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What is the difference between TU/ml and pfu/ml?

TU stands for Transducing Units. PFU stands for Particle Forming Units. All of our viral particle offerings are titered as TU/ml. This means that we use FACS to identify functional particles that actually deliver the packaged RNA of interest in HEK293T cells. The term pfu/ml is used in reference to a titer calculated by p24 ELISA which just calculates the number of viral particles formed in a specific volume, not the functional particles. The two terms should not be used interchangeably.