A new DNA aptamer which binds to SARS-CoV-2 spike protein and reduces pro-inflammatory response.

COVID-19 caused by SARS-CoV-2 spread rapidly around the world, endangering the health of people globally. The SARS-CoV-2 spike protein initiates entry into target cells by binding to human angiotensin-converting enzyme 2 (ACE2). In this study, we developed DNA aptamers that specifically bind to the SARS-CoV-2 spike protein, thereby inhibiting its binding to ACE2. DNA aptamers are small nucleic acid fragments with random structures that selectively bind to various target molecules. We identified nine aptamers targeting the SARS-CoV-2 spike protein using the systematic evolution of ligands by exponential enrichment (SELEX) method and selected three optimal aptamers by comparing their binding affinities. Additionally, we confirmed that the DNA aptamers suppressed pro-inflammatory cytokines induced by the SARS-CoV-2 spike protein in ACE2-overexpressing HEK293 cells. Overall, the DNA aptamer developed in this study has the potential to bind to the SARS-CoV-2 spike protein and inhibit or block its interaction with ACE2. Thus, our DNA aptamers can be used as new biological tools for the prevention and diagnosis of SARS-CoV-2 infection.

Acoustofluidic separation of prolate and spherical micro-objects.

Most microfluidic separation techniques rely largely on object size as a separation marker. The ability to separate micro-objects based on their shape is crucial in various biomedical and chemical assays. Here, we develop an on-demand, label-free acoustofluidic method to separate prolate ellipsoids from spherical microparticles based on traveling surface acoustic wave-induced acoustic radiation force and torque. The freely rotating non-spherical micro-objects were aligned under the progressive acoustic field by the counterrotating radiation torque, and the major axis of the prolate ellipsoids was parallel to the progressive wave propagation. The specific alignment of the ellipsoidal particles resulted in a reduction in the cross-sectional area perpendicular to the wave propagation. As a consequence, the acoustic backscattering decreased, resulting in a decreased magnitude of the radiation force. Through the variation in radiation force, which depended on the micro-object morphology enabled the acoustofluidic shape-based separation. We conducted numerical simulations for the wave scattering of spherical and prolate objects to elucidate the working mechanism underlying the proposed method. A series of experiments with polystyrene microspheres, prolate ellipsoids, and peanut-shaped microparticles were performed for validation. Through quantitative analysis of the separation efficiency, we confirmed the high purity and high recovery rate of the proposed acoustofluidic shape-based separation of micro-objects. As a bioparticle, we utilize Thalassiosira eccentrica to perform shape-based separation, as the species has a variety of potential applications in drug delivery, biosensing, nanofabrication, bioencapsulation and immunoisolation.

Elasto-inertial microfluidic separation of microspheres with submicron resolution at high-throughput.

Elasto-inertial microfluidic separation offers many advantages including high throughput and separation resolution. Even though the separation efficiency highly depends on precise control of the flow conditions, no concrete guidelines have been reported yet in elasto-inertial microfluidics. Here, we propose a dimensionless analysis for precise estimation of the microsphere behaviors across the interface of Newtonian and viscoelastic fluids. Reynolds number, modified Weissenberg number, and modified elastic number are used to investigate the balance between inertial and elastic lift forces. Based on the findings, we introduce a new dimensionless number defined as the width of the Newtonian fluid stream divided by microsphere diameter. The proposed dimensionless analysis allows us to predict whether the microspheres migrate across the co-flow interface. The theoretical estimation is found to be in good agreement with the experimental results using 2.1- and 3.2-µm-diameter polystyrene microspheres in a co-flow of water and polyethylene oxide solution. Based on the theoretical estimation, we also realize submicron separation of the microspheres with 2.1 and 2.5 µm in diameter at high throughput, high purity (>95%), and high recovery rate (>97%). The applicability of the proposed method was validated by separation of platelets from similar-sized Escherichia coli (E.coli).

Rapid acoustofluidic mixing by ultrasonic surface acoustic wave-induced acoustic streaming flow.

