Book excerpt: This book provides up-to-date information on the prototypes used to develop medical devices and explains the principles of biosensing and theranostics. It also discusses the development of biosensor and application-orientated design of medical devices. In addition to summarizing the clinical validation of the developed techniques and devices and the regulatory steps involved in their commercialization, the book highlights the latest research and translational technologies toward the development of point-of-care devices in the health care. Lastly, it explores the current opportunities, challenges and provides troubleshooting on the use of biosensors in precision medicine. The book is helpful for researchers and medical professionals working in the field of clinical theranostics, and medical-device development wanting to gain a better understanding into the principles and processes involved in the development of biosensors.