TF and cancer: Biologically relevant molecules [e.g., transferrin (Tf) (Nishimura et al., 2013), sugar (Lai et al., 2016), targeting peptides (Song et al., 2015; Zhou et al., 2017), and polyethylenimine (PEI) (Pang et al., 2016), etc.] have been utilized to functionalize SiNPs, producing the SiNPs-based biofunctional nanoprobes for dynamically studying carbohygrate-carbohydrate interactions, single Tf receptor (TfR) molecule tracking, and targeting specific cancer cells.