SPIE Proceedings [SPIE 7th International Symposium on Advanced Optical Manufacturing and Testing Technologies (AOMATT 2014) - Harbin, China (Saturday 26 April 2014)] 7th International Symposium on Advanced Optical Manufacturing and Testing Technologies: Smart Structures and Materials for Manufacturing and Testing - Polyvinylpyrrolidone/reduced graphene oxide nanocomposites thin films coated on quartz crystal microbalance for NO 2 detection at room temperature