Serologic diagnosis of Entamoeba histolytica infection based on the gradient-based digital immunoassay.

Background: Entamoeba histolytica is a parasite that could cause severe amebiasis, an extremely contagious parasitic disease with critical clinical symptoms. Timely diagnosis and treatment of E. histolytica are crucial for preventing complications and fatalities. However, current methods for E. histolytica diagnosis still rely on traditional and laborious methods such as stool examinations and serological immunoassay. Those methods urgently need improved diagnostic sensitivity, diagnostic specificity, detection time, and diagnostic accuracy.

Results: Herein, we developed a rapid and accurate gradient-based digital immunoassay system for diagnosing E. histolytica. This method uses a homemade pre-coated recombinant Igl-C fragment with high binding affinity, designed, recombinantly expressed, and purified by our lab on a one-shot observation microfluidic chip to capture the disease biomarker, specific anti-Igl-C antibodies in the serum. The captured antibodies are detected by anti-human IgG-coated gold nanoparticles, forming a digital binding sandwich immunocomplex. After simple imaging processing, the number of gold nanoparticles bound to the reaction surface within the same field of view of the microscope image was analyzed. Then, it can be easily determined in about 15 min whether specific anti-Igl-C antibodies are in the serum, allowing quicker identification of E. histolytica infection. The detection and diagnosis performance were confirmed by testing 25 clinical serum samples.

Significance And Novelty: The novel diagnostic method provided a digital immunoassay platform and has a strong potential to be a high-efficiency tool for the clinical diagnosis of E. histolytica infection with heightened diagnostic sensitivity and diagnostic specificity. It offers the potential for rapid point-of-care testing, facilitating prompt treatment initiation and improved patient outcomes in resource-limited healthcare settings, making it a valuable asset in the fight against amebiasis.