A. Kamińska

Nanostructured silver–gold bimetallic SERS substrates for selective identification of bacteria in human blood

Surface-enhanced Raman spectroscopy (SERS) is a potentially important tool in the rapid and accurate detection of pathogenic bacteria in biological fluids. However, for diagnostic application of this technique, it is necessary to develop a highly sensitive, stable, biocompatible and reproducible SERS-active substrate. In this work, we have developed a silver-gold bimetallic SERS surface by a simple potentiostatic electrodeposition of a thin gold layer on an electrochemically roughened nanoscopic silver substrate. The resultant substrate was very stable under atmospheric conditions and exhibited the strong Raman enhancement with the high reproducibility of the recorded SERS spectra of bacteria (E. coli, S. enterica, S. epidermidis, and B. megaterium). The coating of the antibiotic over the SERS substrate selectively captured bacteria from blood samples and also increased the Raman signal in contrast to the bare surface. Finally, we have utilized the antibiotic-coated hybrid surface to selectively identify different pathogenic bacteria, namely E. coli, S. enterica and S. epidermidis from blood samples.

Detection of Hepatitis B virus antigen from human blood: SERS immunoassay in a microfluidic system

A highly sensitive immunoassay utilizing surface-enhanced Raman scattering (SERS) has been developed with a new Raman reporter and a unique SERS-active substrate incorporated into a microfluidic device. An appropriately designed Raman reporter, basic fuchsin (FC), gives strong SERS enhancement and has the ability to bind both the antibody and gold nanostructures. The fuchsin-labeled immuno-Au nanoflowers can form a sandwich structure with the antigen and the antibody immobilized on the SERS-active substrate based on Au-Ag coated GaN. Our experimental results indicate that this SERS-active substrate with its strong surface-enhancement factor, high stability and reproducibility plays a crucial role in improving the efficiency of SERS immunoassay. This SERS assay was applied to the detection of Hepatitis B virus antigen (HBsAg) in human blood plasma. A calibration curve was obtained by plotting the intensity of SERS signal of FC band at 1178cm(-1) versus the concentration of antigen. The low detection limit for Hepatitis B virus antigen was estimated to be 0.01IU/mL. The average relative standard deviation (RSD) of this method is less than 10%. This SERS immunoassay gives exact results over a broad linear range, reflecting clinically relevant HBsAg concentrations. It also exhibits high biological specificity for the detection of Hepatitis B virus antigen.

Bowing of the band gap pressure coefficient in InxGa1-xN alloys

The hydrostatic pressure dependence of photoluminescence, dEPL/dp, of InxGa1−xN epilayers has been measured in the full composition range 0 0.4 and a relatively steep dependence for x<0.4. On the basis of the agreement of the observed PL pressure coefficient with our calculations, we confirm that band-to-band recombination processes are responsible for PL emission and that no localized states are involved. Moreover, the good agreement between the experimentally determined dEPL/dp and the theoretical curve of dEG/dp indicates that the hydrostatic pressure dependence of PL measurements can be used to quantify changes of the band gap of the InGaN ternary alloy under pressure, demonstrating that the disorder-re...

Highly reproducible, stable and multiply regenerated surface-enhanced Raman scattering substrate for biomedical applications

We fabricated a Surface Enhanced Raman Scattering (SERS)-active surface based on photo-etched and Au-coated GaN. The highest enhancement factor (EF) in SERS and high reproducibility of spectra were obtained from surfaces covered with bunched nanopillars which were produced by relatively long defect-selective photo-etching. The surfaces exhibited SERS enhancements of the order of 2.8 × 106 for malachite green isothiocyanate (MGITC) and 2 × 106 for p-mercaptobenzoic acid (PMBA). These SERS enhancement factors were comparable to those of conventional SERS substrates, while the EF for MGITC was two orders of magnitude larger than the corresponding one reported for the SERS platform made on porous GaN. The standard deviation of the relative intensity of the 1180 cm−1 mode of MGITC was less than 5% for 100 randomly distributed locations across a single platform and less than 10% between different platforms. The SERS signal of MGITC at our GaN/Au surface (kept under ambient conditions) was extremely stable. We could not detect any peak shift or appreciable change of intensity even after three months. We used these surfaces to detect biological molecules such as amino acids and bovine serum albumin (BSA) at low concentration and with short detection time. We developed simple and effective cleaning procedures for our substrates. After cleaning, the same substrate could be used multiple times retaining the SERS activity. We are not aware of any other multiply regenerated SERS substrate which provides simultaneously such high stability with high enhancement, good uniformity, and high reproducibility.

