Plasma-Assisted Large-Scale Nanoassembly of Metal-Insulator Bioplasmonic Mushrooms

Large-scale plasmonic substrates consisting of metal-insulator nanostructures coated with a biorecognition layer can be exploited for enhanced label-free sensing by utilizing the principle of localized surface plasmon resonance (LSPR). Most often, the uniformity and thickness of the biorecognition layer determine the sensitivity of plasmonic resonances as the inherent LSPR sensitivity of nanomaterials is limited to 10-20 nm from the surface. However, because of time-consuming nanofabrication processes, there is limited work on both the development of large-scale plasmonic materials and the subsequent surface functionalizing with biorecognition layers. In this work, by exploiting properties of reactive ions in an SF₆ plasma environment, we are able to develop a nanoplasmonic substrate containing ∼10⁶/cm² mushroom-like structures on a large-sized silicon dioxide substrate (i.e., 2.5 cm by 7.5 cm). We further investigate the underlying mechanism of the nanoassembly of gold on glass inside the plasma environment, which can be expanded to a variety of metal-insulator systems. By incorporating a novel microcontact printing technique, we deposit a highly uniform biorecognition layer of proteins on the nanoplasmonic substrate. The bioplasmonic assays performed on these substrates achieve a limit of detection of 10^-17 g/mL (∼66 zM) for biomolecules such as antibodies (∼150 kDa). Our simple nanofabrication procedure opens new opportunities in fabricating versatile bioplasmonic materials for a wide range of biomedical and sensing applications.