543 Analytische Chemie
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Gold Plasmophores for Plasmon-Enhanced Photoelectrochemical Sensing Based on Metal Nanostructures
(2026)
Surface plasmon-enhanced photoelectrochemical (PE–PEC) processes have garnered growing interest due to their high sensitivity and reduced energy consumption. In this work, a semiconductor-free PE–PEC platform is developed by integrating plasmonic gold nanorods (Au NRs) with gold nanoclusters (Au NCs). The system is constructed by depositing a monolayer of Au NRs with a thin SiO2 spacer layer onto an Au NC-modified gold electrode. Experimental results supported by theoretical simulations demonstrate that near-field enhancement arising from plasmonic coupling between adjacent Au NRs significantly improves charge carrier excitation and photocurrent generation in the Au NCs. The PE–PEC platform was evaluated for the detection of biologically relevant model analytes, namely, hydrogen peroxide and catechol. Compared to electrodes modified with Au NCs alone, the PE–PEC system exhibits markedly enhanced sensitivity for both analytes. These results highlight the potential of rationally designed plasmon-enhanced architectures for improving photoelectrochemical performance and advancing multifunctional PEC-based bioanalysis.
The coupling of enzymes to electrodes has emerged as a key research area with applications in sensing, bioenergetics, and bioelectrocatalysis. Here, we present a minimalistic manufacturing strategy of such an enzyme electrode showing that the conducting polymer PEDOT:PSS deposited on gold electrodes serves as an excellent platform for mediator-free, oxygen-independent glucose detection using pyrroloquinoline quinone-dependent glucose dehydrogenase (PQQ-GDH). Adsorptive immobilisation of PQQ-GDH onto PEDOT:PSS yields significant catalytic currents in the presence of glucose. The glucose concentration dependent analysis results in an apparent Km-value of 0.16 ± 0.03 mM. The catalytic signal can be tuned by adjusting polymer thickness and enzyme loading, while remaining stable across a pH range of 5.5 to 7.2. A less commonly used, but powerful method – faradaic impedance spectroscopy (f-EIS) - was successfully employed to monitor the enzymatic activity on the polymer layer. These findings support mediator-free bioelectrocatalysis and are consistent with direct electron transfer (DET) of the enzyme at the polymer-modified electrode. Our work opens new possibilities for biosensing applications, including flexible and stretchable field-effect transistor (FET) electronics where PEDOT:PSS is widely used.
Indium gallium nitride (InGaN) nanowire structures were investigated as photoelectrochemical transducers for bioanalytical applications. Chopped-light voltammetry in HEPES buffer (pH 7.0) revealed a light intensity-dependent anodic photocurrent that varies with applied potential. In the presence of hypoxanthine unmodified InGaN showed no photocurrent changes when electrode potentials around 0 mV vs Ag/AgCl or below have been applied. The three-dimensional surface of the nanowires was then used to adsorb the enzyme xanthine dehydrogenase (XDH). After this modification, the InGaN electrode exhibited a distinct increase in anodic photocurrent in the presence of hypoxanthine. The photocurrent showed a clear concentration-dependent behavior. This is indicative for a direct electron transfer from XDH to the semiconductor material. These findings highlight the suitability of InGaN nanowires for coupling with redox enzymes and their potential for developing light-driven biosensing platforms.
G-quadruplexes can be important as three-dimensional structures for aptamers as they improve the properties of the nucleic acids like higher nuclease degradation resistance. For the characterization of the quadruplex type and its formation, circular dichroism (CD) spectroscopy is one of the most common used identification methods. It is possible to differentiate the parallel and antiparallel G-quadruplex forms as well as the different number of nucleic acid strands by very specific CD spectral patterns at distinct absorption wavelengths. In this chapter, the protocol describes the model characterization of the anthracycline aptamer DRN-10 by CD spectroscopy, in order to show the usefulness and simple handling of this method for analyzing three-dimensional nucleic acid structures.
