Fiber-optic Setup Research Articles

Chemiluminometric enzyme sensors for flow-injection analysis

Chemiluminometric monoenzyme sensors were developed for the flow-injection analysis (FIA) of hydrogen peroxide, xanthine and hypoxanthine in the concentration range between 10 −3 and 10 −6 M. Both a fibre optic set-up with a photomultiplier tube (PMT) and a photodiode with an integrated preamplifier were investigated to detect the chemiluminescence. Microbial peroxidase or xanthine oxidase was immobilized covalently on a preactivated membrane, which was placed in the 7.5 μl flow detector cell. The photodiode and the PMT based H 2O 2 sensor achieve detection limits of 10 −6 and 10 −7 M, respectively. To develop bienzyme sensors for glutamate, lysine and xanthine the microbial peroxidase was coimmobilized with the corresponding oxidases on the sensor membrane. These analytes can be detected in the range between 10 −3 and 10 −6 M. The fibre optic H 2O 2 sensor was combined with packed bed enzyme reactors to determine, e.g., glucose, lactate, glutamine, glutamate, ammonia, xanthine, hypoxanthine and phosphate in the range between 10 −3 and 10 −7 M. On this basis a fully automated FIA set-up with 5 parallel arranged enzyme reactor channels was developed for the ondashline monitoring of animal cell cultures.

In vivo detection of ultrasonically induced cavitation by a fibre-optic technique

The measurement of cavitation events in tissue in vivo would greatly assist us to better understand how pulsed high energy ultrasound (PHEUS) interacts with living tissues, especially with regard to cancer therapy. To accomplish this, we designed and built a fibre-optic hydrophone. The principle was to couple the light of a laser diode into a lightfibre and to register the ultrasound induced modification of the refractive index in tissue. In this manner, the cavitation event could be quantitatively investigated both in water and in vivo. The structure of the bubble dynamic is in reasonable agreement with theoretical predictions, and in vitro measurements. With the fibre-optic set-up, the pressure signal can also be detected. PHEUS was generated by an electromagnetic source adapted from a commercial lithotripter (Lithostar TM Siemens). As biological tissue we used the experimental R3327-AT1 Dunning prostate tumor growing subcutaneously in the thigh of male Copenhagen rats. The lifetime of the cavitation bubble in water increased with the energy level of the ultrasonic pulse from 250 μs at 13 kV capacitor voltage to 750μs at 21 kV, while the lifetime inside the tumor tissue in vivo increased only from 100μs at 13 kV to 220μs at 21 kV capacitor voltage.

The synthesis of (poly)hydroxycarboxylates Part IV. Eu(III) promoted O-alkylation of glycolate with maleate as studied on-line by luminescence

The O-alkylation of glycolate with maleate yielding carboxymethoxysuccinate (cmos) is a lanthanide(III) promoted reaction. It is demonstrated that the reaction can be studied on-line with the help of an optical fiber setup, monitoring the luminescence of the Eu(III) optical probe. During the reaction the 5D 0→F 0 transition shifts to lower wavenumbers and the average lifetime of the excited 5D 0 level of the Eu(III) ion increases, when substantial amounts of Eu(cmos) 2 are formed. The average number of OH oscillators in the first coordination sphere of the Eu(III) ion is decreased by two if one cmos per Eu(III) is formed. The concentration of cmos can be obtained by on-line measurements of the lifetime of the 5D 0 excited stare.

Fiber-optical quasi-elastic light scattering of concentrated dispersions

A fiber-optical experimental setup is presented to measure the quasi-elastic light scattering from concentrated dispersions. The geometry of the setup is described and the coherence requirements are discussed. Experimental results are obtained for two systems of latex spheres with diameters of 0.13 and 0.61 μm in the concentration range from φ = 0.02 to φ = 0.5. At all concentrations the observed correlation functions consist of a fast initial decay followed by a more slowly decaying tail. The initial decay is attributed to multiple scattering. For the 0.61-μm latex, the tail of the correlation function is shown to be due to self-diffusion, whereas for the 0.13-μm latex collective motions may also contribute. The concentration dependence of the diffusion coefficients has been measured. The observed slopes are discussed in the light of theoretical predictions.