Experience and Expertise
The development of a microarray-based assay from a biomarker to a reliable and useful diagnostic tool needs long-time experience since many crucial steps have to be considered: The right type of interaction, the choice of surface (chemistry) and its quality control.
Types of Recognition Site
If a biomarker is detected, the type of recognition has to be chosen with appropriate care as it heavily affects the sensitivity and selectivity of the assay. Mostly, antibodies are used for the recognition of different non-nucleic acid based analytes. For nucleic acids the complementary strand is chosen and a hybridization is performed. Beside that, also different other recognition elements such as peptides, aptamers or artificial receptors may be used to enhance the performance of the assay.
With regard to the type of receptor unit, the surface of the array slide has to match the chemical nature of the receptor and the analyte. On the one hand the receptor has to be immobilized onto the substrate using the appropriate coupling chemistry. On the other hand the analyte should not bind to the surface because unspecific binding leads to lower sensitivity and therefore an inferior assay performance. Thus, the right choice of surface modification combined with reducing the amount of unspecific binding is a fine balancing act which has to be taken into account.
The next step of development is the choice of labelling, which is needed to match the type of detection. For the Fraunhofer ivD-platform, so far, either a fluorescence or electrochemical read-out was demonstrated. With the kind of label the sensitivity can be tuned. In cases in which the sensitivity is not sufficient also on-chip amplification methods can be used to enhance the signal for the analysis.
The last step on the way to a functional microarray is the quality control. Within a single array, different control spots have to be included to show that the assay has worked properly and no cross-contamination has occurred. But secondly, also the manufacturing of thousands of microarrays has to match quality control standards to fulfill different standardization protocols for the accreditation of ivD-products.