Highly sensitive and homogeneous detection of unamplified RNA based on the light scattering properties of gold nanoparticle probes

RNA is a crucial diagnostic biomarker for several human diseases. Hence, a simple, rapid, sensitive, and cost-effective assay for detecting pathogen-derived RNAs (e.g., RNA viruses) in water is necessary for transcriptomic analysis. Here, we present a highly sensitive assay to detect unamplified RNA based on the light scattering properties of oligonucleotide-functionalized gold nanoparticle probes (Au-nanoprobes). In this assay, Au-nanoprobes recognize and hybridize to the target RNA. Subsequently, they scatter light when the sample solution is placed onto a quartz waveguide slide and is excited with an evanescent wave. This assay enables highly sensitive quantification (approximately 102 copies/μL) of bacterial 16S rRNA and mRNA without reverse transcription and cDNA amplification within 10 min of RNA extraction. Moreover, this assay was three orders of magnitude sensitive than previously reported assays for direct RNA quantification.