Biochemical Ratiometric Sensing By Single Chirality Carbon Nanotubes in Living Tissues

Single walled carbon nanotubes (SWNT) are well positioned to act as single particle sensors in living organisms as they do not photobleach and fluoresce in the near infrared (NIR) in which tissues are relatively transparent. However, lack of specificity of SWNT fluorescence response to biochemical compounds has limited their applications as sensors in vivo. Here we show that SWNT localized inside leaves enable a more selective ratiometric sensing of plant free radicals and pollutants like nitric oxide and hydrogen peroxide. Using a novel method for rapid and efficient coating exchange of single chirality SDS-SWNT, we synthesized the first SWNT ratiometric sensor with 6,5 and 7,6 chiralities coated with single stranded DNA and Polyvinyl alcohol. These ratiometric platform was designed for 7,6 SWNT NIR fluorescence to quench in the presence of the free radicals while being unresponsive in the 6,5 SWNT chirality. Thus creating a multimodal NIR spectral signature that increases selectivity to biochemicals generated by plants or pollutants in the environment. Spatial and temporal patterns of the ratio sensor nIR fluorescence in the leaf lamina in response to exogenously and endogenously generated nitric oxide and hydrogen peroxide were monitored in vitro and imaged in vivo in real time. This nanobionic approach of interfacing nanosensors with leaves will lead to the development of cost effective, selective, and stable plant biochemical detectors.