Designed Co-DNA-Locker and Ratiometric SERS Sensing for Accurate Detection of Exosomes Based on Gold Nanorod Arrays

Exosomes, which can transfer and deliver information about the original cell, are considered to be ideal candidates for early cancer diagnosis and evaluation of therapeutic efficacy due to their high abundance and stability. However, the highly expressed proteins on the surface of exosomes are usually associated with a variety of cancers; it is difficult to distinguish them by a single marker. Herein, a controlled self-assembly of gold nanorod (AuNR) arrays was prepared to construct a surface-enhanced Raman spectroscopy (SERS) sensor for the specific detection of exosomes secreted by SK-Br-3 cells based on a designed colocalization-dependent system (Co-DNA-Locker) and ratiometric strategy. After the exosomes are captured in the sensing array by the EpCAM aptamer modified on the surface of AuNRs, the DNA logic process occurs because the other two proteins, CD63 and HER2, are expressed simultaneously on the surface of exosomes secreted by SK-Br-3 cells, and the SERS signal intensity of the Rhodamine 6G (R6G) tagged on the terminal of DNA T_E increased with an increase in the concentration of the exosomes, while the SERS signal intensity of Cy5 linked on the terminal of the EpCAM aptamer, which acts as an internal standard, remains stable. The AuNRs are uniformly arranged in a hexagonal shape, and the dense "hot spots" produce "hot surfaces," which greatly improve the sensitivity and uniformity of detection. In the presence of target exosomes, the DNA colocalization three-signal input switch and the ratiometric strategy realize the specific and accurate detection of exosomes. This sensing strategy achieves a wide detection range (1.0 × 10⁴-5.0 × 10⁶ particles/mL) and a lower detection limit (5.3 × 10³ particles/mL), without using any signal amplification mechanism, demonstrating promising applications in health care monitoring and clinical diagnostics.