Label-free imaging of cancer cells using photonic crystal biosensors and application to cytotoxicity screening of a natural compound library

A rapid and accurate quantitative method for screening the effects of drug compounds upon cells utilizing label-free photonic crystal optical biosensors incorporated within 96-well microplates is described. The biosensors and associated imaging detection instrument enable visualization and quantitative measurement of cell populations attached to the sensor surface with sensitivity sufficient for the detection of individual cells without the use of labels or stains that typically induce the death of the cells under study. The detection method allows repeated measurement of the same cells without removing them from their culture environment, and thus allows direct determination of proliferation and apoptosis rates. In this work, a biosensor-based cell assay is used to screen the effect of a 61-member compound library of plant extracts upon human breast cancer cells, in which some members of the library are shown to induce apoptosis, while others increase the rate of cancer cell proliferation. The results are broadly applicable to a wide range of cell types and compounds, while the assay is simpler and more rapid than alternative apoptosis/proliferation assays.