Ultrasonic surface acoustic wave (SAW)-induced acoustic streaming flow (ASF) has been utilized for microfluidic flow control, patterning, and mixing. Most previous research employed cross-type SAW acousto-microfluidic mixers, in which the SAWs propagated perpendicular to the flow direction. In this configuration, the flow mixing was induced predominantly by the horizontal component of the acoustic force, which was usually much smaller than the vertical component, leading to energy inefficiency and limited controllability. Here, we propose a vertical-type ultrasonic SAW acousto-microfluidic mixer to achieve rapid flow mixing with improved efficiency and controllability. We conducted in-depth numerical and experimental investigations of the vertical-type SAW-induced ASF to elucidate the acousto-hydrodynamic phenomenon under varying conditions of total flow rate, acoustic wave amplitude, and fluid viscosity conditions. We conducted computational fluid dynamics simulations for numerical flow visualization and utilized micro-prism-embedded microchannels for experimental flow visualization for the vertical SAW-induced ASF. We found that the SAW-induced vortices served as a hydrodynamic barrier for the co-flow streams for controlled flow mixing in the proposed device. For proof-of-concept application, we performed chemical additive-free rapid red blood cell lysis and achieved rapid cell lysis with high lysis efficiency based on the physical interactions of the suspended cells with the SAW-induced acoustic vortical flows. We believe that the proposed vertical-type ultrasonic SAW-based mixer can be broadly utilized for various microfluidic applications that require rapid, controlled flow mixing.

Acoustofluidic separation of proteins from platelets in human blood plasma using aptamer-functionalized microparticles.

Microfluidic liquid biopsy has emerged as a promising clinical assay for early diagnosis. Herein, we propose acoustofluidic separation of biomarker proteins from platelets in plasma using aptamer-functionalized microparticles. As model proteins, C-reactive protein and thrombin were spiked in human platelet-rich plasma. The target proteins were selectively conjugated with their corresponding aptamer-functionalized microparticles of different sizes, and the particle complexes served as a mobile carrier for the conjugated proteins. The proposed acoustofluidic device was composed of an interdigital transducer (IDT) patterned on a piezoelectric substrate and a disposable polydimethylsiloxane (PDMS) microfluidic chip. The PDMS chip was placed in a tilted arrangement with the IDT to utilize both vertical and horizontal components of surface acoustic wave-induced acoustic radiation force (ARF) for multiplexed assay at high-throughput. The two different-sized particles experienced the ARF at different magnitudes and were separated from platelets in plasma. The IDT on the piezoelectric substrate could be reusable, while the microfluidic chip can be replaceable for repeated assays. The sample processing throughput with the separation efficiency >95% has been improved such that the volumetric flow rate and flow velocity were 1.6 ml/h and 37 mm/s, respectively. For the prevention of platelet activation and protein adsorption to the microchannel, polyethylene oxide solution was introduced as sheath flows and coating on to the walls. We conducted scanning electron microscopy, x-ray photoemission spectroscopy , and sodium dodecyl sulfate- analysis before and after the separation to confirm the protein capture and separation. We expect that the proposed approach will provide new prospects for particle-based liquid biopsy using blood.

Antibacterial Nanopillar Array for an Implantable Intraocular Lens.

Postsurgical intraocular lens (IOL) infection caused by pathogenic bacteria can result in blindness and often requires a secondary operation to replace the contaminated lens. The incorporation of an antibacterial property onto the IOL surface can prevent bacterial infection and postoperative endophthalmitis. This study describes a polymeric nanopillar array (NPA) integrated onto an IOL, which captures and eradicates the bacteria by rupturing the bacterial membrane. This is accomplished by changing the behavior of the elastic nanopillars using bending, restoration, and antibacterial surface modification. The combination of the polymer coating and NPA dimensions can decrease the adhesivity of corneal endothelial cells and posterior capsule opacification without causing cytotoxicity. An ionic antibacterial polymer layer is introduced onto an NPA using an initiated chemical vapor deposition process. This improves bacterial membrane rupture efficiency by increasing the interactions between the bacteria and nanopillars and damages the bacterial membrane using quaternary ammonium compounds. The newly developed ionic polymer-coated NPA exceeds 99% antibacterial efficiency against Staphylococcus aureus, which is achieved through topological and physicochemical surface modification. Thus, this paper provides a novel, efficient strategy to prevent postoperative complications related to bacteria contamination of IOL after cataract surgery.