Here we present a facile sample partitioning method to enable rapid and low-cost digital PCR(dPCR)assays.This method uses the self-digitization(SD)chip platform,a microfluidic device without requirement of external pumping and valving components that rapidly subdivides a high percentage of the sample volume into a large number of partitions.As shown schematically in Figure 1,the SD chip contains a set of parallel microfluidic channels used for sample delivery,and each channel is connected with two rows of cylindrical wells to hold the droplets.In addition,the end of each channel is connected to a chamber which serves a dual function as an internal pumping source and as a waste tank.The basic operating procedure of the SD chip is outlined in Figure 2.Firstly,a blank PDMS slab which serves as a detachable pump was reversibly attached to the patterned layer [1].Then,the assembly was degassed under vacuum.After chip removal from vacuum,an aliquot of PCR premix was immediately added in the inlet of the chip.About 2 min later,all of wells were completely filled with the sample and the sample in the inlet port was consumed,and then air was pulled into the microchannels to remove the excess liquid,isolating the fluid in each chamber.Once the removal of sample in the channels was completed,a few drops of oil was added in the inlet port,and the cover PDMS slab was peeled off.During peeling off,the oil in the inlet port easily covered the exposed portion of the patterned PDMS layer due to the wettability of oil to PDMS and the capillary effect.After the cover PDMS slab was peeled off and the oil covered the entire chip,the patterned PDMS was sealed against a glass slide coated with a thin layer of uncured PDMS.Finally,the chip was transferred to a flat PCR apparatus for amplification reaction.In order to demonstrate the feasibility of the SD chip,we first tested its capabilities of automatic sample partitioning.In contrast to our previous work [2],this system used air rather than oil to partition the liquid sample,providing faster sample partitioning because the viscosity of air is much lower than that of oil(Figure 3).Furthermore,this digitization chip can partition more 90%of a sample volume,which is important for the applications where the amount of material available is small.Finally,we also demonstrated the utility of the proposed SD chip by applying it to a dPCR assay(Figure 4).