General Sensitive Detecting Strategy of Ions through Plasmonic Resonance Energy Transfer from Gold Nanoparticles to Rhodamine Spirolactam

Plasmonic resonance energy transfer (PRET), which occurs between the plasmonic nanoparticles and organic dyes, has significant potential in target sensing chemistry owing to its sensitivity at the single nanoparticle level. In this contribution, by using AuNPs, which has localized surface plasmonic resonance light scattering (LSPR-LS) around 550 nm, as the donor of PRET, a general sensitive detecting strategy of ions were developed. Targets can specifically react with a ring-close structured rhodamine spirolactam, which was prepared from rhodamines in the presence of different primary amine wherein the option of the primary amine is up to the targets, forming ring-open structured rhodamine spirolactam with the strong absorption around 550 nm. This process triggered the PRET from gold nanoparticles (AuNPs) to the ring-open structured rhodamine spirolactam. As a proof of concept, Cu²⁺ and Hg²⁺ were detected by using rhodamine B hydrazide and <i>N</i>-(rhodamine B)­lactam-ethylenediamine, respectively. With the aid of a dark field microscope, the LSPR-LS of AuNPs gets decreased within 10 min with the addition of Cu²⁺ or Hg²⁺. The scattering light spectra get red-shifted during the targets addition due to the quenching dip phenomenon. Further theoretical simulation indicated the PRET process could be aroused by the electric field diminishment of AuNPs via the interaction of rhodamine. This single nanoparticle based detecting strategy could be further applied for other anions, cations, or small organic molecules detection by simply changing the rhodamine spirolactam