FN1 and breast cancer: In this paper, we focus on prolonged detection of triple (−) breast cancer at sub-mg NP dosages, using poly(ethylene glycol) (PEG)-stabilized AuNPs conjugated with a fibronectin–mimetic peptide [42,43,44,45], reported to recognize and bind specifically to α5β1 integrins overexpressed in MDA-MB-231 breast cancer cells.