OR48-2 Point-of-Care Salivary Cortisol Immunoassay Using a Smartphone

Program: Abstracts - Orals, Poster Preview Presentations, and Posters
Session: OR48-Novel Aspects of the HPA Axis: Bench to Smartphone
Tuesday, June 24, 2014: 9:30 AM-11:00 AM
Presentation Start Time: 9:45 AM
W470 (McCormick Place West Building)
Joel R L Ehrenkranz, MD1, Randall Polson, Ph.D.2 and Theodure Espiritu2
1Intermountain Healthcare, Murray, UT, 2University of Utah, Salt Lake City, UT
Measuring salivary cortisol by laboratory immunoassay or mass spectroscopy requires instrumentation and technical personnel and is unable to deliver timely results. We have developed a smartphone-based quantitative salivary cortisol immunoassay that provides results in 5 minutes and can be performed at the point of care.

Disposable cortisol immunoassay strips consisted of nitrocellulose membranes to which cortisol-BSA conjugate (test line) and goat anti-mouse IgG antibody (control line) were attached.  A glass fiber element containing colloidal gold labeled murine anti-cortisol antibodies and a saliva collection pad were inserted at the proximal end of the nitrocellulose membrane and a wicking sump placed at the membrane’s distal end. These tests, read by a spectrophotometer, were able to detect cortisol in PBS in 0.1 mcg/ml increments between 0.1-30 mcg/ml.  Samples of artificial saliva containing cortisol in concentrations between 0.012 and 3.0 mcg/dl were deposited on the strip’s saliva collection pad.  The assay strip was then inserted into a reader that aligned a collimating lens and light diffuser with a smartphone’s camera and flash and the strip was imaged 5 minutes after specimen addition. Because gold nanoparticles with a diameter of 70-100 nm have a plasmon surface resonance peak around 600 nm, a smartphone flash can illuminate and camera image the color generated by colloidal gold labeled anti-cortisol antibodies.  A smartphone image analysis app identified the control and test lines on the assay strip and quantified the pixel density of the green color channel of the test line image.  An algorithm derived by fitting an exponential curve to a graph of observed versus reference salivary cortisol values converted the pixel density of the green color channel of the test line image to a cortisol value. The R value of this curve was 0.996 for salivary cortisol in the range of 0.012-3.0 mcg/dl.

This smartphone-based immunochromatographic quantitative salivary cortisol technology can measure cortisol with a detection limit and dynamic range sufficient to diagnose adrenal insufficiency, hypercortisolism, and monitor physiologic variations in cortisol concentration.  Measuring salivary cortisol at the point-of-care in 5 minutes using an inexpensive immunochromatographic assay, reader, and smartphone may obviate the need to presumptively treat patients for adrenal insufficiency and makes cortisol assays available to regions of the world which currently lack access to this diagnostic test.

Nothing to Disclose: JRLE, RP, TE

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