Effects of three-layered nanodisk size on cell detection sensitivity of plasmon resonance biosensors

The double resonance plasmonic biosensors based on Au nanodisks (NDs) with a thin SiO₂ spacer between the top and bottom Au layers were employed to detect MCF-7 breast cancer cells. The hybridized modes between the localized surface plasmon resonance of Au NDs and the gap coupling resonance of NDs with the Au film underneath have been observed. These multiple metallic layer NDs exhibit higher sensitivity than the common single metallic layer NDs. The extinction spectra showed double resonance bands that could be tailored by varying the ND size. Three sizes of multiple layer NDs ranging from 60 to 200nm diameter (dia.) were generated and their refractive sensitivity to the surrounding media were analyzed for cell detection. Nanodisks with 120 dia. showed the highest refractive sensitivity up to 230nm/refractive index unit. These sensors could be used to detect a broad range of MCF-7 cells from a low cell concentration down of 1.0 × 10³ cells/ml up to a high cell concentration of 1.7 × 10⁷ cells/ml.