An understanding of fluid transport through porous materials is critical for the development of lateral flow assays and analytical devices based on paper microfluidics. Models of fluid transport within porous materials often assume a single capillary pressure and permeability value for the material, implying that the material comprises a single pore size and that the porous material is fully saturated behind the visible wetted front. As a result, current models can lead to inaccuracies when modeling transport over long distances and/or times. A new transport model is presented that incorporates a range of pore sizes to more accurately predict the capillary transport of fluid in porous materials. The model effectively predicts the time-dependent saturation of rectangular strips of Whatman filter no. 1 paper using the manufacturer's data, published pore-size distribution measurements, and the fluid's properties.

Background Western blotting is used to measure protein expression in cells and tissues. Appropriate interpretation of resulting data is contingent upon antibody validation. Objectives We assessed several commercial anti‐human and anti‐mouse tissue factor (TF) antibodies for their ability to detect TF by western blotting. Material and Methods We used human pancreatic cancer cell lines expressing different levels of TF and a mouse pancreatic cancer cell line expressing TF with a matched knockout derivative. Results Human and mouse TF protein detected by western blotting correlated with levels of TF mRNA in these cell lines. The apparent molecular weight of TF is increased by N‐linked glycosylation and, as expected, deglycosylation decreased the size of TF based on western blotting. We found that four commercial anti‐human TF antibodies detected TF in a TF‐positive cell line HPAF‐II whereas no signal was observed in a TF‐negative cell line MIA PaCa‐2. More variability was observed in detecting mouse TF. Two anti‐mouse TF antibodies detected mouse TF in a TF‐positive cell line and no signal was observed in a TF knockout cell line. However, a third anti‐mouse TF antibody detected a nonspecific protein in both the mouse TF‐positive and TF‐negative cell lines. Two anti‐human TF antibodies that are claimed to cross react with mouse TF either recognized a nonspecific band or did not detect mouse TF. Discussion Our results indicate that there is a range in quality of commercial anti‐TF antibodies. Conclusion We recommend that all commercial antibodies should be validated to ensure that they detect TF.

Simple fl uid pumps have been developed to improve microfl uidic device portability, but they cannot be easily programmed, produce repeatable pumping performance, or generate complex fl ow profi les -key requirements for increasing the functionality of portable microdevices. We present a detachable, paper-based, "hydraulic battery" that can be connected to the outlet of a microfl uidic channel to pump fl uid at varying fl ow rates over time, including step changes, ramping fl ows, and oscillating fl ows.Keywords: Paper Microfl uidics; Capillary Pump; Microfl uidic; Lateral Flow; Microfl uidic Pump; Point of Care. INNOVATIONTh e hydraulic battery demonstrated here is a novel, paper-based pump that uses paper geometry to achieve preprogrammed fl ow rates and durations. Pumps are designed by choosing the dimensions of the resistive neck and absorption region, which control the pumping fl ow rate and volume, respectively. Lamination encapsulates the paper and minimizes the evaporation that plagues other paper microfl uidics, improving pumping reproducibility. Th e pumps are fabricated using a simple, scaleable procedure: here, chromatography paper is laminated and then cut to the desired shape with a laser cutter, although a variety of porous materials can be used. Multiple pumps can be stacked with or without dissolvable delays to create complex fl ow profi les. Using hydraulic batteries, users can generate varying fl ow rate profi les in microfl uidic devices, including both increasing and decreasing step changes, ramping fl ow, and oscillating fl ow. NARRATIVE IntroductionFluid transport in microfl uidic devices is usually controlled by pumps that require external power and cumbersome fl uidic connections, limiting the portability of the system 1 . On-chip pumps exist, but achieving a desired fl ow rate can be an empirical process and the pumps cannot generate complex fl ow behavior [2][3][4][5][6][7] . Capillary pumps have been fabricated via photolithography within microfl uidic devices to pull fl uids through microchannels [8][9][10] , but their integration within the device prevents exchanging or replacing the pumps. To lower the cost and fabrication time of capillary pumps, several groups have used paper connected to the distal end of a microfl uidic channel to pull fl uid [11][12][13][14] . Th ese paper pumps use simple geometric shapes to generate a single fl ow rate but they only work on channels with relatively low fl uidic resistances and are built into the analytical test substrate. Wang et al. demonstrated a clever approach for programming detachable paper-based pumps to pump at progressively slower fl ow rates 15 . However, this strategy cannot be used to create more complex fl ow profi les, such as increasing fl ow rates, oscillating fl ow, or delayed-onset fl ow.Paper devices have been enhanced by improvements such as delays and evaporation barriers, among others. Lamination strategies for paper-based devices include the use of printer toner 16 , tape 17 and lamination with plastic sheets 18,19 . D...

Some of the most efficacious antiviral therapeutics are ribonucleos(t)ide analogs. The presence of a 3′-to-5′ proofreading exoribonuclease (ExoN) in coronaviruses diminishes the potency of many ribonucleotide analogs. The ability to interfere with ExoN activity will create new possibilities for control of SARS-CoV-2 infection. ExoN is formed by a 1:1 complex of nsp14 and nsp10 proteins. We have purified and characterized ExoN using a robust, quantitative system that reveals determinants of specificity and efficiency of hydrolysis. Double-stranded RNA is preferred over single-stranded RNA. Nucleotide excision is distributive, with only one or two nucleotides hydrolyzed in a single binding event. The composition of the terminal basepair modulates excision. A stalled SARS-CoV-2 replicase in complex with either correctly or incorrectly terminated products prevents excision, suggesting that a mispaired end is insufficient to displace the replicase. Finally, we have discovered several modifications to the 3′-RNA terminus that interfere with or block ExoN-catalyzed excision. While a 3′-OH facilitates hydrolysis of a nucleotide with a normal ribose configuration, this substituent is not required for a nucleotide with a planar ribose configuration such as that present in the antiviral nucleotide produced by viperin. Design of ExoN-resistant, antiviral ribonucleotides should be feasible.

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Some of the most efficacious antiviral therapeutics are ribonucleos(t)ide analogs. The presence of a 3'-to-5' proofreading exoribonuclease (ExoN) in coronaviruses diminishes the potency of many ribonucleotide analogs. The ability to interfere with ExoN activity will create new possibilities for control of SARS-CoV-2 infection. ExoN is formed by a 1:1 complex of nsp14 and nsp10 proteins. We have purified and characterized ExoN using a robust, quantitative system that reveals determinants of specificity and efficiency of hydrolysis. Double-stranded RNA is preferred over single-stranded RNA. Nucleotide excision is distributive, with only one or two nucleotides hydrolyzed in a single binding event. The composition of the terminal basepair modulates excision. A stalled SARS-CoV-2 replicase in complex with either correctly or incorrectly terminated products prevents excision, suggesting that a mispaired end is insufficient to displace the replicase. Finally, we have discovered several modifications to the 3'-RNA terminus that interfere with or block ExoN-catalyzed excision. While a 3'-OH facilitates hydrolysis of a nucleotide with a normal ribose configuration, this substituent is not required for a nucleotide with a planar ribose configuration such as that present in the antiviral nucleotide produced by viperin. Design of ExoN-resistant, antiviral ribonucleotides should be feasible.