A unified sensor architecture for isothermal detection of double-stranded DNA, oligonucleotides, and small molecules

Pathogen detection is an important problem in many areas of medicine and agriculture, which can involve genomic or transcriptomic signatures or small-molecule metabolites. We report a unified, DNA-based sensor architecture capable of isothermal detection of double-stranded DNA targets, single-stranded oligonucleotides, and small molecules. Each sensor contains independent target detection and reporter modules, enabling rapid design. We detected gene variants on plasmids by using a straightforward isothermal denaturation protocol. The sensors were highly specific, even with a randomized DNA background. We achieved a limit of detection of ∼15 pM for single-stranded targets and ∼5 nM for targets on denatured plasmids. By incorporating a blocked aptamer sequence, we also detected small molecules using the same sensor architecture. This work provides a starting point for multiplexed detection of multi-strain pathogens, and disease states caused by genetic variants (e.g., sickle cell anemia).

Microcompartments for Protection and Isolation of Nanoscale DNA Computing Elements

Physical isolation of molecular computing elements holds the potential for increasing system complexity by enabling the reuse of standardized components and by protecting the components from environmental degradation. However, once elements have been compartmentalized, methods for communicating into these compartments are needed. We report the compartmentalization of steroid-responsive DNA aptamers within giant unilamellar vesicles (GUVs) that are permeable to steroid inputs. Monodisperse GUVs are loaded with aptamers using a microfluidic platform. We demonstrate the target-specific activation of individual aptamers within the GUVs and then load two noninterfering aptamers into the same GUV and demonstrate specific responses to all possible combinations of the two input steroids. Crucially, GUVs prevent the degradation of DNA components by nucleases, providing a potential mechanism for deploying nucleic acid components in vivo. Importantly, our compartments also prevent nonspecific cross-talk between complementary strands, thereby providing a method for parallel execution of cross-reacting molecular logic components. Thus, we provide a mechanism for spatially organizing molecular computing elements, which will increase system modularity by allowing standardized components to be reused.

Multiplexed Lipid Bilayers on Silica Microspheres for Analytical Screening Applications

Most druggable targets are membrane components, including membrane proteins and soluble proteins that interact with ligands or receptors embedded in membranes. Current target-based screening and intermolecular interaction assays generally do not include the lipid membrane environment in presenting these targets, possibly altering their native structure and leading to misleading or incorrect results. To address this issue, an ideal assay involving membrane components would (1) mimic the natural membrane environment, (2) be amenable to high-throughput implementation, and (3) be easily multiplexed. In a step toward developing such an ideal target-based analytical assay for membrane components, we present fluorescently indexed multiplexed biomimetic membrane assays amenable to high-throughput flow cytometric detection. We build fluorescently multiplexed biomimetic membrane assays by using varying amounts of a fluorescently labeled lipid, NBD-DOPE [1,2-dioleoyl-sn-glycero-3-phosphoethanolamine-N-(7-nitro-2-1,3-benzoxadiazol-4-yl)], incorporated into a phospholipid membrane bilayer supported on 3 μm silica microspheres. Using flow cytometry, we demonstrate this multiplexed approach by measuring specific affinity of two well-characterized systems, the fluorescently labeled soluble proteins cholera toxin B subunit-Alexa 647 and streptavidin-PE/Cy5, to membranes containing different amounts of ligand targets of these proteins, GM1 and biotin-DOPE, respectively. This work will enable future efforts in developing highly efficient biomimetic assays for interaction analysis and drug screening involving membrane components.

A Microsphere-Supported Lipid Bilayer Platform for DNA Reactions on a Fluid Surface

We report a versatile microsphere-supported lipid bilayer system that can serve as a general-purpose platform for implementing DNA nanotechnologies on a fluid surface. To demonstrate our platform, we implemented both toehold-mediated strand displacement (TMSD) and DNAzyme reactions, which are typically performed in solution and which are the cornerstone of DNA-based molecular logic and dynamic DNA nanotechnology, on the surface. We functionalized microspheres bearing supported lipid bilayers (μSLBs) with membrane-bound nucleic acid components. Using functionalized μSLBs, we developed TMSD and DNAzyme reactions by optimizing reaction conditions to reduce nonspecific interactions between DNA and phospholipids and to enhance bilayer stability. Additionally, the physical and optical properties of the bilayer were tuned via lipid composition and addition of fluorescently tagged lipids to create stable and multiplexable μSLBs that are easily read out by flow cytometry. Multiplexed TMSD reactions on μSLBs enabled the successful operation of a Dengue serotyping assay that correctly identified all 16 patterns of target sequences to demonstrate detection of DNA strands derived from the sequences of all four Dengue serotypes. The limit of detection for this assay was 3 nM. Furthermore, we demonstrated DNAzyme reactions on a fluid lipid surface, which benefit from free diffusion on the surface. This work provides the basis for expansion of both TMSD and DNAzyme based molecular reactions on supported lipid bilayers for use in molecular logic and DNA nanotechnology. As our system is multiplexable and results in fluid surfaces, it may be of use in compartmentalization and improved kinetics of molecular logic reactions and as a useful building block in a variety of DNA nanotechnology systems.