Determination of Estriol 16-glucuronide in human urine with surface plasmon resonance and lateral flow immunoassays

A rapid quantitative immunoassay for estriol-16-glucuronide by Surface Plasmon Resonance (SPR) sensing has been developed and applied to urine samples from non-pregnant and pregnant subjects. The assay was based on a partially-purified polyclonal antibody (pAb) raised in sheep, which showed negligible cross-reactivity with estrone-3-glucuronide and estriol-17-glucuronide. Colloidal gold coated by the pAb was used as the signal generator in the SPR-based inhibition immunoassay. An estriol-16-glucuronide-ovalbumin conjugate with an oligoethylene glycol (OEG) as linker was used to immobilize the steroid on the biosensor chip surface. The SPR assay had a limit of detection of 0.016 ng/mL, and could be performed rapidly giving results in two minutes. The assay can be carried out directly on any urine samples without complicated sample pretreatment. A one-step lateral flow strip test was also developed using the same pAb nanogold conjugates and bovine serum albumin estriol-16-glucuronide conjugates as the capture agent spotted onto a nitrocellulose membrane as the test line. A sensitive and repeatable lateral flow assay was achieved with a limit of detection of 0.49 ng/mL in time-diluted urine using a low coating concentration of the polyclonal antibody. Despite the strip sensor displaying adequate sensitivity in a standard curve generated by exposure to estriol-16-glucuronide in a spiked urine blank, the application of the strip sensors to real urine samples was not so successful due to matrix effects.