Chemiluminescent Immunoassay (CLIA):
CLIA is an immunoassay technique that is similar to the ELISA except it uses a different reporter or detector label as an indicator of the analytic reaction. The technique is based on the science of chemiluminescence (CL) which is the emission of electromagnetic radiation caused by a chemical reaction to produce light. The CLIA technique combines CL with immunochemical reactions using chemical probes that generate light emission when labeled to the antibody.
CLIA's main advantage is that it provides a simple way to detect and record data. Using chemiluminescence, light can be emitted without the need of excitation from a light source or a detector for a wide range of wavelengths. This is also advantageous because there will be no potential for background from the substance being observed since the only light emitted will be from the chemiluminescent reaction. Unlike other ELISA techniques, CLIA typically does not require separation of absorption and emission wavelengths to understand the readout, therefore it is more direct.
Lateral flow immunoassay (LFIA):
The principle behind the LFIA is rather simple in that a liquid sample proceeds laterally along the surface of a pad that has reactive molecules which bind to the targeted analyte and then migrates along the pad into a detection zone. A liquid sample (or its extract) containing the analyte of interest is applied to the sample pad and moves laterally by capillary flow (without the assistance of external forces) through various zones of polymeric strips, on which are attached molecules that can interact with the analyte. The liquid sample is applied at one end of the strip on the adsorbent sample pad which allows for the sample to migrate through a sample release pad that contains antibodies specific to the targeted analyte and are conjugated to colored or fluorescent particles. The sample along with the conjugated antibody bound to the targeted analyte then migrates along the strip into the detection zone which is usually a porous membrane of nitrocellulose containing immobilized detection components such as antibodies or antigens. These components then react with the analyte bound to the conjugated antibody. Typically, the detection zone has a test zone line and a control zone line. The analyte is captured at the test line with the rest of the sample continuing to migrate until reaching the absorbent wicking pad at the other end of the strip. The detection reagent binds at the control line to indicate that the assay has run successfully. The read-out, represented by the lines appearing with different intensities, can be assessed by eye or by using a dedicated reader. LFIA is a fast, low-cost, portable, and easy to perform assay with many LFIA’s generating a qualitative test result. These characteristics typically make LFIAs ideal for an initial and rapid screening test. (See Illustration for an overview of LFIA method).
