectral changes. These spectral changes could be due to the formation of coordination bond between ligand and metal ion. The binding stoichiometry of both sensors with Fe3+ ions is studied with the help of Job's plot, which gives a 1:2 coordination ratio; this is further confirmed through DFT, IR and NMR studies. The association constants of 4BHC and 4BBHC are calculated through Benesie-Hildebrand plots, and they are found to be 6 × 104M-1 and 11.2 × 104M-1 respectively. Following, LOD is calculated to define the range of sensitivity of the proposed sensors and is found to be 3.43μM and 2.14μM respectively. The chemical hardness parameter suggested that both sensors are soft molecules. In addition, low cytotoxicity levels of 4BHC and 4BBHC led to the demonstration of their efficacy in In-Vitro imaging of Fe3+ ions inside living cells, which ensures that these sensors are promising candidates for bioimaging.

Dual Ratiometric Fluorescence Monitoring of Mechanical Polymer Chain Stretching and Subsequent Strain-Induced Crystallization.

Tracking the behavior of mechanochromic molecules provides valuable insights into force transmission and associated microstructural changes in soft materials under load. Herein, we report a dual ratiometric fluorescence (FL) analysis for monitoring both mechanical polymer chain stretching and strain-induced crystallization (SIC) of polymers. SIC has recently attracted renewed attention as an effective mechanism for improving the mechanical properties of polymers. A polyurethane (PU) film incorporating a trace of a dual-emissive flapping force probe (N-FLAP, 0.008 wt %) exhibited a blue-to-green FL spectral change in a low-stress region (<20 MPa), resulting from conformational planarization of the probe in mechanically stretched polymer chains. More importantly, at higher probe concentrations (∼0.65 wt %), the PU film showed a second spectral change from green to yellow during the SIC growth (20-65 MPa) due to self-absorption of scattered FL in a short wavelength region. The reversibility of these spectral changes was demonstrated by load-unload cycles. With these results in hand, the degrees of the polymer chain stretching and the SIC were quantitatively mapped and monitored by dual ratiometric imaging based on different FL ratios (I525/I470 and I525/I600). Simultaneous analysis of these two mappings revealed a spatiotemporal gap in the distribution of the polymer chain stretching and the SIC. The combinational use of the dual-emissive force probe and the ratiometric FL imaging is a universal approach for the development of soft matter physics.

Amyloid dye pairs as spectral sensors for enhanced detection and differentiation of misfolded proteins.

Protein misfolding with subsequent formation of cross-β-sheet-rich fibrils is a well-known pathological hallmark of various neurodegenerative conditions, including Alzheimer's disease (AD). Recent evidence suggests that specific protein conformations may be the primary drivers of disease progression, differentiation of which remains a challenge with conventional methods. We have previously described a unique phenomenon of light-induced fluorescence enhancement and spectral changes of the amyloid dyes K114 and BSB, and demonstrated its utility in characterizing different amyloid fibrils. In this study, we further characterize and explore the potential of photoconversion, coupled with dual-probe staining, for improved detection of heterogeneity of amyloids using silk fibers and 5xFAD mouse brain sections. BSB and K114 were paired with either Nile Red or MCAAD-3, aiming to increase the sensitivity and specificity of staining and misfolded protein detection via complementary binding and FRET. Principal component analysis of spectral data revealed significant differences between various amyloids, and was able to detect subtle amyloid pathology in the 5xFAD mouse background brain parenchyma.

Spectroscopy and dynamics of beta-lactoglobulin complexed with rifampicin

In this paper, we report the binding interaction of milk protein, beta-lactoglobulin (BLG), with an antibiotic against tuberculosis, rifampicin (RIF). BLG intrinsic fluorescence from tryptophan (Trp) amino acids was monitored to understand protein-drug interactions. Binding parameters and stoichiometry were estimated with the help of fluorescence spectral changes. Synchronous fluorescence spectroscopy was employed to exclusively monitor the Trp and Tyrosine (Tyr) environment in the presence of RIF. With the help of steady state fluorescence at different temperatures supported by time-resolved fluorescence, we confirmed that the protein forms a static complex with RIF. Thermodynamic parameters, ΔH and ΔS values, showed the involvement of hydrophobic forces between the RIF and BLG. Competitive displacement assay with ANS confirmed the BLG calyx as the binding site for RIF. Energy transfer mechanism from Trp to RIF was attributed to the fluorescence changes in protein upon complexation. The Förster resonance energy transfer (FRET) was used to find distance, energy transfer efficiency and rate of energy transfer between donor (BLG) and acceptor (RIF). Fourier-transform infrared (FTIR) spectroscopy was utilized for estimating changes in the secondary structure of BLG induced by RIF. Molecular docking was used to visualise the binding location of RIF on BLG. Molecular dynamics (MD) simulation studies showed a consistent binding interactions between BLG and RIF during the 100 ns simulation period and this well supported the increased beta sheet content in FTIR. Overall our results establish the potential of intrinsic fluorescence of BLG in combination with biophysical tools to rationalize drug-protein interactions. Communicated by Ramaswamy H. Sarma