The world of beer is a rich tapestry woven with diverse styles, each with its unique character. Lager, known for its crispness, ferments at lower temperatures, while ale, at warmer ones, boasts a wide spectrum of aromas. Belgian beers dazzle with their complexity, from fruity Trappist ales to sour lambics. German wheat beers, like hefeweizens, charm with their effervescence and fruity undertones. India Pale Ales (IPAs) showcase a hoppy burst, while sour ales tantalize with their tanginess. Craftsmanship, history, and regional ingredients intertwine in this world of brewing, offering aficionados an array of delightful experiences. Research on craft beer aromas is limited, and molecular fingerprint could be crucial. To date, there have been no studies focused on characterizing compound profiles to differentiate beer styles. The Headspace Solid Phase Microextraction (HS-SPME) method provides a rapid and solvent-free approach to volatile compound. The present study aims to characterize the aroma profile of a wide range of beers by using HS-SPME/GC–MS technique combined with multivariate data processing. A total of 120 beer samples were collected and divided into five categories: Pilsen (n = 28); Lager (n = 23); Ale (n = 32); Sour (n = 24); and Belgian Ales (n = 13). Among the Pilsen beers, 18 unique compounds were found for beers with hop extract and hops, and 2 for beers with hop extract (Octyl acetate; and alpha-Terpineol). When comparing the remaining groups to each other, Belgian beers exhibited 5 unique compounds, and Lagers had one (nonanal). Sours and Ales did not have unique compounds but shared 2 distinct compounds with the Belgian group each. We concluded that Belgian beers are the most complex in terms of various aroma-related compounds, and that it is possible to distinguish beers that use pure hops from hop extract.
Drug delivery systems play a pivotal role in targeted pharmaceutical transport and controlled release at specific sites. Liposomes, commonly used as drug carriers, constitute a fundamental part of these systems. Moreover, the drug–liposome model serves as a robust platform for investigating interaction processes at both cellular and molecular levels. To advance our understanding of drug carrier uptake mechanisms, we employed fluorescence lifetime imaging microscopy (FLIM) and fluorescence correlation spectroscopy (FCS), leveraging the unique benefits of two-photon (2P) excitation. Our approach utilized giant unilamellar vesicles (GUVs) as a simplified model system for cell membranes, labelled with the amphiphilic fluorescent dye 3,3′-dioctadecyloxa-carbocyanine (DiOC18(3)). Additionally, large unilamellar vesicles (LUVs) functioned as a drug carrier system, incorporating the spectrally distinct fluorescent sulforhodamine 101 (SRh101) as a surrogate drug. The investigation emphasized the diverse interactions between GUVs and LUVs based on the charged lipids employed. We examined the exchange kinetics and structural alterations of liposome carriers during the uptake process. Our study underscores the significance of employing 2P excitation in conjunction with FLIM and FCS. This powerful combination offers a valuable methodological approach for studying liposome interactions, positioning them as an exceptionally versatile model system with a distinct technical advantage.
In modern electrochemical coating technology, it is common practice to create uniform layers. However, this study focuses on the deposition of non-uniform layers achieved through a deliberate arrangement of micro structured electrodes on the anode side. The "dog bone effect” was employed as the primary approach [1]. When electroplating on an otherwise uniform surface, this effect selectively processes an area influenced by the geometric edge effect (figure 1 left). The coating within this area is intended to be (i) unevenly distributed and (ii) non-reproducible. Process data was obtained through electrochemical simulations and subsequently applied to a specially designed micro-galvanic setup. This enabled the production of suitable micro structured anodes, validation of coating parameters, and the deposition of visually imperceptible structured areas with inhomogeneous properties using "adhesive gold" on appropriate substrates such as silver and nickel. The layers and their local topography were characterized and analyzed using confocal laser microscopy, X-Ray fluorescence analysis (XRF), as well as a self-designed and constructed laser interference device. As a result, this specific galvanic process technology successfully produced metallic layers that (i) cannot be visually confirmed by the naked eye, (ii) exhibit varied microstructural anode geometries, (iii) display unique differences in layer thickness, (iv) possess non-reproducible and chaotic topographies, and (v) can be detected and identified using conventional analysis techniques or a simple interference setup.
