Figure 1.

Feasibility testing of the assay: The negative (control) test. (a) shows the schematic of the assay, where the DNA is absent, and the UCNP and AuNP will not bind, resulting in higher fluorescence intensity from UCNPs. (b) shows the schematic of the assay, where the DNA is present, and the UCNP and AuNP will bind, resulting in lower fluorescence intensity from UCNPs due to quenching caused by LRET coupling. (c) shows the 3D schematic of conjugated UCNP surrounded by conjugated AuNPs linked by SARS-CoV-2 cDNA. (d) shows an overlay of the AuNP absorption spectrum and UCNP fluorescence spectrum of the negative (control, no DNA) and positive tests (original DNA, 100 nM). The positive test shows lower fluorescence, particularly around the 550 nm wavelength, while the quenching effect is less pronounced at the 667 nm and 792 nm wavelengths.