Improving images of fluorescent cell labeling by background signal subtraction.

The uptake and selective accumulation of fluorescent labels and drugs into organelles of cultured cells currently are widely investigated in biomedical research. In such studies, co-localization procedures are frequently used to identify the accumulation sites of compounds with biological activity. A drawback with fluorescent labeling is the autofluorescence of some cell organelles, which can hinder the precise assessment of co-localization. We report here labeling of the Golgi apparatus of A-549 cells using the photosensitizer zinc(II)-phthalocyanine (ZnPc) and co-localization with the Golgi probe NBD C6-ceramide. The blue autofluorescence signal of mitochondria can be subtracted easily from the original picture by image processing, after which the co-localization of the isolated red ZnPc signal with the green signal from the Golgi probe is considerably improved.