A temperature sensor based on Er3+/Yb3+ co-doped tellurite fiber for real-time thermal monitoring of transformers

In this paper, a temperature sensor based on fluorescence intensity ratio (FIR) technique is prepared by the dual curing method. The pumping threshold is only 0.1 mW for the application of real-time thermal monitoring on small transformers. This not only greatly reduces the thermal effects accumulated by laser irradiation but also contributes to the integration and portability of the light source. Based on the FIR, the temperature information could be demodulated through tracking the fluorescence spectral changes. The basic temperature sensing characteristics of this sensor were evaluated, which showed that the maximum stability deviation and reproducibility error were within ±1.1 K and ±0.8 K, respectively. Notably, it has a maximum measurement error of only 0.61 K when applied to the temperature monitoring of transformers. And a fast time response of 2.1 s was exhibited in the cyclic exhalation experiment. This proposed sensor is suitable for mass production due to its resistance to electromagnetic interference, low pumping power, fast time response, excellent stability and reproducibility.

Synthesis, characterization of 4,4′-((1E,1′E)-hydrazine-1,2-diylidenebis(methanylylidene)) diphenol and the inclusion complex with γ-cyclodextrin as a fluorescent probe for detection of Al3+

The 4, 4′- ((1E, 1′E)-hydrazine-1,2-diylidenebis(methanylylidene)) diphenol (4-HBA) is successfully synthesized utilizing 4-hydroxybenzaldehyde (4-HB) and hydrazine hydrate as the starting materials. The synthesized 4-HBA is confirmed by the spectral analysis of 1H NMR, FT-IR, UV–Visible, and HR-Mass spectroscopy. The inclusion complexes of 4-HBA with γ-cyclodextrin are therefore investigated using UV and fluorescence spectroscopy. When γ-CD combined with 4-HBA, a 1:1 inclusion complex (ICs) is created that causes absorption and fluorescence spectral changes. The molecular computational analysis is carried out utilizing PM3 Gaussian software revealing the orientation of the synthetic 4-HBA within the γ-CD cavity. The HOMO-LUMO band gap and the DFT analysis specifically support the ICs, with the help of energy values and the H-bond distance. The hydrophobic contact between the host and guest molecules is strongly supported by the 1H NMR and 2-D NMR data, with the matching Ar-H proton moving to higher chemical shift values and the strong cross-correlation spot validating the conclusion. Al3+ sensing activity is observed using fluorescent probes in conjunction with UV and FL spectral analysis. Other metal ions are present in the solutions even though they are not readily available, most notably the Al3+ that binds to the fluorescent probe. Here, the Al3+ selective responses, the colour changes at the wavelength regions, and a fluorescence microscopic image of the solution media are also shown. The selected metal ions recovery percentage is used to determine the concentrations in a variety of clean water samples, including tap water, pond water, and also sea water.

Development of piperazine conjoined 1,2,3-triazolyl-γ-propyltriethoxysilanes: Fluorometric detection of Cr3+ ions and computational study

Chromium is essential for some biochemical processes, and excess is a big concern that shows adverse effects on human health and the environment. Therefore, it is urgent to design new sensors to detect chromium ions rapidly. The present study discusses the synthesis of piperazine conjoined 1,2,3-triazolyl-γ-propyltriethoxysilanes (4a-4b) and development of 4a as fluorescence turn-on sensor for the detection of Cr3+ ions. The mechanistic insights reveal to the restricted CN rotation and inhibited intramolecular charge transfer (ICT) process. In addition, Job's plot and Benesi-Hildebrand plot justify the 1:1 binding affinity with a binding constant of 9.96 × 105 M−1 for [ligand 4a + Cr3+] complex and the limit of detection for Cr3+ ions is observed as 6.06 × 10-8 M. The fluorescence spectral changes, 1H NMR spectra and DFT studies provide evidences for ligand 4a and Cr3+ ions interactions. Further, the reversibility of the ligand 4a from [ligand 4a + Cr3+] complex on the addition of EDTA can be used in the construction of molecular logic gate where Cr3+ and EDTA are considered as inputs and the fluorescence intensity at 398 nm as output. Further, compounds 4a-4b were then evaluated for their antibacterial activity against bacterial strains (Escherichia coliand Staphylococcus aureus), revealing a modest activity. The binding mode of ligand 4a to Staphylococcus aureus (PDB ID − 3U2K) and Escherichia coli (PDB ID − 5Z4O) was investigated using an in-silico molecular docking technique, which revealed that the triazole ring and silanyl group are involved in hydrogen bonding with proteins and may be the cause of the ligand's antibacterial activity. The ligand 4a demonstrated a high affinity for binding within the active sites of proteins with binding energies of −7.97 kcal/mol (3U2K) and −8.68 kcal/mol (5Z4O).

