Oxidative stress on-chip: Prussian blue-based electrode array for in situ detection of H₂O₂ from cell populations

A Prussian blue-based electrode array (PBEA) constituted by eight stencil-printed electrodes on a flexible PET (polyethylene terephthalate) substrate is proposed for in-situ HeLa cell culturing and real-time detection of the released H₂O₂. The array was suitably interfaced with a poly- (methyl methacrylate) (PMMA) well-containing holders resulting in a low cost multichambered chip. PBEA fabrication was carried out employing a xurography-based cost-effective benchtop microfabrication technology using just a desktop cutting plotter and office grade thermal-laminator. The hydrophobicity of the PET isolating layer allows to constrain cell-containing drops directly on top of the electrochemical cells. HeLa cells growth in the very close vicinity of the working electrode ensures in-situ cell seeding, incubation, and further electrochemical detection of the H₂O₂ released, enabling high-throughput analysis. Selective and sensitive electrochemical sensing of hydrogen peroxide was carried out at -100 mV vs Ag|AgCl; the resulting LOD was 1.9 μM. Remarkably, the analytical exploitability of the approach was demonstrated by detection of the hydrogen peroxide released from HeLa cells stimulated with N-Formyl-L-methionyl-L-leucyl-L-phenylalanine (fMLP) and after pretreatment of the cells with cocoa polyphenols, that induced a decreased oxidative stress levels. These data make our approach a promising tool for oxidative stress evaluation in cell cultures and biological systems.