Detection of Biomarker Clusterin in SERS Immunoassays on Al Foil After Substrate Selection and Assay Optimization with Fluorescently Labeled Antibodies

Clusterin plays an important role in carcinogenesis and serves as an important diagnostic biomarker of various clinical conditions. This work describes an application of a surface-enhanced Raman scattering (SERS)-based immunoassay using Al foil substrate that has the potential for the detection of clusterin. We first optimized the parameters of the assay using anti-human IgG/human IgG (hIgG) as a model antibody/antigen system using various substrates based on Au film, Si, Al tape and Al foil. Among the tested substrates, Al foil exhibited better performance, when assay of human IgG on Al foil demonstrated a detection limit of 2 pM and a semi logarithmic trend range from 10 pM to 1000 pM. Afterwards, the same SERS immunoassay method was implemented for detection of clusterin and resulted in a good semi-logarithmic calibration line with a high R² value of 0.99, which was obtained in the range from 1 ng/mL to 1000 ng/mL. The low detection limit for clusterin antigen was found to be 3 ng/mL, which is better than most LODs for clusterin reported in the literature and also nearly 4 orders of magnitude lower than possible concentrations of clusterin in human blood. Moreover, the assay requires a relatively low volume of sample (10 μL). Overall, the assay performance demonstrates the significant potential of SERS on Al foil as a low-cost/high-availability substrate for sensing and biosensing, including detection of cancer biomarkers.