This chapter highlights the novel application of quantum dots (QDs) in the detection of breast tumors, with an emphasis on detecting crucial biomarkers such as HER2. QDs luminous tiny semiconductor nanocrystals with distinct optical properties, have emerged as prospective diagnostic agents for breast cancer. Their size-tunable emission spectra, strong photostability, and multiplexing capabilities allow for the simultaneous detection of several biomarkers, which is critical for understanding the heterogeneity of breast cancers. The combination of QDs with antibodies, such as trastuzumab (Herceptin), allows for precise localization and assessment of HER2 levels in breast cancer cells, surpassing standard approaches like fluorescence in situ hybridization (FISH) and immunohistochemistry (IHC). Furthermore, QDs can be used for In Vivo imaging of tumor xenografts and metastatic locations, providing important information about disease development. While QDs have great potential, issues like toxicity and long-term stability in biological systems are being addressed through the creation of biocompatible and surface-engineered QDs. Ongoing research aims to translate promising preclinical findings into clinically practical diagnostic tools, paving the door for more precise and customized breast cancer treatment.