Diamond microelectrodes arrays for the detection of secretory cell activity

Diamond applications potential for biosensing devices have been highlighted by several authors, especially concerning the long-term stability of covalent functionalisations on its surface. Additionally, in electrochemistry boron doped diamond electrodes (N(Lambda) similar to 10(20) cm(3)) show high corrosion resistance and a large hydrolysis window. These features, recognised and exploited in industrial applications, have up to now found little resonance in the life-sciences. Here we present diamond microelectrode arrays based on (1) nanocrystalline diamond (NCD) thin films and (2) single crystal diamond (SCD). NCD is necessary for large area applications like arrays, but graphitic grain boundaries may influence its behaviour. The ideal case SCD is covered here for comparison. The array design consists of four electrodes whose sensitive area is delimited by means of a patterned photoresist. Two different patterns were used to realise a layout with four independent openings (15 mm diameter) for simultaneous detection on multiple cells and a layout with one single window (25 mm diameter) intersecting all four electrodes to create a quadrupolar detector suitable for mapping the activity of single cells. Early results validated the suitability of both NCD and SCD devices: (1) cyclic-voltammetry measurements confirmed the adrenaline oxidation potential on the presented microelectrodes around 650 mV; (2) alternating applications of 1 mM adrenaline and saline rinsing solutions showed negligible electrode fouling; and (3) interfaced to single adrenal chromaffin cells, the devices clearly detected sustained sequences of quantal events (10-100pA amplitude, 50-100 ms duration) associated to the vesicular release of adrenaline and noradrenaline during exocytosis induced by cell-depolarisation.