Differential Cyclic Voltammetry - a Novel Technique for Selective and Simultaneous Detection using Redox Cycling Based Sensors

Redox cycling (RC) is an effect that is used to amplify electrochemical signals. However, traditional techniques such as cyclic voltammetry (CV) do not provide clear insight for a mixture of multiple redox couples while RC is applied. Thus, we have developed a new measurement technique which delivers electrochemical spectra of all reversible redox couples present based on concentrations and standard potentials. This technique has been named differential cyclic voltammetry (DCV). We have fabricated micrometer-sized interdigitated electrode (IDE) sensors to conduct DCV measurements in mixtures of 1mM catechol and 4mM [Ru(NH3)6]Cl3. To simulate the electrochemical behavior of these sensors we have also developed a finite element model (FEM) in Comsol®. The\ud experimental data corresponds to the calculated spectra obtained from simulations. Additionally, the measured spectra can be used to easily derive standard potentials and concentrations simultaneously and selectively.\u

Redox cycling at nanospaced electrodes

‘redox cycling’ aan electrodes op nanometer afstand in de richting van elektrochemisch versterkte biomoleculaire detectie Molecuul synthese is gemakkelijker uit te voeren op klein formaat terwijl elektrode fabricage makkelijker is op groot formaat. In dit project is gezocht naar een compromis tussen deze twee aspecten om een ontwerp met twee elektroden te realiseren, waarbij redox actieve moleculen vast zitten aan het elektrode oppervlak. Deze moleculen ondergaan ’redox cycling’ tussen deze twee elektroden. Het onderzoek is gericht op nieuwe toepassingen van dit ’redox cycling’ effect, fabricage van elektroden met een onderlinge afstand in de nanometers, en het elektrochemische gedrag van aan een oppervlak vastgezet polyethyleenglycol (PEG) molecuul met ferroceen als redoxactief label. De opgedane kennis over deze verschillende onderwerpen is gecombineerd in experimenten waar de PEG moleculen ’redox cycling’ ondergaan tussen twee elektroden met een afstand kleiner dan 100 nanometer. Deze opstelling kan worden gebruikt als een transducerend element van een elektrochemische sensor indien de vastzittende moleculen zodaning worden gemodificeerd dat ze kunnen reageren op andere chemicali¨en

Submicron electrode gaps fabricated by gold electrodeposition at interdigitated electrodes

Electrodes with submicron gaps are desired for achieving high amplification redox cycling sensors. In this contribution we report the use of electrodeposition of gold in order to decrease the inter-electrode spacing at interdigitated electrodes. Using this method submicron spacings can be obtained without expensive techniques such as e-beam lithography or focused ion beam milling. Initially, gold interdigitated electrodes with a finger spacing of 2.5 μm were realized by lift-off processing. Using a commercial gold sulphite bath (ECF64D) and 100 ms current pulses of -1.78 μA, these gold electrodes were plated with an additional gold layer. As a result, the inter-electrode spacing, as measured using atomic force microscopy and conventional microscopy, was reduced to 0.6 μm. The achieved gap spacing is limited by electrode imperfections resulting from the lift-off process. At these imperfections the electrodes become shorted. Additional experiments with wet etched electrodes are expected to yield smaller gap spacings

Solid state nanogaps for electrochemical detection fabricated using edge lithography

Nanogap electrodes have uses in fields such as chemical sensing, molecular transport, plasmonics and DNA sequencing. In this contribution a new fabrication strategy for nanogap electrodes is reported. Using this fabrication strategy, electrodes have been successfully created featuring gap sizes of 100 and 50 nm. For the electrodes with a gap size of 50 nm the electrochemical behavior is evaluated by means of cyclic voltammetry in combination with redox cycling. The obtained voltammogram corresponds to finite element simulations and the shape of the voltammogram indicates an almost Nernstian quasi-reversible CV is obtained for a reversible redox couple, which means the devices are suited for electrochemical detection. Fabrication of these devices is reliable as a yield of >95% was obtained. (C) 2013 Elsevier B.V. All rights reserve

Differential cyclic voltammetry for selective and amplified detection

We propose to combine two existing electrochemical techniques, cyclic voltammetry (CV) and redox cycling (RC), in order to obtain amplified and selective detection of redox active species. This combination is achieved by applying CV waveforms to two electrodes spaced 1.20 mu m apart, with one of the electrodes at a constant potential offset compared to the other. Due to this potential offset we have named this technique differential cyclic voltammetry (DCV). Analytical expressions for the DCV voltammogram are derived and an optimal potential offset is calculated. The optimal voltage difference for the trade-off between peak height and width is 0.1 V for redox couples with n = 1. Experimental voltammograms show good agreement with the analytical expressions. The voltammogram for ferrocenedimethanol has been fitted (R-2 = 0.9985) using only the distance between the electrodes as fitting parameter. Therefore, this technique shows promise as a tool for amplified and selective detection of redox active species