Gold nanoparticle-based colorimetric assay for cancer diagnosis

A novel gold nanoparticle (GNP)-based colorimetric assay was developed for cancer diagnosis. This system is based on the noncrosslinking aggregation mechanism with a cationic protein kinase C (PKC) alpha-specific peptide substrate, which is used as a coagulant of citrate-coated GNP with anionic surface charges. The phosphorylation of peptide substrates by PKCalpha suppressed GNP aggregation, resulting in a red color, but in the case of non-phosphorylation, the color of the GNP solution changed from red to blue, indicating particle aggregation. Moreover, a correlation between the color change of the GNP dispersions and the level of activated PKCalpha was identified from experiments using cancer cell lines, or xenografted mouse cancer and normal mouse tissues. When our system was applied to human breast cancers and normal human breast tissues, cancer tissue lysates became red in color, indicating GNP dispersion, while all lysates from normal tissue turned the GNP solution blue. MALDI-TOF MS analysis and Western blotting experiment confirmed that these different results between cancer and normal tissues reflected the difference in PKCalpha activity. This study is the first report on the application of the GNP-based colorimetric assay to the diagnosis of cancer.