Sensitive and Specific Colorimetric Detection of Cancer Cells Based on Folate-Conjugated Gold–Iron-Oxide Composite Nanoparticles

A sensitive and specific colorimetric analytical strategy for cancer-cell detection based on folate-conjugated gold-iron-oxide composite nanoparticles (Au-Fe₂O₃ CNPs) has been developed. The synthesized Au-Fe₂O₃ CNPs demonstrated peroxidase-like activity and could catalyze the oxidation of 3,3′,5,5′-tetramethylbenzidine in the presence of the hydrogen peroxide. In this method, the Au-Fe₂O₃ CNPs were used as the signal transducer, and the conjugated folic acid acted as the cancer-cell recognition tool. The generated colorimetric signals could be detected by the naked eye or via a UV-vis spectrophotometer at an absorbance of 450 nm from the final yellow product. This folate-conjugated Au-Fe₂O₃ CNP-based colorimetric method allows the detection of cancer cells in the linear range from 50 to 500 cells/mL with a limit of detection of 5 cells/mL for the HeLa cells, which is much lower than that of other colorimetric detection methods for cancer cells. The specificity of this colorimetric detection method was indicated by both fluorescence microscopy images and UV-vis absorbance spectra. Moreover, the colorimetric detection of cancer cells in serum was performed to verify the feasibility of this colorimetric detection method in a complex biological environment. The folate-conjugated Au-Fe₂O₃ CNPs enabled the formation of a colorimetric-responsive multifunctional analysis platform with target recognition for cancer cell detection.