A magnetic bead fluorescent sandwich immunoassay has been developed that allows rapid serum measurement of the novel inflammation marker at the point of care (POC) that could aid pneumonia diagnosis.

Pneumonia is an acute infection caused by various bacteria and virus species and the disease is characterized by augmented bronchoalveolar liquid and pus congesting the respiratory tract, resulting in shortness of breath.

Scientists at the Technische Universität München (Munich, Germany) obtained healthy blood donor sera, and patient sera were collected from those with radiologically confirmed pneumonia. A rapid and simple magnetic bead-based immunoassay was developed for the detection of the novel biomarker chitinase-3-like protein 1 (CHI3L1), and also known as YKL40, in an innovative POC-ready device for assistance in the diagnosis of pneumonia.

The study was performed using the ESE Quant Tube Scanner device (QIAGEN Lake Constance GmbH; Stockach Germany). Excitation and emission wavelengths were adjusted to 625 and 680 nm, respectively, to fit the spectral properties of the fluorescent 7-hydroxy-9H-(1,3-dichloro-9,9-dimethylacridin-2-one (DDAO). The ESE Quant Tube Scanner uses a confocal microfluorescence reader, which is small enough to be automatically positioned under each tube. The measurement is repeated every 20 seconds, leading to the recording of the time course of substrate turnover.

The assay procedure, from sample addition to data retrieval, consists of three steps and is performed in less than 20 minutes. The assay has a linear range from 3 ng/mL to 111 ng/mL, with a limit of detection of 2.9 ng/mL. The average recoveries were found between 101 and 111%. The mean calculated serum concentration of patients with pneumonia was 334 ng/mL ± 225 ng/mL (median 300 ng/mL, range 107–821 ng/mL), while serum samples from healthy donors averaged at 50 ng/mL ± 49 ng/mL (median 35 ng/mL, range 9–199 ng/mL).

The authors concluded that the magnetic bead fluorescence immunoassay is a proof of concept that can accurately and rapidly receive protein biomarker data using antibodies bound to magnetic beads in a POC-ready device, providing a simple alternative immunoassay that could help optimize pneumonia diagnosis in low resource settings. The key features of the presented assay are a rapid fluorescence measurement below 20 minutes, a detection limit that corresponds well to the lower reference range of this inflammation serum marker, and usage of an inexpensive and robust device. The study was published in the December 2015 issue of the Journal of Immunological Methods.

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Technische Universität München 
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