ERBB2 and breast cancer: Another simultaneous detection of ovarian and breast cancer markers using a photonic crystal surface mode for real-time analyte ligand monitoring was described by Petrova et al. In the above method, the limit of detection for the human epidermal growth factor receptor 2 (HER2) biomarker was 620 fg/mL, with a linearity range of up to 50 pg/mL, and the minimal detectable concentration for biomarkers CA15-3 and CA125 was 1.84 U/mL and 0.55 U/mL, respectively [21].