Reaction-Based Multisignal Detection of Palladium with High Sensitivity, Selectivity, and Reliability

Due to vast application of palladium in academia and industry and its toxicity, it is critical to develop user-friendly, portable, and affordable methods for accurately detecting ultratrace Pd. In this study, a highly sensitive and selective fluorescent probe (N-butyl-4-alloxy-1,8-naphthalimide, compound 2) was synthesized, which demonstrated multiple signals [enhanced fluorescence (FL), ratiometric FL, and colorimetric responses] upon interaction with palladium. The compound 2 was designed by incorporating a naphthalimide-based fluorescent dye as the fluorophore and an allyl ether group as a responsive unit. Utilizing a Pd⁰-triggered cleavage reaction by a deallylation reaction through the Tsuji–Trost reaction, compound 2 exhibited rapid response, wide linearity, exceptional sensitivity with a limit of detection as low as 2.2 pM, and high selectivity toward palladium species. In addition, as a ratiometric and enhanced FL response, the probe could be developed as a portable sensor via naked eye visualization for semiquantitative and selective detection of palladium. Integrating with an easily available smartphone (with a camera and a color-analysis app), potential in situ quantitative detection was achieved at a low cost. The probe shows multiple signals for palladium detection and potential as a portable sensor, and this work provides valuable insights into developing sensors with good sensitivity, selectivity, improved reliability, and portability for detection of palladium and other analytes of interest.