Protein microarray spots are modulated by patterning method, surface chemistry and processing conditions

The uniformity of the protein patterns, their shape, and the contrast between the fluorescence signal of the pattern and the background, critically modulate the quantitative accuracy of the microarray-derived data. While significant research focused of the identification of the factors that impact the protein microarray patterns, these studies usually have focused on the optimization of one set of these factors, e.g., how the spot uniformity is affected by different additives, or by different surfaces. However, the complex interaction between proteins, carrier fluids, surfaces, and patterning methodologies used would suggest a systematic and more comprehensive study that considers all these parameters, as well as their inter-relationship. The present work compared the patterning of two fluorescently-tagged proteins, i.e., IgG, BSA, on surfaces with different hydrophobicity and chemistry, and printed by inkjet, pin, and microcontact printing (µCP). The quantification of the spot size regularity, its morphology, the signal intensity and its distribution within spots were used to assess the quality of a specific printing method, on a specific surface, with a specific solute of the printed protein. It was found that the optimal uniformity for both droplet-based methods depend on surface chemistry, with glass slides modified with 3-Glycidoxypropyl-dimethoxymethyl silane (GPS) and 3-(Aminopropyl)-triethoxy silane (APTES) exhibiting the greatest uniformity, while uniformity of the µCP patterns was relatively independent of the surface chemistry. For the inkjet and pin printing, the largest fluorescence signal and contrast with the background was found on APTES modified glass slides, whereas for the µCP the fluorescence signal increased with increasing hydrophilicity.