Solution Processable Carbon Nanotube Biosensors with Multisensing Capability
Authors: Xu Xinzhao , Clement Pierrick , Eklöf Johnas Victor Roland , Moth-Poulsen Kasper , Chavez Jorge , Palma Matteo 
Published: February 2020

The rapid development of nano-biosensors, combining nanomaterials (as detectors) and biological components (as receptors), offers great opportunities for enhancing the efficiency of biomarkers’ detection. Establishing a practical platform with low cost processability and multi-sensing capability is of significance to both fundamental biology and practical diagnosis.
Devices consisting of one-dimensional nanostructured materials and bioreceptors, in particular single walled carbon nanotubes (SWCNTs) and aptamers, have been used to fabricate nanoscale biosensors. CNTs have been considered as one of the best nanomaterials for the fabrication of nanoscale biosensors, because of their intrinsic nanoscale size and their low charge carrier density. Additionally, due to their high affinity and specificity to biotargets, aptamers can improve the selectivity of biosensing devices. In this regard, efforts have been dedicated to fabricate CNT-aptamer based biosensors. However, it is still challenging to fabricate CNT-aptamer biosensing devices possessing both low cost processability (i.e. ideally from solution) and multi-sensing capability.
Herein, we report a solution processable strategy for the fabrication of ultra-sensitive, selective and reconfigurable nanoscale biosensors, based on SWCNTs and aptamers (Figure 1). Briefly, SWCNTs wrapped with DNA (therefore water-soluble) were functionalized with aptamers in solution, which were then used as selective bioreceptors for particular analytes of interest. Atomic Force Microscopy (AFM) images demonstrated the successful formation of SWCNT-aptamer hybrids; these SWCNT-aptamer hybrids were then immobilized in a device configuration between electrodes via dielectrophoresis (DEP).
We initially verified whether the nucleotide recognition element within the SWCNT-aptamer hybrids was accessible, by exposing these devices to the aptamers’ complementary strands. The change in source-drain current indicated the successful hybridization between the aptamers in the devices and the complementary strands. This specific hybridization was further confirmed by a control experiment employing a non-complementary ss-DNA. Moreover, the denaturation of the hybridized DNA induced by a simple cleaning procedure, demonstrated the re-configurability of our devices. We finally investigated the electrical response of our devices for the detection of biomarkers indicative to stress and neuro-trauma conditions. Our results showed that these devices are able to detect concentrations of relevant analytes from pM to µM, with high selectivity and reversibility.
We extended this idea towards the fabrication of a multi-sensing platform, by immobilizing on the same chip different SWCNT-aptamer hybrids selective to distinct biomarkers. Notably, we obtained evidence of selective recognition without any crosstalk nor false-positive signals; detection in serum and real time measurement further demonstrated the potential of our multi-sensing nanoscale devices.
In conclusion, we present an environmentally friendly and low-cost strategy for the fabrication of label-free biosensing devices that allow for the real time and reversible electrical detection of biomolecules. Because we assembled SWCNT-aptamer hybrids with distinct bio-recognition elements on the same chip, the devices exhibit multi-sensing capability in addition to high sensitivity and selectivity. The general applicability of this solution-processable method makes it suitable for different practical applications, including for point of care clinical diagnosis.

Figure 1