The promise of graphene-based transistors for democratizing multiomics studies.

As biological research has synthesized genomics, proteomics, metabolomics, and transcriptomics into systems biology, a new multiomics approach to biological research has emerged. Today, multiomics studies are challenging and expensive. An experimental platform that could unify the multiple omics approaches to measurement could increase access to multiomics data by enabling more individual labs to successfully attempt multiomics studies. Field effect biosensing based on graphene transistors have gained significant attention as a potential unifying technology for such multiomics studies. This review article highlights the outstanding performance characteristics that makes graphene field effect transistor an attractive sensing platform for a wide variety of analytes important to system biology. In addition to many studies demonstrating the biosensing capabilities of graphene field effect transistors, they are uniquely suited to address the challenges of multiomics studies by providing an integrative multiplex platform for large scale manufacturing using the well-established processes of semiconductor industry. Furthermore, the resulting digital data is readily analyzable by machine learning to derive actionable biological insight to address the challenge of data compatibility for multiomics studies. A critical stage of systems biology will be democratizing multiomics study, and the graphene field effect transistor is uniquely positioned to serve as an accessible multiomics platform.

Etching of surfactant from solution-processed, type-separated carbon nanotubes and impact on device behavior.

Semiconducting single-walled carbon nanotubes (SWCNTs) have great potential for use in electronic and optoelectronic devices. However, methods for synthesizing SWCNTs produce a mixture of metallic and semiconducting materials, which require additional processing to separate by electronic type. Purification and enrichment of the semiconducting fraction is readily achieved by using the centrifugation of aqueous suspensions of SWCNTs with the help of surfactants, but this leaves residual surfactant on the SWCNT surface that can impact their electronic and optical properties. Here, we present a detailed study of the sodium taurodeoxycholate (STDC) surfactant removal process during vacuum annealing, showing that it occurs through fragmentation of the surfactant, and that complete removal requires exceedingly high temperatures, which indicates strong binding to the SWCNTs. We then present an approach based on air oxidation and mild annealing to completely remove the surfactant while maintaining the SWCNT properties. Using this approach, we compare single SWCNT electronic devices with and without STDC and show that, despite the very strong surfactant binding, it does not affect device performance substantially.

Photothermoelectric p-n junction photodetector with intrinsic broadband polarimetry based on macroscopic carbon nanotube films.

Light polarization is used in the animal kingdom for communication, navigation, and enhanced scene interpretation and also plays an important role in astronomy, remote sensing, and military applications. To date, there have been few photodetector materials demonstrated to have direct polarization sensitivity, as is usually the case in nature. Here, we report the realization of a carbon-based broadband photodetector, where the polarimetry is intrinsic to the active photodetector material. The detector is based on p-n junctions formed between two macroscopic films of single-wall carbon nanotubes. A responsivity up to ~1 V/W was observed in these devices, with a broadband spectral response spanning the visible to the mid-infrared. This responsivity is about 35 times larger than previous devices without p-n junctions. A combination of experiment and theory is used to demonstrate the photothermoelectric origin of the responsivity and to discuss the performance attributes of such devices.

Physical removal of metallic carbon nanotubes from nanotube network devices using a thermal and fluidic process.

Electronic and optoelectronic devices based on thin films of carbon nanotubes are currently limited by the presence of metallic nanotubes. Here we present a novel approach based on nanotube alkyl functionalization to physically remove the metallic nanotubes from such network devices. The process relies on preferential thermal desorption of the alkyls from the semiconducting nanotubes and the subsequent dissolution and selective removal of the metallic nanotubes in chloroform. The approach is versatile and is applied to devices post-fabrication.

Hydrogen sensing and sensitivity of palladium-decorated single-walled carbon nanotubes with defects.

