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The tracer, the antigen or antibody labelled with a chemiluminescent tag for CLIA, is the next vital optimization step of a chemiluminescent immunoassay. As mentioned earlier, chemiluminescent labels generate light from a chemical reaction. Widely used CLIA labels  are based on luminol derivatives or acridinium esters.

Free PDF guide:  "Biofunctionalization of magnetic beads in CLIA"

CLIA label desired properties 

CLIA labels should have the following characteristics for optimizing the Tracer design:

Stability– The CLIA label should be stable in order to prevent the decay of response over the time, providing extended reagent shelf life and extended reagent on-board stability. This is especially important during the reagent shipment to assure the stability of the CLIA label under extreme conditions of temperature

Chapter 5 Tracer Optimization

High signal to noise ratio – For a CLIA assay it is important to have as much more signal than noise as possible.This helps ensure that the limit of detection can be low because the signal can be distinguished from noise at small concentrations. 

Versatility – The versatility of a tracer can expand your ability to design a CLIA. The same CLIA label should be used to bind small haptens to large antigens or antibodies, the label should be able to bind efficiently to any molecule of interest. 

Simplicity – Ideally, the tracer mechanism should not be complicated so that the emission of light is easily triggered. A simpler tracer reaction will decrease the likelihood of error when using the assay.

Rapid Kinetics – For a CLIA assay it is important to provide a result the sooner the better so it is preferable that the light of emission will be completed in seconds for having high throughput. 

Hydrophilicity – The CLIA label should be hydrophilic in order to improve the tracer solubility, this can be made by modifying the CLIA label with groups that can improve solubility such as PEG structures. This will reduce the non-specific adsorption of the tracer being able to detect lower concentration of the analyte. 

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Lluis M. Martínez | SEPMAG Chief Scientific Officer

Founder of SEPMAG, Lluis holds a PhD in Magnetic Materials by the UAB. He has conducted research at German and Spanish academic institutions. Having worked in companies in Ireland, USA and Spain, he has more than 20 years of experience applying magnetic materials and sensors to industrial products and processes. He has filed several international patents on the field and co-authored more than 20 scientific papers, most of them on the subject of magnetic particle movement.

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