Species selective vapour sensing has been demonstrated using a coated Long Period Grating with a period and coating thickness that gives rise to a dual resonant response. A calixarene coating with nanostructured features was deposited using the Langmuir-Blodgett technique. A nanoscale cavity in the calixarene molecule adsorbs the analyte molecule causing an increase in the density and thereby the refractive index of the coating. Preliminary vapour sensing experiments were performed and indicate the sensor's selectivity, demonstrating strong responses to toluene and benzene, while exhibiting lower sensitivity to hexane and cyclohexane.