The article reviews the development and applications of gold nanoshells as theranostic agents in cancer diagnosis and treatment. Gold nanoshells, composed of a silica core and a gold shell, have gained significant attention due to their unique optical properties, including strong absorption and scattering in the near-infrared (NIR) region. These properties make them suitable for both imaging and photothermal therapy. The authors discuss the design and synthesis of nanoshell-based theranostic agents, their plasmon-derived optical properties, and their applications in various diagnostic and therapeutic settings. Key topics include: 1. **Photothermal Properties**: Nanoshells can absorb light and convert it into heat, leading to photothermal ablation of cancer cells. The physical mechanisms behind this process are explained, including the rapid heating and cooling dynamics. 2. **Fluorescence Enhancement**: Nanoshells can enhance the fluorescence of nearby fluorophores, making them useful for imaging. The underlying physics of this enhancement is discussed, including the role of plasmon-induced electromagnetic field modification and photonic mode density. 3. **Optical Imaging and Therapy**: Nanoshells have been used as contrast agents in optical coherence tomography (OCT) and dark-field scattering imaging for breast cancer detection. They have also been shown to enhance the efficacy of photothermal therapy in vivo. 4. **Multimodal Imaging and Therapy**: Nanoshells can be combined with MRI and near-infrared fluorescence imaging to provide comprehensive diagnostic information. The authors describe the design of nanocomplexes that can target breast cancer cells, enhance imaging, and deliver therapeutic heat upon photothermal actuation. 5. **Gene Therapy**: Nanoshells can serve as light-controlled delivery vectors for gene therapy, allowing precise temporal control over the release of DNA sequences. The authors demonstrate the light-induced release of antisense DNA and the delivery of small molecules into cells. The article concludes by discussing the future prospects of nanoshells in theranostics, emphasizing the potential for multifunctional nanoparticles to revolutionize cancer diagnosis and treatment. Challenges and future directions, including nanoparticle size, surface characteristics, toxicity, and biocompatibility, are also highlighted.The article reviews the development and applications of gold nanoshells as theranostic agents in cancer diagnosis and treatment. Gold nanoshells, composed of a silica core and a gold shell, have gained significant attention due to their unique optical properties, including strong absorption and scattering in the near-infrared (NIR) region. These properties make them suitable for both imaging and photothermal therapy. The authors discuss the design and synthesis of nanoshell-based theranostic agents, their plasmon-derived optical properties, and their applications in various diagnostic and therapeutic settings. Key topics include: 1. **Photothermal Properties**: Nanoshells can absorb light and convert it into heat, leading to photothermal ablation of cancer cells. The physical mechanisms behind this process are explained, including the rapid heating and cooling dynamics. 2. **Fluorescence Enhancement**: Nanoshells can enhance the fluorescence of nearby fluorophores, making them useful for imaging. The underlying physics of this enhancement is discussed, including the role of plasmon-induced electromagnetic field modification and photonic mode density. 3. **Optical Imaging and Therapy**: Nanoshells have been used as contrast agents in optical coherence tomography (OCT) and dark-field scattering imaging for breast cancer detection. They have also been shown to enhance the efficacy of photothermal therapy in vivo. 4. **Multimodal Imaging and Therapy**: Nanoshells can be combined with MRI and near-infrared fluorescence imaging to provide comprehensive diagnostic information. The authors describe the design of nanocomplexes that can target breast cancer cells, enhance imaging, and deliver therapeutic heat upon photothermal actuation. 5. **Gene Therapy**: Nanoshells can serve as light-controlled delivery vectors for gene therapy, allowing precise temporal control over the release of DNA sequences. The authors demonstrate the light-induced release of antisense DNA and the delivery of small molecules into cells. The article concludes by discussing the future prospects of nanoshells in theranostics, emphasizing the potential for multifunctional nanoparticles to revolutionize cancer diagnosis and treatment. Challenges and future directions, including nanoparticle size, surface characteristics, toxicity, and biocompatibility, are also highlighted.