A BODIPY derivative for colorimetric fluorescence sensing of Hg2+, Pb2+ and Cu2+ ions and its application in logic gates

Dual detection of Hg2+ and Pb2+ by a coumarin-functionalized Schiff base in environmental and biosystems

Fluorescent chemosensors are often preferred for tracking toxic ions because of their non-destructive measurement and ease of use in environmental real samples and biosystems. Exploring high selectivity, great sensitivity, and biocompatible fluorophores with facile, accessible and dual-responsive features is currently highly demanding. A coumarin-based naphthol hydrazone Schiff base chemosensor, NaChro, is designed and synthesized in a two-step process to detect toxic metal ions with strong emission. Fluorescence spectra analysis demonstrates that the probe binds to Hg2+ and Pb2+ ions with a 1:1 and a 2:1 stoichiometry, respectively, with high sensitivity, short response time and minimal interference from other metal ions. The observed reversible turn-on reaction was attributed to the inhibition of C = N isomerization and excited-state intramolecular proton transfer (ESIPT) processes once the ions were introduced. The practical applications of NaChro are successfully addressed in paper strips, various water samples, HeLa cells and Zebrafish, demonstrating that the probe can detect and track Hg2+ and Pb2+ ions in environmental samples and biosystems.

A highly sensitive triazole-based perfectly water soluble novel bis-Schiff base reversible fluorescent-colorimetric chemosensor for fast detection of Pb2+ ions

A reversible fluorescent-colorimetric azino bis-Schiff base receptor for the detection of Pb2+ in aqueous medium has been developed for the first time. Receptor L exhibits an excellent selective and rapid fluorescent-colorimetric response towards Pb2+. The sensitivity of the fluorescent-based assay (0.53 nM) and colorimetric assay (1.0 nM) for Pb2+ is sufficiently good in comparison to previously reported literature. From 1H NMR data, Job plot measurement and the ESI-MS spectrum, a 1 : 2 stoichiometric complexation between L and Pb2+ has been established. Receptor L shows a remarkable detection ability in a wide pH range of 4-8 and it has been successfully utilised in the determination of Pb2+ in aqueous solution of bovine serum albumin protein and in real samples. The geometry of L has been optimized by both DFT studies and NMR, FTIR and mass spectra. Moreover, we have studied molecular docking of the probe L.

A visible BODIPY-based sensor for 'Naked-Eye' recognition of Ag+ and its application on test paper strips

In this study, a novel, highly sensitive fluorescent sensor (E)-2-((2-(benzo[d] thiazol-2-yl) quinolin-8-yl) oxy)-N'-(4-(5, 5-difluoro-1, 3, 7, 9-tetramethyl-5H-4λ4, 5λ4-dipyrrolo [1, 2-c:2', 1'-f] [1, 3, 2] diazaborinin-10-yl) benzylidene) acetohydrazide (TQB) was developed for dual mode of Ag+ detection (colorimetric/fluorescence), and its structural and spectral properties were characterized by 1H NMR, ESI-MS, X-ray, ultraviolet and fluorescence photometry. It is found that TQB could specifically and efficiently identify Ag+ among many other metal ions in CH3OH/H2O (7:3 v/v, pH = 7.23) buffer. The maximum absorption wavelength of TQB is red-shifted while its fluorescence is quenched with a quenching rate of 88.7%. The energy difference between TQB and TQB-Ag+ complex was calculated by DFT, and the applicability of TQB was verified by paper strip test. In addition, TQB has been successfully applied to the determination of Ag+ in real water samples with good reversibility and recoveries.

