User-friendly expression plasmids enable the fusion of VHHs to application-specific tags.

One of the advantages of using recombinant instead of conventional antibodies is that these can be easily manipulated by means of standard molecular biology techniques. Therefore this opportunity can be exploited to prepare fusion constructs composed of VHHs and suitable tags. According to the applications in which the antibodies will be applied, molecules such as fluorescent probes, biotin, and PEG can be either covalently or non-covalently linked to the antibodies. Within this chapter, practical tips for the choice and expression of the most appropriate among the available plasmids are listed, keeping in mind the experimental conditions in which usually the fusion antibodies will be applied.