Autonomic Molecular Transport for Ultrasensitive Surface-Enhanced Infrared Absorption Spectroscopy

Nanoantenna-based surface-enhanced infrared absorption (SEIRA) is a powerful platform for the detection of biological and chemical species due to its ability to strongly enhance infrared absorption of a relatively narrow band of vibrational modes. However, SEIRA only detects molecules within order of 100 nm of the nanoantenna, and thus, it requires diffusion of analyte into the local vicinity of the nanoantenna to provide enhanced sensing. Here, we demonstrate the use of a polyacrylamide hydrogel film with imbedded radial chemical gradient to locally concentrate analytes in the local vicinity of SEIRA-active nanoantenna to improve the detection limit over that provided by SEIRA alone. Using a positive charge gradient, embedded in a hydrogel film, a nerve agent simulant, 4-methylumbelliferyl phosphate, was concentrated 15-fold above a SEIRA-active array of nanoantenna. The combined effect of molecular concentration and SEIRA resulted in the potential ability to detect the agent of interest at concentrations 2 orders of magnitude below that provided by ATR spectroscopy using a conventional, gradient-free substrate.