S. L. Burrs

A nanoceria–platinum–graphene nanocomposite for electrochemical biosensing

Most graphene-metal nanocomposites for biosensing are formed using noble metals. Recently, development of nanocomposites using rare earth metals has gained much attention. This paper reports on the development of a nanoceria-nanoplatinum-graphene hybrid nanocomposite as a base transducing layer for mediator-free enzymatic biosensors. The hybrid nanocomposite was shown to improve detection of superoxide or hydrogen peroxide when compared to other carbon-metal hybrid nanocomposites. Based on this finding, the nanocomposite was applied for biosensing by adding either a peroxide-producing oxidase (glucose oxidase), or a superoxide-producing oxidase (xanthine oxidase). Material analysis indicated that nanoceria and nanoplatinum were equally distributed along the surface of the hybrid material, ensuring detection of either superoxide or hydrogen peroxide produced by oxidase activity. Glucose biosensors demonstrated a sensitivity (66.2±2.6μAmM(-1)cm(-2)), response time (6.3±3.4s), and limit of detection (1.3±0.6μM) that were comparable to other graphene-mediated electrodes in the current literature. Remarkably, XOD biosensor sensitivity (1164±332μAmM(-1)), response time (5.0±1.5s), and limit of detection (0.2±0.1μM) were higher than any reported biosensors using similar metal-decorated carbon nanomaterials. This material is the first demonstration of a highly efficient, diverse nanoceria/nanoplatinum/graphene hybrid nanocomposite for biosensing.

Emerging technologies for non-invasive quantification of physiological oxygen transport in plants

Oxygen plays a critical role in plant metabolism, stress response/signaling, and adaptation to environmental changes (Lambers and Colmer, Plant Soil 274:7–15, 2005; Pitzschke et al., Antioxid Redox Signal 8:1757–1764, 2006; Van Breusegem et al., Plant Sci 161:405–414, 2001). Reactive oxygen species (ROS), by-products of various metabolic pathways in which oxygen is a key molecule, are produced during adaptation responses to environmental stress. While much is known about plant adaptation to stress (e.g., detoxifying enzymes, antioxidant production), the link between ROS metabolism, O2 transport, and stress response mechanisms is unknown. Thus, non-invasive technologies for measuring O2 are critical for understanding the link between physiological O2 transport and ROS signaling. New non-invasive technologies allow real-time measurement of O2 at the single cell and even organelle levels. This review briefly summarizes currently available (i.e., mainstream) technologies for measuring O2 and then introduces emerging technologies for measuring O2. Advanced techniques that provide the ability to non-invasively (i.e., non-destructively) measure O2 are highlighted. In the near future, these non-invasive sensors will facilitate novel experimentation that will allow plant physiologists to ask new hypothesis-driven research questions aimed at improving our understanding of physiological O2 transport.

Lignin and silicate based hydrogels for biosensor applications

Advances in biocompatible materials and electrocatalytic nanomaterials have extended and enhanced the field of biosensors. Immobilization of biorecognition elements on nanomaterial platforms is an efficient technique for developing high fidelity biosensors. Single layer (i.e., Langmuir–Blodgett) protein films are efficient, but disadvantages of this approach include high cost, mass transfer limitations, and Vromer competition for surface binding sites. There is a need for simple, user friendly protein-nanomaterial sensing membranes that can be developed in laboratories or classrooms (i.e., outside of the clean room). In this research, we develop high fidelity nanomaterial platforms for developing electrochemical biosensors using sustainable biomaterials and user-friendly deposition techniques. Catalytic nanomaterial platforms are developed using a combination of self assembled monolayer chemistry and electrodeposition. High performance biomaterials (e.g., nanolignin) are recovered from paper pulp waste and combined with proteins and nanomaterials to form active sensor membranes. These methods are being used to develop electrochemical biosensors for studying physiological transport in biomedical, agricultural, and environmental applications.

Hybrid Metallic Nanoparticles: Enhanced Bioanalysis and Biosensing via Carbon Nanotubes, Graphene, and Organic Conjugation

Composite materials, incorporating noble metal and metal oxide nanoparticles, have attracted much interest as active substrates for biosensor electronics. These nanoparticles provide a viable microenvironment for biomolecule immobilization by retaining their biological activity with desired orientation and for facilitating transduction of the biorecognition event. Herein, we discuss various methods for fabrication of metal and metal oxide nanoparticle composite materials and their applications in different electrochemical biosensors. The materials are organized by the corresponding component with the nanoparticles, i.e. carbon-based composites, polymers, and DNA. The performance of hybrids is compared and examples of biosensing apparatus are discussed. In all cases, the engineering of morphology, particle size, effective surface area, functionality, adsorption capability, and electron-transfer properties directly impact the resultant biosensing capabilities. Ultimately, these attractive features of metal and metal-oxide hybrid materials are expected to find applications in the next generation of smart biosensors.

Non-invasive microsensors for studying cell/tissue physiology

Non-invasive tools that allow real-time quantification of molecules relevant to metabolism, homeostasis, and cell signaling in cells and tissue are of great importance for studying physiology. Several microsensor technologies have been developed to monitor concentration of molecules such as ions, oxygen, electroactive molecules (e.g., nitric oxide, hydrogen peroxide), and biomolecules (e.g., sugars, hormones). The major challenges for microsensors are overcoming relatively low sensitivity and low signal-to-noise ratio. Modern approaches for enhancing microsensor performance focus on the incorporation of catalytic nanomaterials to increase sensitivity, reduce response time, and increase operating range. To improve signal-to-noise ratio, a non-invasive microsensor modality called self-referencing (SR) is being applied. The SR technique allows measurement of temporal and spatial transport dynamics at the cell, tissue, organ, and organismal level.

A paper based graphene-nanocauliflower hybrid composite for point of care biosensing

Graphene paper has diverse applications in printed circuit board electronics, bioassays, 3D cell culture, and biosensing. Although development of nanometal-graphene hybrid composites is commonplace in the sensing literature, to date there are only a few examples of nanometal-decorated graphene paper for use in biosensing. In this manuscript, we demonstrate the synthesis and application of Pt nano cauliflower-functionalized graphene paper for use in electrochemical biosensing of small molecules (glucose, acetone, methanol) or detection of pathogenic bacteria (Escherichia coli O157:H7). Raman spectroscopy, scanning electron microscopy and energy dispersive spectroscopy were used to show that graphene oxide deposited on nanocellulose crystals was partially reduced by both thermal and chemical treatment. Fractal platinum nanostructures were formed on the reduced graphene oxide paper, producing a conductive paper with an extremely high electroactive surface area, confirmed by cyclic voltammetry and electrochemical impedance spectroscopy. To show the broad applicability of the material, the platinum surface was functionalized with three different biomaterials: 1) glucose oxidase (via chitosan encapsulation); 2) a DNA aptamer (via covalent linking), or 3) a chemosensory protein (via his linking). We demonstrate the application of this device for point of care biosensing. The detection limit for both glucose (0.08 ± 0.02 μM) and E. coli O157:H7 (1.3 ± 0.1 CFU mL-1) were competitive with, or superior to, previously reported devices in the biosensing literature. The response time (6 sec for glucose and 10 min for E. coli) were also similar to silicon biochip and commercial electrode sensors. The results demonstrate that the nanocellulose-graphene-nanoplatinum material is an excellent paper-based platform for development of electrochemical biosensors targeting small molecules or whole cells for use in point of care biosensing.