Synthesis of PbS/CdS/ZnS Core/Shell/Shell Quantum Dots for Multiplexed Shortwave Infrared Imaging

This chapter describes a systematic approach for synthesizing high-quality lead sulfide/cadmium sulfide/zinc sulfide (PbS/CdS/ZnS) core/shell/shell quantum dots (QDs) with tunable emission in the shortwave infrared (SWIR) wavelength range (1000-1700 nm). This protocol details the synthesis of three distinct QD formulations with emission peaks at approximately 1150, 1250, and 1515 nm, enabling multiplexed in vivo imaging applications. The synthetic route involves three key steps: (1) size-controlled synthesis of PbS cores through hot injection precipitation, (2) formation of a CdS shell through cation exchange, and (3) deposition of a ZnS outer shell using a low-temperature single-source precursor approach to enhance stability while preserving optical properties. The protocol ends with a postsynthetic surface treatment to enhance quantum yield. These QDs exhibit excellent brightness, narrow emission linewidths, and superior stability compared to conventional SWIR emitters, making them ideal for deep-tissue, multiplexed imaging applications.