Immunodiagnostics: Major Advances and Future Insights

Abstract

There have been tremendous advances in immunodiagnostics during the last five decades, which have led to the emergence of potential diagnostic technologies, new immunoassay formats and diagnostic platforms. The radioimmunoassay and Enzyme Linked Immunosorbent Assay (ELISA) were the predominant techniques during the initial era of immunodiagnostics. The strenuous research efforts during the last three decades have enabled the development of potential antibodies for a wide range of analytes. Till date,t ELISA has been the gold standard of clinical immunodiagnostics, which has also been used very frequently for industrial analysis, environmental monitoring, food analysis and bioanalytical sciences. Despite the numerous advances in the field, it is difficult for any other technique to achieve the same high sensitivity, specificity, precision and throughput as ELISA. Various robotic work stations have been devised to perform automated ELISAs in high volume settings, such as in hospitals and industry. Similarly, the Microtiter Plate (MTP) readers have been improved significantly in terms of optics, technology and data analysis. In addition to conventional 96-well MTP format, various high throughput formats, such as 384 and 1536 wells, have also been devised for specific needs. The last two decades have seen considerable improvements in antibody immobilization strategies [1][2][3], which have significantly improved the analytical performance of ELISA in terms of higher sensitivity, greater detection range, lower limit of detection and reduced assay duration [4][5][6]. Similarly, the sample preparation strategies and screening of immunological components have also been critically improved, which enables highly reproducible immunoassays [7,8]. The development of highly sensitive enzyme substrates have led to ultrasensitive ELISAs and chemiluminescent immunoassays [9], while the use of superior fluorescent dyes improved the fluorescent immunoassays. Additionally, the use of infra-red dyes, quantum dots, gold nanoparticles, beads, and other nanomaterial/nanocomposites enabled the development of new ELISA formats, such as the naked-eye ELISA that was demonstrated using gold nanoparticles [10].The development of bead-based AlphaLISA by Perkin Elmer [11] is another major development in immunodiagnostics as it has critically reduced the immunoassay duration and complexity. It employs a streptavidin-coated Alpha donor bead and anti-analyte-conjugated AlphaLISA acceptor bead, which come into close proximity to generate the signal in the presence of analyte. These chemiluminescent immunoassays do not employ any washing step and have high sensitivity, greater dynamic range and superior analytical perfromance than the conventional ELISA.The continuous developments in microfluidic technologies have critically reduced the assay duration and number of process steps apart from enabling the automated handling of process steps. The emergence of surface plasmon resonance (SPR)-based real-time and label-free immunoassays using the Biacore ...