K.-H. Feller

Analysis of Wine Bouquet Components Using Headspace Solid‐Phase Microextraction‐Capillary Gas Chromatography

Headspace solid-phase microextraction (HS/SPME) was studied and optimized for the capillary gas chromatographic (CGC) analysis of wine aroma compounds. The results were compared with those obtained using the direct sampling mode (DI/SPME) and using liquid/liquid extraction with Kaltron. The aromatic patterns obtained by HS/SPME-CGC were applied to the chemometric classification of wine varieties. The HS/SPME-CGC standard additional method is an appropriate technique for the quantitative analysis of volatile wine aroma compounds.

Sensitive and rapid detection of aflatoxin M1 in milk utilizing enhanced SPR and p(HEMA) brushes

The rapid and sensitive detection of aflatoxin M1 (AFM1) in milk by using surface plasmon resonance (SPR) biosensor is reported. This low molecular weight mycotoxin is analyzed using an indirect competitive immunoassay that is amplified by secondary antibodies conjugated with Au nanoparticles. In order to prevent fouling on the sensor surface by the constituents present in analyzed milk samples, an interface with poly(2-hydroxyethyl methacrylate) p(HEMA) brush was employed. The study presents a comparison of performance characteristics of p(HEMA)-based sensor with a regularly used polyethylene glycol-based architecture relying on mixed thiol self-assembled monolayer. Both sensors are characterized in terms of surface mass density of immobilized AFM1 conjugate as well as affinity bound primary and secondary antibodies. The efficiency of the amplification strategy based on Au nanoparticle is discussed. The biosensor allowed for highly sensitive detection of AFM1 in milk with a limit of detection (LOD) as low as 18pgmL(-1) with the analysis time of 55min.

Annihilation enhanced four-wave mixing in molecular aggregates

The influence of exciton annihilation on the efficiency of four-wave mixing process was investigated theoretically. The study was performed in the framework of the full semiclassical description of light and matter interaction to account for the interplay of nonlinear effects for high pump intensities. Significant enhancement of the four-wave mixing efficiency in the region of saturation due to the annihilation processes of excitons was found. The contribution of annihilation to intensity and wavelength dependence of DFWM signal was analysed and found to be in good qualitative agreement with recent experimental findings of DFWM at the excitonic resonance in J-aggregates of pseudoisocyanine chloride.

Wavelength and intensity-dependent transient degenerate four-wave mixing in pseudoisocyanine J-aggregates

The results of transient degenerate four-wave mixing (DFWM) and “pump-probe” spectroscopy in aggregates of 1,1′-diethyl-2,2′-cyanine (pseudoisocyanine, PIC) chloride at 300 K are reported. Spectral dispersion of DFWM efficiency within the J-band and near exciton resonance has been measured. Time response of both transient absorption changes and DFWM signal is found to be strongly dependent on pump photon fluence and wavelength. This behavior is qualitatively explained within a physical model of nonlinear optical dynamics in aggregate domains which accounts for exciton annihilation, and the effect of nonthermal phonons produced as a result of decay of two-exciton states. Intensity-dependent evolution of excess dynamic disorder due to nonthermal phonons manifests itself in pump-probe experiments as dispersion-type differential spectrum appearing at high pump intensity. The third-order nonlinear susceptibility of PIC aggregates has been calculated supposing highest density packing. The nonlinear figure of me...

Wavelength dependent nonlinear optical properties of pseudoisocyanine J-aggregates

Abstract Degenerate four wave mixing of tunable picosecond pulses were carried out in pseudoisocyanine J-aggregates near resonance. The conversion efficiency was very high even at very low intensities of interacting beams. The power of intensity dependence of the converted signal was shown to change with wavelength within the J-band. The range of the power dependence was from ≈ 1.5 (in the center of the J-band) to three (at the wings of the J-band). This effect is related to the saturation of population density, to singlet-singlet annihilation and secondary processes of local vibrational excitation or heating. The different extent of saturation and heating causes the deviation from third order power dependence on intensity within the J-band. The dependence of the timing of the three pulses supports the interpretation of such a behaviour by an annihilation and secondary processes. The cubic susceptibility was estimated at the wings of the J-band to a value of 10 -8 esu.

