Scholarly article on topic 'Field-effect Devices Functionalised with Gold-Nanoparticle/Macromolecule Hybrids: New Opportunities for a Label-Free Biosensing'

Field-effect Devices Functionalised with Gold-Nanoparticle/Macromolecule Hybrids: New Opportunities for a Label-Free Biosensing Academic research paper on "Materials engineering"

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Procedia Engineering
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Keywords
{"Field-effect sensor" / "label-free detection" / "gold nanoparticles" / "charged macromolecules" / poly-D-lysine}

Abstract of research paper on Materials engineering, author of scientific article — A. Poghossian, M.H. Weil, M. Bäcker, D. Mayer, M.J. Schöning

Abstract Field-effect capacitive electrolyte-insulator-semiconductor (EIS) sensors functionalised with citrate-capped gold nanoparticles (AuNP) have been used for the electrostatic detection of macromolecules by their intrinsic molecular charge. The EIS sensor detects the charge changes in the AuNP/macromolecule hybrids induced by the adsorption or binding events. A feasibility of the proposed detection scheme has been exemplary demonstrated by realising EIS sensors for the detection of poly-D-lysine molecules.

Academic research paper on topic "Field-effect Devices Functionalised with Gold-Nanoparticle/Macromolecule Hybrids: New Opportunities for a Label-Free Biosensing"

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Procedía Engineering

ELSEVIER

Procedía Engineering 47 (2012) 273 - 276

www.elsevier.com/locate/proeedia

Proc. Eurosensors XXVI, September 9-12, 2012, Krakow, Poland

Field-effect devices functionalised with gold-nanoparticle/macromolecule hybrids: New opportunities for a

label-free biosensing

A. Poghossiana'b'*, M.H. Weilc, M. Backera, D. Mayerb, M.J. Schoninga,b

aInstitute of Nano- and Biotechnologies, Aachen University of Applied Sciences, Campus Jülich, Heinrich-Mußmann-St. 1, 52428

Jülich, Germany

bPeter Grünberg Institute (PGI-8), Research Centre Jülich GmbH, 52425 Jülich, Germany cDepartment of Informatics and Microsystem Technology, University of Applied Sciences Kaiserslautern, Campus Zweibrücken,

Amerikastr. 1, 66482 Zweibrücken, Germany

Field-effect capacitive electrolyte-insulator-semiconductor (EIS) sensors functionalised with citrate-capped gold nanoparticles (AuNP) have been used for the electrostatic detection of macromolecules by their intrinsic molecular charge. The EIS sensor detects the charge changes in the AuNP/macromolecule hybrids induced by the adsorption or binding events. A feasibility of the proposed detection scheme has been exemplary demonstrated by realising EIS sensors for the detection of poly-D-lysine molecules.

©2012TheAuthors. PublishedbyElsevier Ltd. Selection and/or peer-review under responsibility of the Symposium Cracoviense Sp. z.o.o.

Keywords: field-effect sensor; label-free detection; gold nanoparticles; charged macromolecules; poly-D-lysine

1. Introduction

Assemblies of bare and functionalised gold nanoparticles (AuNP) are highly attractive class of electrically or chemically tunable functional materials with unique catalytic, optical, and electronic properties. AuNPs have widely been applied not only in fundamental research involving, for instance, bio-

* Corresponding author. Tel.: +49-2461-612605; fax: +49-241-6009-53235. E-mail address: a.poghossian@fz-juelich.de.

Abstract

1877-7058 © 2012 The Authors. Published by Elsevier Ltd. Selection and/or peer-review under responsibility of the Symposium Cracoviense Sp. z.o.o.

doi:10.1016/j.proeng.2012.09.136

and photocatalysis, adsorption and binding of molecules, and electron-transport phenomena in nano-scaled materials (see, e.g., [1-3]), but also in application-oriented research ranging from biosensors and biochips [4-12] over drug delivery systems [13,14] up to optical, electronic, and memory devices [3,15,16]. A coupling of a solid assembly of AuNPs with a macroscopic semiconductor transducer allows for the active tuning of electrochemical properties of the nanoparticle/transducer interface [3]. In addition, recently, semiconductor field-effect devices have been used to trace of the excess charge of supported AuNPs induced by oxygen plasma treatment or by exposing to aqueous oxidation and reduction solutions [17]. In this context, an integration of AuNP/macromolecule inorganic/organic hybrids with field-effect devices could open new possibilities for the development of biosensors and biochips [4-6,10,11].

In this work, the capacitive field-effect electrolyte-insulator-semiconductor (EIS) sensors functionalised with citrate-capped AuNPs have been applied for a label-free sensing of charged macromolecules by their intrinsic molecular charge. The experimental results of a detection of positively charged poly-D-lysine molecules are presented.

2. Experimental

Fig. 1 shows a schematic of the AuNP-modified EIS structure which represents a (bio-)chemically sensitive field-effect capacitor. Our approach is based on the idea that the adsorption or binding of charged macromolecules (in this study, positively charged poly-D-lysine molecules) on the surface of the citrate-capped negatively charged AuNPs will modulate the flatband potential and space-charge capacitance in the semiconductor, resulting in a shift of the capacitance-voltage (C-V) curve of the functionalised EIS structure.

reference electrode

silanised Si02

depletion layer Si

Fig. 1. Schematic of the AuNP-modified EIS structure.

For the experiments, Al-p-Si-SiO2 structures (p-Si, p=5-10 Qcm, 30 nm thermally grown SiO2) were prepared. As a contact layer, a 300 nm Al film was deposited on the rear side of the Si wafer, and then the wafer was cut into single pieces of 10 mm x 10 mm size. The surface of an EIS sensor has been silanised and modified with citrate-capped AuNPs (15-20 nm). Fig. 2 shows a scanning-electron microscopy picture of the EIS sensor surface modified with AuNPs.

The AuNP-modified EIS sensors were characterised by means of capacitance-voltage (C-V) method [18] using an impedance analyser (Zahner Elektrik, Germany). For the experiments, the EIS sensor chip was mounted into a home-made measuring cell, sealed by an O-ring, and contacted on its front side by the electrolyte and a reference electrode (conventional liquid-junction Ag/AgCl electrode, Metrohm). The contact area of the EIS sensor with the solution was about 0.5 cm2.

Fig. 2. Scanning-electron microscopy picture of the EIS sensor surface modified with AuNPs.

3. Results and discussions

Fig. 3 shows an example of a label-free electrical detection of poly-D-lysine adsorption with the AuNP-modified EIS sensor. In this experiment, the C-V curve of the AuNP-modified EIS sensor was recorded before and after the poly-D-lysine adsorption. The measurements were performed in phosphate buffer solution of pH 7. As can be seen, the adsorption of positively charged poly-D-lysine molecules on the surface of the negatively charged citrate-capped AuNPs shifts the C-V curve of the original EIS structure along both the capacitance and voltage axis. The change in the maximum (or geometrical) capacitance in the accumulation range of the C-V curve was very small (~3%). At the same time, a large potential shift of ~160 mV has been observed along the voltage axis in the depletion range of the C-V curve. The obtained results demonstrate the feasibility of the field-effect capacitive EIS sensors for a label-free detection of charge changes in AuNP/macromolecule inorganic/organic hybrids.

Voltage (V)

Fig. 3. C-V curve of the AuNP-modified EIS sensor before and after the poly-D-lysine adsorption.

Acknowledgements

The authors thank P. Mehndratta and H.-P. Bochem for technical support.

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