Molecularly imprinted sol-gel/Au@Ag core-shell nano-urchin localized surface plasmon resonance sensor designed in reflection mode for detection of organic acid vapors.

A molecularly imprinted sol-gel (MISG)/Au@Ag core-shell NU sensor is proposed for organic vapor detection in an optical fiber-based reflection mode. The compact structure design of the system in the reflection model is promising for practical use as a portable and rapid responsivity sensing probe. Volatile organic acids (OAs) are analogs to biogenetic volatile organic vapors related to specific human diseases. Here, Au@Ag core-shell nano-urchins exhibiting branched tips were synthesized and deposited on indium tin oxide (ITO) glass in small dimer and trimmer clusters to generate an enhanced electric field. A MISG solution was then spin-coated on the substrate to fabricate MISG-LSPR sensors, and three types of MISGs were developed for the detection of hexanoic acid, heptanoic acid and octanoic acid. The normalized spectral response indicated selectivity of the MISG-LSPR sensors for the corresponding template OAs. With Native Bayes and linear discriminant analysis of the sensor responses, where the latter were detected by the proposed system, single- and mixed-OA vapors could be classified into separate clusters. This signified that the proposed MISG-LSPR sensor can be applied toward pattern recognition of single vapors or multiple vapor mixtures.