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<p>Quantitative measurement of small-molecule metabolites is now emerging as an effective way to link
the metabolite profile to disease state. Surface plasmon resonance (SPR) is a sensing platform that has
demonstrated applicability for a large range of biomolecules. However, direct detection of small molecules with SPR challenges the refractive index based detection mechanism. Herein, we utilized an indirect detection format and developed an inhibition immunoassay for the quantitative measurement of
17β-estradiol (E2) using SPR. One competitor, BSA-E2 conjugate, was immobilized to the SPR chip via
the reaction between the primary amino group of the conjugate and the succinimide group (NHS) introduced by the formation of a thiol-NHS monolayer on gold surface. Free E2 molecules compete with
BSA-E2 on chip surface for binding sites provided by a monoclonal anti-E2 antibody. It was found the
binding affinity of the antibody to BSA-E2 conjugate increases with decreasing surface coverage of
BSA-E2 conjugate. Under optimal conditions, a sigmoidal calibration curve with a negative slope and a
dynamic range from 10 pM to 2 nM was generated. The detection limit of the immunoassay is estimated to be 0.3 pM. Moreover, the immunoassay exhibits high specificity for E2 detection using estrone (E1)
as a potential interference.</p></div></div></div>
Reusable TiN Substrate for Surface Plasmon Resonance Heterodyne Phase Interrogation Sensor
