Surface characterization of a biochip prototype for cell-based biosensor applications

Time-of flight secondary ion mass spectrometry (ToF-SIMS) has been employed to characterize and evaluate the surface of a novel biochip prototype, consisting of an array of gold microelectrodes on which the laminin-derived oligopeptide CDPGYIGSR-NH2 was immobilized. The microelectrodes were isolated from each other via a thin, film of amorphous Teflon (Teflon AF). Prior to studying biochip surfaces, characterization of gold surfaces (supported on oxidized silicon wafers) incorporating the oligopeptide was carried out, to serve as reference standards. With positive-mode ToF-SIMS, the whole peptide could be observed, and in addition, ions that were characteristic of the constituent amino acids of the oligopeptide could also be observed. The microfabrication process for biochip realization comprised several steps which included the use of compounds that could potentially contaminate the resultant surface. Therefore, it was important to: investigate the chemical composition of these surfaces with the highest level of sensitivity. With ToF-SIMS imaging it was possible to detect oligopeptide-related ions only on the microelectrodes and nowhere else. Assessment of the spectral data from user-defined regions within the imaged areas revealed that the microelectrode and Teflon surfaces were devoid of any process-related contamination. In some cases, ToF-SIMS revealed some defects on the biochip surface, which would otherwise not be readily detectable, thereby offering some insight into areas that might require further optimization in the fabrication process.