Flapping motion as a fluorescent probe for assembly process involving highly viscous liquid-like cluster intermediates during evaporative crystallization.

Fluorescence probes are widely used to assess the molecular environment based on their photo-physical properties. Specifically, flexible and aromatic photo-functional system (FLAP) is unique viscosity probe owing to the excited-state planarization of anthracene wings. We have previously applied fluorescence spectroscopy to monitor the evaporative crystallization of solvents. The fluorescence color and spectral changes, which depend on the aggregation form, enable direct fluorescence visualization during evaporative crystallization. The fluorescence visualization of the liquid-like cluster intermediate proposed in the two-step nucleation model for the nucleation process has been achieved. However, the physical properties of these clusters, especially the viscosity, molecular motion, and intermolecular interactions, are still unclear. In this study, FLAPs are used as probes for local-viscosity changes and space limitations of the liquid-like cluster state during evaporative crystallization by observing the fluorescence-spectral changes and using hyperspectral-camera (HSC) imaging. Green emission originates from the monomer in the solution owing to the free-flapping motion. The fluorescence color turns blue with increasing viscosity under crowding conditions. If the survival time of the liquid-like cluster state is sufficient, crystalline phase (R-phase) formation proceeds via a 2-fold π-stacked array of the V-shaped molecules. It is difficult to form the V-shaped stacked columnar structures in the liquid-like cluster state region, resulting in the deposition of head-to-tail dimer structures, such as the yellow-emissive phase (Y-phase). In the case of the FLAP, the stacking intermediate does not form during solvent evaporation in the liquid-like cluster; rather, it is deposited in an amorphous form that exhibits blue emission (B-phase). These findings suggest that it is important to the maintenance of the survival time of the liquid-like cluster states to organize and rearrange the stacking forms. We have achieved the fluorescence probing of viscosity changes at local molecular motion with solvent depletion during solvent evaporation for the first time.

A Reliable Anti-Interference Probe Based on Fluorescence Intensity Ratio Technique for Cryogenic Temperature Detection

In this paper, a reliable anti-interference probe based on fluorescence intensity ratio technique is proposed for cryogenic temperature detection in refrigeration process, the sensing unit of which is based on a self-made coreless tellurite optical fiber (TOF) co-doped with Er <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3+</sup> /Yb <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3+</sup> ions. The temperature information was demodulated by analyzing the fluorescence spectral changes. In order to meet the needs of practical applications, the dual-curing method was applied to realize the TOF splicing, and the thin-walled silica tube was used to provide robust packaging. For the first time, the anti-cross-sensitive properties of the fluorescent probe under vibration and liquid interference were quantified, and the repeated response deviation was on the order of 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−5</sup> . The actual working capacity of the probe was experimentally investigated by applying it to measuring the circulating exhale and cryogenic equipment, in which a fast time response of about 2.11 s and a small absolute error of 0.80 K were obtained. The probe has good stability and repeatability, and can work stably even in complex environments with vibrations and liquids, showing strong anti-interference ability. In addition, the robust package and easy method make the probe suitable for mass fabrication.

Molecular logic with ferrocene-rylene conjugates: A comparison of naphthalenediimide, naphthalimide and perylenediimide Pourbaix sensor designs

Four molecules designed as Pourbaix sensors with rylene dyes (naphthalenediimide, 4-amino-1,8-naphthalimide, perylenediimide) are compared. Each molecule is constructed modularly according to an electron-donor–spacer–fluorophore–spacer–receptor format based on photoinduced electron transfer (PET). The modules consist of ferrocene as the electron donor, a tertiary alkyl amine as the proton receptor, and a rylene dye as the fluorophore connected by a methylene and ethylene spacer, respectively. The proton and oxidant-induced fluorescent spectral changes of the 4-amino-1,8-naphthalimide models include internal charge transfer (ICT) character. Two of the discussed logic gates switch on emitting fluorescence in the presence of acid (H+) and oxidant (Fe3+) according to two-input AND logic, while two of the logic gates remain off according to two-input PASS 0 logic.

