Hybridization chain reaction and magnetic beads-assisted highly sensitive detection of microRNA-21 with helical gold nanorods as dark-filed light scattering optical probe

As a promising cancer biomarker, microRNA-21 (miRNA-21) has attracted great attention. However, the assay sensitivity of miRNA-21 is highly demanded due to its low abundance. In this work, a highly sensitive sensing platform for miRNA-21 detection was developed based on hybridization chain reaction (HCR) and magnetic beads (MBs)-assisted cascade signal amplification strategy with helical gold nanorods (HGNRs) as dark-field light scattering probes. The target miRNA-21 triggered triiodide (I₃⁻)-mediated etching of HGNRs, leading to the decrease in scattering intensity of HGNRs. Compared with the common gold nanorods, the protuberant helical structure on the rough surface endowed HGNRs with larger specific surface area and higher reactivity, resulting in a higher sensitivity with a linear range of 0.1–3 pmol/L and a limit of detection as low as 61.33 fmol/L, which realized the detection of miRNA-21 in serum samples from cancer patients. Moreover, the proposed strategy offered the remarkable specificity and high accuracy, which was capable of distinguishing mismatch sequences and offering the similar result obtained from polymerase chain reaction, supplying a new idea for early diagnosis of cancers.