Plasmonic properties of anchored nanoparticles fabricated by reactive ion etching and nanosphere lithography

摘要

Aqueous environments pose unique challenges to the use of nanoparticle platforms for development of robust in vitro and in vivo sensors. A method is developed to anchor nanoparticles into a glass substrate by combining nanosphere lithography (NSL) and reactive ion etching (RIE) to create a mechanically durable sensing platform. The increased mechanical performance is attributed to the higher adhesion strength of NSL nanoparticles anchored in shallow nanowells formed by RIE. Using atomic force microscopy (AFM), anchored and conventional NSL nanoparticle arrays were subjected to increasing normal forces. The anchored nanoparticles were able to withstand normal forces 3 times greater (35.1 nN) compared to the conventional NSL nanoparticles (12.4 nN) prior to separation from the glass substrate. Superior adhesion in a constant flow aqueous environment is demonstrated by extinction measurements. After 1 h of 1.5 mL/min flow, extinction intensity decreased by 53% for bare and 13% for functionalized nanoparticles that were not anchored while extinction intensity decreased by only 15% for bare and less than 1% for functionalized nanoparticles that were anchored. A systematic shift to longer wavelengths is observed in the localized surface plasmon resonance (LSPR) spectra of the nanoparticle arrays as the embedded depth increases. This systematic shifting behavior of the LSPR wavelength maximum, lambda(max), in the range from 678 to 982 nm, can be used to tune the plasmon position. LSPR shifting is used to demonstrate the detection of Alzheimer's precursor ligands as a potential biosensing application of the anchored nanoparticle arrays. Furthermore, we estimate the enhancement factors for SERS of the anchored nanoparticles are on the same order of magnitude (10(8)) as the nanoparticles on flat substrates. Theoretical modeling is conducted to understand the shifting behavior of the anchored nanoparticle arrays.