Fluorescent Polyamide-Based Rhodamine Hydrazide Moieties with Oxethyl as Spacer for Detection of Cr3+, Fe3+, and Hg2+ Ions in Water

Diaminonaphthalene functionalized LUS-1 as a fluorescence probe for simultaneous detection of Hg2+ and Fe3+ in Vetiver grass and Spinach

One of the important problems in the environment is heavy metal pollution, and fluorescence is one of the best methods for their detection due to its sensitivity, selectivity, and relatively rapid and easy operation. In this study, 1,8-diaminonaphthalene functionalized super-stable mesoporous silica (DAN-LUS-1) was synthesized and used as a fluorescence probe to identify Hg2+ and Fe3+ in food samples. The TGA and FT-IR spectra illustrated that 1,8-diaminonaphthalene was grafted into LUS-1. XRD patterns verified that the LUS-1 and functionalized mesoporous silica have a hexagonal symmetrical array of nano-channels. SEM images showed that the rod-like morphology of LUS-1 was preserved in DAN-LUS-1. Also, surface area and pore diameter decreased from 824 m2 g⁻1 and 3.61 nm for the pure LUS-1 to 748 m2 g⁻1 and 3.43 nm for the DAN-LUS-1, as determined by N₂ adsorption-desorption isotherms. This reduction demonstrated that 1,8-diaminonaphthalene immobilized into the pore of LUS-1. The DAN-LUS-1 fluorescence properties as a chemical sensor were studied with a 340/407 nm excitation/emission wavelength that was quenched by Hg2+ and Fe3+ ions. Hg2+ and Fe3+ were quantified using the fluorescence response in the working range 8.25-13.79 × 10-6 and 3.84-10.71 × 10-6 mol/L, with detection limits of 8.5 × 10-8 M and 1.3 × 10-7 M, respectively. Hg2+ and Fe3+ were measured in vetiver grass and spinach. Since the Fe3+ quenching can move in the opposite direction with sodium hexametaphosphate (SHMP) as a hiding compound for Fe3+, consequently, the circuit logic system was established with Fe3+, Hg2+, and SHMP as inputs and the fluorescent quench as the output.

An indolino-spironaphthooxazine probe for colorimetric detection of ferric ions in drinking water

The sensing performance of a novel indolino-spironaphthooxazine derivative (SPNO), 6′(3,4-dihydroisoquinolin-2(1H)-yl)-3,3-dimethyl-1-phenethylspiro[indoline-2,3′-naphtho[2,1-b][1,4]oxazine], was investigated for rapid colorimetric detection of ferric ions (Fe³⁺) in drinking water.

Novel dual-functional fluorescent sensors based on bis(5,6-dimethylbenzimidazole) derivatives for distinguishing of Ag+ and Fe3+ in semi-aqueous medium

Three novel bisbenzimidazole derivatives have been synthesized and developed as dual-functional fluorescent sensors for the rapid and highly selective detection of Ag⁺ and Fe³⁺ ions in semi-aqueous medium with distinct spectral response for the first time. The absorption intensity is drastically decreased after the addition of Ag⁺. Contrarily, it is markedly increased upon the addition of Fe³⁺. And there is a good linear relation at low concentration of both Ag⁺ and Fe³⁺, which provides a quantitative method for their detection. Similarly, the sensors show a distinct fluorescence response towards Ag⁺ and Fe³⁺ with a different fluorescence color change under UV light. In addition, no significant changes and interference can be observed with other metal ions. The sensing mechanism studies confirm that the N atom in CN of benzimidazole ring of sensor 4a may bind with Ag⁺ or Fe³⁺ ion to form metal complex. And there is only a static quenching process for the 4-Ag⁺ complex system, but both dynamic and static quenching processes occur in the 4-Fe³⁺ complex system. Moreover, sensors 4 can steadily work in solution with a wide range of pH 4-13 and rapidly respond to Ag⁺ and Fe³⁺ with a response time of 10 s. Finally, the sensors have been successfully applied to the visual detection of Ag⁺ and Fe³⁺ not only in solution, but also in test paper.

Peptide nucleic acid as a selective recognition element for electrochemical determination of Hg2

A novel electrochemical PNA-based biosensor for the determination of Hg²⁺ is described. The receptor layer, containing single strands of polythymine PNA (peptide nucleic acid), was formed at the surface of gold electrode. Due to the presence of thymine bases and peptide bonds, an interaction between Hg²⁺ ion and receptor layer occurs. The influence of chain modification - PNA vs. DNA - and type of redox marker - anionic AQMS-Na (sodium salt of anthraquinone-2-sulfonic acid) and Fe^II/III (potassium ferri/ferrocyanide) or cationic MB (methylene blue) and RuHex (hexaammineruthenium(III) chloride) - were studied. Proposed PNA-based biosensor with anionic AQMS-Na as a redox marker demonstrated significantly better analytical parameters, as compared to results obtained for other tested redox markers (for measurements at pH6.0). The linear response towards Hg²⁺ was in the range from 5 to 500nmol·L^-1 with the detection limit of 4.5nmol·L^-1. The developed sensor distinguishes itself with high selectivity towards Hg²⁺, even for solutions containing several interfering cations. Interactions between Hg²⁺ and PNA receptor layer were studied using square wave voltammetry (SWV) and electrochemical impedance spectroscopy (EIS).