Individual single-walled carbon nanotubes (SWCNTs) become sensitive to H(2) gas when their surfaces are decorated with Pd metal, and previous reports measure typical chemoresistive increases to be approximately 2-fold. Here, thousand-fold increases in resistance are demonstrated in the specific case where a Pd cluster decorates a SWCNT sidewall defect site. Measurements on single SWCNTs, performed both before and after defect incorporation, prove that defects have extraordinary consequences on the chemoresistive response, especially in the case of SWCNTs with metallic band structure. Undecorated defects do not contribute to H(2) chemosensitivity, indicating that this amplification is due to a specific but complex interdependence between a defect site's electronic transmission and the chemistry of the defect-Pd-H(2) system. Dosage experiments suggest a primary role is played by spillover of atomic H onto the defect site.

Graphitic electrical contacts to metallic single-walled carbon nanotubes using Pt electrodes.

We investigate electronic devices consisting of individual, metallic, single-walled carbon nanotubes contacted by Pt electrodes in a field effect transistor configuration, focusing on improvements to the metal-nanotube contact resistance as the devices are annealed in inert environments including ultrahigh vacuum. At moderate temperatures (T < 880 K), thermal processing results in high resistance contacts with thermally activated barriers. Higher temperatures (T > 880 K) achieve nearly transparent contacts. In the latter case, analytical surface measurements reveal the catalytic decomposition of hydrocarbons into graphene layers on the Pt surface, suggesting that improved electronic behavior is primarily due to the formation of an all-carbon nanotube-graphite interface rather than to the improvement of the nanotube-Pt one.

Mechanism-guided improvements to the single molecule oxidation of carbon nanotube sidewalls.

Real-time monitoring of carbon nanotube conductance during electrochemical and chemical etching reveals the electronic signatures of individual bond alteration events on the nanotube sidewall. Tracking the conductance of multiple single-molecule experiments through different synthetic protocols supports putative mechanisms for sidewall derivatization. Insights gained from these mechanistic observations imply the formation of sidewall carboxylates, which are useful as handles for bioconjugation. We describe an electronic state required for efficacious chemical treatment. Such real-time monitoring can improve carboxylate yields to 45 % or more. The experiments illustrate the power of molecular nanocircuits to uncover and direct the mechanisms of chemical reactions.

Monitoring single-molecule reactivity on a carbon nanotube.

Using point-functionalized carbon nanotube devices, we demonstrate continuous, multihour monitoring of a single carboxylate group interacting with its immediate environment. The conductance of the nanotube device directly transduces single-molecule attachments and detachments in the presence of the carboxylate-selective reagent 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride (EDC). Because only one carboxylate is present in the device, it can be studied through hundreds of reactions, providing the statistical accuracy to directly determine a 12 s lifetime of the carboxy-EDC complex. An additional instability of the complex is transduced in real time and observed to have a median lifetime of 2 ms. By determining a turnover time in good agreement with bulk measurements and simultaneously illuminating additional dynamics, these results demonstrate this platform's potential for complementing optical methods in single-molecule research.

Conductance-controlled point functionalization of single-walled carbon nanotubes.

We used covalent attachments to single-walled carbon nanotubes (SWNTs) to fabricate single-molecule electronic devices. The technique does not rely on submicrometer lithography or precision mechanical manipulation, but instead uses circuit conductance to monitor and control covalent attachment to an electrically connected SWNT. Discrete changes in the circuit conductance revealed chemical processes happening in real time and allowed the SWNT sidewalls to be deterministically broken, reformed, and conjugated to target species. By controlling the chemistry through electronically controlled electrochemical potentials, we were able to achieve single chemical attachments. We routinely functionalized pristine, defect-free SWNTs at one, two, or more sites and demonstrated three-terminal devices in which a single attachment controls the electronic response.

Polarity-directed analog electro-optic switching in a low-polarization chiral smectic liquid crystal with positive dielectric anisotropy.

We describe an analog electro-optic (EO) switching mechanism occurring in thin cells filled with a low-polarization ferroelectric liquid crystal mixture with positive dielectric anisotropy. The mixture is composed of an achiral nonpolar smectic-C (Sm-C) host doped with a small amount of a commercially available unichiral compound. The switching mechanism provides analog EO behavior, and thus could be attractive for information display applications. The process is polarization-driven for weak fields, while for higher field strength the dielectric coupling dominates the process.