Krystyna Drozdowicz-Tomsia

Ultrabright Eu–Doped Plasmonic Ag@SiO2 Nanostructures: Time-gated Bioprobes with Single Particle Sensitivity and Negligible Background

Fluorescence has become one of the key detection methods in genomics, proteomics and cell biology and its applications extend as far as biomedical diagnostics. [ 1–4 ] Advances in this area have been accelerated by the development of new nanotechnology-inspired bioprobes such as quantum dots and silica or polymer encapsulated nanoparticles as well as smart detection strategies. [ 2 , 3–7 ] In parallel, photonic techniques have been pursued to take advantage of special optical properties, such as long fl uorescence decay times or infrared multi-photon excitation wavelength (to name just a few) to suppress background noise in fl uorescence detection. [ 2 , 8 ] However, these developments have often occurred in isolation from one another, and, as a result, an ideal fl uorescence detection strategy is yet to be developed. It should combine ultrabright bioprobes that have high absorption coeffi cients and high quantum yields and are clearly distinguishable and stable (free from bleaching and/or blinking). It should also provide high signal to noise ratio achievable by using photonics approaches such as timegating. Lanthanide fl uorophores with their long lifetimes are desirable as bioprobes for ultrasensitive detection, since they can be used in a time-gating mode that offers exceptionally high background rejection. [ 5 , 9–12 ] However the fl uorescence intensity of all lanthanide-based fl uorophores is very low compared with traditional fl uorescent dyes, due to long (ms) fl uorescence lifetimes. Recent efforts have been made to encapsulate lanthanide-based molecular complexes into nanoparticles, which produce amplifi ed signals due to increased number of lanthanide ions per nanoparticle, [ 7 ] but the limitation of slow radiative rates remains. The application of metallic nanostructures, particularly silver, provides a way to favorably modify the luminescence properties of close lanthanide fl uorophores and to alleviate their classical constraints. [ 13 ] The metal-enhanced fl uorescence (MEF) effect

Doping effect on dark currents in In0.5Ga0.5As∕GaAs quantum dot infrared photodetectors grown by metal-organic chemical vapor deposition

Stacked self-assembled In0.5Ga0.5As∕GaAs quantum dot infrared photodetectors grown by low-pressure metal-organic chemical vapor deposition, with and without silicon dopants in the quantum dot layers, are investigated. The increase of dark currents observed at higher doping levels is attributed to higher defect density leading to stronger sequential resonant tunneling and to lowering of the operating temperature of the device.

Enhanced Flow Cytometry-Based Bead Immunoassays Using Metal Nanostructures

While the principle of fluorescence enhancement of metal nanostructures is well-known, the utility of this effect in practical methodologies used in analytical laboratories remains to be established. In this work, we explore the advantage of fluorescence enhancement for flow cytometry. We report the observation of metal-enhanced fluorescence emission of fluorophores located on the surface of silica beads coated with nanostructured silver, suitable for flow cytometry detection. The fluorescence enhancement was investigated using a model AlexaFluor 430 IgG immunoassay and AlexaFluor 430 labeling. Approximately 8.5-fold and 10.1-fold higher fluorescence intensities at 430 nm excitation were, respectively, observed from silvered approximately 400 nm and 5 microm silica beads deposited on glass as compared to the control sample. The 400 nm and 5 microm beads were compatible with the flow cytometry readout, although lower enhancement factors of 3.0 and 3.7 were obtained. We show that such values are consistent with less favorable overlap of the plasmon resonance in silver nanostructures with 488 nm excitation wavelength used in the flow cytometry experiment. We, thus, demonstrated that the silvered silica beads are able to provide intensified fluorescence signals in flow cytometry which can improve the sensitivity of flow cytometry-based bioassay systems.

Multiphoton fluorescence lifetime imaging microscopy reveals free-to-bound NADH ratio changes associated with metabolic inhibition

Measurement of endogenous free and bound NAD(P)H relative concentrations in living cells isa useful method for monitoring aspects of cellular metabolism, because the NADH∕NAD⁺ reduction-oxidation pair is crucial for electron transfer through the mitochondrial electron transport chain. Variations of free and bound NAD(P)H ratio are also implicated in cellular bioenergetic and biosynthetic metabolic changes accompanying cancer. This study uses two-photon fluorescence lifetime imaging microscopy (FLIM) to investigate metabolic changes in MCF10A premalignant breast cancer cells treated with a range of glycolysis inhibitors: namely, 2 deoxy-D-glucose, oxythiamine, lonidamine, and 4-(chloromethyl) benzoyl chloride, as well as the mitochondrial membrane uncoupling agent carbonyl cyanide m-chlorophenylhydrazone. Through systematic analysis of FLIM data from control and treated cancer cells, we observed that all glycolytic inhibitors apart from lonidamine had a slightly decreased metabolic rate and that the presence of serum in the culture medium generally marginally protected cells from the effect of inhibitors. Direct production of glycolytic L-lactate was also measured in both treated and control cells. The combination of these two techniques gave valuable insights into cell metabolism and indicated that FLIM was more sensitive than traditional biochemical methods, as it directly measured metabolic changes within cells as compared to quantification of lactate secreted by metabolically active cells.

