Highly sensitive SERS detection of IL-6 in serum by Au@Fe3O4 nanoring-based sandwich immunoassay

Detection of tumor markers is a key to realize the early diagnosis of cancer patients and improve the survival rate of patients. However, there are still great challenges in developing a highly sensitive and selective method to detect the tumor marker interleukin-6 (IL-6) of primary liver cancer, because the concentration of IL-6 in biological samples is limited and various interfering substances exist. Herein, a magnetic SERS immunoassay based on Fe3O4 nanoring (R-Fe3O4) was developed. The method could realize quantitative detection in 0.1–1000 pg/mL according to the sandwich principle and the detection limit of IL-6 reached 0.028 pg/mL. The excellent detection capability was mainly attributed to the characteristics of R-Fe3O4. Strong magnetism of R-Fe3O4 can enrich target molecules at low concentration, and the ring structure can facilitate the deposition of precious metal particles due to the high specific surface area, so as to promote the generation of hot spots and form electromagnetic enhancement. The method exhibited high selectivity for the identification of IL-6 and showed favorable detection results for IL-6 in serum samples. The ultra-sensitivity and high selectivity of the magnetic SERS immunoassay based on R-Fe3O4 would exhibit great development prospects in medical detection.