Ultrasensitive on-chip immunoassays with a nanoparticle-assembled photonic crystal.

Electrophoretic particle entrapment system (EPES) is employed to generate 2D array of nanoparticles coated with biological molecules (i.e., antibodies). Phase matching of the excitation and the emission in the 2D arrays with particles produces a highly enhanced fluorescence signal that was shown to improve the limit of detection in immunoassays. The phase matching is achieved when the particle are in the sub-100 nm range. A comparison between different size particles shows that the sensitivity of an immunoassay is extended to a range that is difficult to achieve with standard technology (e.g., enzyme-linked immunosorbent assay-ELISA). The effectiveness of this novel configuration of particle-in-a-well was demonstrated with an assay for human epidermal growth factor receptor 2 (HER2; breast cancer biomarker), with a detection limit as low as 10 attomolar (aM) in less than 10 μL of serum-based sample. The limit of detection of HER2 indicated far superior assay performance compared to the corresponding stand...