Binding mode dependent signaling for the detection of Cu2+: An experimental and theoretical approach with practical applications

Relay detection of Cu2+ and bovine serum albumin by a dansyl derivative-based fluorescent probe

A dansyl derivative-based fluorescent probe, namely, DGly, was developed for relay detection of Cu²⁺ and bovine serum albumin (BSA) with high selectivity and sensitivity. The fluorescence intensity of DGly at 540 nm displayed "on-off-on" phenomenonafter Cu²⁺ and BSA were added in sequence. Correspondingly, the solution color changed from yellow to dark and then to yellowish white under 365 nm UV light irradiation; thus, the solution could be detected by the naked eye. The association constant of DGly-Cu²⁺ was stronger than that of DGly-BSA and DGly-Cu²⁺-BSA. Hence, BSA was detected after a complex was formed between DGly and Cu²⁺. The relay detection of Cu²⁺ and BSA was not influenced by other competitive interferents, and the detection limits of Cu²⁺ and BSA were 1.32 and 0.26 μM, respectively. Analysis of Cu²⁺ in real water samples validated the detection performance of the method proposed herein; it achieved satisfactory recovery and relative standard deviation values. This work demonstrated that introducing metal ions can be an effective way to improve the sensitivity of BSA detection.

A "Turn-On" fluorescent probe for detection and removal of Zn2+ in aqueous and its application in living cells

Using 3-hydroxy-2-naphthoic acid hydrazine and 4-(diethylamino) salicylaldehyde. as raw materials, compound L with an acylhydrazones structure was synthesized. The structure of compound L was characterized by nuclear magnetic resonance spectroscopy, X-ray single crystal diffraction, Fourier transform infrared spectroscopy, and mass spectrometry. The results show that Compound L can quickly and selectively recognize zinc ions in the H₂O/DMSO (V:V = 3:7) solvent system. After that, the spectral performance of probe L was studied by fluorescence spectroscopy and UV-vis spectroscopy. The results show that the combination with Zn²⁺ can significantly enhance the fluorescence intensity of probe L while being almost unaffected by other coexisting ions. After that, Job's curve method, nuclear magnetic titration analysis, and mass spectrometry were used to study the binding mechanism of probe L and Zn²⁺. The results showed that probe L coordinated with Zn²⁺ is 1:1. The linear equations of different concentrations of Zn²⁺ and fluorescence intensity were obtained by fitting, and the detection limit of probe L for Zn²⁺ was determined to be 6.75 × 10^-9 mol/L. The experimental study of standard addition and recovery showed that probe L could be used for the quantitative detection of Zn²⁺ in natural water samples. After that, we prepared L-doped sodium alginate hydrogel (SAL). The research results show that SAL has obvious adsorption capacity for Zn²⁺ in solution, and the color change before and after adsorption can be easily distinguished by the naked eye under ultraviolet light. SEM-EDS study showed that the microscopic morphology and composition of SAL changed significantly before and after adsorption. This fluorescent probe can be used for detection and removal of Zn²⁺ in aqueous solution. Also, probe L is effective for sensing for zinc (II) in living tumor cells. Overall, this work allows us to obtain a great potential to be applied to detect and remove Zn²⁺.

A Novel Quinoline Derivative for Selective and Sensitive Visual Detection of PPB Level Cu2+ in an Aqueous Solution

Aim:

Selective and sensitive visual detection of Cu2+in aqueous solution at PPB level using easily synthesized compound.

Background:

The search for a chemosensor that can detect Cu2+ is very long owing to the fact that an optimum level of Cu2+ is required for human health and the recommended amount of Cu2+ in drinking water is set to be 1-2 mgL-1 . Thus, it is very important to detect Cu2+ even at a very low concentration to assess the associated health risks.

Objective:

We are still seeking for the easiest, cheapest, fastest and greenest sensor that can selectively, sensitively and accurately detect Cu2+ with lowest detection limit. Our objective of this work is to find one such Cu2+ sensor.

Methods:

We have synthesized a quinoline derivative following very easy synthetic procedures and characterize the compound by standard methods. For sensing study, we used steady state absorption and emission spectroscopy.

Results:

Our sensor can detect Cu2+ selectively and sensitively in aqueous solution instantaneously even in the presence of excess amount of other salts. The pale-yellow color of the sensor turns red on the addition of Cu2+ . There is no interference from other cations and anions. A 2:1 binding mechanism of the ligand with Cu2+ is proposed using Jobs plot with binding constant in the order of 109 M-2 . We calculated the LOD to be 18 ppb, which is quite low than what is permissible in drinking water.

Conclusion:

We developed a new quinoline based chemo-sensor following straightforward synthetic procedure from very cheap starting materials that can detect Cu2+ visually and instantaneously in aqueous solution with ppb level sensitivity and zero interference from other ions.

Low cost, high sensitivity detection of waterborne Al3+ cations and F- anions via the fluorescence response of a morin derivative dye

Morin dye is known as a cheap and readily available selective 'off → on' fluorescent sensitiser when immobilised in a phase transfer membrane for the detection of Al³⁺ ions. Here, a morin derivative, NaMSA, which readily dissolves in water with good long-term stability is used in conjunction with a fibre optic transducer with lock-in detection to detect Al³⁺ in drinking water below the potability limit. The combination of a water soluble dye and the fibre optic transducer require neither membrane preparation nor a fluorescence spectrometer yet still display a high figure-of- merit. The known ability to recover morin-based Al³⁺ cation sensors selectively by exposure to fluoride (F^-) anions is further developed enabling a complementary sensing of either fluoride anions, or aluminium cations, using the same dye with a sub-micromolar limit-of-detection for both ions. The sensor performance parameters compare favourably to prior reports on both aqueous aluminium and fluoride ion sensing.

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.

Thiazoline-pyrene selective and sensitive fluorescence "turn-on" sensor for detection of Cu2

A thiazoline and pyrene containing sensor 1 was synthesized via one-pot reaction and utilized as a highly selective and sensitive fluorescence "turn-on" sensor for Cu²⁺ detection, via the fluorescence enhancement of pyrene monomer emission. The 2:1 stoichiometry of 1 and Cu²⁺ was calculated from Job's plots based on fluorescent titrations, and the complexation of 1 with Cu²⁺ was also supported by mass spectra, Fourier transform infrared spectra, proton NMR spectra and density functional theory analysis. The fluorescence intensity of 1 at 389 nm and 410 nm increased significantly upon the addition of Cu²⁺. Limit of detection and association constant value of 1-Cu²⁺ were calculated using standard deviations and linear fittings, respectively. Results showed that 1 was active for Cu²⁺ detection in the wide pH range of 2.0-11.0.