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(Invited) Controlling CNT-Biomolecule Interfaces -and Their Orientation- to Tune Electrostatic Gating in CNT-Based Biosensing Devices

The development of novel bioelectronics interfaces via the bottom-up assembly of platforms capable of monitoring and exploiting biomolecular interactions with nanoscale control is a central challenge in nanobiotechnology. Biomolecular interactions can be used to electrostatically gate conductance in nanomaterials-based field effect transistors (FETs), but this can be exploited far more effectively than currently done by defining the interface between the biomolecule and the transducer. This strategy forms the basis of greatly improved electrical-based biosensors and offers great potential for building next generation biosensing devices.
 We will first present different approaches to control the assembly of carbon nanotube (CNT)-protein interfaces towards the fabrication of bioelectronic devices, with a particular focus on the development of real-time biosensors with engineered protein interfacing. We will report the construction of nanoscale protein-based sensing devices designed to present proteins in defined orientations; this allowed us to control the local electrostatic surface presented within the Debye length, and thus modulate the conductance gating effect upon binding incoming protein targets.[1] We systematically tested how protein orientation dictates current response through a CNT-FET device by defining the interface site on the capture protein. Presentation of different protein-protein electrostatic surfaces within the Debye length led either to increase or decrease in conductance: defined and homogenous attachment allows distinctive conductance profiles to be sampled based on the unique electrostatic features of individual proteins, and can support the identification of preferred proteins orientations for optimal sensing. In our case this was done for the detection of a range of concentrations of a class b-lactamase enzymes, that degrade antibiotics, in the context of investigating antimicrobial resistance (AMR).
 Additionally, we will present the controlled assembly of CNT–GFP hybrids employing DNA as a linker, with protein attachment occurring predominantly at the terminal ends of the nanotubes, as designed.[2] The electronic coupling of the proteins to the nanotubes was confirmed via in-solution fluorescence spectroscopy, that revealed an increase in the emission intensity of GFP when linked to the CNTs. The strategies presented here are of general applicability for the controlled assembly of CNT-protein interfaces toward biosensing and optoelectronics applications.
 Finally, we will report the tuning of electrostatically gated conductance changes in CNT-aptamer biosensing FETs. We have developed diverse strategies for the construction of such nanoscale devices via in-solution assembly and (self)organization on surfaces. We will discuss how this can lead to distinct conformational changes of the CNT-bound aptamers upon biomarker recognition , leading to opposite electrical response of our biosensors , i.e. increase or decrease in current.[3] These studies highlight the need to define CNT-biomolecule interfaces in order to control and tune by design the electrostatic gating in CNT-based devices, toward the construction of optimized biosensors.
 [1] Angew. Chem. Int. Ed. 2021, 60, 20184 –20189
 [2] Biomolecules 2021, 11(7), 955
 [3] in preparation