A new benzothiazole azo dye colorimetric chemosensor for detecting Pb2+ ion

In this work, a new benzothiazole azo dye sensor (BTS) was synthesized, and its cation binding affinity was studied using the colorimetric method, UV-vis, and ¹H NMR spectral data. The results revealed that the sensor BTS exhibits a remarkable tendency for Pb²⁺ ion to perform spontaneous visual color change from blue (BTS) to pink (BTS + Pb²⁺), without any color change in the aqueous solutions of other cations such as Hg²⁺, Cu²⁺, Al³⁺, Ni²⁺, Cd²⁺, Ag⁺_, Ba²⁺, K⁺, Co²⁺, Mg²⁺, Na⁺, Ca²⁺, Fe²⁺, and Fe³⁺ ions. The observed selectivity could be due to the formation of the complex (BTS + Pb²⁺⁾, which led to a blue shift from 586 nm (BTS) to 514 nm (BTS + Pb²⁺) in the UV spectrum. The job's plot provided the stoichiometry ratio of the complex (BTS + Pb²⁺) to be 1:1. The limit of detection (LOD) of BTS for Pb²⁺ ion sensing was obtained at 0.67 µM. Additionally, the binding constant for BTS toward Pb ²⁺ ion was studied using the Benesi-Hildebrand equation. As a result of the BTS test paper strips investigations, it was found that the synthesized sensor BTS could be used as a rapid colorimetric chemosensor for the detection of the Pb²⁺ ions in the distilled, tap, and sea waters.

Photophyical and photosensitizing properties of BODIPYs substantially changed by alkyl- and phenyl-amino groups on meso carbon

meso-RNH (R = C₃H₇, C₄H₉, PhCH₂, H, and Ph) substituted BODIPY compounds have been prepared to examine their photophysical properties and photosensitizing abilities. We have measured the UV-vis absorption, steady state and time resolved fluorescence, excited triplet state formation using laser flash photolysis, singlet oxygen generation ability using chemical trapping method. The results show that the presence of meso-RNH leads to large blue shift of absorption and emission wavelength, remarkable decrease in fluorescence quantum yield and lifetime values, and significant increase in singlet oxygen formation quantum yield. Quantum chemical calculation also reveals the photoinduced charge transfer (PCT) mechanism. We conclude that property changes are due to: 1) S₀ and S₁ geometry, 2) ground state structural isomerization, and 3) intramolecular PCT. These results and mechanisms are helpful for designing new functional materials.

Synthesis and Photophysics Characterization of Boronic Styril and Distyryl BODIPYs for Water-Based Dye-Sensitized Solar Cells

In this study, two boronic acid BODIPYs are obtained through a microwave-assisted Knoevenagel reaction. The aim is to use them for the first time as dyes in a photosensitized solar cell (DSSC) to mimic chlorophyll photosynthesis, harvesting solar light and converting it into electricity. The microwave-assisted Knoevenagel reaction is a straightforward approach to extending the molecular conjugation of the dye and is applied for the first time to synthesize BODIPY’s boronic acid derivatives. These derivatives have proved to be very useful for covalent deposition on titania. This work studies the photo-physical and electrochemical properties. Moreover, the photovoltaic performances of these two new dyes as sensitizers for DSSC are discussed. Experimental data show that both dyes exhibit photosensitizing activities in acetonitrile and water. In particular, in all the experiments, distyryl BODIPY was more efficient than styryl BODIPY. In this study, demonstrating the use of a natural component as a water-based electrolyte for boronic BODIPY sensitizers, we open new possibilities for the development of water-based solar cells.

A spectroscopic probe for hypochlorous acid detection

A spectroscopic probe CMBT was synthesized and characterized. CMBT showed the specific recognition for HClO based on the turn-on blue fluorescence and naked-eye change from pink to colorless. NMR, IR, HRMS-ESI, and spectral analysis suggested that colorimetric and fluorescent change of CMBT to HClO originated from the conversion of CMBT to starting material coumarin-aldehyde 1 caused by the oxidization of HClO, which was responsible for the fluorescence recovery. The detection limit was calculated to be 1.61 μM and 6.58 μM for fluorescence and UV-vis analysis with a range up to 1 mM. HClO's fluorescence detection was successfully achieved in tap and river water samples. The prepared convenient paper test strips showed a distinct color change in varying concentrations of HClO. A multi-input molecular logic circuit was constructed.

