Detection of lipopolysaccharide binding peptides by the use of a lipopolysaccharide-coated piezoelectric crystal biosensor

A method has been developed to monitor the interaction between a lipopolysaccharide (LPS) and LPS-binding peptides using a piezoelectric quartz crystal (PQC). Different pH conditions were evaluated to coat LPS onto AT-cut crystals that had been sputtered with gold and carboxylated with a 4,4-dithiodi(n-butyric acid). The optimal pH for LPS coating onto the crystal was 4–5. Synthetic peptides that represent different regions of human bactericidal/permeability-increasing protein, BPI (BPI 85–99, BPI 90–101, BPI 157–167) and polymyxin B (PmB) as well as negative control peptide (HBsAg 139–147) were utilized to compare their binding ability to this LPS-coated PQC sensor. The results showed that PmB gave the greatest decrease to the resonant frequency indicating greatest binding ability. BPI 85–299, considered the main part of the LPS binding domain of BPI, was the next greatest, while BPI 157–167 and HBsAg 139–147 showed little response. In addition, BPI 90–101 and PmB-mimicking peptide showed intermediate LPS-binding ability, which was less than that of BPI 85–99, but was higher than that of BPI 157–167. These results suggest the PQC biosensor is potentially useful for the detection and comparison of the LPS-binding ability of different peptides by using an LPS-coated piezoelectric crystal.