Field-effect transistor (FET) devices based on functionalized nanocarbon materials are a promising technology for biomolecular sensing applications. Nanocarbon-based field-effect transistor (NC-FET) devices allow for label-free detection of biomolecules with the advantage of easy and direct electrical readout compared to most routine techniques.
Study: Fabrication and Functionalisation of Nanocarbon-based Field-Effect Transistor Biosensors. Image Credit: Marcin Janiec/Shutterstock.com
NC-FET biosensors are ideal candidates for next-generation diagnostic technologies. Integrating biomolecules into electrically conducting carbon-based platforms results in the fabrication of highly sensitive, real-time multiplexed sensors.
Due to their user-friendly, environment-friendly, and label-free sensing characteristics, NC-FETs are anticipated to empower the rapidly progressing fields of environmental monitoring, healthcare, and biosensing. A review published in ChemBioChem presented an overview of NC-FETs, highlighting their fabrication strategies and functionalization for biosensing applications.
NC-FET Biosensors and Their Advantages
A biosensor is an analytical device incorporating a biological recognition element in direct spatial contact with a transduction element. This integration ensures the rapid and convenient conversion of biological events to detectable signals.
In an electrical biosensor, the receptor (proteins or nucleic acids) and transducer are the two key components. The latter converts biological interactions (binding) with the biosensors into electrical signals in the form of current, resistance, or conductance. Among diverse electrical biosensing architectures, devices based on FETs are ideal biosensors.
NC-FET biosensors use carbon nanomaterials, including graphene and carbon nanotubes (CNTs), as transduction material due to their intrinsic properties such as rapid electron transport, facile functionalization strategies, large surface area to volume ratio, and ease of synthesis.
As the FET setup is a label-free sensing technique, it is more advantageous for electrical biosensor applications. When the target binds to the receptor, the FET-biosensor promotes a gating effect on conductance, thereby generating an output.
Although metal-oxide-semiconductors (MOS) or organic semiconductors were proposed as cost-effective and scalable channel materials, their low on/off ratio, slow mobility, poor signal-to-noise ratio, and short lifetime restrict their application. Carbon nanomaterials can overcome these shortcomings due to their unique physical and chemical properties, increasing the sensitivity in detecting target biomarkers.
Current Fabrication Techniques of NC-FETs and Future Prospects
To fabricate NC-FETs with CNTs, either the electrode is patterned onto CNTs or CNTs from the solution are deposited onto pre-patterned electrodes. The latter fabrication method is more suitable for the mass production of NC-FETs.
On the other hand, the most crucial step in the fabrication of graphene FETs is the transfer of the synthesized graphene to the substrate. Graphene synthesized via chemical vapor deposition (CVD) on a copper substrate is transferred to the target using a stamping method. Alternatively, solution-synthesized graphene is drop-casted onto the substrate, followed by patterning of the electrodes by metal evaporation.
Previous researchers adopted an advanced model in which lysozyme and DNA were used in a complex with single-walled CNTs (SWCNTs), which allowed the investigation of the origin of the electrostatic gating effect that can help assess the size, orientation, and affinity of prospective molecular recognition elements.
Furthermore, device uniformity has been previously achieved using semiconducting CNT dispersion methods, and functionalization uniformity are yet to be addressed to regulate the number of biomolecules that may connect to an NC-FET device.
Other researchers developed a unique DNA-guiding technique to regulate the order and amount of covalent functionalization of CNTs, which can be applied in biofunctionalization schemes. Additionally, non-specific analyte binding can be addressed by simply producing high-affinity receptors, such as aptamers and nanobodies, simplifying the methods by minimizing the requirement for passivation.
After determining the best NC-FET arrangement, the next task is to incorporate multiplexed arrays with transistors to facilitate multianalyte sensing. Engineers' inputs can be used to design logic circuits with integrated decision-making, resulting in tiny portable diagnostic devices that allow real-time monitoring of complicated samples.
While conventional methods, such as microbial culturing, require days to yield results, point-of-care diagnostic tests can provide results within minutes. The adaptability of NC-FETs can help target new analytes and pave the way for next-generation bio-transistors with superior sensitivity for analyte detection.
Conclusion
Overall, FET-based biosensors have substantial potential for future applications. Due to the outstanding electrical properties and environmental ultra-sensitivity of carbon nanomaterials, many strategies have been developed to create NC-FET-based biosensors.
Despite this remarkable progress, none of the NC-FET-based electrical biosensors has yet advanced to commercialization. The primary challenge stems from the device-to-device heterogeneity of baseline electronic properties.
Developing a reliable and scalable fabrication technique for mass-producing identical carbon nanomaterials arrays and integrating individuals into functional FET devices with high yields are some of the issues to be addressed in the future.
Reference
Lee, C., Gwyther, R.E., Freeley, M., Jones, D.D., Palma, M. (2022), Fabrication and Functionalisation of Nanocarbon-based Field-Effect Transistor Biosensors. ChemBioChem. https://chemistry-europe.onlinelibrary.wiley.com/doi/10.1002/cbic.202200282
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