Lateral flow tests and hand-held analyzers facilitate diagnostic testing in resource limited settings and at the point-of-care. However, many of these devices require sample preparation such as plasma separation to remove cells and isolate the liquid portion of blood. Specifically, the separation of plasma from blood is necessary for routine health assessments such as comprehensive metabolic panels and chronic HIV viral load monitoring. Away from laboratories, this type of processing has been addressed by unconventional, hand-operated centrifuge devices (high volume) or plasma separation membranes (PSM) coupled with lateral flow tests (low volume). Herein, we describe a device that separates and stores plasma from undiluted blood using only passive filtration in less than 10 min. Integrating a PSM with a prefilter and absorbent material yields a 3-fold increase in separation efficiency compared to similar devices using passive filtration. We demonstrate the reproducibility of our device across the physiological range of hematocrits (20−50%) with an average recovered plasma volume of 61.7 ± 2.6 μL. Maximum separation efficiency (53.8%, 65.6 ± 3.9 μL plasma) was achieved for a sample of whole blood (30% hematocrit) in 10 min. We evaluate the purity of our plasma sample by quantitation of hemoglobin and report hemolysis as either minimal (≤5%) or undetectable (≤1%). Specific recovery of human IgG, IFN-γ, and HIV-1 RNA indicate the diagnostic utility of plasma obtained from our device is unchanged compared to plasma obtained via centrifugation. Finally, we demonstrate the use of recovered plasma, applied via "stamping", to successfully conduct a commercial lateral flow immunochromatographic assay for tetanus antibodies. This device platform is capable of producing pure plasma samples from blood to facilitate tests in resource limited settings to improve access to healthcare.
DNA aptamers that enhance calcium phosphate mineral formation were identified using a novel precipitation SELEX method. The evolved DNA library was substantially enriched in G nucleotides and in predicted G-quadruplex structures, suggesting their importance in the mechanism of mineralization. This work could readily be extended to provide additional novel DNA aptamers for materials synthesis.
Dried blood spot (DBS) cards perform many functions for sampling blood that is intended for subsequent laboratory analysis, which include: (i) obviating the need for a phlebotomist by using fingersticks, (ii) enhancing the stability of analytes at ambient or elevated environmental conditions, and (iii) simplifying the transportation of samples without a cold chain. However, a significant drawback of standard DBS cards is the potential for sampling bias due to unrestricted filling caused by the hematocrit of blood, which often limits quantitative or reproducible measurements. Alternative microsampling technologies have minimized or eliminated this bias by restricting blood distribution, but these approaches deviate from clinical protocols and present a barrier to broad adoption. Herein, we describe a patterned dried blood spot (pDBS) card that uses wax barriers to control the flow and restrict the distribution of blood to provide enhanced sampling. These patterned cards reproducibly fill four replicate extraction zones independent of the hematocrit effect. We demonstrate a 3-fold improvement in accuracy for the quantitation of hemoglobin using pDBS cards compared to unpatterned cards. Patterned cards also facilitate the near quantitative recovery (ca. 95%) of sodium with no evidence of a statistically significant difference between dried and liquid blood samples. Similarly, the recovery of select amino acids was conserved in comparison to a recent report with improved intercard precision. We anticipate that this approach presents a viable method for preparing and storing samples of blood in limited resource settings while maintaining current clinical protocols for processing and analyzing dried blood spots.
Hematocrit increases with storage time, leading to a decrease in transport distance in our paper-based hematocrit device.
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