Amino-coumarin-based colorimetric and fluorescent chemosensors capable of discriminating Co2+, Ni2+, and Cu2+ ions in solution and potential utilization as a paper-based device

New chemosensors, L1-L3, based on the coumarin Schiff base scaffold with substituent modifications, have been designed and synthesized. The chemosensors L1-L3 exhibited the absorbance and fluorescence spectral changes that can discriminate Co2+, Ni2+, and Cu2+ ions. Sensor L1 demonstrated the ability to respond to Co2+, Ni2+, and Cu2+ ions. Remarkably, the slight modification of substituent on L2 has been observed to cause selective binding to Ni2+ and Cu2+ ions while L3 can specifically detect Cu2+ ions. The in-situ formation of metal and ligand complexes was determined by Job’s plot analysis. The limit of detection and the sensing ability of all probes are estimated to be within the range of safe drinking water. Incorporation of the sensing compounds into a paper-based detection system using a laminated paper-based analytical device (LPAD) was demonstrated and found to be consistent to those obtained from the batchwise solution measurements.

Ratiometric fluorescence probe based on monochromatic dual-emission carbon nanodots with fluorescence spectral change

We report a monochromatic dual-emission carbon nanodot (CD) as an unusual ratiometric fluorescence probe. The CD exhibits fluorescence spectral change from monochromatic blue to green emission, which is induced by Fe(III) ions as well as hydroxyl radicals. The monochromatic fluorescence spectral change of CD is utilized for a ratiometric fluorescence assay distinguishing Fe(III) and Fe(II) in aqueous media.

An AIE-active probe for selective fluorometric–colorimetric detection of HSO3− in aqueous solution and real samples

We report herein a new biphenylcarbonitrile derivative, 4′-hydroxy-3′ -((2-imidazolylimino) methyl)-4-biphenyl carbonitrile (HIBC), which interestingly exhibits an aggregation-induced emission property. HIBC was employed for selective dual mode (fluorimetric and colorimetric) assay of HSO3− ions in nearly 100% aqueous medium at pH 7.4. The nucleophilic addition of HSO3− on the imino group in HIBC breaks its π-electron conjugation and results in a noticeable absorption and fluorescence spectral changes accompanied by a visible color change. Moreover, the formation of anionic addition product weakened the aggregation effect and meanwhile inhibited ESIPT process in HIBC, causing quenching of keto fluorescence of the probe. The probe shows good selectivity for HSO3− ions over all other competitive anions, which renders it a promising candidate for ratiometric fluorescent assay of HSO3− in aqueous systems. The limit of detection is 1.83 × 10−7 mol/L. For the practical applicability, handy paper strips were fabricated from HIBC for convenient recognition of HSO3−. Additionally, HIBC was applied for the living HeLa cells bio-imaging.

Naked-eye colorimetric and turn-on fluorescent Schiff base sensor for cyanide and aluminum (III) detection in food samples and cell imaging applications

A new efficient Schiff base sensor SB3 for fluorescent and colorimetric “naked-eye” “turn-on” sensing of cyanide anion (CN–) with excellent sensitivity and selectivity was developed. The 4,4'-(perfluoropropane-2,2-diyl)bisphenol group and two phenyl groups were covalently linked by two C = N bonds to extend the conjugation length. The four hydroxyl groups can improve the water solubility of the SB3 sensor. The SB3 sensor exhibited high specificity towards CN− by interrupting its intramolecular charge transfer, resulting in a color change and remarkable “turn-on” green fluorescence emission. The sensing mechanism is caused by the nucleophilic addition of CN– toward imine groups of the SB3 sensor, leading to breaks of the conjugation, fluorescent spectral changes, and color change. It was confirmed by 1H NMR titration and Mass spectra. The detection limits for CN– and Al3+obtained by fluorescence spectrum are 0.80 µM and 0.25 µM, respectively. The SB3 sensor can act as an efficient chemical sensor for detecting the CN– and Al3+ ions under common environmental and physiological conditions (pH 5–12). Besides, the sensor can also detect CN− in food materials (such as sprouting potatoes and cassava flour) and imaging CN−in living cells with strong “turn-on” fluorescence at 490 nm. SB3 is an excellent CN– sensor that exhibits some advantages, including easy synthesis, distinct fluorescence and color change, high selectivity, low detection limit, and good anti-interference ability to analyze solution and food samples, together with fluorescence cell imaging.