Electronic structure of Ce3+ multicenters in yttrium aluminum garnets

Low temperature, infrared, and visible-ultraviolet absorption spectra of yttrium aluminum garnet (YAG) bulk crystals and epitaxial layers doped with Ce are presented. In the region of intra-configurational 4f–4f transitions, the spectra of the bulk YAG crystals exhibit existence of at least two different Ce3+ related centers, a major one associated with Ce in regular positions substituting yttrium and also additional center, due to so called antisite positions in the garnet host, i.e., ions in the Al positions. Crystal field analysis based on exchange charge model exhibit excellent agreement with the experimental data for major Ce3+ center.

Nd3+-doped yttrium aluminum garnet crystal as a near-infrared pressure sensor for diamond anvil cells

Pressure-induced shift of various luminescence lines of Nd3+-doped yttrium aluminum garnet crystal in the pressure range of 0–120kbars and temperatures between 10 and 300K is reported. Spectral positions of all these lines in the region of 900–960nm shift linearly towards lower energies with the pressure coefficient values from −0.01to−0.99cm−1∕kbar in the examined pressure range. Two of these lines have similar pressure coefficients than those of the R lines of Cr3+ in ruby. Therefore, they can be readily used for pressure calibration in diamond anvil cells.

Built-in electric field and large Stokes shift in near-lattice-matched GaN∕AlInN quantum wells

Near-lattice-matched GaN∕AlInN quantum wells are investigated by means of contactless electroreflectance (CER) and temperature-dependent photoluminescence (PL). Large Stokes shifts, up to 400meV, between PL peak energies and CER resonances are identified. This Stokes shift is attributed to large potential profile fluctuations (PPFs) in the AlInN barriers. Further evidence for such PPFs and for the additional influence of QW width fluctuations is provided by temperature-dependent PL measurements, demonstrating large PL halfwidths and clear “S-shape” behavior. The influence of a large Stokes shift on the correct determination of the value of the built-in electric field is discussed, and it is shown that PL measurements may lead to a significant overestimation of the built-in electric field in GaN∕AlInN QWs.

Different pressure behavior of GaN/AlGaN quantum structures grown along polar and nonpolar crystallographic directions

High quality GaN/AlGaN multiquantum well (QW) structures were grown by ammonia molecular beam epitaxy along the (0001) polar and (11 20) nonpolar directions. Each sample contains three QWs with thicknesses of 2, 3, and 4 nm as well as 10 nm Al0.30Ga0.70N barriers. The measured photoluminescence (PL) spectrum consists of three peaks originating from the radiative recombination of excitons in individual QWs. In the nonpolar sample, the energy positions (EPL) of the observed peaks are separated because of the quantum confinement effect, whereas in the polar sample an additional redshift is induced by the quantum confined Stark effect. The dependence of EEPL on QW width was used to estimate the built-in electric field magnitude in the latter sample to be about 2 MV/cm. Hydrostatic pressure studies of the PL in both samples gave qualitatively different results. In the polar sample, the pressure shift of EPL, dEPL/dp decreases significantly with QW width. The important finding is derived from the observation of a QW width independent dEPL/dp in the nonpolar sample. It shows that for GaN/Al0.30Ga0.70N, the quantum confinement remains practically independent of the applied hydrostatic pressure. This result reveals that in the polar sample, the variation in dEPL /dp with the QW width is due to the pressure-induced increase in the built-in electric field Fint. Thus, a more quantitative analysis of the latter effect becomes justified. We found that the Fint increases with pressure with a rate of about 80 kV (cm GPa)-1.

Nephelauxetic effect in luminescence of Cr3 + -doped lithium niobate and garnets

Abstract The model based on Harrison theory of bonding is used to explain quantitatively the nephelauxetic effect in LiNbO 3 and Y 3 Al 5 O 12 crystals doped with chromium, studied by high-hydrostatic pressure spectroscopy. The model uses only one adjustable parameter and can also be used for other dopant–ligands systems in different compounds. We show that not only ligands, but also the second neighbors of the dopant, influence the nephelauxetic effect.

Gold Micro-Flowers: One-Step Fabrication of Efficient, Highly Reproducible Surface-Enhanced Raman Spectroscopy Platform

We present a new method enabling simultaneous synthesis and deposition of gold micro-flowers (AuMFs) on solid substrates in a one-pot process that uses two reagents, auric acid and hydroxylamine hydrochloride, in aqueous reaction mixture. The AuMFs deposited onto the substrate form mechanically stable gold layer of expanded nanostructured surface. The morphology of the AuMFs depends on and can be controlled by the composition of the reaction solution as well as by the reaction time. The nanostructured metallic layers obtained with our method are employed as efficient platforms for chemical and biological sensing based on surface-enhanced Raman spectroscopy (SERS). SERS spectra recorded by such platforms for p-mercaptobenzoic acid and phage lambda exhibit enhancement factors above 106 and excellent reproducibility.