This chapter explores the primary use of aptamer-based biosensors in the imaging and diagnosis of cancer. Aptasensors provide several benefits over conventional antibody-based sensors, including enhanced specificity, lower cost, and simpler synthesis and modification processes. The short strands of DNA or RNA that exhibit a strong affinity for cancer biomarkers position aptamers as the perfect detection component for biosensors. The chapter will discuss the basics of aptamers, the Systematic Evolution of Ligands by Exponential Enrichment (SELEX) selection process, design principles for aptamer-based biosensors, their working mechanisms, and applications in cancer imaging. The discussion will further be extended to the description of several aptasensors, which include optical, electrochemical, and fluorescent biosensors. In addition, the advantages and limitations of these biosensors, particularly concerning cancer imaging, will be reviewed and explored for possible future developments through nanotechnology and artificial intelligence (AI). The chapter discusses emerging trends and the future clinical applications of aptamer-based biosensors in personalized cancer treatment.