Anthracyclines like daunorubicin (DRN) and doxorubicin (DOX) play an undisputed key role in cancer treatment, but their chronic administration can cause severe side effects. For precise anthracycline analytical systems, aptamers are preferable recognition elements. Here, we describe the detailed characterisation of a single-stranded DNA aptamer DRN-10 and its truncated versions for DOX and DRN detection. Binding affinities were determined from surface plasmon resonance (SPR) and microscale thermophoresis (MST) and combined with conformational data from circular dichroism (CD). Both aptamers displayed similar nanomolar binding affinities to DRN and DOX, even though their rate constants differed as shown by SPR recordings. SPR kinetic data unravelled a two-state reaction model including a 1 : 1 binding and a subsequent conformational change of the binding complex. This model was supported by CD spectra. In addition, the dissociation constants determined with MST were always lower than that from SPR, and especially for the truncated aptamer they differed by two orders of magnitude. This most probably reflects the methodological difference, namely labelling for MST vs. immobilisation for SPR. From CD recordings, we suggested a specific G-quadruplex as structural basis for anthracycline binding. We concluded that the aptamer DRN-10 is a promising recognition element for anthracycline detection systems and further selected aptamers can be also characterised with the combined methodological approach presented here.
Nowadays pharmaceutical analysis and industry could not be imagined without using chromatographic methods like the High Performance Liquid Chromatography (HPLC) and Gas Chromatography (GC). Therefore, the field of chromatography is already firmly anchored in the three important, regional pharmacopeias: EP, USP and JP. Deficits of specifications within these pharmacopoeias relating to the detector parameters sampling rate and signal filtration are the major motivation of this thesis. Furthermore investigations on the data acquisition and processing within the detectors and software products dealing with collected data were done. Several concepts like double entry method, smoothing optimization and signal filtration based on persistence have been developed and are used as tools to examine the data integrity of commercial Chromatography Data System (CDS), improve the signal-to-noise ratio of small peaks to lower the LOD and LOQ by efficient denoising, and determine the suitable filter parameters and sampling rates an user can apply on his system to accelerate the method development and validation. All developments have been tested on simulated and real chromatograms and have shown that they are suitable for their specific purposes. In the end optimizations in the concepts still exist but some new aspects in the long-term investigated field of chromatography have been discovered.
Die Kontamination von Flächen mit Rüstungsaltlasten durch sprengstofftypische Verbindungen (STV) wie 2,4,6-Trinitrotoluol (TNT) ist nach wie vor ein großes Risiko für Gesundheit und Umwelt. Die Hochdruckflüssigchromatographie (HPLC) ist in Kombination mit der Tandem-Massenspektrometrie (MS/MS) ein besonders sensitives und exaktes Verfahren zur Konzentrationsbestimmung derartiger Umweltkontaminanten. Jedoch benötigen die derzeit eingesetzten Methoden zur Extraktion und Quantifizierung viel Zeit und Bodenmaterial. Wir haben daher eine 20-minütige LC-MS/MS-Methode entwickelt, die in einer Probe simultan acht STV qualitativ und quantitativ nachweisen kann. Im Vergleich zur EPA-Referenzmethode konnte bei der Extraktion die eingesetzte Bodenmenge von 10 g auf 2 g reduziert und die Extraktionsdauer von 18 h auf 30 min verkürzt werden. Die abschließende Validierung zeigte eine gute Reproduzierbarkeit und mit etablierten Protokollen vergleichbare Detektions- (LOD) und Quantifizierungslimits (LOQ), so dass die optimierten Methoden für eine schnelle und zuverlässige Analyse von Realproben eingesetzt werden konnten.
