A novel, on-line method of accurately parametrizing the shape of sprea
ding cells is described. The substrate on which the cells are deposite
d serves as an optical waveguide. The method is based on the interacti
on between the evanescent part of the guided waves and the cells. No s
pecial labelling of the cells is required. A mathematical framework fo
r interpreting the results is derived, and some illustrative results a
re presented. (C) 1995 Wiley-Liss, Inc.