Controlling Fluorescent Readout in Paper-based Analytical Devices

Abstract

Paper is an ideal candidate for the development of new disposable diagnostic devices because it is a low-cost material, allows transport of the liquid on the device by capillary action, and is environmentally friendly. Today, colorimetric analysis is most often used as a detection method for rapid tests (test strips or lateral flow devices) but usually gives only qualitative results and is limited by a relatively high detection threshold. Here, we describe studies using fluorescence as a readout tool for paper-based diagnostics. We study how the optical readout is affected by light transmission, scattering, and fluorescence as a function of paper characteristics such as thickness (grammage), water content, autofluorescence, and paper type/composition. We show that paper-based fluorescence analysis allows better optical readout compared to that of nitrocellulose, which is currently the material of choice in colorimetric assays. To reduce the loss of analyte molecules (e.g., proteins) due to adsorption to the paper surface, we coat the paper fibers with a protein-repellent hydrogel. For this purpose, we use hydrophilic copolymers consisting of N,N-dimethyl acrylamide and a benzophenone-based cross-linker, which are photochemically transformed into a fiber-attached polymer hydrogel on the paper fiber surfaces in situ. We show that the combination of fluorescence detection and the use of a protein-repellent coating enables sensitive paper-based analysis. Finally, the success of the strategy is demonstrated by using a simple LFD application as an example.

Basic evaluation of the CRISPR/Cas system stability for application to paper-based analytical devices

“…The situation is less clear for the comparison of the WF1 and WF541 signal intensities. But according to Luongo et al 26 fluorescence emission signal intensities tend to increase with the paper substrate thickness, due to the strong scattering of light from fibres behind the fluorescent dye molecule. For the reason of providing the highest signal to noise ratio, the WF1 substrate was selected for further experiments.…”

“…The fluorescence intensity observed on paper substrates is depending on many factors including paper density, thickness, and material. 26 It is assumed that fluorophores are equally distributed throughout the entire thickness of the paper. This results in a higher fluorophore concentration per unit area for thinner filter papers.…”