Improvement of reproducibility and thermal stability of surface-enhanced Raman scattering-based lateral flow assay strips using silica-encapsulated gold nanoparticles

A surface-enhanced Raman scattering (SERS)-based lateral flow assay (LFA) strip using silica-encapsulated gold nanoparticles (Si-AuNPs) was developed for the diagnosis of mosquito-borne diseases—dengue fever, Zika virus, or malaria—which are endemic to tropical regions. To investigate the thermal stability of the SERS nanoprobes, Raman peak intensity variations for AuNPs and Si-AuNPs were measured and compared at 45°C. SERS mapping images of target human immunoglobulin (IgG) on the test line of the Si-AuNP-loaded LFA strip were also evaluated at the same temperature to test the reproducibility of detection. In this case, the distribution of Raman mapping points on the test line was relatively uniform compared with the AuNP-loaded LFA strips at 45°C. This indicates that the silica encapsulation on the surface of the AuNPs improves the reproducibility of the SERS nanoprobes at high temperatures. The limit of detection (LOD) value of the AuNP-loaded LFA strips was significantly increased when the temperature was increased from 25°C to 45°C. In the case of the Si-AuNP-loaded LFA strips, however, the LOD value at 45°C was almost the same as that at 25°C. This result also shows that the silica encapsulation of the AuNPs improves the thermal stability of the LFA strips at high temperatures. Thus, Si-AuNPs are reproducible and thermally stable labeling agents for use in LFA strips at high temperatures and are suitable for the preparation of rapid kits, which can be used in tropical areas.