Chemically isolated graphene nanoribbons reversibly formed in fluorographene using polymer nanowire masks.

We demonstrated the fabrication of graphene nanoribbons (GNRs) as narrow as 35 nm created using scanning probe lithography to deposit a polymer mask(1-3) and then fluorinating the sample to isolate the masked graphene from the surrounding wide band gap fluorographene. The polymer protected the GNR from atmospheric adsorbates while the adjacent fluorographene stably p-doped the GNRs which had electron mobilities of ∼2700 cm2/(V·s). Chemical isolation of the GNR enabled resetting the device to nearly pristine graphene.

Fluidic force discrimination assays: a new technology for tetrodotoxin detection.

Tetrodotoxin (TTX) is a low molecular weight (approximately 319 Da) neurotoxin found in a number of animal species, including pufferfish. Protection from toxin tainted food stuffs requires rapid, sensitive, and specific diagnostic tests. An emerging technique for the detection of both proteins and nucleic acids is Fluidic Force Discrimination (FFD) assays. This simple and rapid method typically uses a sandwich immunoassay format labeled with micrometer-diameter beads and has the novel capability of removing nonspecifically attached beads under controlled, fluidic conditions. This technique allows for near real-time, multiplexed analysis at levels of detection that exceed many of the conventional transduction methods (e.g., ELISAs). In addition, the large linear dynamic range afforded by FFD should decrease the need to perform multiple sample dilutions, a common challenge for food testing. By applying FFD assays to an inhibition immunoassay platform specific for TTX and transduction via low magnification microscopy, levels of detection of approximately 15 ng/mL and linear dynamic ranges of 4 to 5 orders of magnitude were achieved. The results from these studies on the first small molecule FFD assay, along with the impact to detection of seafood toxins, will be discussed in this manuscript.

Reusable, compression-sealed fluid cells for surface mounting to planar substrates.

We have developed a universal structure and mechanism for the repeatable, rapid-attachment of a fluid cell to a planar substrate. The fluid cell and all fluidic connections are completely contained in a plastic body such that attachment requires neither adhesives nor modification of the substrate. The geometry of the fluid cell is defined by the active area of the planar substrate (e.g. a sensor array). All required components have been quickly prototyped using Computer Numerical Control (CNC) machining. It is also straight-forward to create an array of fluid cells to attach to a single substrate (e.g. a standard microscope slide). All components are easy to assemble and can be cleaned and reused, making this flexible approach applicable for a wide range of lab-on-a-chip applications.

Trace explosives sensor testbed (TESTbed).

A novel vapor delivery testbed, referred to as the Trace Explosives Sensor Testbed, or TESTbed, is demonstrated that is amenable to both high- and low-volatility explosives vapors including nitromethane, nitroglycerine, ethylene glycol dinitrate, triacetone triperoxide, 2,4,6-trinitrotoluene, pentaerythritol tetranitrate, and hexahydro-1,3,5-trinitro-1,3,5-triazine. The TESTbed incorporates a six-port dual-line manifold system allowing for rapid actuation between a dedicated clean air source and a trace explosives vapor source. Explosives and explosives-related vapors can be sourced through a number of means including gas cylinders, permeation tube ovens, dynamic headspace chambers, and a Pneumatically Modulated Liquid Delivery System coupled to a perfluoroalkoxy total-consumption microflow nebulizer. Key features of the TESTbed include continuous and pulseless control of trace vapor concentrations with wide dynamic range of concentration generation, six sampling ports with reproducible vapor profile outputs, limited low-volatility explosives adsorption to the manifold surface, temperature and humidity control of the vapor stream, and a graphical user interface for system operation and testing protocol implementation.

Graphene veils: A versatile surface chemistry for sensors.

Thin spun-coat films (~4 nm thick) of graphene oxide (GO) constitute a versatile surface chemistry compatible with a broad range of technologically important sensor materials. Countless publications are dedicated to the nuances of surface chemistries that have been developed for sensors, with almost every material having unique characteristics. There would be enormous value in a surface chemistry that could be applied generally with functionalization and passivation already optimized regardless of the sensor material it covered. Such a film would need to be thin, conformal, and allow for multiple routes toward covalent linkages. It is also vital that the film permit the underlying sensor to transduce. Here we show that GO films can be applied over a diverse set of sensor surfaces, can link biomolecules through multiple reaction pathways, and can support cell growth. Application of a graphene veil atop a magnetic sensor array is demonstrated with an immunoassay. We also present biosensing and material characterization data for these graphene veils.

Evolution of a magnetic-based biomolecular detection system.

Amongst the plethora of affinity biosensor systems based on biomolecular recognition and labeling assays, magnetic labeling and detection has emerged as a promising approach. Magnetic labels can be detected by a wide range of non-invasive methods, are physically and chemically stable, relatively inexpensive to produce, and can be easily made biocompatible. Over a decade ago, the U. S. Naval Research Laboratory pioneered the use of giant magnetoresistive (GMR) sensors to detect biomolecules labeled with paramagnetic microbeads. Since then, our various investigations and engineering efforts have resulted in significant improvements in both the magnetoelectronic instrumentation and the assays associated with these magnetic labels. This paper and subsequent presentation provides a synopsis of the development of our technology which has evolved into a highly sensitive detection method.