β-Cyclodextrin-Stabilized Silver Nanoparticle Production Combined with Loop-Mediated Isothermal Amplification for the Visual Detection of Contagious Pathogens

β-cyclodextrin (β-CD) is a water-soluble, non-toxic, biocompatible, and cage compound that contains six, seven, or eight α-(1–4)-attached D-glucopyranose residues. The hydroxyl group in the β-CD is responsible for the reduction of metal ions as well as stabilizing the nanoparticles. In this study, we developed a colorimetric assay for identifying contagious pathogens such as SARS-CoV-2 and Enterococcus faecium (E. faecium) via in situ development of β-CD-stabilized silver nanoparticles (AgNPs). In the process, the LAMP amplicons produced a complex with silver nitrate (LAMP amplicon–Ag⁺) which was reduced when heated at 65 °C for 5 min in the presence of β-CD and developed a brown color. The limit of detection was determined to be approximately 10¹ CFU mL⁻¹ and 10 fg µL⁻¹ for E. faecium and SARS-CoV-2, respectively. Significantly, the colorimetric examination of contagious diseases was completed in less than 50 min, including the LAMP assay and detection process. Owing to the high sensitivity and rapid readout mechanism of the β-CD-stabilized AgNP-based colorimetric assay, it is anticipated that the introduced method can be efficiently utilized as a versatile point-of-care testing (POCT) platform for molecular diagnostics in resource-limited areas.