Target-Mediated Assembly of Gold Nanorod Dimers on a Vertically Aligned Gold Nanorod Array for Cooperative Plasmonic Enhanced Fluorescence Detection of Exosomal miRNA

Exosomal miRNA is considered to be an effective type of next-generation noninvasive cancer biomarker for clinical diagnosis. Nowadays, the fluorescence biosensor in exosomal miRNA detection has garnered growing attention owing to its high sensitivity, high selectivity, and wide versatility. However, the limited fluorescence intensity observed during the analysis of low abundance exosomal miRNA remains a persistent challenge in practical application. Herein, a plasmon enhanced fluorescence (PEF) biosensor based on the cooperative coupling effects of a vertically aligned gold nanorod (AuNR) array and end-to-end AuNR dimers was developed for exosomal miRNA detection. In the presence of target miRNA lysed from exosomes, end-to-end AuNR dimers were formed on the vertically aligned AuNR array due to the target-induced strand displacement amplification (SDA) reaction, creating a nanometer-sized gap. Due to the cooperative plasmonic coupling effect, the electric field in the gap was greatly strengthened, leading to an improvement in fluorescence intensity. The developed biosensor showed substantial fluorescence enhancement, along with high sensitivity and high specificity. The detection limit was determined to be 5.4 × 10⁷ particles/mL exosomes by detecting exosomal miRNA-182, which was equal to 1.32 pM exosomal miRNA-182 quantified by quantitative reverse transcription-polymerase chain reaction (qRT-PCR). Additionally, the developed biosensor can be applied to real samples and can effectively discriminate high-tumor-burden mice, low-tumor-burden mice, and healthy mice. All of the results confirmed the potential of the PEF biosensor as a new avenue for cancer diagnosis.