Ultra-Sensitive Colorimetric Plasmonic Sensing and Microfluidics for Biofluid Diagnostics Using Nanohole Array

Figure 4

(a) Lift-off free evaporation (LIFE) method of forming nanoholes. The method involves making holes on the underlying SiNx membrane instead of the PMMA resist. The backetching of Si supporting substrate enables a suspended plasmonic nanohole structure. Both electron-beam lithography (EBL) and interference lithography (IL) were used to make the nanohole structures. SEM images on the right show fabricated devices showing nanohole array with period of 600 nm, and diameter of 180 nm made using EBL process. Using IL process the periodicity was 580 nm and the diameter of the holes was 230 nm. Adapted from [78]. (b) Schematic of template stripping methods to make plasmonic devices with smooth surfaces. This process takes advantage of the poor adhesion and good wettability of noble metals on silicon. SEMs of the silicon template and template stripped silver device are shown at the bottom. Adapted from [90].

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