Interfacially Super-Assembled Benzimidazole Derivative-Based Mesoporous Silica Nanoprobe for Sensitive Copper (II) Detection and Biosensing in Living Cells

Mesoporous silica nanoparticles (MSNs) functionalized with benzimidazole-derived fluorescent molecules (DHBM) are fabricated via a feasible interfacial superassembly strategy for the highly sensitive and selective detection of Cu²⁺ . DHBM-MSN exhibits an obvious quenching effect on Cu²⁺ in aqueous solutions, and the detection limit can be as low as 7.69×10^-8  M. The DHBM-MSN solid-state sensor has good recyclability, and the silica framework can simultaneously improve the photostability of DHBM. Two mesoporous silica nanoparticles with different morphologies were specially designed to verify that nanocarriers with different morphologies do not affect the specific detectionability. The detection mechanism of the fluorescent probe was systematically elucidated by combining experimental results and density function theory calculations. Moreover, the detection system was successfully applied to detect Cu²⁺ in bovine serum, juice, and live cells. These results indicate that the DHBM-MSN fluorescent sensor holds great potential in practical and biomedical applications.

A Pyrazolo Imine-based Colorimetric and Turn-on Fluorescent Sensor Probe for Determination of Hg2+ Ion and its Application in Test Paper Strips

In this work, we synthesized diethylamino substituted pyrazolo imine (3) fluorescent probe for recognition of Hg²⁺ ion.The sensor probe 3 can detect Hg²⁺ by colorimetric method, and there is a 10-fold enhancement in fluorescence response. When the fluorescent probe bound with Hg²⁺ ion, turn-on fluorescence was observed via the coordination. Probe 3 has an excellent selectivity toward Hg²⁺ in the CH₃ CN/H₂ O (8:2, v/v) solution with low limit of detection and high binding association constant of 551 parts per billion (ppb) and 6.6067 × 10⁶  m^-1 for 3+Hg²⁺ , respectively. Furthermore, the formation of 3+Hg²⁺ complex with 1:1 binding mode was evidenced by Job's plot, ¹ H NMR spectroscopy and Mass analysis. In addition, probe 3 is a feasible option to detect Hg²⁺ in various sources of water samples. Bio-imaging experiments have demonstrated that probe 3 can be used to monitor Hg²⁺ in Escherichia coli bacterial cell. The sensor 3 was also used for paper strip application to detect Hg²⁺ ion.

Highly Sensitive and Selective Spiropyran-Based Sensor for Copper(II) Quantification

The metal-binding capabilities of the spiropyran family of molecular switches have been explored for several purposes from sensing to optical circuits. Metal-selective sensing has been of great interest for applications ranging from environmental assays to industrial quality control, but sensitive metal detection for field-based assays has been elusive. In this work, we demonstrate colorimetric copper sensing at low micromolar levels. Dimethylamine-functionalized spiropyran (SP1) was synthesized and its metal-sensing properties were investigated using UV-vis spectrophotometry. The formation of a metal complex between SP1 and Cu²⁺ was associated with a color change that can be observed by the naked eye as low as ≈6 μM and the limit of detection was found to be 0.11 μM via UV-vis spectrometry. Colorimetric data showed linearity of response in a physiologically relevant range (0-20 μM Cu²⁺) with high selectivity for Cu²⁺ ions over biologically and environmentally relevant metals such as Na⁺, K⁺, Mn²⁺, Ca²⁺, Zn²⁺, Co²⁺, Mg²⁺, Ni²⁺, Fe³⁺, Cd²⁺, and Pb²⁺. Since the color change accompanying SP1-Cu²⁺ complex formation could be detected at low micromolar concentrations, SP1 could be viable for field testing of trace Cu²⁺ ions.

A Heterocyclic-based Bifunctional Sensor for Detecting Cobalt and Zinc Ion

A new bifunctional chemosensor HBP ((E)-2-(2-((5-bromopyridin-2-yl)methylene)hydrazinyl) quinoline) based on heterocyclic compounds was designed and studied. The HBP showed successful detecting ability toward cobalt ion with a UV-visible red-shift and a color change of colorless to pink. Moreover, toward zinc ion, the HBP showed an obvious fluorescence turn-on response. The binding ratio of the HBP to cobalt and zinc was a 2 to 1 for both ions. The detection limits were found to be 10 nM for Co2+ and 18 nM for Zn2+. Based on UV-vis and fluorescent spectral variations, Job plots, ESI-MS, FT-IR and calculations, the binding mechanisms of the HBP toward cobalt and zinc ions were proposed.

