The development of sensors and receptors for biologically important anions is currently of great interest because of their indispensable roles in vital (or physiological) processes. Among the anions, fluoride ions are one of the most attractive targets because of their considerable significance for health and environmental issues. As an essential element of the body, the U.S. Public Health Service affirmed the optimal level to be 1 mg of consumed fluoride per day. On the other hand, unnecessary and inappropriate fluoride ingestion can result in fluorosis, urolithiasis, or even cancer. The EPA (United States Environmental Protection Agency) gives an enforceable drinking water standard for fluoride of 4 mg L 1 to prevent osteofluorosis and a secondary fluoride standard of 2 mgL 1 to protect against dental fluorosis. Hence, the accurate determination of the levels of fluoride in drinking water is necessary. To date, the ion-selective electrode, ion chromatography, and standard Willard and Winter methods are generally used for quantitative fluoride analysis. However, all these methods involve disadvantages, such as complicated procedures, high costs, or low mobility. Therefore, it is important to develop highly selective, sensitive, convenient, and rapid fluoride detection methods. Fluorescent chemosensors with high specificity and sensitivity, ease, and safety of handling have received considerable attention, and a number of fluorescence sensors have been reported that are capable of detecting fluoride ions. The recognition proceeded mostly through hydrogen bonding or Lewis acid coordination, and the sensors could only be operated in organic solvents to detect tetrabutylammonium (TBA) fluoride rather than inorganic fluoride salts. This incompatibility with aqueous environments is one of the main drawbacks that restrict the application of these sensors. Unavoidable interference from H2PO4 , AcO , or CN ions is the other disadvantage. To improve the performance of fluoride sensors, another strategy based on the chemical affinity between fluoride and silicon was developed. tertButyldimethylsilyl (TBDMS) and tert-butyldiphenylsilyl (TBDPS) were chosen as additional substituents for the dye molecule, and rendered the dye unreactive to potentially interfering compounds and thus sensitive only to fluoride ions. This approach was pioneered by Kim and Swager, who developed a fluorescent fluoride receptor in organic solvents. Subsequently, several research groups reported different chemodosimeters that can probe NaF in mixtures of organic solvents and water or even pure water. However, several tens of minutes or even hours are needed to complete the detection process because low concentrations of these chemodosimeters severely reduce the reaction rate between the fluoride ions and the silyl moieties. However, the low concentration is necessary for general organic dyes to avoid fluorescence quenching induced by concentration effects, such as self-absorption and self-quenching. To date, most fluorescent sensors were based on the specific fluoride ion dependence of the emission intensity and could be significantly influenced by the excitation power and the detector sensitivity. More importantly, fluorescence intensity changes are not suitable for direct observation with the naked eye. To develop a more convenient fluorescence sensor, it is essential to make use of other fluoridedependent measurable signals other than intensity. The fluorescence color change, which can be measured directly with a colorimeter or even distinguished easily by eye, is thus a good choice. Herein we describe a rapid and portable sensor for fluoride ions in aqueous solution. The sensor, which has a high sensitivity, operates through the special affinity between fluoride ions and silicon, and provides two independent modes of signal transduction based on fluoride-dependent changes of fluorescence color (color metric mode) or intensity (power metric mode), respectively. For the design of the sensor, we chose N-(3-(benzo[d]thiazol-2-yl)-4-(hydroxyphenyl) benzamide (3-BTHPB) as an excited-state intramolecular proton transfer (ESIPT) compound. Just like other ESIPT compounds, 3-BTHPB shows two emission bands, which originate from the enol and keto forms at 418 and 560 nm, respectively. The ratio of the two bands is determined by the number of molecules that could undergo ESIPT reactions. We coupled the tert-butyldiphenylchlorosilane with the sodium salt of 3-BTHPB to afford a derivative N-(3(benzo[d]thiazol-2-yl)-4-(tert-butyldiphenyl silyloxy)phenyl)benzamide (BTTPB). As expected, BTTPB shows only blueviolet fluorescence, which was almost identical to the emission of the enol form of 3-BTHPB (see the Supporting [*] R. Hu, J. Feng, D. H. Hu, Dr. S. Q. Wang, Dr. S. Y. Li, Prof. Dr. G. Q. Yang Beijing National Laboratory for Molecular Sciences Key Laboratory of Photochemistry, Institute of Chemistry Chinese Academy of Sciences Beijing 100190 (China) Fax: (+ 86)10-8261-7315 E-mail: shayuli@iccas.ac.cn gqyang@iccas.ac.cn

A Rapid Aqueous Fluoride Ion Sensor with Dual Output Modes

A rhodamine based highly selective colorimetric and fluorescent probe for fluoride has been designed and synthesized. The fluorescent change is attributed to the fluoride triggered spirolactam ring opening which is augmented by density functional theory calculations and 1H NMR titrations. The sensor has been shown to be feasible for real sample analysis, and imaging of fluoride ions in the HeLa cells.

Rhodamine based sensor for naked-eye detection and live cell imaging of fluoride ions

Capillary electrophoresis of inorganic anions.

A fluorescent probe for rapid aqueous fluoride detection and cell imaging.

Fluoride ion (F-) is one of the most harmful elements in drinking water. Over-intake of F- can result in dental fluorosis, kidney failure, or DNA damage. Therefore, developing affordable, equipment-free, and reliable methods for F- detection is an important goal. In this work, a series of mixed lanthanide metal-organic frameworks were synthesized using a triazine-based planar ligand, 4,4',4″-s-triazine-2,4,6-triyltribenzoate (TATB) and mixed lanthanide ions (Tb3+ and Eu3+). The luminescent color of the Tb/Eu(TATB) can be finely modulated by changing the Tb3+/Eu3+ ratio in the synthesis procedure. Benefiting from the unique host-guest interaction (e.g., Lewis acid-base interaction), between F- and MOF host, a highly selective, sensitive, and reliable fluoride sensor was then developed. Moreover, visual detection of F- was achieved with a smartphone by identifying the RGB value. Drinking water samples were analyzed for F-, and the results obtained by our ratiometric luminescent method were consistent with those by ion chromatographic strategy. This easy-to-use sensor provides reliable detection of F- in everyday applications for nonexpert users, especially in remote rural areas.

Visual Detection of Fluoride Anions Using Mixed Lanthanide Metal-Organic Frameworks with a Smartphone.

Analysis of fluoride in rain water comparison of capillary electrophoresis with ion chromatography and ion-selective electrode potentiometry

Concentrations of anions in environmental water samples such as chloride, nitrate and sulphate, may differ orders of magnitude. Conditions have been investigated under which the quality of ion chromatographic data for series of environmental water samples, comprising samples with low anion concentrations, can be affected by the matrix of previous samples in the series. Effects of a high ionic sample matrix on the elution and retention processes of analytes have also been studied by repeated analyses of standards and blanks. The study was performed using a Dionex 2000i chromatograph and an AS4ASC column. Additionally, a Dionex DX500 chromatograph, equipped with a sodium hydroxide eluent generator and a AS15 column, was applied to investigate effects of low anion concentrations in the (bi)carbonate eluent used in the Dionex 2000i system. The effects are explained by distortions of the distribution of anions over eluent and stationary phase. Simultaneous analyses of major and minor components in routine meas...

Jos Neele

Papers

Analysis of fluoride in rain water comparison of capillary electrophoresis with ion chromatography and ion-selective electrode potentiometry

Matrix Effects in the Determination of Low Anion Concentrations using Suppressed IC