3.

Structural components and configurations of VF-μPADs for enhanced diagnostic performance in POC applications. (A) Basic structure of a VF-μPAD consisting of multiple wax-printed layers, including a NC membrane for detection and an absorbent pad. Reproduced with permission from ref (). Copyright 2023 Elsevier B.V. (B) Schematic showing the inclusion of a conjugation pad in VF-μPADs. Cross-sectional illustration of the conjugation pad with in the layered structure. Reproduced with permission from ref (). Available under a CC-BY license. Copyright 2021 MDPI. (C) Integration of a vertical flow diffusers (VFDs) to ensure uniform fluid distribution across the sensing membrane (Left). Schematic of a VF-μPAD with VFD included, illustrating how fluid flow is directed evenly (Right). Reproduced with permission from ref (). Copyright 2019 Royal Society of Chemistry. (D) Use of a separation membrane for sample filtration in complex biological samples. The separation membrane, placed above the conjugation pad, filters out larger debris, such as cells and proteins, before they reach the sensing layers. Reproduced with permission from ref. (). Available under a CC-BY license. Copyright 2023 Springer Nature. (E) Single-membrane VF-μPAD design for simplified fabrication. A single cellulose membrane functions as both the conjugation pad and sensing membrane, reducing the need for complex layer alignment. Reproduced with permission from ref (). Copyright 2019 Royal Society of Chemistry.