Abstract
Immunoassays typically must be stored under refrigerated conditions because antibodies, after being immobilized to solid surfaces, tend to lose their recognition capabilities to target antigens under non-refrigerated conditions. This requirement hinders application of immunoassays in resource-limited settings including rural clinics in tropical regions, disaster struck areas, and low-income countries, where refrigeration may not be feasible. In this work, a facile approach based on a reversable zeolitic imidazolate framework-8 (ZIF-8) coating is introduced to stabilize surface-bound antibodies on enzyme-linked immunosorbent assay (ELISA) plates under non-refrigerated conditions. Using a sandwich ELISA for the detection of neutrophil gelatinase-associated lipocalin (NGAL), a urine biomarker for acute kidney injury, as a model system, ZIF-8 is demonstrated to be able to uniformly coat the surface-bound anti-NGAL IgG, and stabilize the dynamic range and detection sensitivity of the assay after storage at an elevated temperature (50 °C) for at least 4 weeks. The stabilization efficacy of the ZIF-8 coating is comparable to the current "gold standard" refrigeration approach, and superior to the commonly used sucrose coating method. This approach will greatly improve the shelf-life and stability of antibody-coated ELISAs and other types of assays which utilize surface-bound antibodies, thus extending biomedical research and medical diagnostics to resource-limited settings.