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- ItemTime-resolved study of site-specific corrosion in a single crystalline silver nanoparticle(Berlin : SpringerOpen, 2019) Trautmann, Steffen; Dathe, André; Csáki, Andrea; Thiele, Matthias; Müller, Robert; Fritzsche, Wolfgang; Stranik, OndrejWe followed over 24 h a corrosion process in monocrystalline triangular-shaped nanoparticles at a single-particle level by atomic force microscopy and optical spectroscopy techniques under ambient laboratory conditions. The triangular-shaped form of the particles was selected, because the crystallographic orientation of the particles is well defined upon their deposition on a substrate. We observed that the particles already start to alter within this time frame. Surprisingly, the corrosion starts predominantly from the tips of the particles and it creates within few hours large protrusions, which strongly suppress the plasmon character of the particles. These observations support the crystallographic model of these particles consisting of a high-defect hexagonal closed packed layer, and they could help material scientists to design more stable silver nanoparticles. Moreover, this described technique can be used to reveal kinetics of the corrosion in the nanoscale of other materials.
- Item2-LED-μspectrophotometer for rapid on-site detection of pathogens using noble-metal nanoparticle-based colorimetric assays(Basel : MDPI, 2020) Reuter, Cornelia; Urban, Matthias; Arnold, Manuel; Stranik, Ondrej; Csáki, Andrea; Fritzsche, WolfgangNovel point-of-care compatible methods such as colorimetric assays have become increasingly important in the field of early pathogen detection. A simple and hand-held prototype device for carrying out DNA-amplification assay based on plasmonic nanoparticles in the colorimetric detection is presented. The low-cost device with two channels (sample and reference) consists of two spectrally different light emitting diodes (LEDs) for detection of the plasmon shift. The color change of the gold-nanoparticle-DNA conjugates caused by a salt-induced aggregation test is examined in particular. A specific and sensitive detection of the waterborne human pathogen Legionella pneumophila is demonstrated. This colorimetric assay, with a simple assay design and simple readout device requirements, can be monitored in real-time on-site. © 2020 by the authors.
- ItemStabilizing silica nanoparticles in hydrogels: impact on storage and polydispersity(London : RSC Publishing, 2017) Giovannini, Giorgia; Kunc, Filip; Piras, Carmen C.; Stranik, Ondrej; Edwards, Alison A.; Hall, Andrew J.; Gubala, VladimirFor successful nanomedicine, it is important that the unique, size-dependent physico-chemical properties of the nanomaterial remain predictably constant during both the storage and the manipulation of the material. Here a novel approach to preserve the colloidal stability and degradation of NPs is described. The concept is simple: (a) a solution of monodisperse particles is formulated into a responsive water- or PBS-based hydrogel; (b) the gel can be reversibly turned into a solution after long term storage by shaking it by hand; (c) the NP can be diluted and used in any desired application without the need for excessive manipulation. The differences between the physico-chemical properties of NPs stored in solution and in gel are compared. Two types of NPs were involved in this study: silica NPs of ∼100 nm and Au-NPs of 30 and 80 nm in diameter. The key findings are: the fibrous matrix of the hydrogel limits the NP mobility, significantly reduces NP aggregation and conserves the NP morphology; both the hydrogelator and the NPs show negligible toxicity towards the model U937 human hematopoietic cell line; undesired leaching of cargo material loaded inside the particles is reduced, which could be an important feature for drug delivery systems.
- ItemA new strategy for silver deposition on Au nanoparticles with the use of peroxidase-mimicking DNAzyme monitored by Localized Surface Plasmon Resonance technique(Basel : MDPI, 2017) Kosman, Joanna; Jatschka, Jacqueline; Csáki, Andrea; Fritzsche, Wolfgang; Juskowiak, Bernard; Stranik, OndrejPeroxidase-mimicking DNAzyme was applied as a catalyst of silver deposition on gold nanoparticles. This DNAzyme is formed when hemin binds to the G-quadruplex-forming DNA sequence. Such a system is able to catalyze a redox reaction with a one- or two-electron transfer. The process of silver deposition was monitored via a localized surface plasmon resonance technique (LSPR), which allows one to record scattering spectrum of a single nanoparticle. Our study showed that DNAzyme is able to catalyze silver deposition. The AFM experiments proved that DNAzyme induced the deposition of silver shells of approximately 20 nm thickness on Au nanoparticles (AuNPs). Such an effect is not observed when hemin is absent in the system. However, we noticed non-specific binding of hemin to the capture oligonucleotides on a gold NP probe that also induced some silver deposition, even though the capture probe was unable to form G-quadruplex. Analysis of SEM images indicated that the surface morphology of the silver layer deposited by DNAzyme is different from that obtained for hemin alone. The proposed strategy of silver layer synthesis on gold nanoparticles catalyzed by DNAzyme is an innovative approach and can be applied in bioanalysis (LSPR, electrochemistry) as well as in material sciences.
- ItemPropagating and localized surface plasmon resonance sensing — A critical comparison based on measurements and theory(Amsterdam [u.a.] : Elsevier, 2016) Jatschka, Jacqueline; Dathe, André; Csáki, Andrea; Fritzsche, Wolfgang; Stranik, OndrejWith its potential for ultrasensitive, label-free detection of molecular interactions, sensing methods based on the surface plasmon resonance (SPR) effect fully meet the requirements for modern analytical techniques. Already established by using propagating SPR in thin gold layers, the last years witnessed the emergence of another related technique utilizing extremely miniaturized noble metal sensor structures, based on a localized SPR. This paper provides a critical comparison of these kinds of SPR sensing, reviews the foundation of both general approaches, presents experimental data on exactly the same molecular model system using both techniques, as well as theoretical considerations in order to allow reasonable comparison. It highlights the specific features and effects, in order to provide guidance in choosing the right technique for given bioanalytical tasks. The study demonstrated the capabilities of LSPR for sensing of molecular layers even in the lower nanometer dimension. For the detection of small (bio)molecules, smaller particle diameters are favored regarding highest sensitivity. It also presents an approach to obtain refractive index and the thickness of a molecular film by analyzing the signal response of plasmonic sensors with metal nanoparticles. Moreover, an additional method for the improvement of the parameters' determination is introduced.