Chapter 1 Immunoassays: An Overview Sandeep K. Vashist1, John H.T. Luong 1IDS Immunodiagnostic Systems Deutschland GmbH, Frankfurt am Main, Germany,2University College Cork, Cork, Ireland 1. OVERVIEW OF IMMUNOASSAYS Immunoassays (IAs) play a critical role in various bioanalytical settings, such as clinical diagnostics, biopharmaceutical analysis, environmental monitoring, security, and food testing. During 1995-2017, a wide range of IAs have been developed to provide the quantitative, semiquantitative, or qualitative detec- tion of analytes. The precise early-stage detection of analytes is an essential requirement for all bioanalytical settings to effectively monitor and manage the quality of the biopharmaceutical drugs, foods, and environment. It is even more critical to effectively diagnose, monitor, and manage the patients' health. Considering the prominent role that IAs play in the clinical decision-making, they are indispensable for healthcare settings. Tremendous advances in IA formats, bioanalytical platforms, immunoa- nalytical systems, and complementary technologies have led to various emerging IA formats. Initially, most of the IAs, developed several decades ago, were based on radioimmunoassay (RIA) and enzyme-linked immunosorbent assay (ELISA). Consequently, RIA- and ELISA-based kits for a wide range of analytes became commercially available as the antibodies were generated against such analytes. Owing to extremely high sensitivity, specificity, preci- sion, and throughput of ELISA, this format has served as the gold standard for a plethora of analytes. The last two decades has seen tremendous innovation in ELISA technology. Automated assays are equipped with robotic workstations while the microtiter plate (MTP) readers have also improved drastically in terms of technology, features, and cost-effectiveness. The conventional 96- well MTP formats are transformed into higher-throughput 384- and 1536- well formats. The bioanalytical performance of ELISA has also improved significantly by better antibody immobilization chemistries [23,61,78-80], development of ultrasensitive enzyme substrates, use of micromaterial- or nanomaterial-based signal enhancement strategies [20,71,74], and novel IA concepts [38]. The current trend in ELISA deviates toward wash-free ELISA Handbook of Immunoassay Technologies. https://doi.org/10.1016/B978-0-12-811762-0.00001-3 Copyright @ 2018 Elsevier Inc. All rights reserved. 1
2 Handbook of Immunoassay Technologies such as AlphaLISA by Perkin Elmer [8], which has critically reduced the IA duration and complexity. Advanced bioengineering, microfluidic, and biosensor technologies [24,31,35,55,62] have further led to the development of prominent immu- noanalytical systems including surface plasmon resonance (SPR)-based Bia- Core instruments for label-free IA from GE Healthcare (previously Pharmacia Biosensor AB, Biacore AB Corporation). These systems have become the global standard for developing rapid IA for the detection of analytes and screening of immunological components based on the determination of bio- molecular interactions [27,54]. Although GE Healthcare is still the leader in this domain, other competitors have developed SPR-based immunoanalytical systems. The advent of microfluidics has started the quest for novel IA platforms and formats, which enable rapid IA using the minimal volume of reagents [77]. An example is the Optimiser ELISA by Siloam Biosciences, USA, which involves the conversion of the conventional 96-well MTP-based ELISA into microfluidic ELISA [29]. The analysis time is only a few minutes as this hybrid system employs significantly reduced number of steps and a micro-