A new optical chemical sensor for continuous monitoring of aliphatic aldehydes has been proposed based on the reversible chemical reaction between a new sensing reagent, 3,3',5,5'-tetramethyl-N-(9-anthrylmethyl)benzidine (TMAB), and the analytes. TMAB, containing two receptors and two fluorescent reporters, can perform dual fluorescence responses corresponding to the reactions of hydrogen ion and carbonyl compound. When immobilized in a plasticized poly(vinyl chloride) membrane, TMAB extracts aliphatic aldehydes from aqueous solution into the bulk membrane phase and reacts with the analyte by forming a Schiff base. Since the extraction equilibrium and chemical reaction are accompanied by fluorescence increase of the sensing membrane, the chemical recognition process could be directly translated into an optical signal. At pH 3.20, the sensor exhibits a dynamic detection range from 0.017 to 4.2mM n-butyraldehyde with a limit of detection of 0.003mM. The forward response time (t95) of the sensor is 3-5 min, and the reverse response time is 5-7 min. The responses of the sensor toward different kinds of aldehydes and ketones depend on the lipophilicity and the reactivity of the analytes. Since the fluorescence enhancement of the sensing membrane at 296nm/410nm is only related to the formation of Schiff base, the measurement of aldehydes is independent of pH.

In the present paper, a new cyclodextrin/porphyrin supramolecular sensitizer for zinc ion has been proposed based on the porphyrin dual fluorescence emission ratio. In aqueous solution, meso-tetraphenylporphyrin shows weak fluorescence, while in the presence of alkylated

The design and synthesis of fluorescent sensors with high selectivity and sensitivity for heavy and transition metal ions continues to grow at an unabated pace.1 Regardless of the signal transducing function, signaling changes of a fluorescent molecule at two bands that exhibit enhancement of one band at the expense of the other upon cation binding, a ratiometric measurement can be made which can increase the selectivity and sensitivity of a measurement and can eliminate most or all of the possible variability due to differences in instrumental efficiency and content of effective dye.2 Many investigations have been conducted to make ratiometric fluorescent sensors for metals;3 however, few reports have been explored for AgI.4 As many heavy cations are known as fluorescence quenchers, discrimination between AgI and chemically close ions presents a challenge.

A new supramolecular sensitizer for mercury(Ⅱ) ion based on a cyclodextrin/porphyrin inclusion complex has been proposed. In aqueous base solution, meso-tetraphenylporphyrin (TPP) emits weak fluorescence. In the presence of alkylated-cyclodextrin, significant fluorescence enhancement is observed from TPP by forming a cyclodextrin/porphyrin inclusion complex. In addition, the formation of supramolecular complex causes a remarkable increase of the porphyrin metallation rate following the fluorescence quenching of TPP at its maximum emission wavelength. The quenching of TPP fluorescence at room temperature is fast and nearly complete upon Hg(Ⅱ) interaction. Based on these experimental observations, a simple, fast and low-cost fluorometric method for determination of Hg(Ⅱ) was developed. With the optimum conditions described, Hg (Ⅱ) in water from 5.0×10−8 to 2.0×10−5 mol l−1 can be determined with a limit of detection of 2.0×10−9 mol l−1. The method was applied in the analysis of water samples with satisfactory results.

A new zinc(Ⅱ) porphyrin conjugate with an appended pyrene subunit has been synthesized and shown to exhibit significant and analytical usefulness for fluorescence sensing toward imidazole derivatives. The molecular recognition was based on the bridging interaction of the imidazole ring of analyte with the zinc(Ⅱ) center of the porphyrin, while the transduction signal for the recognition process was the pyrene excimer fluorescence. The sensor was constructed and applied for fluorescence assay of histidine in aqueous solution by immobilizing the sensing material in a plasticized PVC membrane. When the membrane was bathed in an alkaline solution void of histidine, zinc(Ⅱ) porphyrin was present in the monomer form, and pyrene emitted monomer fluorescence at 378 and 397 nm. With the presence of histidine in the sample solution, histidine was extracted into the membrane phase and bridged with the Zn(Ⅱ) center of the porphyrin, causing the monomer porphyrin to be converted to its dimeric species. Since the formation of porphyrin dimmer was accompanied by the enhancement of pyrene excimer emission at 454 nm, the chemical recognition process could be directly translated into a fluorescent signal. With the optode membrane M1 described, histidine in sample solution from 6.76×10-7 to 5.01×10-3 M can be determined. The limit of detection was 1.34×10-7 M. The optical selectivity coefficient obtained for histidine over biologically relevant amino acids and anions met the selectivity requirements for the determination of histidine in biological samples. Serum histidine values obtained by the optode membrane fell in the normal range of the content reported in the literature and were in good agreement with those obtained by HPLC.