Lipocalin based biosensors for low mass hydrophobic analytes; development of a novel SAM for polyhistidine tagged proteins

Lipocalins, which are compact binding proteins for odorants, have potential as bioreceptors for small hydrophobic analytes. Studies on several isoforms of the lipocalin major mouse urinary protein (MUP) showed that self-assembled monolayers (SAMs) containing affinity lipid chelating groups were inadequate for building responsive sensors. Non-specific surface immobilisation generated a more responsive but less reproducible sensor. A new SAM was designed that contained a thiolated Ni2+-nitrilotriacetic acid (NTA) moiety to ensure chelating groups were present over the entire surface, allowing specific immobilisation over the whole SAM. This new SAM was found to give improved reproducibility without sacrificing the responsiveness of the sensor. Further development of this SAM type should result in highly sensitive sensors based on lipocalins.