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Immunochemistry is an important clinical tool for indicating biological pathways leading towards disease. Standard enzyme-linked immunosorbent assays (ELISA) are labor intensive and lack sensitivity at low-level concentrations. Here we report on emerging technology implementing fully-automated ELISA capable of molecular level detection and describe application to exhaled breath condensate (EBC) samples.

The Quanterix SIMOA HD-1 analyzer was evaluated for analytical performance for inflammatory cytokines (IL-6, TNF-alpha, IL-1 beta and IL-8). The system was challenged with human EBC representing the most dilute and analytically difficult of the biological media.

Calibrations from synthetic samples and spiked EBC showed excellent linearity at trace levels (r(2) > 0.99). Sensitivities varied by analyte, but were robust from similar to 0.006 (IL-6) to similar to 0.01 (TNF-alpha) pg ml(-1). All analytes demonstrated response suppression when diluted with deionized water and so assay buffer diluent was found to be a better choice. Analytical runs required similar to 45 min setup time for loading samples, reagents, calibrants, etc., after which the instrument performs without further intervention for up to 288 separate samples.

Currently, available kits are limited to single-plex analyses and so sample volumes require adjustments. Sample dilutions should be made with assay diluent to avoid response suppression. Automation performs seamlessly and data are automatically analyzed and reported in spreadsheet format. The internal 5-parameter logistic (pl) calibration model should be supplemented with a linear regression spline at the very lowest analyte levels, (<1.3 pg ml(-1)). The implementation of the automated Quanterix platform was successfully demonstrated using EBC, which poses the greatest challenge to ELISA due to limited sample volumes and low protein levels.