Nanotube sensors can detect and distinguish gibberellin plant hormones

The nondestructive nanosensors could have wide applications in agricultural science.

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

The Disruptive and Sustainable Technologies for Agricultural Precision (DiSTAP) program aims to change how to plant biosynthetic pathways are discovered, monitored, engineered, and translated to meet global demand for food and nutrients. Scientists from MIT, Temasek Life Sciences Laboratory, NTU, and NUS are collaborating to develop new tools for continuously measuring important plant metabolites and hormones.

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

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 and are thought 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 cause soil salinity to rise, negatively regulating GA biosynthesis and promoting GA metabolism. New nanosensors created by SMART researchers allow the study of GA dynamics in living plants under salt stress at an early stage, allowing farmers to make early interventions when used in the field.

The CoPhMoRe concept introduced by MIT Professor Michael Strano has enabled the development of novel 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 developing 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 salinity stress, lettuce growth was severely stunted and reduced GA levels after just six hours, demonstrating their efficacy as an indicator of salinity 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 act like natural antibodies in that they can recognize and lock onto specific molecules. But they tend to be far more stable than alternatives. We have used this method to successfully create nanosensors for plant signals such as hydrogen peroxide and heavy-metal pollutants like arsenic in plants and soil. The method works to create sensors for organic molecules like synthetic auxin — an important plant hormone — as shown. This latest breakthrough now extends this success to a plant hormone family called gibberellins — an exceedingly difficult one to recognize.”

He adds: “The resulting technology offers a rapid, real-time, and in vivo method to monitor changes in GA levels in virtually any plant, and can replace current sensing methods which are laborious, 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 simply a breakthrough in plant stress detection, we have 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, representing a major advance in the translation of our nanosensing tool sets to the field. In the near future, our sensors can be combined with low-cost electronics, portable optodes, or microneedle interfaces for industrial use, transforming how the industry screens for and mitigates plant stress in food crops and potentially improving growth and yield.”

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

The design and development of nanosensors, creation and validation of the coupled Raman/near-infrared fluorimeter, and 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.

Journal reference:

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