Liposome-aptamer conjugates are powerful tools for bioanalysis and drug
delivery by taking advantage of aptamer binding specificity and liposome encapsulation
capabilities. Here, we developed multipurpose conjugates that specifically and effectively
bind to his-tags and demonstrated their capability as screening tool for his-tagged proteins
and as signaling tool for bioassays. Using the poly histidine-tag (his-tag) binding aptamer
NDM1-H14−01 (his-Apt), we studied aptamer-liposome immobilization with special
focus on retaining aptamer functionality and liposome integrity. This involved various
strategies for modifying liposomes with aptamers, i.e., cholesterol-functionalized aptamers
were inserted into the liposome pre- or post-synthesis, amine-modified aptamers were
covalently coupled to COOH-groups on the liposome surface, and biotinylated aptamers
were incubated with streptavidin-modified liposomes, respectively. Extensive characterization
of liposome and aptamer properties, as well as conjugate functionality via heterogeneous binding assays, proved postinsertion
and biotinylated aptamers successful with a stability of at least 4 months at 4 °C, whereas the other methods destabilized
the aptamer structure. The successful conjugates were further optimized to (i) serve as a tool for easy detection and screening of histag
accessibility in recombinant proteins, which can replace common metal-based formats (ii) enable efficient site-directed
immobilization of proteins onto liposomes while omitting the need of additional protein modifications, and (iii) demonstrate that
aptamers can function as a reliable secondary recognition element for protein-modified liposomes, e.g., as internal control system.
Consequently, these highly functional and stable his-Apt-liposome conjugates represent a versatile platform technology for bioassays,
which can substitute labor- and cost-intensive measurements, as well as improve assay control and reproducibility.