Fluorescent and chromogenic organic probes to detect group 10 metal ions: design strategies and sensing applications

Indium nanocubes based recyclable fluorescent chemosensor for sustainable environmental monitoring: pH-induced fluorescence transition and selective detection of Pd(II) ions

Rapid modern industrialization and urbanization have escalated heavy metal pollution, with palladium (Pd2+) raising significant concerns due to its extensive usage in catalysis, hydrogen storage, and electronics, thereby imposing substantial risks on the environment and human health. In this study, we report a highly fluorescent indium nanocubes based chemosensor (InNCs) functionalized with perylene tetracarboxylic acid (PTCA) and 4-(pyridyl)ethenyl benzene (PEB). The InNCs exhibited emission maximum at 415 nm (λex ∼ 350 nm) with robust chemical and photo-stability, and acted as a fluorogenic probe for selective recognition of Pd2+ in aqueous medium. The fluorescence sensing properties of InNCs were thoroughly assessed via different techniques including steady-state absorption, emission and time-resolved emission spectroscopic methods. Among the various competitive analytes, only Pd2+ could induce a significant fluorescence quenching in the probe. This "turn-off" fluorescence sensing demonstrated a remarkably low LoD of ∼65 nM. Notably, with the addition of EDTA, the probe displayed good recyclability upto 4 cycles. The sensory probe was successfully employed as a reusable platform to estimate Pd(II) in different real water and soil samples with considerable accuracy (∼ 5-10 % error). Moreover, the probe exhibited a pH-induced fluorescence transition, indicating its potential to be applied as a pH sensor. The Pd(II) binding and pH-sensing mechanisms have also been elucidated through density functional theory (DFT) calculations.

An Indole-based Chromofluorogenic Probe for Detection of Trivalent Al3+, Ga3+, In3+ and Fe3+ Ions

An easily synthesizable indole-derived chromofluorogenic probe InNS has been demonstrated for recognition of trivalent metal ions (i. e., Al3+, Ga3+, In3+ and Fe3+). Both UV-Vis and emission spectral studies have been employed to assess the cation sensing ability of InNS in semi-aqueous medium. This probe exhibited a chromogenic response for these metal ions, and the related change was accompanied with the appearance of a new absorption near 376 nm. An obvious color change from pale yellow to dark yellow could also be noticed upon addition of the aforementioned metal ions to the probe's solution. Distinctively from the UV-Vis analysis, the fluorescence behavior of InNS was completely different; it displayed a 'turn-on' fluorescence response for only Al3+ among all the studied cations. The detection limit and the association constant (Ka) for Al3+ were determined to be 12.5 nM and 6.85×106 M-1, respectively. A potential 1 : 1 binding mode of Al3+-InNS has been established based on Job's plot, 1H NMR and DFT analyses. The reversibility experiment was conducted using strongly chelating EDTA ion, and a corresponding logic gate has been devised. In terms of practical applications, the InNS has been utilized to detect Al3+ in human breast carcinoma (MCF-7) cell lines displaying promising 'turn-on' bioimaging experiments.

A quinoline derived Schiff base as highly selective 'turn-on' probe for fluorogenic recognition of Al3+ ion

A quinoline-derived Schiff base QnSb has been synthesized for fluorescent and colorimetric recognition of Al3+ ions in a semi-aqueous medium. The compound QnSb has been characterized by elemental analysis, FT-IR, 1H/13C NMR, UV-Vis and fluorescence spectral techniques. The crystal structure of the QnSb was confirmed by single crystal X-ray diffraction (SC-XRD) analysis. Notably, almost non-fluorescent QnSb served as a 'turn on' responsive probe for Al3+ by inducing a remarkable fluorescence enhancement at 422 nm when excited at 310 nm. The probe QnSb exhibited high selectivity for Al3+ in CH3CN/H2O (4:1, v/v) solution over several competing metal ions (e.g., Mg2+, Pb2+, Zn2+, Cd2+, Co2+, Cu2+, Ca2+, Ni2+, Fe3+/2+, Cr3+, Mn2+, Sn2+, and Hg2+). The limit of detection (LoD) was computed as low as 15.8 nM which is significantly lower than the permissible limit set by WHO for Al3+ ions in drinking water. A 1:1 binding stoichiometry of complex QnSb-Al3+ was established with the help of Job's plot, ESI-MS, NMR and DFT analyses. Based on its remarkable sensing ability, the probe QnSb was utilized to establish molecular logic gates, and the fluorescence detection of Al3+ could clearly be demonstrated on the filter paper test strips.