Zakir Murtaza

A fluorescence lifetime-based solid sensor for water

A fluorescence lifetime-based water sensor was developed, based on a solvent-polarity-sensitive fluorescent metal-ligand compound, dipyrido1[3,2-a:2″,3″-c]phenazine, di[cis-1,2-bis(diphenylphosphino)-ethylene] osmium(II) hexafluorophosphate, [Os(dppz)(dppe)2](PF6)2. When excited in acetone solution, the compound emitted orange-red fluorescence with a peak wavelength of 610 nm. Fluorescence quenching was observed from both intensity and lifetime measurements when water was presented in the acetone. To fabricate a water sensor, the compound was immobilized by ionic bonding onto an ion-exchange resin, carboxymethyl cellulose, and then sandwiched between a thin sol-gel layer and a glass substrate. This formed a water-sensitive solid film sensor that, when re-inserted from a water-free into a water-containing organic solvent, displayed a lifetime decrease. The lifetime change could be measured in the frequency domain using phase-modulation fluorometry. Because of the long decay time of this compound the phase-modulation could be performed using an amplitude-modulated blue LED with a low modulation frequency near 2 MHz. For a change in the water content of an acetone solution from 0% to 20%, 39.6 degrees of phase angle decrease was observed. The degree of the change in phase angle varied from solvent to solvent. The typical response and recovery time for a 90% total signal change was a few seconds. The detection limit was solvent-dependent. When ethyl acetate was used as the solvent, the detection limit could be as low as 0.02% (v/v) of water. The sensor also displayed very good long term stability, as little change in performance was discoverable after two months.

Development of long-lifetime metal-ligand probes for biophysics and cellular imaging

Metal-ligand complexes containing ruthenium, osmium, or rhenium display a high photostability, with polarized emission and decay times from 100 ns to 100 Μs. Such probes have considerable potential in biophysics, clinical chemistry, and fluorescence microscopy. In this review we sumrecent developments from this laboratory on the spectral properties of conjugatable metalligand complexes. We also suggest how improved probes can be developed based on the selection of organic ligands.

Synthesis and spectral characterization of a long-lifetime osmium (II) metal–ligand complex: a conjugatable red dye for applications in biophysics

There is a need for luminescent probes, which display both long excitation and emission wavelengths and long decay times. We synthesized and characterized an osmium metal-ligand complex which displays a mean decay time of over 100 ns when bound to proteins. [Os(1,10-phenanthroline)2(5-amino-1,10-phenanthroline)[(PF6)2 can be excited at wavelengths up to 650 nm, and displays an emission maximum near 700 nm. The probe displays a modest but useful maximum fundamental anisotropy near 0.1 for 488-nm excitation, and thus convenient when using an argon ion laser. [Os(phen)2(aphen)](PF6)2 is readily activated to the isothiocyanate for coupling to proteins. When covalently linked to bovine serum albumin the intensity decay is moderately heterogeneous with a mean decay time of 145 ns. The anisotropy decay of the labeled protein displays a correlation time near 40 ns. This relatively long lifetime luminophores can be useful as a biophysical probe or in clinical applications such as fluorescence polarization immunoassays.

On the Possibility of Glucose Sensing Using Boronic Acid and a Luminescent Ruthenium Metal-Ligand Complex

We describe a new approach to optical sensing of glucose based on the competitive interactions between a ruthenium metal ligand complex, a boronic acid derivative and glucose. The metal-ligand complex [Ru(2,2′-bipyridine)2(5,6-dihydroxy-1,10-phenanthroline)](PF6)2 at pH 8 forms a reversible complex with 2-toluylboronic acid or 2-methoxyphenyl boronic acid. Complexation is accompanied by a several-fold increase in the luminescent intensity of the ruthenium complex. Addition of glucose results in decreased luminescent intensity, which appears to be the result of decreased binding between the metal-ligand complex and the boronic acid. Ruthenium metal-ligand complexes are convenient for optical sensing because their long luminescent decay times allow lifetime-based sensing with simple instrumentation.

Polarized Emission from a Rhenium Metal-Ligand Complex

We report the first observation of polarized emission from a rhenium-phenanthroline complex, Re(CO)3(phen)Cl. Highly luminescent rhenium complexes are known, with quantum yields near 0.5 and lifetimes in excess of 10 μs. The detection of polarized emission suggests the use of rhenium complexes as probes of the hydrodynamics of large macromolecular complexes and for use in fluorescence polarization immunoassays with gated detection.

Lifetime-based sensing of glucose using luminescent ruthenium (II) metal complex

Abstract not available.

Recent Developments in Fluorescence Spectroscopy

Advances in laser technology and probe chemistry are resulting in a rapid introduction of novel fluorescence measurements. One area of rapid growth has been multi-photon excitation, which is now practical due to the increasing availability of ps and fs lasers. The interest in multi-photon excitation is driven in part by the possibility of three-dimensional “confocal” cellular imaging based on the localized excitation possible with multi-photon excitation. In this paper we will show that using the fundamental output of a fs Titanium:Sapphire laser it is possible and practical to observe three-photon excitation of proteins, DNA stains, calcium probes, and labeled membranes.