In a study published in Advanced Optical Materials, a interdisciplinary team from the Shenzhen Institute of Advanced Technology (SIAT) of the Chinese Academy of Sciences (CAS) developed a novel metasurface configuration supporting nonlocal quasi-BICs that can solve the above problems.

This metasurface is composed of periodic four silicon nanodisks, forming two hybridized lattices with a small displacement. The measured bulk sensitivity reaches up to 407 nm/RIU and the limit of detection is down to 20 pg/mL for a protein biomarker for the early-stage breast cancer screening, which is improved by more than an order of magnitude over the state of the art.  

"A quasi-BIC supported by the proposed metasurface configuration is especially suitable for sensing applications. The quality factor remains high even when the dielectric environment is asymmetric. Another feature is the homogeneous and significant near-field enhancement over large volumes outside the silicon nanodisks, which will greatly boost the light-analyte interactions and push down the limit of detection," said Dr. LI Guangyuan, one of the corresponding authors of this study. 

Taking advantage of these unique characteristics, researchers explored the biosensing applications for the label-free detection of the human epidermal growth factor receptor 2 (ERBB2), which is a breast cancer biomarker for early-stage screening.  

They measured the resonance wavelength shifts induced by the antigen-antibody bonding under different ERBB2 concentrations. The results showed an ultralow limit of detection, as low as 20 pg/mL, more than an order of magnitude lower than the literature. 

"We anticipate that this metasurface platform will have broad applications in biosensing beyond the particular cancer biomarker studied in this research and outside the realm of antigen-antibody binding mechanisms," said Dr. LIU Yunhui, another corresponding author of this study.