Oxygen Vacancy-Enriched CoFe₂O₄ for Electrochemically Sensitive Detection of the Breast Cancer CD44 Biomarker

Enhancing the selectivity of detection methods is essential to distinguish breast cancer biomarker cluster of differentiation 44 (CD44) from other species and reduce false-positive or false-negative results. Here, oxygen vacancy-enriched CoFe₂O₄ (CoFe₂O_4-x) was crafted, and its implementation as an electrochemical electrode for the detection of CD44 biomarkers has been scrutinized. This unique electrode material offers significant benefits and novel features that enhance the sensitivity and selectivity of the detection process. The oxygen vacancy density of CoFe₂O_4-x was tuned by adjusting the mass ratios of iron to cobalt precursors (iron-cobalt ratio) and changing annealing atmospheres. Electrochemical characterization reveals that, when the iron-cobalt ratio is 1:0.54 and the annealing atmosphere is nitrogen, the as-synthesized CoFe₂O_4-x electrode manifests the best electrochemical activity. The CoFe₂O_4-x electrode demonstrates high sensitivity (28.22 μA (ng mL)^-1 cm^-2), low detection limit (0.033 pg mL^-1), and robust stability (for 11 days). Oxygen vacancies can not only enhance the conductivities of CoFe₂O₄ but also provide better adsorption of -NH₂, which is beneficial for stability and electrochemical detection performance. The electrochemical detection signal can be amplified using CoFe₂O_4-x as a signal probe. Additionally, it is promising to know that the CoFe₂O_4-x electrode has shown good accuracy in real biological samples, including melanoma cell dilutions and breast cancer patient sera. The electrochemical detection results are comparable to ELISA results, which indicates that the CoFe₂O_4-x electrode can detect CD44 in complex biological samples. The utilization of CoFe₂O_4-x as the signal probe may expand the application of CoFe₂O_4-x in biosensing fields.