Background:

1. Two-dimensional nanohole array surfaceplasmon resonance biosensorAditya Kher, Lin Pang, H. Matthew Chen, and Yeshaiahu Fainman Background: Experiment: • A microfluidic channel is mounted onto the nanohole array • Monitor changes on the surface of the nanohole array by looking at the SPP resonant wavelength • Different liquids in the fluidic channel means different refractive indices at the interface, detected as different resonant wavelengths for the SPP • A surface plasmon-polariton (SPP) is an electromagnetic wave that is confined to the interface between a metal and a dielectric. • SPPs are very sensitive to changes on this surface, such as changes in refractive index • Because of the SPP dispersion relation, a grating coupler is used in order to excite them • In our case, this grating is a two-dimensional nanohole array Fabrication: Measuring surface hydrophilicity: • We have developed a novel bottom-up approach to fabricating these nanohole arrays • Resist is patterned using low-cost holographic lithography • Gold is sputtered at an angle, on top of the resist pillars, leaving holes where there are holes in the resist layer—no etching required • The size of the gold nanoholes can be changed by changing the sputter deposition time: longer deposition yields smaller holes, and smaller holes produce a better SPP signal • We can use this setup to measure the hydrophilicity, or “wetting ability”, of the nanohole array surface with respect to various fluids • Begin monitoring the SPP resonant wavelength after flowing all of the liquid through the chamber (so that air is left inside) • The adsorption thickness is related to the time it takes for the wavelength to shift, and determines the hydrophilicity by the following equation: Recent and future work: • Measuring the binding affinity between biomolecules by flowing them successively over the nanohole array surface • Increasing the sensitivity in several ways, for example by employing a reference channel to subtract off environmental changes Sample with smaller hole diameter has smaller SPP linewidth Side view of sample with gold sputtered onto resist pillars