Reactions templated by a specific nucleic acid sequence have emerged as an attractive strategy for nucleic acid sensing. The Staudinger reaction using an azide-quenched fluorophore and a phosphine is particularly well suited by virtue of its bioorthogonality and biocompatibility. The reaction is promoted by a complementary nucleic acid that aligns the phosphine with the azide-quenched fluorophore. Cellular RNAs can catalyze the Staudinger reaction and signal amplification can be achieved through multiple turnover of the template. Peptide nucleic acids (PNA) provide a convenient platform for the preparation of specific probes as they combine desirable hybridization properties, robust synthesis, ease of fluorophore conjugation, and high biochemical stability. Herein, we describe protocols for fast fluorescent detection of miRNAs in human cells with PNA-based probes via reductive unquenching of bis-azidorhodamine by trialkylphosphine.