Effect of serum on SmartFlare™ RNA Probes uptake and detection in cultured human cells.

SmartFlare™ RNA Detection Probes from Millipore is a novel technology to detect RNA in live cells based on the use of 12 nm gold nanoparticles coated with nucleotides. We proved that SmartFlares™ are internalized by human primary lymphocytes. However, fluorescence signals from target RNA detection can only be observed in the presence of Fetal Bovine Serum (FBS) in the medium, whereas it is not detectable without FBS or when medium is supplemented with human albumin. Image analysis of fluorescence generated from SmartFlare™ Uptake Control (gives constant signal regardless of contact with RNA) and RNA Specific Probes revealed further differences. In the presence of FBS, the fluorescence signal for both reagents was diffused within the cells, whereas in the absence of FBS, it was detected as single spots within the cells only when the Uptake Control was used. It is possible that FBS components are necessary for SmartFlare™ Probes to be released from cellular compartments into the cytoplasm where they can get into contact with target RNA. The exact mechanism of this phenomena should be further determined. However, for the first time, we present here that FBS in the cell culture medium is essential for RNA detection by SmartFlare™ technology in human lymphocytes.