Picogram-level detection of endotoxin in human saliva using ultrasensitive surface enhanced Raman scattering in lateral flow assay devices

Abstract

The lateral flow assay (LFA) is the most popular rapid diagnostic tool due to its low cost, ease-of-use and fast response. However, conventional LFA design suffers from relatively low sensitivity and lack of quantification capability. In this study ultrasensitive and quantitative LFA device has been developed using surface-enhanced Raman scattering (SERS) detection to detect picogram level of P. gingivalis endotoxin, a major oral health biomarker, in human saliva. Silver coated gold nanostars (Ag@AuNS) with high SERS scattering efficiency were conjugated with Raman reporter (label) dye molecules. Saliva samples from multiple individuals were collected and pretreated to successfully remove components that interfere with endotoxin detection in saliva. The use of LFA cassettes leads to dramatic enhancement of LFA sensitivity and consistency by controlling the saliva flow rate (∼29 seconds slower flow rate than the normal LFA strip) and assuring contact between membranes in the LFA. Significant LOD improvements were obtained using Ag@AuNS: 18 pg mL⁻¹ and 0.3 ng mL⁻¹ for SERS and colorimetric detection, respectively.