Human epidermal growth factor receptor 2 (Her2/neu) is a biomarker that is overexpressed in human breast cancers. A quantum dots (QDs) -based genosensor for Her2/neu oncogene was developed with gallium telluride QDs and amine-terminated probe ssDNA (NH₂-5′-AATTCCAGTGGCCATCAA-3′), that is complementary to the DNA sequence of a section of the ERF gene of HER-2/neu (i.e. 5′-GAACATGAAGGACCGGTGGGC-3′). The QDs were highly crystalline, 6 nm (from XRD) in size and had band gap values of 3.3 eV and 3.5 eV calculated from fluorescence emission and UV-visible absorption data, respectively. The sensor sensitivity and limit of detection values were 10.0 μA ng⁻¹ mL⁻¹ and 0.2 pg mL⁻¹ Her2/neu oncogene, respectively.