Immunoglobulins G (IgGs) are interesting candidate molecules for mCP: these Abs are useful on surfaces for heterogeneous immunoassays. Their numerous disulfide linkages make them robust, they adsorb from biological buffers to PDMS in a nonreversible manner [1], and they can be conjugated to fluorescent centers, metal particles, enzymes, or ligands such as biotin. Fluorescence microscopy is a versatile method to follow the results of microcontact printing IgGs onto a glass surface (Figure 1). There, TRITC-labeled anti chicken Abs were inked everywhere on the stamp but transferred to glass only in the regions of contact [2]. The patterns on the glass are accurate and correspond to zones of the stamp where the inked proteins are missing. The contrast of the 1 mm-wide features in the pattern is high and accurate and, as no fluorescence above background is measured in the nonprinted regions, it is clear that no transfer of Ab occurred in the recessed areas of the stamp. This might not always be the case, because small features have limited mechanical stability [3]. Demolding the stamp from the mold, capillary effects during inking and drying the stamp, and the printing itself may compromise the mechanical stability of patterns [4]. Implementing support structures in the design of the pattern, controlling the forces exerted during printing and affixing a stiff backplane to the stamp improve the stability of patterns. Stamps can be very large and have features measuring from micrometers to centimeters, making it possible to print proteins of one kind on large substrates to pattern cells indirectly. Examples include microcontact printing fibronectin [5], polylysine [6,7,8], laminin [9], and adhesion peptides [10].

Fig1. Microcontact printing proteins on glass. Fluorescence microscopy images revealing TRITC- labeled chicken Abs on a stamp after inking and accurately transferred in the regions of contact to a glass substrate. Reproduced with permission from Ref. [11]. (Copyright 1998 American Chemical Society.)

References

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