DNA-crosslinked alginate and layered microspheres to modulate the release of encapsulated FITC-dextran

Exo I signal amplification of a DNA hydrogel film combined with capillary self-driven action for EpCAM detection

Target-responsive aptamer hydrogels are increasingly used in the field of analytical sensing with different morphologies developed by various strategies. Herein, we developed a DNA hydrogel film combined with capillary self-driven action for the specific detection of the tumor marker EpCAM and further introduced Exo I for signal amplification. EpCAM aptamer was used as a crosslinking agent to construct the DNA hydrogel film. When EpCAM was present, it competed for binding with the EpCAM aptamer, resulting in a permeability change of the DNA hydrogel film attached to one end of the capillary, and leading to different solution flow rates through the capillaries that can be utilized for the quantitative detection of EpCAM. This method did not require any instrument and was easy to use. The distance the solution travelled through the capillary was quantified as the concentration of EpCAM, and only a small amount of DNA hydrogel was required for each detection. The detection limit of EpCAM was as low as 0.018 ng mL-1, while offering the advantages of good stability and specificity, and showing great potential in point-of-care testing.

Aptamer Applications in Emerging Viral Diseases

Aptamers are single-stranded DNA or RNA molecules which are submitted to a process denominated SELEX. SELEX uses reiterative screening of a random oligonucleotide library to identify high-affinity binders to a chosen target, which may be a peptide, protein, or entire cells or viral particles. Aptamers can rival antibodies in target recognition, and benefit from their non-proteic nature, ease of modification, increased stability, and pharmacokinetic properties. This turns them into ideal candidates for diagnostic as well as therapeutic applications. Here, we review the recent accomplishments in the development of aptamers targeting emerging viral diseases, with emphasis on recent findings of aptamers binding to coronaviruses. We focus on aptamer development for diagnosis, including biosensors, in addition to aptamer modifications for stabilization in body fluids and tissue penetration. Such aptamers are aimed at in vivo diagnosis and treatment, such as quantification of viral load and blocking host cell invasion, virus assembly, or replication, respectively. Although there are currently no in vivo applications of aptamers in combating viral diseases, such strategies are promising for therapy development in the future.

Hyaluronic Acid and Poly-l-Lysine Layers on Calcium Alginate Microspheres to Modulate the Release of Encapsulated FITC-Dextran

Alginate solutions crosslink into microspheres in calcium alginate, enabling the encapsulation and subsequent release of biological macromolecules and drugs. However, release from calcium alginate into PBS is relatively fast because it will decrosslink the gel relatively quickly. In this research, FITC-dextran (MW 10 kDa) was encapsulated in 2% (w/v) calcium alginate microspheres by electrospraying. The resulting microspheres (diameter = 247 ± 13 μm) were then layered with thin polyelectrolyte films of hyaluronic acid (HA) and poly-l-lysine (PLL) to attempt to slow the diffusion of FITC-dextran out of the microspheres and the coating parameters were modified to modulate diffusion and release. Increasing the concentration of FITC-dextran encapsulated in the microspheres resulted in an increase in its release over time into PBS. Crosslinking PLL/HA layers on the microspheres did not decrease the in vitro release rates of encapsulated FITC-dextran into PBS. Increasing the number of layers on the microspheres from 3 to 5 layers significantly decreased the amount of encapsulated FITC-dextran released. However, increasing the number of layers to 7 did not further sustain the release of FITC-dextran, likely because these microspheres collapsed to a smaller size during the coating procedure, resulting in release controlled by both diffusion and swelling. Multiple layers of PLL and HA provided a robust mechanism to sustain and control release of large molecules from calcium alginate.