Label-free optical detection of miRNA using electrostatic interactions between oppositely charged gold nanoparticles for signal amplification

Abstract

We developed a simple yet innovative biosensing system for the detection of miRNA-155 (miR-155), a promising biomarker for the early diagnosis of breast cancer. This system utilizes two types of gold nanoparticles (Au NPs) with opposing surface charges: (1) negatively charged citrate-stabilized Au NPs (Cit-Au NPs) for probe immobilization and (2) positively charged polyethylenimine-capped Au NPs (PEI-Au NPs) for signal amplification. The DNA probe was covalently attached to Cit-Au NPs via Au–S bonds. In the presence of miR-155, a DNA–miRNA hybrid forms, stabilizing the nanoparticles. The subsequent introduction of PEI-Au NPs enhances the surface plasmon resonance (SPR) signal due to increased nanoparticle dispersion. PEI-Au NPs enhance the diagnostic system's sensitivity by providing a high surface area and improved nanoparticle stability. Upon binding to the DNA–miRNA hybrid, the increased interparticle distance leads to enhanced colloidal stability. This stabilization manifests visually as an intensified red color, indicating the presence of the target when PEI-Au NPs are introduced into the solution. In contrast, in the absence of miR-155, electrostatic interactions cause aggregation of the Au NPs, leading to a measurable SPR shift. This facile method demonstrated a detection limit of approximately 8 pM and a wide linear detection range from 80 pM to 2 μM, making it a promising tool for early diagnostics of breast cancer.