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, BPI90-101, 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 85-99, 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.
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