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

Updated: Apr 14, 2022

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 博士领导的一系列近期工作展示了非标记免疫分析在临床检验环境中的广泛应用。

Luo, et al.在Clin Chem 2020 报告了对于包括阿达木单抗和英夫利昔单抗在内的活性单克隆抗体药物的定量非标记免疫检测方法验证,以及对于这些单克隆抗体药物的抗药抗体的检测方法验证 (1)。其自动化程度、分析测量范围、与报告基因检测的紧密相关性以及高一致率都显示出与其他技术相比的独特优势。 Luo, et al.发表于Clin Chim Acta 2020 的报告还验证了单克隆抗体药物 daratumumab 对血清蛋白电泳干扰的量化方法 (2)。

在 COVID-19 的全球大流行中,了解针对 SARS-CoV2 感染的免疫保护至关重要。Luo, et al.在Clin Infect Dis 2021和J Clin Microbiol 2021 报道了在非标记免疫分析平台上建立的血清抗体亲和力测试以及替代病毒中和试验 (3,4)。前者揭示了患者血清IgG 亲和力与症状出现后的天数之间存在相关性:重症病例的峰值显着高于轻症病例。后者分析了用患者血清抗体中和后 SARS-CoV-2 刺突蛋白受体结合域与血管紧张素转换酶 2 的结合能力,是第一个提供超过 200 天症状发作后的长期中和抗体滴度的研究。中和抗体滴度的动力学表现出最初的上升、平台期,然后在症状发作40 天后开始逐渐下降(某些病例)。此项研究还分析了在该体液免疫过程中测得的 IgG 浓度以及亲和力。尽管 IgG 浓度和中和抗体滴度下降,但 IgG 亲和力指数增加,达到平台期,然后在感染后 8 个月内保持不变。



1. Luo YR, Chakraborty I, Lazar-Molnar E, Wu AHB, Lynch KL. Development of Label-Free Immunoassays as Novel Solutions for the Measurement of Monoclonal Antibody Drugs and Antidrug Antibodies. Clin Chem. 2020;66:1319–28.

2. Luo YR, Chakraborty I, Zuk RF, Lynch KL, Wu AHB. A thin-film interferometry-based label-free immunoassay for the detection of daratumumab interference in serum protein electrophoresis. Clin Chim Acta. 2020;502:128–32.

3. Luo YR, Chakraborty I, Yun C, Wu AHB, Lynch KL. Kinetics of Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) Antibody Avidity Maturation and Association with Disease Severity. Clin Infect Dis. 2021;73:e3095–7.

4. Luo YR, Yun C, Chakraborty I, Wu AHB, Lynch KL. A SARS-CoV-2 Label-Free Surrogate Virus Neutralization Test and a Longitudinal Study of Antibody Characteristics in COVID-19 Patients. J Clin Microbiol. 2021 Jul.

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