SABER enables highly multiplexed and amplified detection of DNA and RNA in cells and tissues

Fluorescent in situ hybridization (FISH) reveals the abun-dance and positioning of nucleic acid sequences in fixed sam-ples and can be combined with cell segmentation to produce a powerful single cell gene expression assay. However, it re-mains difficult to label more than a few targets and to visu-alize nucleic acids in environments such as thick tissue sam-ples using conventional FISH technologies. Recently, meth-ods have been developed for multiplexed amplification of FISH signals, yet it remains challenging to achieve high lev-els of simultaneous multiplexing combined with high sam-pling efficiency and simple workflows. Here, we introduce signal amplification by exchange reaction (SABER), which endows oligo-based FISH probes with long, single-stranded DNA concatemers that serve as targets for sensitive fluores-cent detection. We establish that SABER effectively ampli-fies the signal of probes targeting nucleic acids in fixed cells and tissues, can be deployed against at least 17 targets si-multaneously, and detects mRNAs with high efficiency. As a demonstration of the utility of SABER in assays involv-ing genetic manipulations, we apply multiplexed FISH of reporters and cell type markers to the identification of en-hancers with cell type-specific activity in the mouse retina. SABER represents a simple and versatile molecular toolkit to allow rapid and cost effective multiplexed imaging.