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42 Smart Nanomaterials for Sensor Application, 2012, 42-59
Metal Nanoparticles-Based Affinity Biosensors
Giovanna Marrazza *
Songjun Li, Yi Ge and He Li (Eds)
All rights reserved - © 2012 Bentham Science Publishers
CHAPTER 2
Università di Firenze, Dipartimento di Chimica, Via della Lastruccia, 3; 50019 Sesto Fiorentino (Fi) Italy
Abstract: A new emerging field that combines nanoscale materials and biosensor technology is
receiving increased attention. Nanostructures have been used to achieve direct wiring of enzymes to
electrode surfaces, to promote electrochemical reactions, impose nano barcodes on biomaterials, and
amplify the signal from biorecognition events. NP-based sensors have found wide spread applications
in the environmental and medical applications for their sensitivity, specificity, rapidity, simplicity, and
cost-effectiveness.
The aim of this chapter, without pretending to being exhaustive, is mainly to review recent important
achievements about metal nanoparticles preparation, their bio modification and the new applications for
protein detections by means of a set of selected recent publications.
Keywords: Biosensors; metal nanoparticles; biomodification; protein detections.
INTRODUCTION
According to the International Union of Pure and Applied Chemistry (IUPAC) a biosensor is a selfcontained
integrated device, which is capable of providing specific quantitative or semi-quantitative
analytical information using a biological recognition element which is retained in direct spatial contact with
an electrochemical transduction element.
Affinity biosensors are a subclass of biosensors. The sensing element is a highly specific receptor; it is
generally biologic (bioreceptors) such as enzymes, antibodies and nucleic acids. In the last years, the use of
artificial or semi-artificial receptors is increasing. This class includes PNA (Peptide Nucleic Acid) LNA
(Locked Nucleic Acid), the MIPs (Molecular Imprinted Polymers), the oligopeptides, the aptamers, and
recently affibodies.
In a recent review, the state of the art and the recent developments in immunosensor have been described [1].
Homogeneous immunosensor, heterogeneous immunosensor, integrated immunosensor and biochip format
immunosensor based on optical, electrochemical, magnetic or mechanical detection/transduction systems are
reviewed. Most of the developed immunosensors include a sensing layer supporting a particular immobilised
antigen or antibody. The solid support used is generally in close contact with a transducer needed for the
detection of the formed immune complex. The immunosensors are based either on competitive or sandwich
assay, when applied to the detection of low and high molecular weight molecules, respectively (Fig. 1A, 1B).
Two approaches could be considered when dealing with competitive immunosensor. A first-one in which
immobilised antibodies react with free antigens in competition with labelled antigens (Fig. 1a). A second-one,
using immobilised antigens and labelled antibodies, is generally preferred and prevents all the problems related
to antibody immobilisation (i.e. loss of affinity, orientation) (Fig. 1b).
In protein-sensing devices the immobilised compound determines the specificity of the device, and the
immobilisation method frequently influences parameters such as lower detection limit, sensitivity, dynamic
range, reusability or liability for unspecific binding. Thus, varieties of immobilisation approaches have
been developed, which are applicable to different supports onto which, the compound has to be
immobilised [2]. The immobilization procedure is dependent on the assay format and detection transducer.
*Address correspondence to Giovanna Marrazza: Università di Firenze, Dipartimento di Chimica, Via della Lastruccia, 3; 50019
Sesto Fiorentino (Fi) Italy; Tel. +39-055-5253320; E-mail: giovanna.marrazza@unifi.it; Web: www.unifi.it/dclabi