Dual detection of COVID-19 antigens and antibodies using nanoscale fluorescent plasmonic substrates.

There is a continuing need for biosensors that can be used in the diagnosis of COVID-19 infection and to measure a subject's immune response to the virus itself (SARS-CoV-2). In this study, grating-coupled fluorescent plasmonic (GC-FP)-based detection of SARS-CoV-2 antigens was coupled with antibody detection to yield a dual-mode detection assay. Pairs of capture and detection antibodies were screened for direct detection of the SARS-CoV-2 nucleocapsid (Nuc) antigen, which were then combined with an existing GC-FP antibody detection assay. Nuc could be detected as low as 1 µg/mL concentrations, while antibodies were detectable to 50 ng/mL. The dual detection assay was tested by adding purified Nuc antigen to serum from a polymerase chain reaction (PCR)-positive COVID-19-infected individual. Using this sample, co-detection of Nuc antigen and anti-spike protein antibodies was successfully performed on a single GC-FP chip. Total assay time was 1 h, making this the first known example of rapid dual antibody and antigen detection on the same biosensor chip.

Predictable fabrication of pre-made alginate hydrogel microtubes for stem cell aggregation using needle-in-needle devices.

Alginate hydrogels in microtubular structures have great potential to advance three-dimensional (3D) culture, organoid formation, tissue engineering, and cell therapy. To address the need of fabricating consistent, stable hydrogel microtubes for efficient large organoid generation in a simple and quick manner, we have designed needle-in-needle devices to fabricate alginate hydrogel microtubes without any dead volume of the cell-alginate mixture and demonstrated the feasibility of injecting and culturing embryoid bodies in these pre-made hydrogel microtubes. We further used a reverse engineering approach to find out the optimal flow rates and alginate concentration for fabricating pre-made hydrogel microtubes with desired diameter using particular sets of needle-in-needle devices. We established the relationship of the alginate flow rate with diameter and wall thickness of the microtube using mathematic modeling. It offers a way to determine the flow rate for making microtubes with the desired dimension. Additionally, we evaluated the effect of CaCl2concentration on the diameter as well as stem cell viability. At last, we demonstrated the capacity of fabricating hydrogel microtubes of varying diameters using three sets of needle-in-needle devices and evaluated stem cell growth in these hydrogel microtubes. It provides a new avenue to accessible, repeatable, scalable, and easy to use pre-made 'off-the-shelf' hydrogel microtubes for 3D cell culture including, but not limiting to stem cells.