Gibberellins (GAs) are a family of phytohormones that are essential for plant development, but are difficult to recognize due to their identical chemical structures. MIT researchers build and fabricate polymer-wrapped single-walled carbon nanotubes (SWNTs) with different corona phases that preferentially bind to bioactive GAs, GA3 and GA4, causing variations in near-infrared (NIR) fluorescence intensity.

The Disruptive and Sustainable Technologies for Agricultural Precision (DiSTAP) program aims to change the way biosynthetic pathways are discovered, controlled, developed and translated to meet the global demand for food and nutrients. Scientists from MIT, Temasek Life Sciences Laboratory, NTU and NUS are collaborating to develop new tools for the continuous measurement of key plant metabolites and hormones.

DiSTAP researchers have developed the first nanosensor to detect and distinguish gibberellins (GAs). Unlike conventional collection methods, the nanosensors are non-destructive and have been successfully tested in live plants. They can be transformative for agriculture and plant biotechnology, giving farmers a valuable tool to optimize yields.

Researchers designed near-infrared fluorescent carbon nanotube sensors to detect and distinguish two plant hormones, GA3 and GA4. These hormones are diterpenoid phytohormones produced by plants that are believed to have played a role in the “green revolution” of the 1960s, which averted famine and saved lives. Further study of gibberellins could lead to other breakthroughs in agricultural science and have implications for food security.

Climate change, global warming and rising sea levels are causing soil salinity to rise, negatively regulating GA biosynthesis and promoting GA metabolism. New nanosensors created by SMART researchers make it possible to study GA dynamics in live plants under salt stress at an early stage, enabling farmers to intervene early when used in the field.

The CoPhMoRe concept introduced by MIT professor Michael Strano has enabled the development of new sensors that detect GA kinetics in the roots of model and non-model plant species, as well as GA accumulation during lateral root emergence. This was made possible by the development of a new coupled Raman/near-infrared fluorimeter that enables the self-referencing of nanosensor near-infrared fluorescence with its Raman G-band.

The reversible GA nanosensors detected increased endogenous GA levels in mutant plants producing more significant amounts of GA20ox1, as well as decreased GA levels in plants under salinity stress. When exposed to salt stress, lettuce growth was severely stunted and GA levels decreased after only six hours, demonstrating their efficacy as an indicator of salt stress after ten days.

Strano, the Carbon P. Dubbs Professor of Chemical Engineering at MIT co-corresponding author and DiSTAP co-lead principal investigator, said: “Our CoPhMoRe technique allows us to create nanoparticles that behave like natural antibodies by recognizing and attaching to specific molecules. But they are generally much more stable than alternatives. We have used this method to successfully create nanosensors for plant signals such as hydrogen peroxide and polluting heavy metals such as arsenic in plants and soil. The method works to create sensors for organic molecules such as synthetic auxin – an important plant hormone – as shown. This latest breakthrough now extends this success to a plant hormone family called gibberellins – an extremely difficult species to recognize.”

He adds: “The resulting technology provides a rapid, real-time and in vivo method to track changes in GA levels in virtually any plant, and could replace current detection methods that are labor intensive, destructive, species specific and much less efficient.”

Mervin Chun-Yi Ang, associate scientific director at DiSTAP and co-first author of the paper, says: “More than just a breakthrough in plant stress detection, we also demonstrated a hardware innovation in the form of a new coupled Raman/NIR fluorimeter that enabled self-referencing of SWNT sensor fluorescence with its Raman G-band, providing a represents great progress in the translation of our nanosensing toolsets to the field. In the near future, our sensors could be combined with low-cost electronics, wearable optodes or microneedle interfaces for industrial use, transforming the way industry screens and mitigates plant stress in food crops, potentially improving growth and yield.”

The new sensors could still have a variety of industrial applications and use cases. Daisuke Urano, a principal investigator at the Temasek Life Sciences Laboratory, adjunct assistant professor at the National University of Singapore (NUS) and co-corresponding author of the paper, explains: “GAs are known to regulate a wide variety of plant developmental processes from shoot, root and flower development to seed germination and stress responses in plants. With the commercialization of GAs, these plant hormones are also being marketed to growers and farmers as plant growth regulators to promote plant growth and seed germination Our new GA nanosensors can be applied in the field for early stage plant stress monitoring and can also be used by growers and farmers to monitor GA uptake or metabolism in their crops.”

The design and development of nanosensors, the creation and validation of the coupled Raman/near-infrared fluorimeter, and the statistical analysis of plant sensors for this study were performed by SMART and MIT. The Temasek Life Sciences Laboratory was responsible for the design, execution and analysis of plant-related studies.

Magazine reference:

  1. Mervin Chun-Yi Ang, Michael S. Strano et al. Near-Infrared Fluorescent Carbon Nanotube Sensors for the Plant Hormone Family Gibberellins. NanoLetters.DOI: 10.1021/acs.nanolett.2c04128