Self-assembled vesicle and rod-like aggregates of functionalized perylene diimide: reaction-based near-IR intracellular fluorescent probe for selective detection of palladium

Herein, we report design, synthesis, and self-assembly of perylene diimide (PDI) based near-IR intracellular probe (PS-PDI). PS-PDI molecules undergo aggregation to form self-assembled nanospheres and nanorods morphology in THF: H2O (1:1) and DMSO: H2O (1: 9), respectively. The nanospheres have an open hole on surface reminiscent of vesicle structure (with a diameter of internal void in the range of 20-25 nm) whereas lengths of the nanorods extended up to few Am range. The Pd-o based depropargylation leads to de-aggregation of these PS-PDI aggregates into smaller spherical aggregates as evidenced by DLS, SEM, and TEM studies. Interestingly, these aggregates of PS-PDI in solution show highly sensitive behavior in the presence of Pd showing absorbance changes in NIR region (lambda(max) = 710 nm) and quenching of emission at lambda(em), 630 nm (DMSO: H2O, 1:9) with a limit of detection = 6.6 x 10(-9) M or at lambda(em) 564 nm (THF: H2O, 1:1) with limit of detection = 2.1 x 10(-8) M. Time and concentration dependent kinetics profiles of PS-PDI aggregates revealed an impressive rate constant value of 0.4 s(-1) and 0.21 s(-1) (DMSO : H2O, 1: 9), respectively in fluorescence and UV-Vis spectroscopy using 2 x 10(-5) M concentration of Pd-0. PS-PDI undergoes rapid internalization into HeLa cells with low cytotoxicity and was successfully used as an intracellular imaging reagent for Pd-o in live HeLa cells. For practical applications, we exploited these nano aggregates of PS-PDI for estimation of Pd2+ in the presence of a NaBH4-PPh3 mixture, Pd in drug and environmental samples, and Pd2+ in urine samples with excellent selectivity and sensitivity.