Visual sensing of formaldehyde via a solution-to-gel transition with cholesteryl naphthalimide-based derivatives

It is relevant for individual and public health security to develop a simple protocol for visual sensing of formaldehyde (FA). Herein, two cholesteryl naphthalimide-based derivatives (1a and 1b) were developed to be FA chemosensors with a hydrazine group as the receptor based on Schiff-base reaction. These two compounds were found to be organogelators for several organic solvents. Besides, either 1a or 1b in DMSO could be used to determine FA in an aqueous solution via fluorescence spectral changes with relatively low detection limits. More interestingly, FA could trigger gelation of the DMSO solutions of gelator 1a in a high gelator concentration. However, 1b failed to have such behaviour. The easy-to-visualize solution-to-gel transition in combination with quantitatively fluorescent detection leads us to propose that 1a and related systems could have a role play analyzing FA either in an aqueous solution or in air. Furthermore, this is the first instance ever of a chemosensor using such a sensing mode for FA.

Facile synthesis of carbon dots from Tagetes erecta as a precursor for determination of chlorpyrifos via fluorescence turn-off and quinalphos via fluorescence turn-on mechanisms

Convenient one-pot synthetic route for the fabrication of carbon dots (CDs) from Tagetes erecta flower (TEF), named as “TEF-CDs’, through solvo(hydro)-thermal carbonization of the TEF was developed. The TEF-CDs revealed high selectivity towards chlorpyrifos and quinalphos, acting as a fluorescent probe. The CDs synthesized from T. erecta flower showed a strong blue color at 495 nm when excited at 420 nm, along with the exhibition of a strong quantum yield of 63.7%. The synthesized CDs revealed their richness in the surface-active organic group that synthesized CDs from T. erecta flower are mainly comprised of C, O, and N, which were crystalline in structure that was revealed by TEM image and XRD spectra. Furthermore, when the probe was exposed to different pH conditions, no major noticeable changes were recorded. Moreover, when the probe was exposed to chlorpyrifos and quinalphos, we have noticed that fluorescence spectra was turned off when the probe was exposed to chlorpyrifos and “turned on” after the exposure quinalphos. Moreover, fluorescence spectral changes showed a good linearity with chlorpyrifos and quinalphos concentrations in the range of 0.05–100.0 μM for chlorpyrifos and 0.01–50.0 μM for quinalphos. The limit of detection are 2.1 ng mL−1 and 1.7 ng mL−1 for chlorpyrifos and quinalphos, respectively. Finally, the TEF-CDs-based fluorescent nanoprobe was successfully applied to estimate chlorpyrifos and quinalphos with an effective accuracy in rice and fruit samples with rapid detection time.

Colorimetric “off–on” fluorescent probe for selective detection of toxic Hg2+ based on rhodamine and its application for in-vivo bioimaging

A novel “turn on” fluorimetric sensor 1-benzyl-N-(3',6'-bis(ethylamino)-2',7'-dimethyl-3-oxospiro[isoindoline-1,9'-xanthen]-2-yl)-7-hydroxy-5-oxo-1,2,3,5-tetrahydroimidazo[1,2-a]pyridine-8-carboxamide (RhB) based on rhodamine moiety has been designed and synthesized. The cation sensing ability of RhB was examined and validated using UV–visible, fluorescence, and NMR spectral studies. The probe RhB exhibits selective and sensitive sensing towards Hg2+ over the other competitive metal cations like Ag+, Al3+, Ba2+, Cu2+, Cd2+, Fe3+, Fe2+, K+, Li+, Mg2+, Mn2+, Pb2+, Ni2+, Na+, Zn2+ in EtOH:HEPES buffer solution (1:1, v/v) medium and a rapid 1:1 stoichiometric irreversible reaction were obtained between RhB and Hg2+. The UV–vis and fluorescence spectral changes suggest the effectiveness of the probe and the rapid response of RhB towards Hg2+ could be due to the formation of the coordinate bond between the ligand and metal. The spirolactam ring opening followed by the formation of suitable coordinate geometry in the RhB is the reason for the selective sensing of Hg2+ ion. NMR titration experiments further confirmed this. The binding constant was calculated by the B-H plot and found to be 4.0 × 109 M−1. The LOD for UV–vis and fluorescencebased detection was found to be 2.57 µM (0.516 mg L−1). Likewise, an economically feasible, easy-to-use test strips of RhB was developed for the naked-eye detection of Hg2+ in 100% aqueous solution. However, it was found to be much less sensitive than the spectrophotometric method. Further, in vivo experiments were performed using Drosophila melanogaster that led to demonstrate its efficacy at identifying mercury toxicity within an organism.