Evaluation of low temperature co-fired ceramic and screen printed gold as platforms for microelectrochemical bioassays

The suitability of Low temperature co-fired ceramic (LTCC)and the associated screen printed gold (SPG) paste as a possible platform to perform microelectrochemical immunoassays was investigated These assays are important because of the fast and sensitive detection possible with these methods. We used a model sandwich immunoassay for mouse IgG as a proof-of-concept assay on SPG/LTCC macrochips. In these immunoassays, self-assembled monolayers of 11-mercaptoundecan-l-ol on the SPG surface served as the interface for covalent attachment of the primary antibody. The assay on SPG/LTCC substrates exhibited good reproducibility. Nonspecific adsorption (NSA) to surfaces of both plain LTCC and SPG/LTCC substrates was investigated and a series of blocking solutions were evaluated. We were able to eliminate NSA on plain LTCC using and aqueous solution of 10% acetate Tween bovine serum albumin or an ethanolic solution of 4 mM 1-butanol. The multilayering capability of the SPG/LTCC materials was utilized in order to create microchannel devices with integrated, individually-addressable SPG electrodes. The SPG/LTCC devices contained either two or four integrated SPG electrodes. The electrodes were screen printed on the sidewalls of the microchannels with a gold paste using a pull-through printing technique. The two-electrode device had a channel volume of 0.168 muL and the four-electrode device had a channel volume of 0.501 muL. A complete electrochemical experiment could be carried out without requiring additional external electrodes. The electrodes had well-behaved electrochemical characteristics as demonstrated with a model redox species, hexaamineruthenuim(III)chloride. The immunoassay and electrochemical detection were integrated to perform a self contained immunoassay inside the microchannel device. The immunoassembly and electrochemical detection were carried out within a microchannel device. The enzymatically generated P-amino phenol from the assembly immobilized at the bottom SPG surface in the microchannel could be detected at the internal working electrodes. A measurable signal was obtained within 15 s of introducing the enzyme substrate; P-amino phenyl phosphate. Detection of 5 ng/ml (3.33 x 10-11 M) of mouse IgG was achieved. Some preliminary work towards the detection of dopamine on these SPG/LTCC surfaces was performed and a microcavity design for electrochemical detection using SPG/LTCC materials was also developed.