Immunoplasmonic Nanoprobes With Controlled Orientation Antibodies for Darkfield Microscopy Detection of Biomarker Proteins on Lung and Breast Cancer Cells

Molecular profiling of tumors can help determine patient eligibility for immunotherapy treatments. Immunohistochemistry is widely used to detect biomarker proteins, but it can face challenges for multiplexed screening. As an alternative immunostaining strategy, our team has been exploring the use of antibody‐bioconjugated nanoparticles. With side‐illumination darkfield microscopy, the colored light scattered by individual nanoparticles attached to cancer cells can be observed with high resolution and quantified as a measure of protein expression. Here, we explored using Protein A/G to control antibody orientation on gold nanoparticles that are employed as immunoplasmonic nanoprobes. We used these nanoprobes to screen for biomarker proteins that are relevant to lung and breast cancers, namely, CD44, PD‐L1, and HER2. No further optimization was required when we switched to other types of antibodies that display high binding affinity toward Protein A/G. We observed a concordance of results for immunoplasmonic and immunofluorescence measurements, suggesting that our proposed strategy has high potential for the screening of biomarkers expressed on cellular membranes.