Three-Dimensional Hot-Volume Plasmonic Gold Nanoreactor Array for Ultrasensitive Immunoassays

A three-dimensional hot-volume plasmonic gold nanoreactor array (3D HPNRA) composed of gold nanodimples decorated with high-density gold nanoparticles on a 3D curved surface is developed for ultrasensitive immunoassays. The 3D HPNRA generates volumetric hotspots inside the 3D space, and a significant plasmonic coupling effect is created, forming an inclusion complex with probe gold nanoparticles (AuNP probes) coated with a detection antibody (Ab). Due to multiple plasmonic coupling effects inside 3D spaces, the 3D HPNRA is utilized as an ultrasensitive SERS-based detection platform after functionalization of the 1st Ab for cardiac troponin I (cTnI), which is selected as a model antigen for immunoassay demonstration. After integration of the 3D HPNRA with a 3D-printed well plate, ELISA is performed using the AuNP probes, and a portable Raman instrument is subsequently used for quantitative immunoassays. As a result, the 3D HPNRA coupled with the AuNP probes showed ∼400-fold enhanced sensitivities of 22.9 and 27.8 fg/mL for cTnI spiked in PBS and FBS, respectively, compared to conventional ELISA. The developed 3D HPNRA with the coupling of AuNP probes is expected to be applied for ultrasensitive immunoassays, especially for early disease diagnosis and the discovery of biomarkers that exist in an ultralow concentration range.