(523b) In Planta Detection of Synthetic Auxin Plant Hormones Using Single-Walled Carbon Nanotubes (SWNT) Based Nano-Sensors

1-Naphthalene acetic acid (NAA) is one of the most commonly-used synthetic auxin plant hormones in agriculture as rooting agent or as sprays to prevent premature flowering and fruit drop. NAA is subject in some countries to regulatory control, requiring monitoring of NAA levels in vegetables and fruits. Unfortunately, state-of-the-art NAA sensing methods are destructive and laborious. In this work, we show the development of a novel NAA nano-sensor based on the concept of corona phase molecular recognition, using cationic polymer wrapped single-walled carbon nanotubes (SWNTs). This approach allows real-time non-destructive in planta detection of NAA. Using a semi-rational approach to polymer design, we developed a sensor that is selective for auxins, with particularly large responses to NAA as well as indole-3-butyric acid (IBA), both of which are used as rooting agents. An unresponsive control sensor was also developed to enable a ratiometric sensing platform. The sensor is demonstrated in planta for living spinach plants. We further probed the corona phases of both the active and control sensors, using the molecular probe adsorption (MPA) method to measure their accessible surface area for analyte adsorption. In both sensors, the Gibbs free energy of the riboflavin molecular probe binding to SWNT scales inversely with cube root of accessible surface area, which is in agreement with the structure-property relationship established for corona structures across different systems.

Since its initial discovery and commercialization in the 1940s, 2,4-Dichlorophenoxyacetic acid (2,4-D) has been an selective auxin herbicide commonly used for agricultural purposes. With increased usage of 2,4-D, herbicide resistance in weeds is of concern. To date, there are 28 reported species of weeds resistant to 2,4-D. Application of ineffective herbicides with poor levels of control causes wastage of money to farmers and detriment to the environment. In this work, we have developed a selective SWNT-based nano-sensor for 2,4-D based on the same corona phase molecular recognition approach, which also allows real-time non-destructive in planta detection of 2,4-D. This helps prevent wasteful spraying and ineffective deployment of herbicides onto resistant weeds. It also allows us to calibrate the herbicide dosage to minimize its usage. Further, it provides a rapid screen for herbicide susceptibility without need to monitor plant growth over days. The sensor is demonstrated in planta for living non-model plant species such as spinach, pak choy (Brassica rapa subsp. chinensis) and choy sum (Brassica chinensis var. parachinensis).