Biosensor technologies have emerged as essential instruments that revolutionise diagnostic, monitoring, and analytical processes in current science and engineering. The book chapters address current developments in biosensor technologies and their applications for the early diagnosis of various diseases. The first chapter focuses on the use of nucleic acid-based aptamers in recently developed electrochemical and optical biosensors, evaluating the performance advantages offered by these novel biorecognition elements. The second chapter covers the fundamental principles and application areas of paper-based biosensor technologies, which offer low-cost and portable solutions. The third chapter discusses biosensor design strategies for the early diagnosis of breast cancer, covering topics such as biomarker selection, sensor architecture, and diagnostic performance. The fourth chapter focuses on biosensor systems used in the diagnosis of prostate cancer, examining their scientific basis, technological advancements, and clinical implications. The final chapter discusses current biosensor designs developed for the early diagnosis of neurodegenerative diseases, and evaluates next-generation sensor platforms that enable the sensitive detection of biomarkers with potential for clinical use. This book provides a comprehensive overview of the potential use of biosensors across disciplines and their transformative role in diagnostic technologies.