Keziah König

β-nicotinamide adenine dinucleotide -alcohol dehydrogenase complex was exposed to either UVA irradiation or heat in order to investigate complex stability. Prior to irradiation, frequency-domain fluorescence lifetime measurements indicated the presence of two principal components having short and long fluorescence lifetimes reflecting free and bound NADH respectively. UVA exposure resulted in decreased NADH fluorescence intensity concomitant with decreased absorption at 337 nm. However, UVA irradiation did not reduce the fractional contribution of the long-lived bound NADH. The photoinduced fluorescence decrease appeared to be caused by the formation of oxidized NAD+ and not on UV-induced dissociation of the NADH-protein complex. Such dissociation, detected by a red-shifted fluorescence maximum and decreased fractional contribution of the nanosecond component, was observed when NADH-protein mixtures were heated.

We report on cell damage of single cells confined in continuous-wave, near-infrared multimode optical traps as a result of multiphoton absorption phenomena. Trapping beams at NIR wavelengths less than 800 nm are capable of damaging cells through a two-photon absorption process. Cell damage is more pronounced in multimode cw traps compared with single-frequency true cw NIR traps because of transient power enhancement by longitudinal mode beating. Partial mode locking in tunable cw Ti:sapphire lasers used as trapping beam sources can produce unstable subnanosecond pulses at certain wavelengths that amplify multiphoton absorption effects significantly. We recommend the use of single-frequency long-wavelength NIR trapping beams for optical micromanipulation of vital cells. © 1996 Optical Society of America.

Modifications of the porphyrin fluorescence during photodynamic treatment of ovarian cells, endometrial adenocarcinoma cells and rat uterus after administration of the porphyrin precursor δ-aminolevulinic acid and exposure with 630 nm laser radiation have been studied. The intracellular and intratissue fluorescence was excited with 407 nm radiation of a krypton ion laser and detected by spectral microscopic imaging using a modified microscope equipped with a slow-scan cooled camera and a liquid crystal filter. In particular, singlet oxygen induced effects due to photobleaching as well as formation of chlorin-type fluorescent photoproducts were detected at around 500, 630 and 670 nm. The photodynamically induced fluorescence modifications were found to vary between cell types. The major fluorescence peak of PP IX was photobleached 63% by a phototoxic fluence of about 20-40 J/cm2 in cells and within rat endometrium. Higher fluences were required to bleach the fluorescence at around 670 nm due to the formation of fluorescent photoproducts. No significant photoinduced modifications of autofluorescence occurred around 500 nm. © 2006 Elsevier GmbH. All rights reserved.

Cell damage by low-power 365-nm radiation of a 50-W high-pressure mercury microscopy lamp was studied. Exposure of Chinese hamster ovary cells to ultraviolet-A radiation >10 kJ/m2 resulted in significant modifications of nicotinamide adenine dinucleotide attributed autofluorescence and inhibition of cell division. Single-cell gel electrophoresis revealed UVA-induced single-strand DNA breaks. According to these results, UVA excitation radiation in fluorescence microscopy may damage cells. This has to be considered in vital cell microscopy, e.g., in calcium measurements.