Quantitation of drug concentration by photo-thermal microscopy in a renal tubule of fixed kidney

The quantitation of drug concentration in a cell using a new microscopic method named laser-induced photo-thermal microscopy, was demonstrated We used a paraformaldehyde-glutaraldehyde-fixed guinea pig's kidney to which we administered tobramycin and assayed the quantity of colloidal gold immunologically bound to the tobramycin in the epithelial cell of one renal tubule. We could detect the locally concentrated tobramycin in the epithelial cell, as well as its local distribution quantitatively. The detection limit of the tobramycin concentration (10 zmol) was 10-times superior to that of confocal scanning laser microscopy. The colloidal gold which we used for immunochemical staining remained stable to laser-beam radiation and gave a low background Therefore, it makes possible highly sensitive detection of a drug in fixed organs.