Chemische Charakterisierung und Spurenanalytik
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Heterogeneous sandwich immunoassays are widely used for biomarker detection in bioanalysis and medical diagnostics. The high analyte sensitivity of the current “gold standard” enzyme-linked immunosorbent assay (ELISA) originates from the signal-generating enzymatic amplification step, yielding a high number of optically detectable reporter molecules. For future point-of-care testing (POCT) and point-of-need applications, there is an increasing interest in more simple detection strategies that circumvent time-consuming and temperature-dependent enzymatic reactions. A common concept to aim for detection limits comparable to those of enzymatic amplification reactions is the usage of polymer nanoparticles (NP) stained with a large number of chromophores. We explored different simple NP-based signal amplification strategies for heterogeneous sandwich immunoassays
that rely on an extraction-triggered release step of different types of optically detectable reporters. Therefore, streptavidinfunctionalized polystyrene particles (PSP) are utilized as carriers for (i) the fluorescent dye coumarin 153 (C153) and (ii) hemin (hem) molecules catalyzing the luminol reaction enabling chemiluminescence (CL) detection. Additionally, (iii) NP labeling with hemin-based microperoxidase MP11 was assessed. For each amplification approach, the PSP was first systematically optimized regarding size, loading concentration, and surface chemistry. Then, for an immunoassay for the inflammation marker C- eactive protein (CRP), the analyte sensitivity achievable with optimized PSP
ystems was compared with the established ELISA concept for photometric and CL detection. Careful optimization led to a limit of detection (LOD) of 0.1 ng/mL for MP11-labeled PSP and CL detection, performing similarly well to a photometric ELISA (0.13 ng/mL), which demonstrates the huge potential of our novel assay concept.
The 2023 Nobel Prize in Chemistry was awarded to Aleksey I. Ekimov (prize share 1/3), Louis E. Brus (prize share 1/3), and Moungi G. Bawendi (prize share 1/3) for groundbreaking inventions in the field of nanotechnology, i.e., for the discovery and synthesis of semiconductor nanocrystals, also termed quantum dots, that exhibit size-dependent physicochemical properties enabled by quantum size effects. This feature article summarizes the main milestones of the discoveries and developments of quantum dots that paved the road to their versatile applications in solid-state lighting, display technology, energy conversion, medical diagnostics, bioimaging, and image-guided surgery.
The frequency-domain (FD) method provides an alternative to the commonly used time-domain (TD) approach in characterizing the luminescence kinetics of luminophores, with its own strengths, e.g., the capability to decouple multiple lifetime components with higher reliability and accuracy. While extensively explored for characterizing luminophores with down-shifted emission, this method has not been investigated for studying nonlinear luminescent materials such as lanthanide-doped upconversion nanoparticles (UCNPs), featuring more complicated kinetics. In this work, employing a simplified rate-equation model representing a standard two-photon energy-transfer upconversion process, we thoroughly analyzed the response of the luminescence of UCNPs in the FD method. We found that the FD method can potentially obtain from a single experiment the effective decay rates of three critical energy states of the sensitizer/activator ions involved in the upconversion process. The validity of the FD method is demonstrated by experimental data, agreeing reasonably well with the results obtained by TD methods.
Four donor-acceptor boron difluoride complexes based on the carbazole electron donor and the [1,3,5,2]oxadiazaborinino[3,4-a][1,8]naphthyridine acceptor were designed, synthesized, and systematically spectroscopically investigated in solutions, in the solid states, and dye-doped polymer films. The dyes exhibit an intense blue to red solid-state emission with photoluminescence quantum yields of up to 56% in pure dye samples and 86% in poly(methyl methacrylate) films. All boron complexes show aggregation-induced emission and reversible mechanofluorochromism. The optical properties of these dyes and their solid state luminescence can be tuned by substitution pattern, i.e., the substituents at the naphthyridine unit. Exchange of CH3- for CF3-groups does not only increase the intramolecular charge transfer character, but also provides a crystallization-induced emission enhancement.
