Reversible interactions between DNA and silica are utilized in the solid phase extraction and purification of DNA from complex samples. Chaotropic salts commonly drive DNA binding to silica, but inhibit DNA polymerase amplification. We studied DNA adsorption to silica using conditions with or without chaotropic salts through bulk depletion and Quartz Crystal Microbalance (QCM) experiments. While more DNA adsorbed to silica using chaotropic salts, certain buffer conditions without chaotropic salts yielded a similar amount of eluted DNA. QCM results indicate that under stronger adsorbing conditions, the adsorbed DNA layer is initially rigid, but becomes viscoelastic within minutes. These results qualitatively agreed with a mathematical model for a multiphasic adsorption process. Buffer conditions that do not require chaotropic salts can simplify protocols for nucleic acid sample preparation. Understanding how DNA adsorbs to silica can help optimize nucleic acid sample preparation for clinical diagnostic and research applications.
Molecular detection of microorganisms requires microbial cell disruption to release nucleic acids. Sensitive detection of thick-walled microorganisms such as Bacillus spores and Mycobacterium cells typically necessitates mechanical disruption through bead beating or sonication, using benchtop instruments that require line power. Miniaturized, low-power, battery-operated devices are needed to facilitate mechanical pathogen disruption for nucleic acid testing at the point of care and in field settings. We assessed the lysis efficiency of a very small disposable bead blender called OmniLyse relative to the industry standard benchtop Biospec Mini-BeadBeater. The OmniLyse weighs approximately 3 g, at a size of approximately 1.1 cm 3 without the battery pack. Both instruments were used to mechanically lyse Bacillus subtilis spores and Mycobacterium bovis BCG cells. The relative lysis efficiency was assessed through real-time PCR. Cycle threshold (C T ) values obtained at all microbial cell concentrations were similar between the two devices, indicating that the lysis efficiencies of the OmniLyse and the BioSpec Mini-BeadBeater were comparable. As an internal control, genomic DNA from a different organism was spiked at a constant concentration into each sample upstream of lysis. The C T values for PCR amplification of lysed samples using primers specific to this internal control were comparable between the two devices, indicating negligible PCR inhibition or other secondary effects. Overall, the OmniLyse device was found to effectively lyse tough-walled organisms in a very small, disposable, batteryoperated format, which is expected to facilitate sensitive point-of-care nucleic acid testing.
Solid phase extraction and purification of DNA from complex samples typically requires chaotropic salts that can inhibit downstream polymerase amplification if carried into the elution buffer. Amino acid buffers may serve as a more compatible alternative for modulating the interaction between DNA and silica surfaces. We characterized DNA binding to silica surfaces, facilitated by representative amino acid buffers, and the subsequent elution of DNA from the silica surfaces. Through bulk depletion experiments, we found that more DNA adsorbs to silica particles out of positively compared to negatively charged amino acid buffers. Additionally, the type of the silica surface greatly influences the amount of DNA adsorbed, and the final elution yield. Quartz crystal microbalance experiments with dissipation monitoring (QCM-D) revealed multiphasic DNA adsorption out of stronger adsorbing conditions such as arginine, glycine, and glutamine, with DNA more rigidly bound during the early stages of the adsorption process. The DNA film adsorbed out of glutamate was more flexible and uniform throughout the adsorption process. QCM-D characterization of DNA elution from the silica surface indicates an uptake in water mass during the initial stage of DNA elution for the stronger adsorbing conditions, which suggests that for these conditions the DNA film is partly dehydrated during the prior adsorption process. Overall, several positively charged and polar neutral amino acid buffers show promise as an alternative to methods based on chaotropic salts for solid phase DNA extraction.
Vigorous research efforts have advanced the state-of-the-art nanosensors with ultrahigh sensitivity for bioanalysis. However, a dilemmatic challenge remains: it is extremely difficult to obtain nanosensors that are both sensitive and high-speed for the detection of low-concentration molecules in aqueous samples. Herein, we report how the controlled mechanical rotation (or rotary motorization) of designed opto-plasmonic microsensors can substantially and robustly accelerate the enrichment and detection speed of deoxyribonucleic acid (DNA) with retained high sensitivity. At least 4-fold augmentation of the capture speed of DNA molecules is obtained from a microsensor rotating at 1200 rpm. Theoretical analysis and modeling shed light on the underlying working mechanism, governed by the molecule-motor-flow interaction as well as its application range and limitation. This work provides a device scheme that alleviates the dilemmatic challenge in biomolecule sensing and offers the understanding of the complex interactions of molecules and moving microobjects in suspension. The results may assist the rational design of efficient microrobotic systems for the capture, translocation, sensing, and release of biocargoes.
Mass fluctuations that arise from Mach effects when objects that can store internal energy are accelerated and their application to the production of propellantless thrusts are briefly reviewed. Follow-on experimental work to that reported at STAIF 2004 and 2005 is described. In particular, thrusts in "flux capacitors" made with high voltage disk capacitors wound with coils that produce a magnetic flux therein were sought. An effect of the sort expected continues to be observed. And it displays scaling behavior distinctive to the presence of Mach effects. Various tests for the genuineness of the observed thrusts are described and discussed. The observed effect suggests that the objective of this work, useful propellantless propulsion, may be achievable.
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