Instrumentation-Free Semiquantitative Immunoanalysis Using a Specially Patterned Lateral Flow Assay Device

Abstract

In traditional colorimetric lateral flow immunoassay (LFI) using gold nanoparticles (AuNPs) as a probe, additional optical transducers are required to quantify the signal intensity of the test line because it presents as a single red-colored line. In order to eliminate external equipment, the LFI signal should be quantifiable by the naked eye without the involvement of optical instruments. Given this objective, the single line test zone of conventional LFI was converted to several spots that formed herringbone patterns. When the sandwich immunoassay was performed on a newly developed semi-quantitative (SQ)-LFI system using AuNPs as an optical probe, the spots were colorized and the number of colored spots increased proportionally with the analyte concentration. By counting the number of colored spots, the analyte concentration can be easily estimated with the naked eye. To demonstrate the applicability of the SQ-LFI system in practical immunoanalysis, microalbumin, which is a diagnostic marker for renal failure, was analyzed using microalbumin-spiked artificial urine samples. Using the SQ-LFI system, the calibration results for artificial urine-based microalbumin were studied, ranging from 0 to 500 μg/mL, covering the required clinical detection range, and the limit of detection (LOD) value was calculated to be 15.5 μg/mL. Thus, the SQ-LFI system provides an avenue for the realization of an efficient quantification diagnostic device in resource-limited conditions.

Progression of Paper-Based Point-of-Care Testing toward Being an Indispensable Diagnostic Tool in Future Healthcare

“…Strategies for equipment-free detection in paper-based analysis. Quantification by (A) distance after preconditioning of the μPAD; (B) counting spots (reproduced with permission from ref ; copyright 2020 MDPI); (C) time measurement; and (D) text display, adapted in part from ref .…”

Progress in Biosensors for the Point-of-Care Diagnosis of COVID-19

“…The colored lines can be easily read by the naked eye without any equipment, and also the assay does not need any specific tools or sample processing; therefore, the lateral flow tests are suitable for point-of-care conditions as a simple and inexpensive method. In the linear dynamic concentration range of the assay, the color intensity of the lines is proportional to the analyte concentration [ 61 ]. On the other hand, the common tests are not designed or suitable for the exact determination of the analyte concentration, and they provide only qualitative information on the presence or absence of analyte in a sample, and the intensity of the color is a crude estimation only.…”

A semi-quantitative visual lateral flow immunoassay for SARS-CoV-2 antibody detection for the follow-up of immune response to vaccination or recovery

“…30 In 2020, Lee and collaborators included semi-quantification of microalbumin in urine through naked eye interpretation, based on printing the test zone as multiple spots; the quantitative information was achieved simply by counting the number of coloured spots. 31…”