A-364 The Utility of the Highly Sensitive Detection System for Immunochromatographic Assay by Addition of MPC polymer
Authors: Nakahara T , Matsuda M , Uesugi S , Murakami K , Kobayashi K , Kataoka H , Harata E , Tohyama K 
Published: September 2023

Abstract

Background
Immunochromatographic assay (ICA) is frequently used as a point-of-care testing (POCT) in the field of infectious diseases, but it has a problem of low detection sensitivity. Many interfering substances in ICA test materials have been reported to case a decrease in detection sensitivity. For the purpose of increasing the sensitivity of ICA, bovine serum albumin or a polymer with phosphorylcholine groups (MPC polymer) has been used as an additive to a sample diluent. In this study, we evaluated the usability of the sensitizing effect for the addition of MPC polymer with a serum-based HBs antigen test kit.

Methods
A 2-fold dilution series of a commercially available control serum (Infectrol D, SeraCare Life Sciences, Inc. manufacturer's reference value 108.674 IU/mL) containing 0.05%, 0.10%, 0.5% of several MPC polymers (Biolipidure® from NOF Corporation) as final concentration were prepared with HBs antigen negative serum. The optimal type of MPC polymer and the concentrations added to the sera were determined by comparing the color intensity of their test lines in the evaluation of each test sample with a commercially available test kit (Quick Chaser® from MIZUHO MEDY Co., Ltd.). The color intensities of the test lines were quantified with an immunochromatographic reader.
In addition, the correlation of two different test kits (ESPLINE® from FUJIREBIO and Quick Chaser® from MIZUHO MEDY Co., Ltd.) was evaluated with sera obtained from HBs antigen-positive patients regarding the three types of MPC polymer which were improved the detection sensitivity in the evaluation with the control serum. The measurements were performed in triplicate after 0.5% of MPC polymer as final concentration was added to each diluted serum.

Results
Antigen amount for diluted sera with MPC polymer were determined by CLEIA method, and no difference in the antigen amount was observed regardless of the addition or the types of MPC polymer. In addition, the color intensity in each dilution series was compared to the cutoff value, which is average value of the color intensity of negative control serum without MPC polymer. In the evaluation with control serum, the test line in the case without MPC polymer enabled to detect up to 2-fold diluted control serum while the test line in the case with MPC polymer enabled to detect up to 32-fold diluted control serum. The addition of MPC polymer in the evaluation with sera obtained from HBs antigen-positive patients was also confirmed that the detection sensitivity enhanced up to 8-fold higher in ESPLINE® and up to 4-fold higher in Quick Chaser®.

Conclusion
The color intensity of the test line enhanced by the addition of MPC polymer. In particular, when the highly hydrophilic and anionic MPC polymer was added, the test line was detected narrower and darker, and we believe that the increased color intensity resulted in improved sensitivity. By considering the influence of interfering substances in clinical materials and the physical properties of the MPC polymer (hydrophobicity, molecular size, etc.), it is expected that the sensitivity of the ICA will be increased to be more suitable for clinical materials.