Lateral flow assay (LFA) is a powerful tool for rapid screening of target biomarker. With colorimetric analysis, LFA can be a quantitative tool as well as qualitative one, which allows LFA to be a good point of care testing device. However, the concentration of several biomarkers for disease diagnosis is far lower than the detection limit of colorimetric LFA. Although various labels, such as fluorescent beads, quantum dots, and upconverting nanoparticles, have been applied to LFA for better sensitivity, the detection of a skeletal muscle protein, called cardiac troponin-I (cTnI), needs picogram-level sensitivity and high selectivity.

To address this issue, surface enhanced Raman spectroscopy (SERS) was applied to LFA flatform to achieve ultrasensitive detection of cTnI. Au@Ag core-shell nanoparticle was introduced as a SERS tag to increase Raman intensity than bare gold nanoparticle. The LOD of colorimetric and SERS analysis of cTnI was 5 ng/ml and 50 pg/ml, which was about 100-fold increment by applying SERS and Au@Ag NPs. Also, selectivity to cTnI against other blood proteins such as human serum albumin and gamma globulin was verified. As a result, SERS-LFA is a powerful platform for ultrasensitive detection of picogram-level of biomarkers such as cTnI.