This paper discusses the feasibility of a novel strategy based on the combination of bioprinting nano-doping technology and laser ablation-inductively coupled plasma time-of-flight mass spectrometry analysis for the preparation and characterization of gelatin- based multi-element calibration standards suitable for quantitative imaging. To achieve this, lanthanide up-conversion nanoparticles were added to a gelatin matrix to produce the bioprinted calibration standards. The features of this bioprinting approach were com- pared with manual cryosectioning standard preparation, in terms of throughput, between batch repeatability and elemental signal homogeneity at 5 μm spatial resolution. By using bioprinting, the between batch variability for three independent standards of the same concentration of 89 Y (range 0–600 mg/kg) was reduced to 5% compared to up to 27% for cryosectioning. On this basis, the relative standard deviation ( RSD ) obtained between three independent calibration slopes measured within 1 day also reduced from 16% (using cryosectioning ) to 5% (using bioprinting), supporting the use of a single standard preparation replicate for each of the concentrations to achieve good calibration performance using bioprinting. This helped reduce the analysis time by approximately 3-fold. With cryosectioning each standard was prepared and sectioned individually, whereas using bio-printing it was possible to have up to six different standards printed simultaneously, reducing the preparation time from approximately 2 h to under 20 min (by approxi- mately 6-fold). The bio-printed calibration standards were found stable for a period of 2 months when stored at ambient temperature and in the dark.
For more than 110 years, BAM has been producing reference materials for a wide range of application fields. With the development of new analytical methods and new applications as well as continuously emerging more stringent requirements of laboratory accreditation with regard to quality control and metrological traceability, the demand and requirements for reference materials are increasing. This trend article gives an overview of general developments in the field of reference materials as well as developments in selected fields of application in which BAM is active. This includes inorganic and metal analysis, gas analysis, food and consumer products, and geological samples. In addition to these more traditional fields of application, developments in the areas of optical spectroscopy, particulary fluorescence methods, and nanomaterials are considered.
A brief perspective of BAM on nanocarriers is presented including examples with special emphasis on the characterization of such materials and underlying challenges. In this respect, also ongoing activities at BAM on different types of core/shell nanomaterials and related systems are briefly summarized.
Two sets of polystyrene nanoparticles (PSNPs) with comparable core sizes but different carboxyl group densities were made and separated using asymmetric flow field flow fractionation (AF4), capillary electrophoresis (CE), and the off-line hyphenation of both methods. Our results revealed the significant potential of two-dimensional off-line AF4-CE hyphenation to improve the separation and demonstrated for the first time, the applicability of CE to determine the functional group density of nanoparticles (NPs). Compared to the result acquired with conductometric titration, the result obtained with synthesized 100 nm sized PSNPs revealed only a slight deviation of 1.7%. Commercial 100 nm sized PSNPs yielded a deviation of 4.6 %. For 60 nm sized PSNPs, a larger deviation of 10.6 % between both methods was observed, which is attributed to the lower separation resolution.
Correlating the photoluminescence (PL) properties of nanomaterials like semiconductor nanocrystals (QDs) and upconversion nanocrystals (UCNPs) assessed in ensemble studies and at the single particle level is increasingly relevant for applications of these nanomaterials in the life sciences like bioimaging studies or their use as reporters in microfluidic assays. Here we present a comparison of the spectroscopic properties of ensembles and single emitters for QDs like II/VI QDs and cadmium-free AIS/ZnS QDs as well as different UCNPs. The overall goal of this study was to derive particle architectures well suited for spectroscopic and microscopic applications.
The sensitive detection of the mycotoxin citrinin (CIT) utilizing ist fluorescence requires approaches to enhance the emission. In this respect, we studied the complexation of CIT and ochratoxin A (OTA) with Al3+ in methanol using absorption and fluorescence spectroscopy. In this context, an isocratic high performance liquid chromatography (HPLC) method using a polymer column and a fluorescence detector was also developed that enables the separation of the metal ion complexes from the free ligands and non-complexed Al3+. CIT and OTA showed distinct changes in their absorption and fluorescence properties upon Al3+-coordination, and the fluorescence of CIT was considerably enhanced. Analysis of the photometrically assessed titration of CIT and OTA with Al3+ using the Job plot method revealed 1:2 and 1:1 stoichiometries for the Al3+ complexes of CIT (Al:CIT) and OTA (Al:OTA), respectively. In the case of CIT, only one -diketone moiety participates in Al3+ coordination. These findings can be elegantly exploited for signal amplification and provide the base to reduce the limit of detection for CIT quantification by about an order of magnitude, as revealed by HPLC measurements using a fluorescence detector.