Apoptosis plays a crucial role in many biological processes and pathogenesis of 
various malignancies and diseases of the immune system. In this paper, we 
described a novel method for sensitive detection of drug-induced apoptosis by 
using fluorescence correlation spectroscopy (FCS). The principle of this method 
is based on the assay of DNA fragmentation in the process of the drug-induced 
apoptosis. FCS is a single molecule method, and it can be used for sensitive and 
selective assay of DNA fragmentation without separation. We first developed a 
highly sensitive method for characterization of DNA fragments using a home-built 
FCS system and SYBR Green I as fluorescent DNA-intercalating dye, and then 
established a model of drug-induced apoptosis using human pancreatic cancer 
cells and a drug lidamycin. Furthermore, FCS method established was used to 
directly detect the fragmentation of DNA extracted from apoptotic cells or in 
the apoptotic cell lysate. In FCS assay, the single-component model and the 
multiple-components model were used to fit raw FCS data. The characteristic 
diffusion time of DNA fragments was used as an important parameter to 
distinguish the apoptotic status of cells. The obtained data documented that the 
characteristic diffusion time of DNA fragments from apoptotic cells 
significantly decreased with an increase of lidamycin concentration, which 
implied that DNA fragmentation occurred in lidamycin-induced apoptosis. The FCS 
results are well in line with the data obtained from flow cytometer and gel 
electrophoresis. Compared to current methods, the method described here is 
sensitive and simple, and more importantly, our detection volume is less than 1 
fL, and the sample requirement can easily be reduced to nL level using a 
droplets array technology. Therefore, our method probably becomes a high 
throughput detection platform for early detection of cell apoptosis and 
screening of apoptosis-based anticancer drugs.