Controlling Capillary-Driven Fluid Transport in Paper-Based Microfluidic Devices Using a Movable Valve

Abstract

This paper describes a novel strategy for fabricating the movable valve on paper-based microfluidic devices to manipulate capillary-driven fluids. The movable valve fabrication is first realized using hollow rivets as the holding center to control the paper channel in different layer movement that results in the channel's connection or disconnection. The relatively simple valve fabrication procedure is robust, versatile, and compatible with microfluidic paper-based analytical devices (μPADs) with differing levels of complexity. It is remarkable that the movable valve can be convenient and free to control fluid without the timing setting, advantages that make it user-friendly for untrained users to carry out the complex multistep operations. For the performance of the movable valve to be verified, several different designs of μPADs were tested and obtained with satisfactory results. In addition, in the proof-of-concept enzyme-linked immunosorbent assay experiments, we demonstrate the use of these valves in μPADs for the successful analysis of samples of carcino-embryonic antigen, showing good sensitivity and reproducibility. We hope this technique will open new avenues for the fabrication of paper-based valves in an easily adoptable and widely available way on μPADs and provide potential point-of-care applications in the future. P aper-based microfluidics has shown great potential over the past few decades as a promising and powerful platform. 1−4 It mainly relies on attractive features including cheapness, ease-of-operation, lightweight transport, and compatibility with biological samples. Moreover, the cellulose papers can wick aqueous samples by capillary force, allowing them to operate without any external pump. Inspired by this technique, many researchers have put significant efforts toward the development of microfluidic paper-based analytical devices (μPADs), and this technology has been developing as quickly as a bamboo shoot after a spring rain. 5−10 However, when more complicated or multistep assays are required for the μPADs, 5,11,12 how the fluid should be manipulated is of great importance for realizing the essential function of performing multiple processing steps and assay detection for various applications. 13−15 As a crucial and essential functional component for controlling fluid transport, the valve plays an important role in fluid manipulation and enhances the fluidic capability of μPADs.There is a set of techniques that was reported for manipulating fluid to realize the valve function of μPADs by relying on various mechanisms. 16−19 This mainly consists of three strategies. First, the channel's geometry can be varied to result in different arrival times for controlling the liquid flow.Fu, Osborn, and Songok have demonstrated flow delay through changing the shape of the channel. 20−22 The second strategy makes use of chemicals to influence physicochemical properties, including the viscosity of the fluid and the homogeneity of the paper to manipulate the fluid. For instance, the imp...

Recent Advances of Fluid Manipulation Technologies in Microfluidic Paper-Based Analytical Devices (μPADs) toward Multi-Step Assays

“…This valve can be operated several times and is programmable [106]. Rotational valve (hollow rivet) Switching (ON) ELISA (carcino-embryonic antigen; CEA) [102] Rotational valve (comb binding) Switching (ON) Colorimetric-enzymatic assay (Fe 2+ and nitrite) [103] Rotational valve (circular disk) Switching (ON) Fluorescence-based molecular-imprinting detection (4-nitrophenol and 2,4,6-trinitrophenol) [39] Rotational valves on paper-based analytical devices have been implemented using rotatable disk-type packaging [101], hollow rivets [102], comb binding [103], and rotational paper-based microfluidic chips [39] as ways to bridge separated paper channels. As a representative case using rotational valves, a rotatable disk-type device has a bottom piece with a test strip and a top piece with a pad on which the reagent is dried.…”

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“…Three distinguished branches with hydrophobic barriers made of SU-8 photoresist were patterned on chromatography paper using photolithography process and used for glucose and albumin detection. Since the development of 2D-l PAD, extensive research has been carried out in device design, performance improvement and their utilization in various point-of-care applications in the past decades (Cate et al 2014;Kumar et al 2016aKumar et al , b, 2017aKumar et al , b, 2018Morbioli et al 2017;Li et al 2017;You et al 2017;Yeh et al 2017;Whitesides 2018).…”

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“…The cell entrapping efficiency was significant in the region of 50 and 80%. Capillary valves were unified and facilitated the allocation of fluids and samples [21]. The survival rate increased 20-30% higher in comparison to the 96-well plate assay for single cells analysis.…”