Bifunctional Nano Lycurgus Cup Array Plasmonic Sensor for Colorimetric Sensing and Surface‐Enhanced Raman Spectroscopy

A bifunctional ultrasensitive nanoplasmonic sensor is demonstrated with combined surface plasmon resonance (SPR) and surface‐enhanced Raman spectroscopy (SERS) sensing capabilities. Unlike traditional extraordinary transmission (EOT) devices, nano Lycurgus cup array (nanoLCA) contains a hybrid configuration of periodic quasi‐3D nanostructure array and dense sidewall metal nanoparticles within each nanostructure, which enables both refractive index sensing and SERS chemical identification on the same device with high sensitivity. The visible plasmon resonance sensitivity of nanoLCA is measured to be as high as 796 nm/RIU with the figure of merit (FOM) of 12.7 so that the device is applied for colorimetric liquid sensing with an ordinary microscopic system. Moreover, the SERS enhancement of the very same nanoLCA for liquid sample is calculated to be 2.8 × 10⁷, which is the highest among all reported EOT‐based SERS devices. The urea concentration detection has been demonstrated to show the complementary rapid colorimetric screening and precise SERS identification functions provided by nanoLCA plasmonic sensor for chemical analysis or biological diagnostics in a resource‐limited environment.