Development of a QCM-D biosensor for Ochratoxin A detection in red wine

Ochratoxin A (OTA), a highly toxic compound, is one of the most widely spread mycotoxins that contaminates a large variety of agricultural commodities. Due to its presence in the food chain, it imposes a hazard on both human and animal health. Therefore, there is a need for precise, fast and simple methods for toxin quantification. Herein, a novel sensor based on a quartz crystal microbalance with dissipation monitoring (QCM-D) and antibodies for specific analyte recognition was developed for rapid and sensitive detection of OTA in red wine. The combination of indirect competitive assay with QCM-D gives a straightforward device, which can simultaneously measure frequency (Δf) and dissipation (ΔD) changes resulting in detailed information about the mass attached to the sensor surface as well as conformational changes, viscoelastic properties and the hydration state of the film. Small molecules (such as OTA) suffer from poor LOD due to the high concentration of primary antibody needed to generate adequate signal. In the present study, amplification of the QCM-D signal was obtained by applying secondary antibodies conjugated with gold nanoparticles (AuNPs). Thanks to this, a linear detection range of 0.2-40ngmL-1 has been achieved with an excellent LOD of 0.16ngmL-1, which is one order of magnitude lower than LOD specified by European Union legislation concerning the limit of OTA in food. Moreover, a matrix effect (caused by the occurrence of polyphenols in wine) and associated non-specific interactions with the sensor surface was completely eliminated by a simple pre-treatment of the wine with the addition of 3% poly(vinylpyrrolidone) (PVP).

A whole-cell biosensor as in vitro alternative to skin irritation tests

This study presents the time-resolved detection of chemically induced stress upon intracellular signaling cascades by using genetically modified sensor cells based on the human keratinocyte cell line HaCaT. The cells were stably transfected with a HSP72-GFP reporter gene construct to create an optical sensor cell line expressing a stress-inducible reporter protein. The time- and dose-dependent performance of the sensor cells is demonstrated and discussed in comparison to a label-free impedimetric monitoring approach (electric cell-substrate impedance sensing, ECIS). Moreover, a microfluidic platform was established based on μSlidesI(0,4)Luer to allow for a convenient, sterile and incubator-independent time-lapse microscopic observation of the sensor cells. Cell growth was successfully achieved in this microfluidic setup and the cellular response to a cytotoxic substance could be followed in real-time and in a non-invasive, sensitive manner. This study paves the way for the development of micro-total analysis systems that combine optical and impedimetric readouts to enable an overall quantitative characterization of changes in cell metabolism and morphology as a response to toxin exposure. By recording multiple parameters, a detailed discrimination between competing stress- or growth-related mechanisms is possible, thereby presenting an entirely new in vitro alternative to skin irritation tests.

Intrinsic optical bistablility of an ultrathin film consisting of oriented linear aggregates

A theoretical study of transmittivity of an ultrathin film (of thickness smaller than an optical wavelength) consisting of oriented linear aggregates is carried out. We show that within a certain domain of the incident field amplitude, optical transitions of a single disordered aggregate, the eigenstates of which are represented by the Frenkel exciton states, can be treated in the framework of a two-level approximation. This allows us to claim that an ensemble of linear aggregates is analogous to that comprised of inhomogeneously broadened two-level systems. Based on this analogy, we show that the transmittivity of the film can manifest a bistable behavior originating from the coupling of the aggregates via the emission (far-zone) field. This mechanism of bistability differs from that occurring in a single perfect aggregate. In the latter case, bistability results from the population-dependent resonance frequency shift of an individual aggregate, originating from the coupling of the molecules via the dipo...

Effect of exciton-exciton annihilation on optical bistability of a linear molecular aggregate

Abstract A theoretical study of the optical bistable response of a linear molecular aggregate modelled as a linear chain of molecules is carried out, making use of the one-molecule density matrix approach in which the intermolecular dipole-dipole interaction is included explicitly. The effect of exciton-exciton annihilation on the bistable behaviour is analyzed. One point of view seems to be that the annihilation channel of relaxation can destroy the bistability. However, we found that the bistable behaviour may be observable even when the annihilation constant greatly exceeds the intermolecular dipole-dipole interaction being responsible for the aggregate bistability.

Fluorescence optical spectrally resolved sensor based on molecularly imprinted polymers and microfluidics

Molecularly imprinted polymers (MIPs) are synthetic receptors that can be synthesized for a variety of target molecules. One of their possible applications is in chemical sensors. In this article, a microfluidic measurement setup with immobilized MIPs with fluorescence detection is described. Fluorescence measurements were performed on MIP films specific for the fluorescence‐labeled amino acid dansyl‐L‐phenylalanine. A conventional imprinting protocol with noncovalent interactions between the functional monomers and the template was used. We present the immobilization of the polymers on quartz substrates to form homogenous and stable films over at least six cycles of measurement and regeneration, and their use for microfluidic measurements in a spectrofluorometer. Furthermore, the design and buildup for a reproducible fluorescence measuring system is described. With this system, concentrations of 0.5 μM of dansyl‐L‐phenylalanine could be detected with 3 sigma certainty which is 50 times more sensitive compared with the detection of dansyl‐L‐phenylalanine without MIPs under the same conditions. The binding kinetics indicates that binding is completed after 30 min. Our results show that MIP films in combination with fluorescence detection and microfluidic devices can be a very sensitive tool for the detection of biologically relevant analytes.