Enzyme-linked Immunosorbent Assay (ELISA)

Nowadays ELISA is considered to be the troy horse for the routine clinical practice. This widely applied technique offers specific detection of a wide variety of target analytes in different kinds of samples. Since the invention of the technique four decades ago, ELISA has rapidly found various applications in food quality, environmental, biotechnological, and chemical disciplines among others. In spite of its many advantages, ELISA has certain limitations such as tedious/laborious assay procedure, and insufficient level of sensitivity in bio-recognition of challenging biomolecular entities such as microRNAs. A great number of research works has shown valuable attempts in addressing such shortages of ELISA through modification strategies. This chapter is dedicated to reviewing some of the main promising alternatives to the traditional ELISA. Paper- and fiber-based ELISAs, have shown great potentials for point-of-care (POC) applications due to their cost-effectiveness. Miniaturization of ELISA within micro-devices has increased the number and type of samples that can be analyzed, while much lower sample volume is required. Multiplexing was obtained as a result of micro and nano fabrication strategies and the integration of the assay within lab-on-chip (LOC) and lab-on-compact-disk (LOCD) devices. Taking advantage from a significantly vast surface area of the spheres, ultra-sensitive diagnosis was achieved by using micro-/nano-particles with different optical proprieties, sizes, synthetic variables and compositions. ELISA on the spot made possible to measure the biomolecules in vitro. Plasmonic ELISA offered detection strategies even with the aim of the naked eyes. Finally, the digital era has opened new windows of opportunity for ELISA, as the results of immunoassays can be recorded in remote/rural areas and subsequently analyzed by digital technologies or in centralized laboratories via mass data transfer.