Difference between Digital PCR and Droplet Digital PCR (ddPCR)

How can PCR be digital? 

That is a good question, actually digital PCR has aspects of both conventional PCR and realtime qPCR.

Most importantly, the DNA sample is separated into compartments, then standard endpoint PCR is run on each compartment, and fluorescence is detected using taqman hydrolysis probes that we are familiar with from qPCR.

The partitioning of DNA sample can be done on microfluidic plates, like the Fluidigm system, or microarray plate like ABI Open Array, or droplets like on the Biorad (Quantalife) system.  All of these systems are performing digtal pcr (dPCR).  The data readout is simply counting how many compartments were positive for your target of interest.  

The Biorad (Quantalife) system is specifically referred to as droplet digital because the partitions are created in droplets rather than fixed arrays.  It is an advantage to have a lot of partitions, and ddPCR achieves this.

 

Read about the technical details in this journal by Hindson et al from analytical chemistry

(http://pubs.acs.org/doi/abs/10.1021/ac202028gddPCR explained

 

 

Digital PCR (PCR numerique en francais) is now available in a second generation device called the QX200.  This system makes it even easier than ever to get up and running quickly because it can use reactions that are made with the exact same primer pairs that one would use in qPCR.  The intercalating EVAgreen dye is used for this system.