Colorimetric metal ion sensors

Optical sensor arrays for chemical sensing: the optoelectronic nose

A comprehensive review is presented on the development and state of the art of colorimetric and fluorometric sensor arrays. Optical arrays based on chemoresponsive colorants (dyes and nanoporous pigments) probe the chemical reactivity of analytes, rather than their physical properties. This provides a high dimensionality to chemical sensing that permits high sensitivity (often down to ppb levels), impressive discrimination among very similar analytes and exquisite fingerprinting of extremely similar mixtures over a wide range of analyte types, both in the gas and liquid phases.

A new 3,5-bisporphyrinylpyridine derivative as a fluorescent ratiometric probe for zinc ions

A new 3,5-disubstituted pyridine with two porphyrin moieties was prepared through an efficient synthetic approach involving 2-formyl-5,10,15,20-tetraphenylporphyrin (1), piperidine, and catalytic amounts of [La(OTf)3]. 3,5-Bis(5,10,15,20-tetraphenylporphyrin-2-ylmethyl)pyridine (2) was fully characterized and its sensing ability towards Zn(2+), Cu(2+), Hg(2+), Cd(2+), and Ag(+) was evaluated in solution by absorption and fluorescence spectroscopy and in gas phase by using matrix-assisted laser desorption/ionization (MALDI)-TOF mass spectrometry. Strong changes in the ground and excited state were detected in the case of the soft metal ions Zn(2+), Cd(2+), Hg(2+), and Cu(2+). A three-metal-per-ligand molar ratio was obtained in all cases and a significant ratiometric behavior was observed in the presence of Zn(2+) with the appearance of a new band at 608 nm, which can be assigned to a metal-to-ligand charge transfer. The system was able to quantify 79 ppb of Zn(2+) and the theoretical calculations are in accordance with the stoichiometry observed in solution. The gas-phase sensorial ability of compound 2 towards all metal ions was confirmed by using MALDI-TOF MS and in solid state by using polymeric films of polymethylmethacrylate (PMMA) doped with ligand 2. The results showed that compound 2 can be analytically used to develop new colorimetric molecular devices that are able to discriminate between Hg(2+) and Zn(2+) in solid phase. The crystal structure of Zn(II) complex of 3,5-bisporphyrinylpyridine was unequivocally elucidated by using single-crystal X-ray diffraction studies.

Optical chemosensors based on transmetalation of salen-based Schiff base complexes

We report our systematic studies of novel, simple, selective, and sensitive optical (both colorimetric and fluorescent) chemosensors for detecting Al(3+) based on transmetalation reactions (metal displacement or exchange reactions) of a series of K(I), Ca(II), Zn(II), Cu(II), and Pt(II) complexes containing different ligands of salen-based Schiff bases. Both the chemical structure of the salen ligand and the identity of the central metal ion have a tremendous impact on the sensing performance, which is mainly determined by the stability constant of the complex. Moreover, the selectivities of the salen-complex-based chemosensors are much better than those of the corresponding free salen ligands because of the shielding function of the filled-in metal ion in the complex. Therefore, the present work potentially provides a new and simple way to design optical probes via complex-based transmetalation reactions.

A coumarin-based sensitive and selective fluorescent sensor for copper(ii) ions

A new coumarin-derived fluorescent probe (1) exhibited significant fluorescence quenching in the presence of Cu²⁺ ions.

Visual and surface plasmon resonance sensor for zirconium based on zirconium-induced aggregation of adenosine triphosphate-stabilized gold nanoparticles

Owing to its high affinity with phosphate, Zr(IV) can induce the aggregation of adenosine 5'-triphosphate (ATP)-stabilized AuNPs, leading to the change of surface plasmon resonance (SPR) absorption spectra and color of ATP-stabilized AuNP solutions. Based on these phenomena, visual and SPR sensors for Zr(IV) have been developed for the first time. The A(660 nm)/A(518 nm) values of ATP-stabilized AuNPs in SPR absorption spectra increase linearly with the concentrations of Zr(IV) from 0.5 μM to 100 μM (r=0.9971) with a detection limit of 95 nM. A visual Zr(IV) detection is achieved with a detection limit of 30 μM. The sensor shows excellent selectivity against other metal ions, such as Cu(2+), Fe(3+), Cd(2+), and Pb(2+). The recoveries for the detection of 5 μM, 10 μM, 25 μM and 75 μM Zr(IV) in lake water samples are 96.0%, 97.0%, 95.6% and 102.4%, respectively. The recoveries of the proposed SPR method are comparable with those of ICP-OES method.

