Cheng-Gang Niu

A new fluorescence dye, N-amino-4-(2-hydroxyethylamino)-1,8-naphthalimide (AHN), based on 4-bromo-1,8-naphthalic anhydride was synthesized as a fluorescence probe for determining water content in organic solvents. Changing from a non-polar to a polar solvent increases the solvent interaction with excitation spectrum and emission spectrum shifts to longer wavelengths. The fluorescence intensity of the probe decreased with the increasing concentration of water. In the range of 0.00 – 4.00% (v/v), the AHN fluorescence intensity changed as a linear function of water content. The detection limits were 0.019, 0.038, and 0.060% for dioxane, acetonitrile and ethanol, respectively.

A new fluorescent dye, N-allyl-4-morpholinyl-1,8-naphthalimide (AMN), was synthesized as a fluorescence indicator in the fabrication of a sensor for determining water content in organic solvents. To prevent leakage of the fluorophore, AMN was photo-copolymerized with acrylamide, (2-hydroxyethyl)methacrylate, and triethylene glycol dimethacrylate on a glass surface treated with a silanizing agent. The sensing mechanism is based on the solvatochromic feature of the covalently immobilized AMN. The fluorescence intensity of AMN decreased with increasing water contents when it was excited at 400 nm. In the range of ca. 0.00–4.40% (v/v), the fluorescence intensity of AMN changed as a linear function of water content. The sensor exhibited satisfactory reproducibility, reversibility, and a response time (t ₉₉) of the order of 50 s. The detection limit was solvent-dependent, when acetonitrile was used as the solvent, and the detection limit could be as low as 0.006% (v/v) of water. Additionally, the prepared sensor is pH-insensitive and possesses a relatively long lifetime of at least one month.

This paper describes a novel ratiometric fluorescence sensor for pH measurement. Two pH-sensitive fluorophores, N-allyl-4-(4′-methyl-piperazinyl)-1,8-naphthalimide (AMPN) and meso-5,10,15,20-tetra-(4-allyloxyphenyl)porphyrin (TAPP), which served as referencing indicators for each other, were co-polymerized with acrylamide, hydroxyethyl methacrylate and triethylene glycol dimethacrylate on the silanized glass surface. The proposed sensor is based on the pH-dependent fluorescence intensities of the two fluorophores in different pH ranges. The sensor covers a broad dynamic range of pH 1.5–9.0. It exhibits satisfactory analytical performance in terms of selectivity, reproducibility and stability. The successful fabrication of the proposed sensor provides an alternative concept to utilizing two or more fluorophores for the development of ratiometric sensors covering a broad range of pH.

A fluorescence ratiometric sensor for pH determination is described in this paper. The sensor incorporated the pH-sensitive dye meso-5,10,15,20-tetra-(4-allyloxyphenyl)porphyrin (TAPP) as an indicator and a pH-insensitive dye N-(2-methacryloxyethyl)benzo[k,l]thioxanthene-3,4-dicarboximide (MBTD), a benzothioxanthene derivative, as a reference for fluorescence ratiometric measurement. To prevent leakage of the dyes, both were photocopolymerized with acrylamide, hydroxyethyl methacrylate, and triethylene glycol dimethacrylate on the silanized glass surface. The reproducibility and response time of the prepared sensor were sufficient. Most common coexisting inorganic ions and organic compounds did not interfere with pH sensing. In the acidic pH range from 1.5 to 5.0 the fluorescence intensity ratio of the two dyes varied linearly as a function of pH. The sensing membrane was found to have a lifetime of at least one month. The sensor was applied to the analysis of waste water and artificial samples.

Along with the advances in immunoassay and sensing techniques, the immunosensors based on specific immunoreaction and immobilized antibody (antigen) as recognition element were developed. They can be used for real-time, in-vivo and on-the-spot determination of pesticides, industrial organic pollutants, heavy metals, biotoxins, etc. with high sensitivity and selectivity. They possess a great potential for environmental monitoring. The working mechanism, fabrication and classification of immunosensor are briefly introduced in this paper. The latest study progress on immobilization methods and sensing techniques of immunosensor for determination of trace toxicants is reviewed. The application of immunosensor in environmental monitoring and the future development are also discussed.