A direct electronic readout of the presence of toxic volatile molecules
07.10.2024
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Diagram of the graphene transistor before and after desorption of acetonitrile molecules. Image: José Sánchez Costa. |
- IMDEA Nanociencia researchers are leading the pioneering implementation of coordination polymers, typically insulators, in nanoscale electronic devices.
- The incorporation of coordination polymers in graphene transistors allows an electronic reading of the presence of toxic volatile molecules.
- The structural changes of the polymer, as a result of the absorption or desorption of these molecules, are detected through graphene as abrupt changes in its electrical conductivity.
- Capturing and signalling gases and other pollutant emissions quickly and reliably is crucial for health.
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Madrid, 7th October, 2024. The capture of gases, vapours and other polluting emissions is crucial for health, especially in industrialised societies. The "Switchable Materials" research group at IMDEA Nanociencia, led by Dr. José Sánchez-Costa, is working on the synthesis and characterization of compounds that can not only capture these molecules, but also provide information in situ and in real time that they are indeed being absorbed. Therefore, these compounds, called coordination polymers – a group to which metal-organic networks (MOFs) also belong – can serve as chemical sensors against volatile compounds.
In 2019, Dr. Sánchez-Costa's group synthesized a coordination polymer, a compound that changed color from yellow to orange and vice versa in response to acetonitrile absorption/desorption. The acetonitrile molecules were absorbed and diffused into the crystal lattice, which modified their structure and also their color to the naked eye. This chemical sensor had an advantage over other gas detection methods because it was simple and low-cost, as well as reversible. The compound changed its color from orange to yellow when it absorbed the gas, and returned to its orange color when it expelled the molecules inside.
Now, researchers have studied how to include these typically insulating polymers in micrometric electronic devices. Specifically, they have deposited an organic-metallic hybrid material (with a molecular formula [∞[Fe(H2O)2(CH3CN)2(pyrazine)]) on a graphene sheet forming a field-effect transistor (FET). The polymer sheets, about 300 nanometers thick, are deposited on graphene—an atomically thick layer of carbon—forming a FET transistor. The large difference in electrical conductivities of graphene and polymer ensures that most of the electrical charge is transported through graphene. In this way, they have been able to study the properties of the polymer interacting with graphene, obtaining surprising results.
Conductivity measurements in graphene have shown the transformations that the polymer undergoes as a result of the absorption and desorption of acetonitrile molecules. The structural transformations of the polymer are detected as abrupt changes in the conductivity of the graphene device, which increases dramatically. The origin of this modulation of conductivity lies in the doping (p-type, positive) of graphene by the acetonitrile released by the polymer.
The idea of reducing the coordination polymer and harnessing it at the nanoscale is based on sensitivity, which increases as its dimensions are reduced. By making the compound smaller, fewer molecules are needed to produce an alert, in the form of a color change. Ideally, a small number of acetonitrile molecules would be needed to activate its structural transformation.
In addition, the incorporation of this material, sensitive to gas and in a reversible way, in a transistor has an obvious advantage, and that is that it can be integrated into electronic devices for indirect reading. Graphene's sensitivity to acetonitrile release allows the structural changes of the coordination polymer to be detected through conductivity measurements.
In the "Switchable Materials" group of IMDEA Nanociencia, non-porous and switchable coordination polymers are mainly studied. These materials, which are perhaps not as popular as metal-organic networks (MOFs) because they are not porous, have an advantage precisely for this reason: "As they are not porous, the way they house molecules inside them is highly selective," says Dr. José Sánchez. The selectivity of materials that can absorb molecules is key to device design, since in general it is desired to capture only one type of molecule. The method of manufacturing the devices would be simple: "By depositing a single drop, a new device can be manufactured with a specific application," says Dr. Esther Resines. The collaboration with Dr. Enrique Burzurí, a researcher at the Autonomous University of Madrid, has been crucial for the development of this work. Dr. Burzurí is an expert in the design and characterization of devices based on low-dimensional materials, such as graphene.
The proposed method is a powerful tool for converting crystal transformations into electrical signals. It is also possible to modulate the electronic properties of graphene in a controlled way through the release of molecules.
This work is a collaboration between researchers from IMDEA Nanociencia and the Autonomous University of Madrid, and has been co-funded by the Advanced Materials Network of the Complementary R+D+I Plan and the Severo Ochoa Excellence distinction to IMDEA Nanociencia.
Reference:
Lucía Martín-Pérez, Esther Resines-Urien, José Sánchez Costa, Enrique Burzurí. Graphene conductance modulation through controlled molecular release in a hybrid coordination polymer/graphene field-effect transistor. Carbon, 225, 119145 (2024). DOI: 10.1016/j.carbon.2024.119145.
https://repositorio.imdeananociencia.org/handle/20.500.12614/3731
Contact:
Dr. José Sánchez Costa
jose.sanchezcosta (at) imdea.org
https://www.imdeananociencia.org/switchable-nanomaterials/home
https://x.com/josescostalab
Dr. Enrique Burzurí
enrique.burzuri (at)uam.es
Oficina de Divulgación y Comunicación en IMDEA Nanociencia
divulgacion.nanociencia [at]imdea.org
Twitter: @imdea_nano
Facebook: @imdeananociencia
Instagram: @imdeananociencia
Source: IMDEA Nanociencia.
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