Mechanisms of enhancement of light emission in nanostructures of II-VI compounds doped with manganese

Intra-shell transitions of transition metal and rare earth ions are parity forbidden processes. For Mn2+ ions this is also a spin forbidden process, i.e., light emission should be inefficient. Surprisingly, it has been reported that in nanostructures of ZnMnS the T14 to A16 intra-shell transition of Mn2+ results in a bright photoluminescence characterized by a short PL decay time. The model of a quantum confined atom was introduced to explain the observed experimental results. It was later claimed that this model is incorrect. Based on the results of our photoluminescence, photoluminescence kinetics, time-resolved photoluminescence, electron spin resonance, and optically detected magnetic resonance investigations, we confirm photoluminescence enhancement and decrease of photoluminescence lifetime and relate these effects to spin dependent magnetic interactions between localized spins of Mn2+ ions and spins/magnetic moments of free carriers. This mechanism is active in both bulk and in low-dimensional stru...

Dense Two-Dimensional Silver Single and Double Nanoparticle Arrays with Plasmonic Response in Wide Spectral Range

We report the properties of plasmons in dense planar arrays of silver single and double nanostructures with various geometries fabricated by electron beam lithography (EBL) as a function of their size and spacing. We demonstrate a strong plasmon coupling mechanism due to near-field dipolar interactions between adjacent nanostructures, which produces a major red shift of the localized surface plasmon resonance (LSPR) in silver nanoparticles and leads to strong maximum electric field enhancements in a broad spectral range. The extinction spectra and maximum electric field enhancements are theoretically modeled by using the finite element method. Our modeling revealed that strong averaged electric field enhancements of up to 60 in visible range and up to 40 in mid-infrared result from hybridization of multipolar resonances in such dense nanostructures; these are important for applications in surface enhanced spectroscopies.

Plasmonic Ag/SiO2 composite nanoparticles doped with europium chelate and their metal enhanced fluorescence

We report silver nanostructure-enhanced fluorescence of a europium (Eu) chelate, BHHCT-Eu-DPBT, which was covalently bound in Ag/SiO2 nanocomposites. This design enhances the europium signal intensity by more than one order of magnitude, and accelerates the decay time from 0.3 ms down to 60 microseconds, at low excitation conditions. These nanocomposites were bright enough to be observed in time-gated fluorescence microscopy under 365 nm LED excitation. The increased brightness and reduced lifetime of such fluorescent core-shell nanocomposites will enhance their applicability for ultrasensitive bioassays and bioimaging, especially with time-gating.

Propagating Surface Plasmons and Dispersion Relations for Nanoscale Multilayer Metallic-Dielectric Films

The study of propagating surface plasmons (PSPs) is an important aspect of the understanding of the interaction between light and metallic surfaces. One of the key concepts related to PSPs, is the dispersion relation. This relation is the basis for understanding of coupling of light to PSPs, by using special approaches to match the wavevector. Moreover, it can be used to predict the matching of localised surface plasmons (LSPs) and PSPs to achieve highly enhanced electromagnetic field and/or tailored transmission.

Growth-temperature-dependent cathodoluminescence properties of GaSb/GaAs quantum-dot multilayer structures

Multilayer GaSb/GaAs quantum-dot (QD) structures grown by atmospheric-pressure metalorganic chemical vapor deposition on semi-insulating GaAs (100) substrates with varying growth temperature of the confinement layers are studied by the cathodoluminescence (CL). Two main features assigned to wetting layer and QDs are observed in the CL spectra. Their relative positions strongly depend on the growth conditions of the confinement layers. The highest separation of 270 meV is achieved for GaAs confinement layers grown at 540 °C.

Nanoscale plasmonic resonators with high Purcell factor: spontaneous and stimulated emission

Plasmonic nanoparticles with silver cores and silica shells containing Eu fluorophores near the surface have been produced by wet chemistry method and their spontaneous emission properties characterized. Fluorescence amplification and decreased lifetime is interpreted within the Purcell framework which highlights the role of surface plasmon polariton modes of the nanoparticle. These behave as energy-storing resonators, with values of the Q factor between 50 and 170 at the fluorophore wavelength of 615 nm, and very small mode volumes, in the order of 104 nm3, producing high Purcell factors of over 4000. Comparison of experiment with theoretical calculations by using the Mie theory shows that the values of cavity Q factors are moderated by the nonradiative rate of fluorophore molecules close to metal. The criteria for laser action in such composite nanoparticles are also presented, including lasing frequencies and threshold gain.