Applications of Thin-film Interferometry-based Label-free Immunoassay

Updated: Apr 14

From measurement of monoclonal antibody drugs to SARS-CoV-2 virus neutralization and antibody avidity test



Author: Yiqi Ruben Luo, PhD, DABCC, Assistant Professor, Department of Pathology, School of Medicine, Stanford University

Editor: Jing Cao, PhD, DABCC, FAACC. Assistant Professor, Director of Clinical Chemistry, Clinical Laboratory Director at University of Texas Southwestern Medical Center.


Thin-film interferometry-based label-free immunoassays (LFIA) can achieve real-time immunometric measurement without attaching a reporter molecule (enzyme, fluorophore, etc.) to the immunocomplex. This technology allows for quantitation on initial binding rate of the immunocomplex, which enables fast measurement within a few minutes, therefore offering an innovative solution to clinical diagnostics.

Figure 1. Illustration of the thin-film interferometry (TFI) analyzer, surface chemistry on a sensing probe, and 3 steps of a label-free immunoassays: (i) equilibrating a sensing probe; (ii) loading the ligand onto the sensing probe; and (iii) measuring the interaction between the ligand and the analyte on the sensing probe.

图 1. 生物薄膜干涉分析仪、传感探针上的表面化学和非标记免疫方法的3 个步骤的图示:(i) 平衡传感探针; (ii) 将配体加载到传感探针上; (iii) 测量配体与传感探针上的分析物之间的相互作用。

A series of recent works led by Dr. Y. Ruben Luo, currently an assistant professor in the Department of Pathology and Immunology at Stanford University demonstrated the applications of label-free immunoassay in a wide range of clinical testing settings.

Luo, et al. reported in Clin Chem 2020 the validation of LFIA for the quantitation of active monoclonal antibody drugs including adalimumab and infliximab, and the detection of antidrug antibodies to these monoclonal antibody drugs.(1) The degree of automation, wide analytical measurement range, tight correlation with reporter gene assays, and high concordance rate revealed the unique advantages of LFIA compared with other technologies. Luo, et al.’s report published in Clin Chim Acta 2020 also validated LFIA for the quantitation of monoclonal antibody drug daratumumab to determine the interference in serum protein electrophoresis (2).

Amid the global pandemic of COVID-19, it is crucial to understand the protection from immunity against SARS-CoV2 infection. Luo, et al. reported in Clin Infect Dis 2021 and J Clin Microbiol 2021 a serum antibody affinity assay and a surrogate virus neutralization test established on the LFIA platform (3,4). The former analyzed patient serum IgG affinity to SARS-CoV-2 spike protein receptor-binding domain (RBD) and revealed a correlation between IgG avidity and days since symptom onset: peak readings were significantly higher in severe than mild disease cases. The latter analyzed the binding ability of SARS-CoV-2 spike protein RBD to angiotensin-converting enzyme 2 after neutralization with patient serum antibodies, and it was the first report to provide longitudinal neutralizing antibody titers beyond 200 days post-symptom onset. The kinetics of neutralizing antibody titers showed an initial rise, plateau, and then in some cases a gradual decline at later time points after 40 days post symptom onset. The IgG concentration and avidity to RBD were also measured during this time course of humoral immune response. Despite the decline of IgG concentration and neutralizing antibody titer, IgG avidity index increased, reached a plateau, and then remained constant up to 8 months post-infection.

Further novel applications of this technology are still in the process of research and development, which is expected to bring new directions and advancements to clinical laboratory medicine.

由现任斯坦福大学病理学系助理教授兼斯坦福医学中心临床化学检验室副主任的 Y. Ruben Luo