A novel “turn-on” fluorescent probe based on naphthalimide for the tracking of lysosomal Cu2+ in living cells

The lysosome-targeted probe CuNI exhibits highly effective fluorescence detection ability for Cu²⁺ in aqueous solution and cells. The fluorescent enhancement is due to the Cu²⁺-catalyzed hydrolysis of CuNI and the AIE effect of the hydrolysate MFNI.

Coumarin-based Hg2+ fluorescent probe: Fluorescence turn-on detection for Hg2+ bioimaging in living cells and zebrafish

The need in developing fluorescent probes for trace metal ion detection in biological samples has been an important issue. Herein, a reaction-based fluorescent probe PIC containing a perimidine moiety was designed and synthesized for Hg²⁺ detection. The probe can selectively distinguish Hg²⁺ with 42-fold fluorescent enhancement from the other metal ions at physiological pH. This probe can detect Hg²⁺ with the detection limit of 1.08 μM. The sensor PIC can be applied to real-time detection of Hg²⁺ in cells with blue emission.

Low Molecular Weight Fluorescent Probes (LMFPs) to Detect the Group 12 Metal Triad

Fluorescence sensing, of d-block elements such as Cu2+, Fe3+, Fe2+, Cd2+, Hg2+, and Zn2+ has significantly increased since the beginning of the 21st century. These particular metal ions play essential roles in biological, industrial, and environmental applications, therefore, there has been a drive to measure, detect, and remediate these metal ions. We have chosen to highlight the low molecular weight fluorescent probes (LMFPs) that undergo an optical response upon coordination with the group 12 triad (Zn2+, Cd2+, and Hg2+), as these metals have similar chemical characteristics but behave differently in the environment.

Triazole-based novel bis Schiff base colorimetric and fluorescent turn-on dual chemosensor for Cu2+ and Pb2+: application to living cell imaging and molecular logic gates

A triazole-based novel bis Schiff base colorimetric and fluorescent chemosensor (L) has been designed, synthesized and characterized by elemental analysis, ¹H-NMR, ESI-MS, FTIR spectra and DFT studies. The receptor L showed selective and sensitive colorimetric sensing ability for Cu²⁺ and Pb²⁺ ions by changing color from colorless to yellow and light yellow respectively in CH₃OH–tris-buffer (1 : 1, v/v). However, it displayed strong fluorescence enhancement upon the addition of both Cu²⁺ and Pb²⁺ ions, attributed to the blocking of PET. The fluorometric detection limits for Cu²⁺ and Pb²⁺ were found to be 12 × 10⁻⁷ M and 9 × 10⁻⁷ M and the colorimetric detection limits were 3.7 × 10⁻⁶ M and 1.2 × 10⁻⁶ M respectively; which are far below the permissible concentration in drinking water determined by WHO. Moreover, it was found that chemosensor L worked as a reversible fluorescence probe towards Cu²⁺ and Pb²⁺ ions by the accumulation of S²⁻ and EDTA respectively. Based on the physicochemical and analytical methods like ESI-mass spectrometry, Job plot, FT-IR, ¹H-NMR spectra and DFT studies the detection mechanism may be explained as metal coordination, photoinduced electron transfer (PET) as well as an internal charge transfer (ICT) process. The sensor could work in a pH span of 4.0–12.0. The chemosensor L shows its application potential in the detection of Cu²⁺ and Pb²⁺ in real samples, living cells and building of molecular logic gate.

A novel triazole-based bis Schiff base colorimetric and fluorescent chemosensor (L) has been designed, synthesized and characterized. The chemo-sensor L shows its application potential in the detection of Cu²⁺ and Pb²⁺ in living cells and building molecular logic gate.

Bodipy-based chemosensors for highly sensitive and selective detection of Hg2+ ions

Small molecular chemo-sensors with strong fluorescence were designed and synthesized. Then, corresponding macromolecular sensors were synthesized by introducing the as-prepared small molecular sensors. The macromolecular chemo-sensors not only retained their sensing ability, but also enhanced the sensing ability dramatically.

Gly–Gly–His tripeptide- and silver nanoparticle-assisted electrochemical evaluation of copper(ii) ions in aqueous environment

A sensitive and selective electrochemical sensor for Cu²⁺ assay is developed using tripeptide-based recognition and silver nanoparticle-modified electrode.