The ability to visualize in real-time the expression level and localization of specific RNAs in living cells can offer tremendous opportunities for biological and disease studies. Here we review the recent development of nanostructured oligonucleotide probes for living cell RNA detection, and discuss the biological and engineering issues and challenges of quantifying gene expression in vivo. In particular, we describe methods that use dual FRET (fluorescence resonance energy transfer) or single molecular beacons in combination with peptide-based or membrane-permeabilization-based delivery, to image the relative level, localization, and dynamics of RNA in live cells. Examples of detecting endogenous mRNAs, as well as imaging their subcellular localization and colocalization are given to illustrate the biological applications, and issues in molecular beacon design, probe delivery, and target accessibility are discussed. The nanostructured probes promise to open new and exciting opportunities in sensitive gene detection for a wide range of biological and medical applications.