Geometric Flow Control Lateral Flow Immunoassay Devices (GFC-LFIDs): A New Dimension to Enhance Analytical Performance

Abstract

The nitrocellulose (NC) membrane based lateral flow immunoassay device (LFID) is one of the most important and widely used biosensor platforms for point-of-care (PoC) diagnostics. However, the analytical performance of LFID has limitations and its optimization is restricted to the bioassay chemistry, the membrane porosity, and the choice of biolabel system. These bottom neck technical issues resulted from the fact that the conventional LFID design principle has not evolved for many years, which limited the LFID for advanced biosensor applications. Here we introduce a new dimension for LFID design and optimization based on geometric flow control (GFC) of NC membranes, leading to highly sensitive GFC-LFID. This novel approach enables comprehensive flow control via different membrane geometric features such as the width (w) and the length (l) of a constriction, as well as its input angle (θ ₁) and output angle (θ ₂). The GFC-LFID (w=0.5 mm, l=7 mm, θ ₁ = 60°, θ ₂ = 45°) attained a 10-fold increase in sensitivity for detection of interleukin-6 (IL-6), compared with conventional LFID, whereas reducing by 10-fold the antibody consumption. The GFC-LFID detects IL-6 over a linear range of 0.1-10 ng/mL with a limit of detection (LoD) of 29 pg/mL, which even outperforms some commercial IL-6 LFIDs. Such significant improvement is attained by pure geometric control of the NC membrane, without additives, that only relaying on a simple high throughput laser ablation procedure suitable for integration on regular large-scale manufacturing of GFC-LFIDs. Our new development on GFC-LFID with the combination of facile scalable fabrication process, tailored flow control, improved analytical performance, and reduced antibodies consumption is likely to have a significant impact on new design concept for the LFID industry.

Figure 1

Design and fabrication of GFC-LFIDs with various flow parameters. (a) Scheme illustration of a classical LFID and GFC-LFID, and the corresponding devices. (b) 2D layout indicating the regular membrane geometry, with the flow axis x, and the geometric variables include the width (w) and the length (l) of a constriction, as well as its input angle (θ₁) and output angle (θ₂) in this study, along with an image of the actual GFC-LFID NC membrane. (c) Magnification of the laser ablated NC membrane of a GFC-LFID and the SEM image of corresponding boundary illustrating the NC morphology is affected by the laser processing.

Figure 2

Geometric flow control analysis of laser configured membranes. (a) Flow front displacement of GFC-LFIDs (w, l, 45°, 45°) during 30 s interval recorded at 100 ms resolution as a function of the constriction length (l) and width (w) for fixed θ₁ = θ₂ = 45°. (b) Flow front displacement of GFC-LFIDs (0.4, 0.8 mm, 2 mm, θ₁, θ₂) during 30 s interval recorded at 100 ms resolution as a function of the constriction θ₁ and θ₂ between 0 and 75°, for constants l and w. (c) Flow front displacement at constant constriction width, angles, and length for different locations along the flow axis x.

Figure 3

Affinity analytical performance of GFC-LFIDs with enhanced signal and sensitivity. (a) Capture efficiency evaluated by the intensity of the detection line for different constriction widths and lengths. The images are the crop of the actual simultaneously scanned samples used in the evaluation. Error bars correspond to a 95% confidence interval for samples measured in triplicate. (b) GFC-LFID (0.5 mm, 7 mm, 60°, 45°) shows a ~10-fold increase in sensitivity compared with the conventional LFID for detection of IL-6, while using only 1/10 of the antibody benefit to the small laser configured test zone region.

Figure 4

Flow velocity versus dominant combined geometric factors: restriction width (w), length (l), and input angle (θ₁).