Graphite-epoxy composites as a new transducing material for electrochemical genosensing  M. Isabel Pividori 1 , Arben Merkoc ¸i, Salvador Alegret * Grup de Sensors i Biosensors, Departament de Quı ´mica, Universitat Auto `noma de Barcelona, 08193 Bellaterra, Catalonia, Spain Received 29 October 2002; received in revised form 19 May 2003; accepted 30 June 2003 Abstract The use of a rigid carbon-polymer composite material as an electrochemical transducer in hybridisation genosensors is reported. Graphite-epoxy composites (GEC) have an uneven surface where DNA can be adsorbed using a simple dry-adsorption procedure. Single-stranded-DNA binds strongly to GEC in a way that prevents the strands from self-associating, while permitting hybridisation with complementary DNA. Hybridisation has been detected through biotin  /streptavidin interaction using a streptavidin conjugated to horseradish peroxidase. Non-specific adsorption onto GEC is almost non-existent even when the surface has not been treated by blocking reagents. The analytical signal obtained was higher when compared with other electrochemical genosensors. Results can be achieved in 150 min, and the detection limit is in the order of fmol. Additionally, surface regeneration is possible using a simple polishing procedure, allowing for multiple use. The new genosensor based on GEC fulfils the requirements desired for these devices: ease of preparation as dry-adsorption of DNA is very simple and easily automated, robustness, sensitivity, low cost of production, ease of miniaturisation and simple use and fast response. Additionally, it can be used for field measurements and can be produced as a genosensor kit. Also, this material can be implemented for screen-printing procedures for the mass production of genosensors. The utility of the genosensor based on GEC is also illustrated with the detection of a sequence related to novel determinant of b- lactamase resistance in Staphylococcus aureus . # 2003 Elsevier B.V. All rights reserved. Keywords: Graphite-epoxy composite; Hybridisation genosensor; Amperometric DNA biosensor; Enzyme labelling; Nylon membrane 1. Introduction The growing demand for genetic information in increasingly varied fields has generated new methodol- ogies for DNA analysis. Genosensors (or DNA biosen- sors) are devices combining a biological recognition agent single-stranded-DNA (ssDNA called DNA probe), with a transducer. The former provides selectiv- ity while the latter provides sensitivity and the conver- sion of the recognition event (hybridisation) to a measurable signal (Mikkelsen, 1996). The Human genome project (HGP) (International Human Genome Sequencing Consortium, 2001) has stimulated the devel- opment of analytical methods that yield genetic infor- mation quickly and reliably. An example of this development is the DNA chip (McGall, 1997; Bowtell, 1999; Collins, 1999; Lander, 1999) and, in the near future, labs-on-a-chip based on micro fluidic techniques (Sanders and Manz, 2000; Wang, 2000). Evidence of the success of the DNA chip can be seen in situations where numerous parallel analyses are required. Also, the knowledge obtained from the HGP has expanded the market, which requires genetic devices, hence, generat- ing new applications. However, this expanding market is not contradictory to simple, cheap and easy to use analytical devices */ especially for industrial applications. Some genosensor designs are are based on optical methods, such as optical fibres (Piunno et al., 1995), surface-plasmon resonance (Bondeson et al., 1993),  Presented at the Seventh World Congress on Biosensors (15 /17 May 2002, Kyoto, Japan). * Corresponding author. Tel.:  /34-93-581-2118; fax:  /34-93-581- 2379. E-mail address: salegret@gsb.uab.es (S. Alegret). 1 Present address: Facultad de Bioquı ´mica y Ciencias Biolo ´ gicas, Universidad Nacional del Litoral, Santa Fe, Argentina. Biosensors and Bioelectronics 19 (2003) 473 /484 www.elsevier.com/locate/bios 0956-5663/03/$ - see front matter # 2003 Elsevier B.V. All rights reserved. doi:10.1016/S0956-5663(03)00222-7