Large‐Scale Dried Reagent Reconstitution and Diffusion Control Using Microfluidic Self‐Coalescence Modules

Abstract

what is sometimes called "the tyranny of the pipette" in the life sciences. [7] Microfluidic devices have greatly contributed to overturning this so-called tyranny, achieving large-scale reagent integration using microcompartments. [8] Yet, they lack simple reagent integration mechanisms or require advanced pumping mechanisms to operate. One solution, the "SIMPLE" chip, [9] incorporates stored reagents and pumpless fluid actuation to perform high throughput blood sample analysis. However, the device is prone to Taylor-Aris dispersion, which imposes strong constraints to compartmentalize reagents. Another example of microfluidic device known as the "slip chip," [10,11] offers a simple way to put two reagents in contact with each other at small volumes, with the drawback that it must be manually filled and operated immediately, having no shelf life. Multiphase flow, notably to generate droplets or water-inoil compartments, has also been used very effectively to compartmentalize reagents for advanced combinatorial screening applications. [12][13][14][15][16][17] Reagent storage in picoliter droplets have also been realized on-chip [18,19] and off-chip [20] using thousands of picoliter-sized droplets that can be processed with kHz frequencies, albeit with limited possibility to address individual droplets with specific reagents and posing long term storage challenges in a multiphase storage medium. [21] Another important approach to enable highly multiplexed reactions is to use surface chemistry to pattern some of the reaction components. DNA, peptide, and protein chips can achieve large surface densities of molecules and can be stored dried or freeze-dried. [22][23][24] However, adsorbed molecules have limited activity (diffusion, steric access), are prone to crossreactivity issues, and generate less signal than when they are directly active in solution. [25] In addition, while some methods involving droplet microfluidics [26,27] or picoliter compartments [11] approaches can generate gradients via free interface diffusion on a short scale, the possibilities for gradient generation remain limited due to the physical or phase-based separation of adjacent reaction volumes. A system capable of storing reagents on the long term and able to reconstitute and control the positioning of these reagents in small aliquots with controlled concentrations without requiring complex manipulations would solve all of the above challenges. Among all reagent storage methods, those employing dried or freeze-dried reagents are the most abundant and the easiest to use, and are commonly found in lateral flow assays. [28,29] Reagents can be spotted inside microfluidic chips using picoliter droplets, whichThe positioning and manipulation of large numbers of reagents in small aliquots are paramount to many fields in chemistry and the life sciences, such as combinatorial screening, enzyme activity assays, and point-of-care testing. Here, a capillary microfluidic architecture based on self-coalescence modules capable of storing thousands of drie...