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Albany, New Zealand

Zhu B.,University of Auckland | Booth M.A.,Digital Sensing Ltd | Woo H.Y.,Pusan National University | Hodgkiss J.M.,MacDiarmid Institute for Advanced Materials and Nanotechnology | And 3 more authors.
Chemistry - An Asian Journal | Year: 2015

In this communication, a label-free and sensitive electrochemical method to detect potassium ions is proposed. The conducting polymer polypyrrole was used as both an anchor for the probe and a transducer of the detection event. A K+-specific G-rich aptamer was applied as a recognition element, which folded into the G-quadruplex structure in the presence of K+, and this resulted in an increase in the electrode impedance. The combination of the K+-selective aptamer and the porous conducting polymer as a signal transducer afforded a successful sensor platform. The sensor responded approximately logarithmically over a wide dynamic range of K+ concentrations from 20 fm to 1mm, with a very low detection limit of 14.7fm and excellent discrimination against other ions. Additionally, electrochemical impedance spectroscopy was used to study the kinetics of K+ binding at the conducting polymer-immobilized aptamer surface, which indicated strong binding between the two. This work demonstrates a powerful approach for the sensitive, selective, and direct electrochemical detection of metal ions based on the switching conformation of G-rich aptamers attached to a porous conducting polymer surface. This assay scheme can be expanded to the detection of a wide range of targets by modifying the aptamer structure as a recognizing moiety. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Source

Digital Sensing Ltd | Date: 2012-10-12

The invention relates to a microarray structure including a substrate material layer, a continuous three-dimensional (3D) surface layer on the substrate material layer that is capable of functionalisation for use as an array, and an inert material wherein the structure includes accurately defined and functionalisable isolated areas which are millimeter to nanometer in size. The functionalised areas are part of the continuous 3D surface layer and are isolated by the inert material and are interconnected within the structure by the continuous 3D surface layer.

Zhu B.,University of Auckland | Booth M.A.,Digital Sensing Ltd | Shepherd P.,University of Auckland | Sheppard A.,University of Auckland | And 2 more authors.
Biosensors and Bioelectronics | Year: 2014

In this communication we report on two important effects related to the detection of DNAs. Firstly, we investigate the sensor response to target DNA when the target is in a double stranded (ds) form and compare the response to single stranded (ss) target DNA. The importance in evaluating such an effect lies in the fact that most biological DNA targets are found in ds form. Secondly, we use synthetic ds targets to investigate the effect of DNA methylation on the sensor response. DNA methylation is known to affect functional properties of DNA and is related to a number of diseases, including various cancers. In these studies, we utilize our previously developed sensor platform, which is based on the use of a glassy carbon electrode-confined conducting polymer that is covalently modified with DNA probe sequences. The signal detection methodology we use is measuring a change in the reaction kinetics of ferro-ferricyanide redox couple at the electrode upon hybridization by means of electrical impedance spectroscopy (EIS). Additionally, EIS is utilized to study the kinetics of the hybridization of the conducting polymer-bound probe with methylated vs. non-methylated ds-DNA. Preliminary results are proving valuable as a guide to the future design of sensors for gene methylation. © 2014 Elsevier B.V. Source

Booth M.A.,Digital Sensing Ltd | Kannappan K.,Digital Sensing Ltd | Hosseini A.,Digital Sensing Ltd | Hosseini A.,University of Auckland | And 2 more authors.
Langmuir | Year: 2015

Aminoferrocene is used as an electroactive indicator to investigate carbodiimide coupling reactions on a carboxylic acid-functionalized self-assembled monolayer. The commonly used attachment chemistry with 1-ethyl-3-(3-(dimethylamino)propyl)carbodiimide hydrochloride (EDC) and N-hydroxysuccinimide (NHS) is used for surface activation. A number of conditions are investigated, including EDC and NHS concentration, buffer solutions, incubation timing, and aminoferrocene concentration. Ferrocene is a well-documented electroactive species, and the number of surface-bound ferrocene species can be calculated using electrochemical methods. This capability allows determination of optimal conditions, as well as providing a method for comparing and investigating novel carboxylated surfaces. An EDC-mediated procedure with 5 mM EDC and NHS (1:1) made in water, with a full acid monolayer, with 250 ΜM aminoferrocene for 40 min was found to give the highest ferrocene attachment. An application of this is demonstrated for preparing a probe-DNA-coated surface for DNA sensing. By backfilling with aminoferrocene, a differential quantification of the amount of probe DNA available for sensing can be obtained. This provides an elegant method to monitor an important aspect, namely, probe surface characterization, which will be highly useful for biosensing purposes. © 2015 American Chemical Society. Source

Yeh J.,University of Auckland | Wang K.I.-K.,University of Auckland | Salcic Z.,University of Auckland | Kannappan K.,Digital Sensing Ltd | Partridge A.,Digital Sensing Ltd
Proceedings of the International Conference on Sensing Technology, ICST | Year: 2016

There is a growing need for new biosensing technologies that are more rapid and convenient to use for onsite sensing. Impedance-based electrochemical sensor is a promising candidate due to simplicity of its sensing mechanism. However, like other emerging biosensors, specificity, sensitivity, and reliability are major obstacles that limit their use in real-life applications. Electrode geometry and 3D shape design optimization have been popular research directions for improved sensor performance. The aim of this study is to develop a finite element modelling approach that allows calculation of electrode impedance for different electrode shapes under standard biological test medium. In addition, a method for comparing sensor sensitivity is also developed using bacterial target as case study. Impedance simulations were performed for different electrode shapes, namely flat, ridge, and trough. The effects of target binding on solution conductivity and diffusion were simulated. It was found trough shaped electrode showed the greatest change in diffusion impedance upon target recognition. However, different shapes gave maximum change in solution impedance depending on the position of bound target. © 2015 IEEE. Source

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