Metal-based nanoparticles such as silver (AgNPs), platinum (PtNPs), and palladium (PdNPs) have emerged as a key players in the development of colorimetric sensing technologies due to their unique plasmonic properties, significant catalytic activity, and adaptability for detecting a wide range of analytes. It also covers their size, shape, and surface properties, that determine their optical properties and sensing efficacy in colorimetric detection. Owing to their pronounced surface plasmon resonance, AgNPs have been extensively utilized for the detection of biomolecules, ions, and small molecules, while PtNPs and PdNPs have emerged as promising materials for sensing applications, especially in the fields of environmental monitoring and biomedical diagnostics. Because nanoparticle-based sensors exhibit high sensitivity, reusability, and stability, this chapter discusses the aggregation and signal amplification mechanisms in NPs-based sensors. We also review the conjugation of these nanoparticles to other biosensor platforms (e.g., electrochemical, field-effect transistor (FET), etc.) that significantly improve detection capabilities. Future efforts will focus on improving the stability, specificity and scalability of nanoparticles for real-world implementation.