A photonic crystal biosensor assay for ferritin utilizing iron-oxide nanoparticles.

Iron deficiency anemia afflicts 1 in 3 individuals, mostly women and children worldwide. A novel application using iron-oxide nanoparticles (IONPs) and a photonic crystal (PC) optical biosensor as an immunodiagnostic platform for detection of serum ferritin, a biomarker for iron deficiency, is presented. Human liver ferritin (450 kDa), clinical serum controls, and three commercially available ferritin ELISA tests were used to evaluate the PC biosensor assay in terms of inter- and intra-assay variability, spike-recovery (%), limit of detection (LOD), and matrix effects on binding. For the PC biosensor, signal response from label-free, sandwich with secondary antibody (pAb), and pAb functionalized with iron-oxide nanoparticles (FpAb) assays were detected using the Biomolecular Interaction Detection (BIND) system. Bland-Altman analysis was used to evaluate agreement between expected values for ferritin in control sera and each of the detection platforms. Inter- and intra-assay variability of the PC biosensor were both <10%. Percent mean recovery (±%RSD) of ferritin from two control sera samples were 94.3% (13.1%) and 96.9% (7.6%). Use of FpAb in PC biosensor resulted in two orders of magnitude increase in sensitivity compared to label-free assay; capable of measuring serum ferritin as low as 26 ng/mL. In comparison to ELISA tests, the PC biosensor assay had the lowest bias (-1.26; 95% CI [-3.0-5.5]) and narrower limit of agreement (-11.6-9.1 ng/mL) when determining ferritin concentrations from control sera. These proof-of-concept studies support the use of IONPs to enhance detection sensitivity of PC biosensors for determination of biomarkers of nutritional status.