The limits of multiplexing

We were motivated by three novel technologies, which exemplify a new design paradigm in high throughput genomics: nanostring TM , DNA ‐mediated Annealing, Selection, extension, and Ligation DASL TM , and multiplex real‐time quantitative polymerase chain reaction ( QPCR ). All three are solution hybridization based, and all three employ on 10–1000 DNA sequence probes in a small volume, each probe specific for a particular sequence in a different human gene. nanostring TM uses 50‐mer, DASL and multiplex QPCR use ∼20‐mer probes. Assuming a 1‐ nM probe concentration in a 1 μL volume, there are 10 − 9  × 10 − 9  × 6.23 × 10 23 or 6.23 × 10 5 molecules of each probe present in the reaction compared to 10–1000 target molecules. Excess probe drives the sensitivity of the reaction. We are interested in the limits of multiplexing, i.e., the probability that in such a design a particular probe would bind to any other, sequence‐related probe rather than the intended, specific target. If this were to happen with appreciable frequency, this would result in much reduced sensitivity and potential failure of this design. We established upper and lower bounds for the probability that in a multiplex assay at least one probe would bind to another sequence‐related probe rather than its cognate target. These bounds are reassuring, because for reasonable degrees of multiplexing (10 3 probes) the probability for such an event is practically negligible. As the degree of multiplexing increases to ∼10 6 probes, our theoretical boundaries gain practical importance and establish a principal upper limit for the use of highly multiplexed solution‐based assays vis‐‐ a ‐vis solid‐support anchored designs. WIREs Comput Stat 2015, 7:394–399. doi: 10.1002/wics.1364 This article is categorized under: Applications of Computational Statistics > Genomics/Proteomics/Genetics Data: Types and Structure > Microarrays