Preferences of rhodamine coupled (aminoalkyl)-piperazine probes towards Hg(II) ion and their FRET mediated signaling

The metal ion induced absorption and emission signaling pattern of rhodamine coupled bis-(aminopropyl)-piperazine (1-3) and (aminoethyl)-piperazine (4) based probes evaluated in MeCN as well as in an MeCN-H2O binary mixture medium revealed that these probes exhibit optical signaling perturbations to a varying extent in MeCN, however, their complexation induced signaling could be tuned selectively towards Hg(II) in the presence of an aqueous component in the solvent medium where competitive interactions such as metal-probe interactions and hydration of metal ions play the determining factor to induce aqueous promoted Hg(II) selectivity. Attachment of another fluorophore (anthracene and nitrobenzofurazan moieties in 2 and 3 respectively) at the other end of the rhodamine coupled bis-(aminopropyl)-piperazine receptor enabled these probes to facilitate a complexation induced fluorescence resonance energy transfer (FRET) from the excited fluorophore to the ring-opened rhodamine along with contributions through operative PET inhibition and rhodamine delactonization processes. The enhancement in absorption transition of these probes at ~557 nm upon selective Hg(II)-complexation and consequent colourless to pink colour change in the solution imply a chromogenic signaling pattern whereas simultaneous fluorescence amplification and/or FRET initiation lead to fluorogenic signaling to facilitate detection at lower concentration. The Hg(II)-selective photo-physical spectral modulation in the presence of other competitive metal ions, and their reversible dual channel signaling pattern under the action of counter anions or chelating agents such as EDTA or ethylenediamine establish the potential of these probes for highly selective, sensitive and reversible 'OFF-ON-OFF' detection of Hg(II). The complexation induced optical signaling pattern of probes with a propyl-linker in their receptor (1-3) in comparison with that of 4 consisting of an ethyl-spacer indicate that signaling probe design with a substituted 'aminoalkyl-lactonized-rhodamine' subunit preferentially exhibit Hg(II) selective and sensitive dual mode signaling in an organic-aqueous mixture medium irrespective of carbon-length of the flexible alkyl spacer.

Spectrophotometric and voltammetric characterization of a novel selective electroactive chemosensor for Mg2+

A novel azocalix[4]arene derivative, 5,11,17,23-tetrakis[(acetophenone)azo]-25,26,27,28-tetrahydroxycalix[4]arene (APC4), containing acetophenone azo groups at the upper rim was synthesized as a chemosensor. Its binding and sensing properties with alkali and alkaline earth metal ions (Li+, Na+, K+, Rb+, Cs+, Mg2+, Ca2+, Sr2+, Ba2+) were investigated by UV-vis spectrophotometric and voltammetric techniques. The stoichiometric ratio and the association constant were determined spectrophotometrically as 1:1 and (1.94±0.31)×105 L mol−1 for the complex between Mg2+ and the chemosensor, respectively. Moreover, it was shown that the interaction between Mg2+ and the APC4 occurred by means of the phenol groups at the lower rim by voltammetric methods. The results of spectrophotometric and voltammetric experiments showed that the chromogenic chemosensor has high selectivity towards Mg2+ among the other used metal ions, especially the interfering Ca2+ ion.

Dicyanomethylene-4H-pyran chromophores for OLED emitters, logic gates and optical chemosensors

Dicyanomethylene-4H-pyran (DCM) chromophores are typical donor-π-acceptor (D-π-A) type chromophores with a broad absorption band resulting from an ultra-fast internal charge-transfer (ICT) process. In 1989, Tang et al. firstly introduced a DCM derivative as a highly fluorescent dopant in organic electroluminescent diodes (OLEDs). Integration of ICT chromophore-receptor systems based on DCM chromophores with ion-induced shifts in absorption or emission is a convenient method to perform the logic expression for molecular logic gates. In recent years, various DCM-type derivatives have been explored due to their excellent optical-electronic properties and diverse structural modification. This feature article provides an insight into how the structural modification of DCM chromophores can be utilized for OLED emitters, logic gates and optical chemosensors. In addition, the aggregation-induced-emission (AIE) of DCM derivatives for further optical applications was also introduced.