1. The Horticulture and Food Research Institute of New Zealand, East Street, Private Bag 3123, Hamilton 3240, New Zealand, MacDiarmid Institute for Advanced Materials and Nanotechnology, Department of Electrical and Computer Engineering, University of Canterbury, Private Bag 4800, Christchurch 8020, New Zealand, and Department of Engineering, University of Waikato, Private Bag 3015, Hamilton 3240, New Zealand