Characterization of Reagent Pencils for Deposition of Reagents onto Paper-Based Microfluidic Devices

Abstract

Reagent pencils allow for solvent-free deposition of reagents onto paper-based microfluidic devices. The pencils are portable, easy to use, extend the shelf-life of reagents, and offer a platform for customizing diagnostic devices at the point of care. In this work, reagent pencils were characterized by measuring the wear resistance of pencil cores made from polyethylene glycols (PEGs) with different molecular weights and incorporating various concentrations of three different reagents using a standard pin abrasion test, as well as by measuring the efficiency of reagent delivery from the pencils to the test zones of paper-based microfluidic devices using absorption spectroscopy and digital image colorimetry. The molecular weight of the PEG, concentration of the reagent, and the molecular weight of the reagent were all found to have an inverse correlation with the wear of the pencil cores, but the amount of reagent delivered to the test zone of a device correlated most strongly with the concentration of the reagent in the pencil core. Up to 49% of the total reagent deposited on a device with a pencil was released into the test zone, compared to 58% for reagents deposited from a solution. The results suggest that reagent pencils can be prepared for a variety of reagents using PEGs with molecular weights in the range of 2000 to 6000 g/mol.

Development of Solid-State Storage for Cell-Free Expression Systems

“…Seeking to prototype the SSB platform, we first fabricated SSB pellets using a simple biochemical system containing horseradish peroxidase (HRP) and glucose oxidase (GOx) enzymes , . Fabrication was achieved through the use of a pellet press, where lyophilized material containing HRP and GOx was pressed into pellets and evaluated.…”

“…Lastly, we identified excipients that support “pencil-like” characteristics to facilitate the deposition of SSB material onto paper-based devices. − We reasoned that evaluating SSB compatibility with μPADs would greatly extend the diagnostic capabilities of the platform. To accomplish this, we optimized SSB excipient formulations to facilitate material deposition onto μPADs and optimized μPADs to support rehydration and incubation of SSB-deposited CFPS reactions.…”

“…Excipients can also contribute negatively to biochemical reactions through interactions with active ingredients, which is an important consideration during formulation . The use of excipients to improve the stability and shelf-life of lyophilized systems has enabled novel applications in biochemical systems such as textile-embedded biosensors for pathogen detection described by Nguyen et al, reagent pencils integrated with simple enzymatic reactions described by Mitchell et al, and cell-free protein synthesis systems to facilitate on-demand gene expression. − …”

Reagent-Pencil and Paper Spray Mass Spectrometry: A Convenient Combination for Selective Analyses in Complex Matrixes

“…These were fabricated by patterning a hydrophobic material, via photolithography, in the hydrophilic chromatographic paper. Since then, μPADs have been used for rapid qualitative and quantitative analysis in several applications, including food quality testing, environmental monitoring, forensic analysis, and point-of-care diagnostics. − These devices are desirable, owing to several advantageous characteristics, including portability, low cost, easy fabrication, and operation. − Recently, to make devices even simpler, especially for point-of-care testing, several research groups have been using day-to-day writing tools, such as pencils and pens, for rapid on-demand deposition of conductive patterns, − hydrophobic barriers, , and reagents on μPADs. − These self-draw μPADs have been classified in the microfluidic community as “Do It Yourself” systems. In particular, reagent pencils provide an alternative (solvent-free) way to deposit solid reagents onto μPADs by the simple drawing of lines.…”

“…When the sample solution is introduced to the device, the reagent dissolves and becomes available to react with the analytes. Reagent pencils are usually prepared by mixing and pressing a solid matrix (e.g., graphite particles, clay) and a binder (wax, resins, or high polymer) with the desired reagent. , Issues on low device-to-device reproducibility and unfeasibility of mass production were recently overcome by Dossi and collaborators using an adapted digitally controlled plotter, enabling faster and more precise control of the deposition of components (graphite and hydrophobic ink) onto the μPADs.…”