Micro fluorescence in situ hybridization (μFISH) for spatially multiplexed analysis of a cell monolayer

We here present a micrometer-scale implementation of fluorescence in situ hybridization that we term μFISH. This μFISH implementation makes use of a non-contact scanning probe technology, namely, a microfluidic probe (MFP) that hydrodynamically shapes nanoliter volumes of liquid on a surface with micrometer resolution. By confining FISH probes at the tip of this microfabricated scanning probe, we locally exposed approximately 1000 selected MCF-7 cells of a monolayer to perform incubation of probes - the rate-limiting step in conventional FISH. This method is compatible with the standard workflow of conventional FISH, allows re-budgeting of the sample for various tests, and results in a ~ 15-fold reduction in probe consumption. The continuous flow of probes and shaping liquid on these selected cells resulted in a 120-fold reduction of the hybridization time compared with the standard protocol (3 min vs. 6 h) and efficient rinsing, thereby shortening the total FISH assay time for centromeric probes. We further demonstrated spatially multiplexed μFISH, enabling the use of spectrally equivalent probes for detailed and real-time analysis of a cell monolayer, which paves the way towards rapid and automated multiplexed FISH on standard cytological supports.