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An imatinib intermediate, 6-methyl-N-[4-(pyridin-3-yl)pyrimidin-2-yl]benzene-1,3-diaminepyridopyrimidotoluidine (PPT-1), was developed for the colorimetric sensing of Cu(2+) ions in aqueous solution. With Cu(2+), the receptor PPT-1 showed a highly selective naked-eye detectable color change from colorless to red over the seventy other tested cations. The colorimetric sensing ability of PPT-1 was successfully utilized in the preparation of test strips and supported silica for the real samples analysis to detect Cu(2+) ions from 100% aqueous environment. Moreover, the iodide-sensing ability of receptor PPT-1 was explored among the ten examined anions.

This communication demonstrates a rapid, reproducible and highly selective colorimetric nanosensor for the detection of Cr3+ ions in aqueous medium using the functionalized gold nanoparticles. The functionalized AuNPs were obtained in three steps: (i) the citrate capped Cit‐AuNPs were prepared by standard procedure, (ii) the thiolated Schiff base CAPLP was generated in‐situ by reacting vitamin B6 cofactor pyridoxal 5′‐phosphate and cysteamine, and then (iii) the CAPLP was decorated over the surface of Cit‐AuNPs via ligand exchange method yielding spherical and well dispersed nanoparticles of size ∼16±2 nm. The wine red color of CAPLP‐AuNPs solution turned to purplish blue upon addition of Cr3+ ions along with the SPR band was red‐shifted from 525 nm to 650 nm due to the complexation‐induced aggregation of nanoparticles. With a high selectivity and specificity, this nano‐assembly shows the detection limit down to 2.34 μM and finds applicability over a wide range of pH. The developed nanosensor was applied in environmental water samples for Cr3+ ions detection and achieved ideal results. More significantly, the visually detectable color change of CAPLP‐AuNPs has been successfully integrated with a smartphone RGBColorValue app to make it useful for on‐site fast measurement and real‐time online analysis of Cr3+ with the detection limit down to 11 μM.

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This communication focusses on the synthesis of red fluorescent lysozyme cocooned gold nanoclusters (Lyso-AuNCs) that have been successfully applied for the selective and specific recognition of the vitamin B cofactor pyridoxal-5'-phosphate (PLP). The red fluorescence of Lyso-AuNCs showed remarkable color change to yellow upon conjugation with PLP due to the formation of a Schiff base between the free -NH present in the lysozyme and the -CHO group of PLP. The developed PLP conjugated Lyso-AuNCs (PLP_Lyso-AuNCs) was applied for the selective turn-on recognition of Zn ions in aqueous medium. The yellow fluorescence of PLP_Lyso-AuNCs exhibited significant enhancement at 475 nm in the presence of Zn producing bluish-green fluorescence attributed to the complexation-induced aggregation of nanoclusters. The nanoprobe exhibits nanomolar limit of detection for Zn ions (39.2 nM) and the practicality of the nanoprobe was validated in various environmental water samples and biological plasma, urine, and beetroot extract, with fairly good recovery percent. Also, the system was successfully implemented for the intracellular detection and monitoring of Zn in live HeLa cells. Graphical abstract Applications of red emitting lysozyme cocooned gold nanoclusters (Lyso-AuNCs) for the selective recognition of the vitamin B cofactor pyridoxal-5'-phosphate (PLP) and the conjugated nano-assembly PLP_Lyso-AuNCs for turn-on detection of Zn ions in various environmental and biological samples.

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