Figure 1.

DUV-excitation fluorescence of MCF-7 cells stained with and without Tb³⁺. (A–G) Fluorescence images of the cells treated with (A) a Tb³⁺ solution of H₂O, (B) an H₂O solution without Tb³⁺, (C) a Tb³⁺ solution of D₂O, and (D) a D₂O solution without Tb³⁺. For comparison, fluorescence images of the cells stained with (E) Rhodamine B, (F) eosin Y, (G) PI, and (H) Hoechst 33342 are also shown. Scale bar corresponds to 50 µm. All the images were converted to 8-bits grayscale images from the RGB images measured with an RGB camera. Maximal values of brightness in (D–H) were adjusted so that difference in the fluorescence intensity distributions could be easily found. Brightness in (A–C) were adjusted to be the same as that in (D) so that the remarkably high fluorescence intensity of Tb³⁺ in D₂O could be recognized. (I–K) Dependencies of fluorescence intensity on (I) Tb³⁺ concentration, (J) treatment period, and (K) solution pH. Squares and error bars indicate means and standard deviations of fluorescence intensity for 100 cells under each condition. (L) Excitation and emission spectra of the cells immersed in the 10 mM Tb³⁺ solution of D₂O, as well as an excitation spectrum of the 10 mM Tb³⁺ solution of D₂O. The excitation wavelength was 285 nm. The emission wavelength detected for measuring the excitation spectra was adjusted to 546 nm. The Tb³⁺ concentration, treatment period, and solution pH were 50 mM, 5 min, and 7, respectively, unless noted.