Gold nanoparticles (AuNPs) have been extensively employed in the development of interfacial platforms for biosensors, since they can be conjugated with biomolecules without interfering with their biochemical activity [1,2]. Particularly, in electrochemical biosensors AuNPs have been used to improve the electron transfer rate and the current response of target electroactive centres/analytes due to their large surface area, high surface free energy and biocompatibility [3].

One of the most important steps in the construction of biosensors is the immobilization of the biomolecule on the substrate and recently, we have demonstrated [4] that a simple one-step method in the presence of CS₂ could be successfully employed in the direct immobilisation of Glucose Oxidase (GOx), from aqueous medium, with the preservation of its bioactivity.

The purpose of this work is to biofunctionalise AuNPs through the one-step reaction between AuNPs, CS₂ and amine groups present in aminoacids (e.g. tryptophan) and enzymes (e.g. glucose oxidase), followed their immobilization onto flat gold electrodes, in order to improve the electrochemically transduced reaction. The redox behaviour of modified flat gold with AuNPs and tryptophan via dithiocarbamate formation indicates a substantial increase of aminoacid amount on the gold surface due to the presence of nanoparticles. The AuNPs modified with glucose oxidase and CS₂, upon gold surface attachment were also studied and their biological activity was evaluated towards glucose in the presence of a redox mediator. Atomic Force Microscopy (AFM) was used to characterize the morphology of the functionalised AuNPs and the modified electrodes.

Ackowledgements

The authors ackowledge L.M. Abrantes for helpful discussions, V. Ferreira for the synthesis of AuNPs, and to FCT for financial support: PTDC/QUI/66612/2006, PEst-OE/QUI/UI0612/2011 and Programme Ciência 2007.

References

[1] U. Saxena, M. Chakraborty, P. Goswami, Biosensors and Bioelectronics 26 (2011) 3037

[2] X. Cao, Y. Ye, S. Liu, Analytical Biochemistry (2011), doi: 10.1016/j.ab.2011.05.027

[3] C. Li , Y. Ya, G.Zhan , Colloids and Surfaces B: Biointerfaces 76 (2010) 340

[4] I. Almeida, A. C. Cascalheira, A. S. Viana, Electrochimica Acta 55 (2010) 8686

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1. (Bio)Functionalisation of gold surfaces based on CS₂ – amine reaction