Fabrication of glucose biosensors by inkjet printing
  Inkjet printing has been used to fabricate glucose sensors using glucose oxidase and screen printed carbon electrodes. By appropriate selection of printing and drying conditions we are able to fabricate sensor structures that show a good linear response to glucose concentration. In order to achieve these structures we must carefully control the spreading and drying of the enzyme solution on the carbon electrode. Carbon electrode suirfaces are hydrophobic and Triton X was used as a surfactant to allow full coverage of the electrode surface. During drying, under ambient conditions the enzyme solution segregates to form a ring deposit (coffee staining). Coffee staining is shown to be deleterious to sensor performance and it can be removed by drying in a reduced humidity environment. 
Tianming Wang, Christopher C. Cook, Simona Serban, Tarif Ali, Guido   Drago and Brian Derby
cond-mat.mtrl-sci physics.bio-ph physics.chem-ph