Functional Molecular Interfaces for Impedance-Based Diagnostics.

In seeking to develop and optimize reagentless electroanalytical assays, a consideration of the transducing interface features lies key to any subsequent sensitivity and selectivity. This review briefly summarizes some of the most commonly used receptive interfaces that have been employed within the development of impedimetric molecular sensors. We discuss the use of high surface area carbon, nanoparticles, and a range of bioreceptors that can subsequently be integrated.

Optimized Diagnostic Assays Based on Redox Tagged Bioreceptive Interfaces.

Among the numerous label free electronic biomarker assay methodologies now available, impedance based electrochemical capacitance spectroscopy (ECS), based upon mapping the perturbations in interfacial charging of redox elements incorporated into a biologically receptive interface, has recently been shown to be a convenient and highly sensitive mode of transduction and one which, additionally, requires no predoping of analytical solution. We present, herein, a data acquisition and analysis methodology based on frequency resolved immittance function analysis. Ultimately, this enables both a maximization of assay sensitivity and a reduction in assay acquisition time by an order of magnitude.

Graphene-based protein biomarker detection.

An ability to detect and quantify protein molecules, harbingers of specific pathologies, potentially underpins both early disease diagnosis and an assessment of treatment efficacy. However, the specific detection of a particular protein biomarker in a complex environment is by no means an easy task and requires a progressive improvement in sensor technology. The high surface area, volume, electrical conductance, atomic level thickness and apparent biocompatibility of graphene makes it potentially an exceedingly powerful transducer of biorecognition events; the demands of its application in biosensing, and progress to date are reviewed herein.

Graphene oxide interfaces in serum based autoantibody quantification.

A reliable quantification of protein markers will undoubtedly underpin profound developments in disease surveillance, diagnostics, and improved therapy. Although there potentially exist numerous means of achieving this, electrochemical impedimetric techniques offer scale of sensitivity, cost, convenience, and a flexibility with which few alternatives can compete. Though there have been marked developments in electroanalytical protein detection, the demands associated with accessing the inherent assay sensitivity in complex biological media largely remains.

Immittance electroanalysis in diagnostics.

Impedance derived electroanalytical assays are inherently spectroscopic (frequency resolved) and potentially exceedingly sensitive indicators of interfacial change (such as target binding at an appropriate receptor). We introduce here the use of a portfolio of mathematically derived immittance functions and related components, capable, from the same raw data sets, of enabling increased assay sensitivity and markedly shorter assay times in comparison to traditional impedance analyses. The methodology, applied herein to faradaic (redox probe amplified) and non-faradaic assays, requires no equivalent circuit analysis or prior assumption of response.

Label-free in-flow detection of single DNA molecules using glass nanopipettes.

With the view of enhancing the functionality of label-free single molecule nanopore-based detection, we have designed and developed a highly robust, mechanically stable, integrated nanopipette-microfluidic device which combines the recognized advantages of microfluidic systems and the unique properties/advantages of nanopipettes. Unlike more typical planar solid-state nanopores, which have inherent geometrical constraints, nanopipettes can be easily positioned at any point within a microfluidic channel. This is highly advantageous, especially when taking into account fluid flow properties.

Engineered bacteriorhodopsin: a molecular scale potential switch.

Bacteriorhodopsin, BR, is a natural, photoresponsive, biomolecule that has potential application in data storage, imaging and sensing. Being membrane-bound, however, it is coupled with metallic electronic surfaces only with some difficulty. We report herein a facile method to generate uniformly orientated, anchored and active monolayers of BR on metallic electrodes.

Molecular scale conductance photoswitching in engineered bacteriorhodopsin.

Bacteriorhodopsin (BR) is a robust light-driven proton pump embedded in the purple membrane of the extremophilic archae Halobacterium salinarium . Its photoactivity remains in the dry state, making BR of significant interest for nanotechnological use. Here, in a novel configuration, BR was depleted from most of its endogenous lipids and covalently and asymmetrically anchored onto a gold electrode through a strategically located and highly responsive cysteine mutation; BR has no indigenous cysteines.

Enhanced photocurrent in engineered bacteriorhodopsin monolayer.

The integration of the transmembrane protein bacteriorhodopsin (BR) with man-made electrode surfaces has attracted a great deal of interest for some two decades or more and holds significant promise from the perspective of derived photoresponse or energy capture interfaces. Here we demonstrate that a novel and strategically engineered cysteine site (M163C) can be used to intimately and effectively couple delipidated BR to supporting metallic electrode surfaces. By virtue of the combined effects of the greater surface molecular density afforded by delipidation, and the vicinity of the electrostatic changes associated with proton pumping to the transducing metallic continuum, the resulting films generate a considerably greater photocurrent density on wavelength-selective illumination than previously achievable with monolayers of BR.

Experimental investigation of NIRS spatial sensitivity.

Near infrared spectroscopy (NIRS) is regarded as a potential medical diagnostic technique for investigation of hemodynamic changes. However, uncertainties pertaining to the origin of NIRS signals have hampered its clinical interpretation. The uncertainities in NIRS measurements especially in case of living tissues are due to lack of rigorous combined theoretical-experimental studies resulting in clear understanding of the origin of NIRS signals.

Visualizing and tuning thermodynamic dispersion in metalloprotein monolayers.

In coupling the redox state of an adsorbed molecule to its spectral characteristics redox profiles can be directly imaged by means of far-field fluorescence. At suitable levels of dilution, on optically transparent electrode surfaces, reversible interfacial electron transfer processes can be followed pixel by pixel down to scales which approach the molecular. In mapping out switching potentials across a surface population, thermodynamic dispersion, related to variance in the orientation, electronic coupling, protein fold, electric field drop, and general surface order, can be quantified.

Fabrication and characterization of polymer insulated carbon nanotube modified electrochemical nanoprobes.

Electrochemical nanoprobes were fabricated from polymer insulated multiwalled carbon nanotube modified tapping mode atomic force microscope probes. An electrochemically active length of carbon nanotube was exposed by laser ablation of the insulating polymer. Characterization of these probes is done by cyclic voltammetry of ferrocenemethanol in an aqueous solution and by finite element analysis.