Here we describe the detection of live Pseudomonas aeruginosa using a sensing film containing a fourth-generation hydroxy-terminated polyamidoamine (PAMAM) dendrimer (i.e., G4-OH) and SYTOX Green fluorescent nucleic acid stain. The films are configured on simple, disposable plastic coupons or optical fibers and are interrogated using a miniature fiber-optic spectrometer. SYTOX Green is generally considered a dead cell stain because it is not able to cross the membranes of live cells. In the presence of PAMAM-OH (G4-OH) in water, the bacterial cell becomes permeable to the SYTOX dye and the fluorescence is significantly enhanced. The fluorescence increases with the bacteria concentration, and the intensity at 5.4 x 10(7) cells mL(-1) is 350% higher than the liquid controls without PAMAM-OH. We also demonstrate that dendrimers stabilize the sensing film. After drying and desiccation, the SYTOX Green/PAMAM-OH films are still able to quantitatively detect P. aeruginosa in water. Incorporation of glucose into the SYTOX Green/ PAMAM-OH film may improve the homogeneity of the film and enhances the fluorescence signal an additional 11-25%.

The measurement of low-level dissolved CO(2) using a fiber-optic sensor is described. The sensor, based on the Severinghaus CO(2) electrode principle, consists of a CO(2)-sensitive bicarbonate buffer solution containing the pH-sensitive fluorescent dye carboxy-SNAFL-1 immobilized at the end of an optical fiber using a gas-permeable membrane. The sensor is used in a ratiometric mode and has a reversible working dynamic range between 200 and 1000 ppm pCO(2) and a sensitivity ±1 ppm. Results are presented for the sensor calibration, effects of temperature, and response time characteristics. An integrated measurement system with electrooptic and data acquisition modules coupled to a satellite transmission system was tested in Vineyard Sound, MA, and data are presented that demonstrate continuous monitoring of pCO(2) in surface seawater.

Here we describe on-line, real-time detection of waterborne bacteria using an optical sensor based on a starburst dendrimer film containing a lipophilic fluorophore. The sensor is constructed via covalent coupling between amine-terminated polyamidoamine dendrimer and silanized glass through an amide bond. The reporter molecule is embedded in the dendrimer layer through host-guest interaction. Real-time automated detection and quantitation of the bacteria are realized by using a charge-coupled detector camera and customized imaging and analysis software. The sensor responds to bacteria introduced to an aqueous flow system within 1 min. The limit of detection is approximately 10(4)cells/mL. The operational lifetime is more than 64 h, and the storage lifetime of the sensor is at least 7 months.

The concept of using immobilized nucleic acid stains as detection chemistry to fabricate optical bacterial sensors is first demonstrated. SYTO 13 (a green fluorescent cell stain) is used as the molecular recognition element and fluorescent reporter in the sensor. The sensor responds to aqueous and aerosolized bacterial samples in 15 and 30 min, respectively. In addition, the sensor can discriminate a change in Pseudomonas aeruginosa (Pa) cell concentration of 1 order of magnitude or less and can detect down to 2.4 x 10(5) cells/mL of Pa cells. The utility of the sensor is demonstrated by monitoring the growth of a Pa cell culture over a period of 50 h.

Articles you may be interested inReactions of pulsed laser produced boron and nitrogen atoms in a condensing argon stream J. Chem. Phys. 98, 922 (1993); 10.1063/1.464256 Laser fluorescence study of ytterbium plus halomethane reactions J. Chem. Phys. 73, 3831 (1980); 10.1063/1.440614 Calculation of Raman scattering parameters for methane and halomethanes from an atom dipole interaction model J. Chem. Phys. 66, 3455 (1977); 10.1063/1.434431Chemiluminescence from the gas phase reaction of atomic boron with the alkali metal fluorides Rate constants have been measured for the reactions of boron atoms with a series of halomethanes. The experiments were performed in a linear flow tube apparatus at 300 K. The measured rate constants in units ofcm 3 molecule-I S-I are CCI 4 :9.. The reaction of boron with all the chloromethanes is facile. The chlorofluoromethanes present a more complex pattern. Noteworthy is the low reactivity of the channel to produce BF, furthermore, the presence of fluorine in the halomethanes reduces the reactivity at the chlorine site. Semiempirical MNDO calculations were performed on the reacting systems. These calculations suggest possible explanations for the observed results.