Abstract: Ultra near-field index modulated plasmonic nano-aperture label-free imaging methods and techniques are useful for imaging and detection of biological microparticles and nanoparticles such as circulating tumor exosomes (CTEs), bacteria and vimses. The methods and techniques utilize a high-density array of gold, silver, or gold/silver alloy nanodisks, in some cases on an undercut or invisible substrate. Given the relatively large nanodisk dimensions, the nanodisk array may feature a significantly blue-shifted LSPR extinction peak due to both far-field plasmonic coupling and substrate undercut. The ultra near-field imaging methods have the ability to image nanoparticles as small as 25 nm.