Academy of Diagnostics & Laboratory Medicine - Scientific Short

Can Spatial Proximity Reagent Capture Luminescence (SPARCL) replace the colorimetric ELISA (Enzyme- Linked Inmmunosorbent Assay)?

Mark Cameron

Many detection technologies used for the quantification of antibodies, antigens, drugs and protein biomarkers are antibody based and are frequently some variation of the colorimetric ELISA.  The colorimetric ELISA is now over 40 years old and is still routinely used in a number of industries including basic research, drug development, drug safety, agriculture and clinical diagnostics.  Applications include lab developed tests, antibody development screening, pharmacokinetics, and determination of safety biomarker levels (skeletal and cardiac troponin for example) and many others.

Ideally, any replacement to the ELISA would make improvements to the ELISA process and provide better data faster.  The ELISA methodology can be slow and labor intensive, difficult to automate and have a limited dynamic range.  The ELISA, even those formats that are fluorescent or chemiluminescent, are saddled with plate coating, plate blocking, multiple reagent addition steps and many washes.  The colorimetric ELISA typically uses an acid addition step to stop color development.  To address many of the detrimental characteristics of the ELISA, we developed a homogeneous (no washing steps) proximity based immunoassay format that can be widely applied to a number of industries in a number of formats (sandwich, competitive, antigen down, and bridging).

The SPARCL format is simple, flexible and offers many advantages over ELISA.  SPARCL is proximity based and homogeneous.  The key components to a SPARCL assays are a small molecule (acridan) and a commonly used enzyme, horse radish peroxidase (HRP).  When acridan and HRP are in close proximity due to a specific antibody to antigen binding event, light is emitted after the addition of a hydrogen peroxide based trigger solution.  No coated or blocked plates (or associated labor and material costs) are needed with the SPARCL format.  There are also no washing steps and no acid stop.  Simply incubate an acridan-conjugated antibody, the HRP-conjugated antibody with the target for 15 minutes and add the trigger solution.  Simple, fast and easy with a number of advantages that may include a significant reduction in labor costs, a reduction of antibody requirements and assays that can be developed in just 2 days.  The SPARCL format runs in 96 or 384 well plates, making it easy to automate.  The data is acquired with software packages already in place and is non-proprietary.  Data is easily imported to Laboratory Information Management Systems (LIMS).

SPARCL is changing the way labs in different industries develop and run immunoassays of many types.  SPARCL offers efficiency and throughput not possible with any other platform or technology.  A single technician with a robotic assist can run 200 plates a day with the SPARCL technology.  SPARCL is flexible and can be formatted for sandwich, competitive, direct or indirect ELISA.  It is rapidly becoming the technology of choice for immunoassay development, validation and sample analysis.

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Fellows of the Academy use the designation of FADLM. This designation is equivalent to FACB and FAACC, the previous designations used by fellows of the National Academy of Clinical Biochemistry and AACC Academy. Those groups were rebranded as Academy of Diagnostics & Laboratory Medicine in 2023.