Plasmonic enhancement of fluorescence for biomedical diagnostics

The enhancement of fluorescence that can result from the proximity of fluorophores to metallic nanoparticles (NP’s) is investigated. This plasmonic enhancement, which is a result of the localized surface plasmon resonance (LSPR) at the metal surface, can be exploited in order to improve the signal obtained from optical biochips and thereby lower the limits of detection. The scale of the enhancement depends on many parameters such as NP size and shape, metal type and NP-fluorophore separation. Throughout the work, theoretical calculations were carried out, and, where relevant, theoretical predictions were compared with experimental measurements. Characterisation techniques used include TEM, AFM as well as optical fluorescence and absorption. The first section deals with the production of ordered arrays of nanostructures, of varying size and composition, on glass substrates using a nanosphere lithography technique. The ability to tune the peak wavelength of LSPR was demonstrated. Fluorescent dyes were then pin-printed onto the NP layer and the fluorescence enhancement was measured. The second body of work involved characterising the enhanced fluorescence from dyes attached to free NPs in solution. NPs of sizes ranging from 5 to 50nm radius and with different gold/silver alloy compositions were prepared by wet chemistry. The NPs were coated with silica shells to control the dye-NP separation and to minimise quenching. The dependence of the enhancement on NP size was found to agree well with theoretical calculations based on the Mie theory. The final body of work focused on the development of strategies applicable to polymer biochips. This included the development of techniques for immobilising NPs on plastic substrates. A range of dyes and a range of NP shapes were investigated. Dye-NP separation was controlled to nanometer precision by layer-by-layer deposition of polyelectrolytes. In this configuration, both dye quenching and enhancement effects were observed and characterised. The key result to emerge from this work was that it is possible to design an optical biochip enhancement platform where the NP shape, size and composition are optimised for the selected dye label and where the average dye-NP separation is designed to achieve maximum enhancement

Antibiotic treatment reduces the intensity of intraamniotic inflammation in pregnancies with idiopathic vaginal bleeding in the second trimester of pregnancy

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Plasmonic enhancement in the fluorescence of organic and biological molecules by photovoltaic tweezing assembly

This is the peer reviewed version of the following article: Advanced Materials Technologies 2.8 (2017): 1700024, which has been published in final form at http://dx.doi.org/10.1002/admt.201700024. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Self-ArchivingThe potential of photovoltaic tweezers to produce plasmonic platforms for fluorescence enhancement of organic or biological molecules is demonstrated. 1D and 2D patterns of silver nanoparticles have been produced on the surface of LiNbO3:Fe substrates using this photovoltaic tool, which allows depositing in parallel a large number of particles in accordance with imposed 1D and 2D light profiles. The nanoparticle patterns reveal a variety of plasmonic features whose resonances cover a broad spectral range and are able to produce efficient fluorescence enhancement. First a remarkable average enhancement factor of ten has been measured for Disperse Red 1 organic molecules deposited on the patterns. Clear enhancements have been also obtained from fluorescein labeled biological molecules (DNA and asynthetic peptide). Finally, the possibility of using the photo-electrically generated metallic patterns with other substrates is also demonstrated by enhancement experiments for which the nanoparticle pattern has been transferred to a non-photovoltaic substrateThis work was supported by the funding of the Ministerio de Economía y Competitividad of Spain under the project MAT2014-57704-C3. M. A. Díaz also acknowledges Spanish Government (MINECO) and the European Community (FEDER) through Grant MAT2015-66586-

Propagating and localized surface plasmon resonance sensing — A critical comparison based on measurements and theory

With 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

A new strategy for silver deposition on Au nanoparticles with the use of peroxidase-mimicking DNAzyme monitored by Localized Surface Plasmon Resonance technique

Peroxidase-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

2-LED-μspectrophotometer for rapid on-site detection of pathogens using noble-metal nanoparticle-based colorimetric assays

Novel 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

Acute Histological Chorioamnionitis and Birth Weight in Pregnancies With Preterm Prelabor Rupture of Membranes: A Retrospective Cohort Study

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Prevalence and Load of Cervical Ureaplasma Species With Respect to Intra-amniotic Complications in Women With Preterm Prelabor Rupture of Membranes Before 34 weeks

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