Dual-channel luminescent Ir(III) complex for detection of GSH and Hcy/Cys in cells.

Glutathione (GSH), homocysteine (Hcy) and cysteine (Cys) play important roles in many physiological processes. However, due to their structural and functional similarities, it is still a challenge to develop a probe that can differentiate between GSH and Hcy/Cys simultaneously. In this work, a luminescent probe Ir-NBD was designed and synthesized, which emit weakly due to the presence of photo induced electron transfer (PET) interaction. When it reacted with the three biothiols, NBD dissociated and luminescence of Ir-OH was enhanced in the near-infrared (NIR) region due to the disappearance of the PET effect. On the other hand, the products obtained from the reaction of GSH with NBD were hardly luminescent, but the products from the reaction of Hcy/Cys with NBD could undergo an intramolecular rearrangement, resulting in an enhanced luminescence of the solution in the visible region. Ir-NBD enabled highly selective and sensitive detection of GSH and Cys/Hcy in a relatively short time (15 min). The two luminescent colors were clearly differentiated without spectral interference and the detection limit reached 1.32 µM (GSH), 0.42 µM (Hcy) and 0.51 µM (Cys), respectively. Ir-NBD also had low cytotoxicity, it realized the simultaneous detection of GSH and Hcy/Cys by dual-channel luminescence, and also provided ideas for the design of multifunctional luminescent probes.

Aggregation-Induced Near-Infrared Emission and Electrochemiluminescence of an Iridium(III) Complex for Ampicillin Sodium Sensing.

A new iridium(III) complex was synthesized and characterized. Its photophysical properties and aggregation-induced emission and electrochemiluminescence in the near-infrared range were studied. The large conjugated cyclometallic ligand 1,2-phenylbenzoquinoline (pbq) was selected to form the Ir-C bond with the metal iridium(III) center and provide near-infrared emission of the complex. The auxiliary ligand 4,4'-diamino-2,2'-bipyridine (dabpy) can form hydrogen bonds, which was beneficial for the generation of aggregation-induced emission. The complex was aggregated into small spherical nanoparticles in 80% water and fascinating nanorings in 90% water. The sensing of ampicillin sodium (AMP) antibiotic by the iridium(III) complex were also investigated by photoluminescent and electrochemiluminescent methods. The complex showed a good selectivity toward AMP antibiotic compared to sodium phenylacetate and other eight antibiotics. The detection limits for AMP antibiotic was 0.76 µg/mL. This work provided a new strategy for the design of iridium(III) complex-based aggregation-induced emission and electrochemiluminescence probes for the sensing application.

Amino group-driven distinguishing homocysteine from cysteine and glutathione in photoluminesecent signal of the iridium(III) complexes.

In this work, six iridium(III) complexes have been designed, synthesized and characterized. The molecular structures of complex 1 ([(pba)2Ir(bpy-2N(CH3)2)]PF6), 2 ([(pba)2Ir(bpy-2NH2)]PF6) and 3 ([(pba)2Ir(bpy-2CH3)]PF6) were determined by single crystal X-ray diffraction. Upon addition of Hcy (homocysteine) to the solution of complex 1, a luminescent variation from orange red to green was observed by the naked eye, corresponding to a large blue shift from 604 nm to 498 nm (~106 nm). While the emission intensity of complex 1 was almost no change after addition of other common amino acids including Cys (cysteine) and GSH (glutathione). The aldehyde group of complex 1 formed a new thiazinane/thiazolidine ring with Hcy/Cys confirmed by 1H NMR and high-resolution mass spectrometry. And the new product 1-Hcy had a higher quantum yield than 1-Cys. Theoretical calculations showed that the HOMO (highest occupied molecular orbital) of 1-Hcy was located on the newly formed six-membered thiazinane ring, which was different from the HOMO of 1-Cys. Compared with the other iridium(III) complexes, we can speculate that the large blue shift and enhancement of the emission intensity of the complex 1 were related to the strong electron donating ability of the modified amino groups on bipyridine ligand. This will provide an idea for the design of ratio-based luminescence probes for Hcy in future.

An Ir(III) complex capable of discriminating homocysteine from cysteine and glutathione with luminescent signal and imaging studies.

A new cationic Ir(III) complex with aldehyde and amino groups was synthesized and characterized. The Ir(III) complex has rich photophysical properties. The reaction of the aldehyde group in the Ir(III) complex with homocysteine (Hcy) afforded thiazinane derivatives which resulted in obvious changes in the luminescence spectra. After addition of Hcy to the Ir(III) complex containing 4,4'-diamino-2,2'-bipyridine, the luminescence intensity at ca. 580-610 nm decreased, and a new band at ca.490-520 nm appeared and enhanced strongly with a large blue shift of ca.90 nm, and the luminescent color changed from orange red to green. Based on this ratiometric probe, it can sensitively and selectively recognize Hcy by the ratio of emission intensity at two wavelengths to the concentrations of Hcy. While after addition of cysteine (Cys) or glutathione (GSH), the luminescence band showed a mild decrease in intensity with an unnoticeable shift. These different phenomena make it capable of discriminating homocysteine from cysteine and glutathione. The cytotoxicity and imaging of the complex were also studied in this work. The complex exhibited very low cytotoxicity on HeLa cells and showed sensitivity toward Hcy in living cells. These advantages provide it a good candidate for the application in the analytical and bioanalytical field.

Sensitive determination of lysozyme by using a luminescent and colorimetric probe based on the aggregation of gold nanoparticles induced by an anionic ruthenate(II) complex.

The negatively charged ruthenate(II) complex [Ru(bpy)(PPh3)(CN)3]- and gold nanoparticles (AuNPs) were used for detecting lysozyme (LYS). The luminescence of the ruthenate(II) complex is quenched by AuNPs, and this induces the aggregation of AuNPs and a color change from red to blue. After addition of lysozyme, the positively charged lysozyme and the negatively charged ruthenate(II) complex bind each other by electrostatic interaction firstly. This prevents AuNPs from aggregation and quenches the emission of the ruthenate(II) complex. Its luminescence and the degree of aggregation of the AuNPs can be used to quantify LYS. The fluorometric calibration plot is linear in the 0.01 to 0.20 µM LYS concentration range, and the calibration plot is linear between 0.02 and 0.20 µM of LYS. The color of the solution can be easily distinguished by bare eyes at 0.08 µM or higher concentration of LYS. The applicability of the method was verified by the correct analysis of LYS in chicken egg white. Graphical abstract Schematic of a luminometric and colorimetric probe based on the induced aggregation of gold nanoparticles by an anionic luminescent ruthenate(II) complex or sensitive lysozyme detection.