Biosensing at disk microelectrode arrays. Inter-electrode functionalisation allows formatting into miniaturised sensing platforms of enhanced sensitivity

Biosensor performance depends on the effective functionalisation of a transducer with suitable biorecognition elements. During functionalisation, surface blocking steps are normally carried out to avoid later binding of undesirable molecules and thus guarantee biosensor specificity. However, these blocking steps may be deleterious in electrochemical systems where transduction ultimately relies on electron transfer between the electrode and a redox species in solution. This work presents a novel approach to develop improved amperometric biosensing platforms using microfabricated disk microelectrode arrays, based on the functionalisation of the inert surface surrounding the active microdisks. These devices more than doubled assay sensitivity compared to conventional biosensors produced using the same arrays. This approach benefits from three advantages: the functionalisation of a broader surface, the possibility to activate the microelectrodes immediately before detection, and access to enhanced rates of mass transport to microelectrodes that improve device sensitivity. To demonstrate this, we first studied the electrochemical behaviour of tetramethylbenzidine (TMB) at gold disk microelectrode arrays, and then used TMB as the redox mediator for the amperometric biosensing of HRP/H(2)O(2). Down to 0.54 pM H(2)O(2) or as little as 25 pM HRP were detected within 5 s of enzyme activity in just 10 mu l of enzyme substrate solution. We postulate that microelectrode arrays may be used to develop novel electrochemical biosensing platforms that are faster and more sensitive than conventional biosensors. (C) 2009 Elsevier B.V. All rights reserved.