Peptide nanowires for coordination and signal transduction of peroxidase biosensors to carbon nanotube electrode arrays

The use of engineered protein materials in electrochemical devices

Bioelectrochemical technologies have an important and growing role in healthcare, with applications in sensing and diagnostics, as well as the potential to be used as implantable power sources and be integrated with automated drug delivery systems. Challenges associated with enzyme-based electrodes include low current density and short functional lifetimes. Protein engineering is emerging as a powerful tool to overcome these issues. By taking advantage of the ability to precisely define protein sequences, electrodes can be organized into high performing structures, and enable the next generation of medical devices.

Versatile multi-functionalization of protein nanofibrils for biosensor applications

Protein nanofibrils offer advantages over other nanostructures due to the ease in their self-assembly and the versatility of surface chemistry available. Yet, an efficient and general methodology for their post-assembly functionalization remains a significant challenge. We introduce a generic approach, based on biotinylation and thiolation, for the multi-functionalization of protein nanofibrils self-assembled from whey proteins. Biochemical characterization shows the effects of the functionalization onto the nanofibrils' surface, giving insights into the changes in surface chemistry of the nanostructures. We show how these methods can be used to decorate whey protein nanofibrils with several components such as fluorescent quantum dots, enzymes, and metal nanoparticles. A multi-functionalization approach is used, as a proof of principle, for the development of a glucose biosensor platform, where the protein nanofibrils act as nanoscaffolds for glucose oxidase. Biotinylation is used for enzyme attachment and thiolation for nanoscaffold anchoring onto a gold electrode surface. Characterization via cyclic voltammetry shows an increase in glucose-oxidase mediated current response due to thiol-metal interactions with the gold electrode. The presented approach for protein nanofibril multi-functionalization is novel and has the potential of being applied to other protein nanostructures with similar surface chemistry.

Nanoelectrodes for biological measurements

Nanoelectrodes are electrodes with a critical dimension in the range of one to hundreds of nanometers and include individual electrodes, nanoelectrode ensembles, and arrays. Metallic nanowires, carbon nanotubes, magnetic nanoparticles, and metal oxide nanowires have been employed to fabricate nanoelectrodes and platforms. In this review, applications of single electrodes, nanoelectrode arrays, and ensembles are briefly evaluated, with emphasis on biological analysis. Nanoelectrodes offer great advantages in numerous areas of biological investigations, particularly in single cells studies, fabrication of microchips, design of coordinated biosensors, and in addressable patterned electrodes. Consequently, nanoelectrodes have immense potential in the development of efficient, specific, sensitive, and intelligent sensors. In conjunction with the rapidly evolving, cost-effective fabrication and materials development approaches, these sensors can be used as direct, point-of-care clinical devices, enabling more personalized medical care. The development and application of nanodevices in biology and medicine will have enormous implications for society and human health.

High sensitivity electrochemical cholesterol sensor utilizing a vertically aligned carbon nanotube electrode with electropolymerized enzyme immobilization

In this report, a new cholesterol sensor is developed based on a vertically aligned CNT electrode with two-step electrochemical polymerized enzyme immobilization. Vertically aligned CNTs are selectively grown on a 1 mm(2) window of gold coated SiO(2)/Si substrate by thermal chemical vapor deposition (CVD) with gravity effect and water-assisted etching. CNTs are then simultaneously functionalized and enzyme immobilized by electrochemical polymerization of polyaniline and cholesterol enzymes. Subsequently, ineffective enzymes are removed and new enzymes are electrochemically recharged. Scanning electron microscopic characterization indicates polymer-enzyme nanoparticle coating on CNT surface. Cyclic voltammogram (CV) measurements in cholesterol solution show the oxidation and reduction peaks centered around 450 and -220 mV, respectively. An approximately linear relationship between the cholesterol concentration and the response current could be observed in the concentration range of 50-300 mg/dl with a sensitivity of approximately 0.22 μA/mg·dl(-1), which is considerably higher compared to previously reported CNT bioprobe. In addition, good specificity toward glucose, uric acid acetaminophen and ascorbic acid have been obtained. Moreover, sensors have satisfactory stability, repeatability and life time. Therefore, the electropolymerized CNT bioprobe is promising for cholesterol detection in normal cholesterol concentration in human blood.

Ionic-complementary peptide matrix for enzyme immobilization and biomolecular sensing

A novel electrochemical biosensing platform is described using biocompatible, self-assembled ionic-complementary peptide nanofibers. The compatibility of a graphite electrode modified by these peptide nanofibers with enzymes is demonstrated using a model enzyme glucose oxidase (GOx). A glucose biosensor has been successfully fabricated by incorporating this enzyme into the modified electrode. From measurement of its electrode response and sensitivity, this nanofiber-modified electrode shows promise as an enzyme-based biosensor. The findings presented here demonstrate excellent potential of the use of ionic-complementary peptides to modify electrode surfaces for biomolecular sensing and diagnostics.

Ultra-sensitivity glucose sensor based on field emitters

A new glucose sensor based on field emitter of ZnO nanorod arrays (ZNA) was fabricated. This new type of ZNA field emitter-based sensor shows high sensitivity with experimental limit of detection of 1 nM glucose solution and a detection range from 1 nM to 50 μM in air at room temperature, which is lower than that of glucose sensors based on surface plasmon resonance spectroscopy, fluorescence signal transmission, and electrochemical signal transduction. The new glucose sensor provides a key technique for promising consuming application in biological system for detecting low levels of glucose on single cells or bacterial cultures.