Detection of low-molecular-weight domoic acid using surface plasmon resonance sensor

An immunosensor based on surface plasmon resonance (SPR) was used for the detection of a low-molecular-weight analyte, domoic acid (DA) (MW 310 g/mol), using an inhibition assay. A novel surface functionalization method was developed to chemically immobilize DA molecules onto a gold-coated SPR chip functionalized with mixed oligo(ethylene glycol) (OEG) self-assembled monolayers (SAMs), where the long-chain HS(CH₂)₁₁(C ₂H₅O)₆NH₂ thiol served as a functional site to react with carboxyl groups on DA while the short-chain HS(CH₂)₁₁(C₂H₅O)₄OH thiol served as a protein non-fouling background. Control experiments showed that there was no detectable non-specific protein adsorption on the sensor surface immobilized with DA. The binding of monoclonal anti-DA antibodies onto the sensor surface was measured using SPR and the concentration of the antibody used in the inhibition assay was optimized to provide the desired detection limit and operating range. A lowest detection limit of 0.1 ng/ml DA was established using the inhibition assay. In addition, the regeneration and storage of sensor chips were studied. The detection curve obtained from a chip which was stored for 1 week and regenerated for each measurement is almost the same as that from freshly prepared chips.