The hepatitis C virus (HCV) is a single-stranded (ss) RNA virus that is responsible for chronic liver diseases, such as cirrhosis, end-stage liver disease, and hepatocellular carcinoma. Driven by the need to detect the presence of the HCV viral sequence, herein it is demonstrated for the first time that the nonlinear optical (NLO) properties of gold nanoparticles can be used for screening and quantifying HCV RNA without any modification, with excellent detection limit (80 pM) and selectivity (single base-pair mismatch). The hyper-Rayleigh scattering (HRS) intensity increases 25 times when label-free, 145-mer, HCV ss-RNA is hybridized with 400 pM target RNA. The mechanism of HRS intensity change is discussed with experimental evidence for a higher multipolar contribution to the NLO response of gold nanoparticles.