The water/graphene interface has received considerable attention in the past decade due to its relevance in various potential applications including energy storage, sensing, desalination, and catalysis. Most of our knowledge about the interfacial water structure next to graphene stems from simulations, which use experimentally measured water contact angles (WCAs) on graphene (or graphite) to estimate the water-graphene interaction strength. However, the existence of a wide spectrum of reported WCAs on supported graphene and graphitic surfaces makes it difficult to interpret the water-graphene interactions. Here, we have used surface-sensitive infrared-visible sum frequency generation (SFG) spectroscopy to probe the interfacial water structure next to graphene supported on a sapphire substrate. In addition, the ice nucleation properties of graphene have been explored by performing in situ freezing experiments as graphitic surfaces are considered good ice nucleators. For graphene supported on sapphire, we observed a strong SFG peak associated with highly coordinated, ordered water next to graphene. Similar ordering was not detected next to bare sapphire, implying that the observed ordering of water molecules in the former case is a consequence of the presence of graphene. Our analysis indicates that graphene behaves like a hydrophobic (or negatively charged) surface, leading to enhanced ordering of water molecules. Although liquid water orders next to graphene, the ice formed is proton disordered. This research sheds light on water-graphene interactions relevant in optimizing the performance of graphene in various applications.

Understanding the factors that influence the interaction between biomolecules and abiotic surfaces is of utmost interest in biosensing and biomedical research. Through phage display technology, several peptides have been identified as specific binders to abiotic material surfaces, such as gold, graphene, silver, and so forth. Using graphene-peptide as our model abiotic-biotic pair, we investigate the effect of graphene quality, number of layers, and the underlying support substrate effect on graphene-peptide interactions using both experiments and computation. Our results indicate that graphene quality plays a significant role in graphene-peptide interactions. The graphene-biomolecule interaction appears to show no significant dependency on the number of graphene layers or the underlying support substrate.

Transmission electron microscopy (TEM) is being pushed to new capabilities which enable studies on systems that were previously out of reach. Among recent innovations, TEM through liquid cells (LC-TEM) enables in operando observation of biological phenomena. This work applies LC-TEM to the study of biological components as they interact on an abiotic surface. Specifically, analytes or target molecules like neuropeptide Y (NPY) are observed in operando on functional graphene field-effect transistor (GFET) biosensors. Biological recognition elements (BREs) identified using biopanning with affinity to NPY are used to functionalize graphene to obtain selectivity. On working devices capable of achieving picomolar responsivity to neuropeptide Y, LC-TEM reveals translational motion, stochastic positional fluctuations due to constrained Brownian motion, and rotational dynamics of captured analyte. Coupling these observations with the electrical responses of the GFET biosensors in response to analyte capture and/or release will potentially enable new insights leading to more advanced and capable biosensor designs.

Photo-thermal oxidation yields no pores in the graphene layer and suggests pathways for oxygen defect engineering in a controlled manner.

Breathing-air quality within commercial airline cabins has come under increased scrutiny because of the identification of volatile organic compounds (VOCs) from the engine bleed air used to provide oxygen to cabins. Ideally, a sensor would be placed within the bleed air pipe itself, enabling detection before it permeated through and contaminated the entire cabin. Current gas-phase sensors suffer from issues with selectivity, do not have the appropriate form factor, or are too complex for commercial deployment. Here, we chose isopropyl alcohol (IPA), a main component of de-icer spray used in the aerospace community, as a target analyte: IPA exposure has been hypothesized to be a key component of aerotoxic syndrome in pre, during, and postflight. IPAs proposed mechanism of action is that of an anesthetic and central nervous system depressant. In this work, we describe IPA sensor development by showing (1) the integration of a polymer as an IPA capture matrix, (2) the adoption of a redox chemical additives as an IPA oxidizer, and (3) the application of carbon nanotubes as an electronic sensing conduit. We demonstrate the ability to not only detect IPA at 100–10 000 ppm in unfiltered, laboratory air but also discriminate among IPA, isoprene, and acetone, especially in comparison to a typical photoionization detector. Overall, we show an electronic device that operates at room temperature and responds preferentially to IPA, where the increase in the resistance corresponds directly to the concentration of IPA. Ultimately, this study opens up the pathway to selective electronic sensors that can enable real-time monitoring in a variety of environments for the force health prevention and protection, and the potential through future work to enable low parts-per-million and possibly high parts-per-billion selective detection of gas-phase VOCs of interest.

An approach for printing micron-scale electronic devices built from two-dimensional materials is presented. Experimental phage display techniques and computational atomistic simulation approaches were used to identify a peptide molecule that effectively anchors to the basal plane surface of two-dimensional (2D) MoS2 to SiO2 surfaces. This peptide was suspended in water to develop an ink suitable for aerosol jet printing. The printed substrates were then dip coated with a suspension of liquid phase exfoliated 2D MoS2 particles. Strong adhesion of physically continuous lines of these particles was observed only on regions of the substrate patterned with the peptide-based ink, thereby enabling aerosol jet printing as a template for devices based on 2D materials. Graphene was also bound to SiO2 via a similar approach, but with a different peptide known from prior work to selectively adhere to the basal plane of graphene. Fundamental peptide-surface interactions for MoS2, graphene, and SiO2 were explored via simulation and experiment. This printing method is proposed as a route towards large-scale, low temperature patterning of 2D materials and devices. The electrical properties of continuous lines of MoS2 particles printed in a single pass of peptide ink printing were measured via transmission line measurements. The results indicate that this molecular attachment approach to printing possesses several advantages such as overcoming nozzle clogging due to nanomaterial aggregation, decoupling of particle size from any dimensions associated with the printer, and single-pass printing of electrically continuous films.

Recognition and manipulation of graphene edges enable the control of physical properties of graphene-based devices. Recently, the authors have identified a peptide that preferentially binds to graphene edges from a combinatorial peptide library. In this study, the authors examine the functional basis for the edge binding peptide using experimental and computational methods. The effect of amino acid substitution, sequence context, and solution pH value on the binding of the peptide to graphene has been investigated. The N-terminus glutamic acid residue plays a key role in recognizing and binding to graphene edges. The protonation, substitution, and positional context of the glutamic acid residue impact graphene edge-binding. Our findings provide insights into the binding mechanisms and the design of peptides for recognizing and functionalizing graphene edges.

Atomically thin two-dimensional (2D) materials are ideal gas sensing materials with ultrahigh sensitivity due to the high surface-to-volume ratio, low electronic noise, and tunable Fermi level alignment. However, obtaining selectivity to a target analyte in the presence of other confounding gases in the environment remains an issue preventing selective gas sensing using 2D materials. In the present work, we fabricate a selective nitrogen dioxide (NO2) sensor using WSe2 by adding a simple oil layer as a filter. For this proof of concept study, we used polydimethylsiloxane (PDMS) due to its dipole moment being similar to NO2 (∼0.3 D). This PDMS layer helps selectively detect NO2 and filter out both more polar gases, such as ammonia (NH3) and hydrogen sulfide (H2S), as well as nonpolar gases, such as carbon monoxide (CO), that are likely to be present in the background environment. Not only did we obtain a selective response for single components but also we observed an improved sensing response (around 200%) when NO2 is mixed with other gases compared to the intrinsic WSe2 device without modification. The obtained results were found to be reproducible and reversible. The charge transfer effect of different gases to WSe2 devices was characterized by an atomic force microscope (AFM) through phase imaging techniques.