Manfred A. Kessler

New highly fluorescent ketocyanine polarity probes

Abstract The syntheses and spectral properties of three new and highly fluorescent solvent polarity probes are described. They are found to be extremely sensitive to solvent polarity in that spectral red shifts in both absorption and fluorescence spectra occur upon increasing solvent polarity. Excitation and emission data of the dyes in a set of different polar solvents are given. The emission data are compared with the standard ET N values of solvent polarity and a linear correlation is obtained over a wide range. The origin of the unusual solvatochromic properties is discussed in terms of the resonance structures of this new group of molecular probes. Their outstanding features include high spectral sensitivity to polarity, high molar absorptivities, high fluorescence quantum yields, longwave excitation and emission, insignificant quenching by oxygen, and a sufficient stability in aqueous solution. Therefore, the new probes are considered to be advantageous over other polarity probes used so far in probing biochemical and biological systems.

ET(33), a solvatochromic polarity and micellar probe for neutral aqueous solutions

The preparation and electronic spectra of a new proble which is applicable to polarity studies at neutral pH is described. The probe (2,6-dichloro-4-(2,4,6-triphenyl-N-pyridinio)-phenolate) is called ET (33) and has a pKa value of 4.78 which makes it the first probe of the ET series that exists as a phenolate at near neutral pH. All other probes of this type require pHs above 10 to be applicable to aqueous solutions. ET(33) shows an extremely large shift in absorption in going from water (λmax = 409 nm) to tretrahydrofurane (THF) (λmax = 646 nm). Spectral properties of ET(33) have been studied in various solvents and ethanol—water mixtures. An excellent correlation with standard ET(30) values is obtained. Since the dye is applicable in neutral aqueous solution, it has been used for determination of the critical micellar concentration of hexadecyl-trimethyl-ammonium bromide (CTAB) at both pH 11 and at near neutral pH. The absorption of the probe is shifted from 409 nm in the sub-critical micellar concentration (CMC) range of CTAB to 462 nm at well above the CMC. The very good agreement of the data with literature data demonstrates that ET(33) is a useful and longwave-absorbing probe for micellar (and probably also lipid) studies at near neutral pH.

Laser-induced fluorometric determination of albumin using longwave absorbing molecular probes

A novel fluorescence assay for HSA is described. It is based on longwave-absorbing probes that selectively bind to HSA to form fluorescent complexes. The two probes reported here (Albumin Blue 633 and Albumin Blue 670) are tailored to match the lines of the 633-nm HeNe laser and the 670-nm diode laser, respectively. In both cases, the strong laser-induced fluorescence of the HSA/probe complexes makes the assay sensitive to HSA at trace levels. Detection limits of 0.2 mg/liter were obtained. In addition to its sensitivity, the assay is highly selective for HSA in that the response to other serum proteins is weaker by a factor of at least 100. It also works well on urine, and no significant interferences could be located. Potential interferents are bovine serum albumin and some detergents. Parameters of the probe--HSA interaction were obtained from a Scatchard evaluation. The high specificity and sensitivity of the assay are discussed in terms of molecular geometry of the probes. A photophysical mechanism that leads to the effect is proposed. The assay presents a promising alternative to immunological determinations of HSA since it is less expensive and much more quickly performed.

Optical sensor for on-line determination of solvent mixtures based on a fluorescent solvent polarity probe

Abstract A new optical sensor for determination of solvent mixtures (such as water in organic solvent) is based on a fluorescent solvent polarity (SP) probe immobilized on an ion-exchange membrane. The fluorescent probe responds to changes in SP by both a shift in the fluorescence emission maximum and a change in fluorescence quantum yield. In this sensor, the analytical information is the relative fluorescence intensity measured at 620 nm (500 nm excitation). The sensor can be applied over a wide range of solvents. The response time (t90) is of the order of 15 s. Given the unique applications of fibre optic sensors (e.g., for remote sensing and sensing in explosive areas), the new sensor is expected to be applicable in process control.

New lipophilic rhodamines and their application to optical potassium sensing.

New lipophilic fluorescent rhodamines were synthesized directly from 3,6-dichlorofluoresceins and the respective long-chain amines with excellent solubility in lipids and lipophilic membranes. Spectrophotometric and luminescent properties of the dyes are reported and discussed with respect to their application in new optical ion sensors. One rhodamine (2a) was applied in a poly(vinyl chloride)-based sensor membrane for continuous and sensitive optical determination of potassium ion, using valinomycin as the neutral ion carrier.