A sensitive, selective colorimetric Fe³⁺ detection method has been developed by using pyrophosphate functionalized gold nanoparticles (P₂O₇ ^{4 −}–AuNPs). Gold nanoparticles were prepared by reducing HAuCl₄ with sodium borohydride, in the presence of Na₄P₂O₇. IR spectra suggested that pyrophosphates were capped on the surface of the gold nanoparticles. Aggregation of P₂O₇ ^{4 −}–AuNPs was induced immediately in the presence of Fe³⁺ ions, yielding a color change from pink to violet. This Fe³⁺-induced aggregation of P₂O₇ ^{4 −}–AuNPs was monitored using first the naked eye and then UV-vis spectroscopy with a detection limit of 5.6 μM. The P₂O₇ ^{4 −}–AuNPs bound by Fe³⁺ showed excellent selectivity compared to other metal ions (Ca²⁺, Cd²⁺, Co²⁺, Fe²⁺, Hg²⁺, K⁺, Mg²⁺, Mn²⁺, Na⁺, Ni²⁺, Pb²⁺, and Zn²⁺). The best detection of Fe³⁺ was achieved in a pH range from 3 to 9. In addition, the P₂O₇ ^{4 −}–AuNPs were also used to detect Fe³⁺ in lake water samples, with low interference.

A new coumarin-derived fluorescent probe ( 1 ) exhibited significant fluorescence quenching in the presence of Cu ²⁺ ions.

In this study, a boron-dipyrromethene (BODIPY)-based fluorescent chemosensor CBS was developed for metal ion sensing. It was found that CBS containing an NSe₂ moiety exhibited high selectivity for Cu²⁺ detection while CBS in the presence of Cu²⁺ displayed significant fluorescence enhancement. However, the metal ions Ag⁺, Ca²⁺, Co²⁺, Cr³⁺, Fe²⁺, Fe³⁺, Hg²⁺, K⁺, Mg²⁺, Mn²⁺, Ni²⁺, Pb²⁺, and Zn²⁺ produced only minor changes in the fluorescence values of the system. The binding constant (K_a) of Cu²⁺ binding to CBS was found to be 7.28 × 10³ M⁻¹. The binding ratio of CBS–Cu²⁺ complexes was determined from the Job plot to be 1 : 1. The maximum fluorescence enhancement caused by Cu²⁺ binding to CBS was observed over the pH range 5.0–9.0. Additionally, the methyl thiazolyl tetrazolium (MTT) assay demonstrated the CBS to have low cytotoxicity. Confocal fluorescence microscopy imaging using RAW264.7 cells showed that CBS could be used as an effective fluorescent probe for detecting Cu²⁺ in living cells.

9,10-Anthraquinone-based chemosensor 1 indicates the presence of Cu(II) ions among other transition metal ions with high selectivity by a color change from yellow to dark red. Chemosensor 2 shows binding toward Cu(II), Ni(II) and Co(II) with color changes from yellow to dark red, red and pale green, respectively. Especially, Co(II) binding with chemosensor 2 causes significantly green fluorescence. On addition of Cu(II), 1 and 2 exhibit 76 and 80 nm red shifts in absorption wavelength (pH 7.0). The effect on pH by the formation of these 1-Cu(II) and 2-Cu(II) complexes was determined by UV-vis spectroscopic pH titration. In the pH range of 6–7.5, a maximum absorption was observed at 473 nm and exhibited the formation of deprotonated 1-Cu(II) and 2-Cu(II) complexes.