The surface enhanced raman scattering (SERS) signal from the l-tyrosine (tyr) molecule adsorbed on gold nanoparticles (Au-tyr) is compared with the SERS signal assisted by the presence of gadolinium ions (Gd(3+)) coordinated with the Au-tyr system. An enhancement factor of the SERS signal in the presence of Gd(3+) ions was ∼5 times higher than that produced by l-tyrosine adsorbed on gold nanoparticles. The enhancement of the SERS signal can be attributed to a corresponding increase in the local electric field due to the presence of Gd(3+) ions in the vicinity of a gold dimer configuration. This scenario was confirmed by solving numerically Maxwell equations, showing an increase of 1 order of magnitude in the local electric scattered field when the Gd(3+) ion is located in between a gold dimer compared with naked gold nanoparticles.
The potential use of magnetic nanoparticles (MNPs) in biomedicine as magnetic resonance, drug delivery, imagenology, hyperthermia, biosensors, and biological separation has been studied in different laboratories. One of the challenges on MNP elaboration for biological applications is the size, biocompatibility, heat efficiency, stabilization in physiological conditions, and surface coating. Magnetoliposome (ML), a lipid bilayer of phospholipids encapsulating MNPs, is a system used to reduce toxicity. Encapsulated MNPs can be used as a potential drug and a gene delivery system, and in the presence of magnetic fields, MLs can be accumulated in a target tissue by a strong gradient magnetic field. Here, we present a study of the effects of DC magnetic fields on encapsulated MNPs inside liposomes. Despite their widespread applications in biotechnology and environmental, biomedical, and materials science, the effects of magnetic fields on MLs are unclear. We use a modified coprecipitation method to synthesize superparamagnetic nanoparticles (SNPs) in aqueous solutions. The SNPs are encapsulated inside phospholipid liposomes to study the interaction between phospholipids and SNPs. Material characterization of SNPs reveals round-shaped nanoparticles with an average size of 12 nm, mainly magnetite. MLs were prepared by the rehydration method. After formation, we found two types of MLs: one type is tense with SNPs encapsulated and the other is a floppy vesicle that does not show the presence of SNPs. To study the response of MLs to an applied DC magnetic field, we used a homemade chamber. Digitalized images show encapsulated SNPs assembled in chain formation when a DC magnetic field is applied. When the magnetic field is switched off, it completely disperses SNPs. Floppy MLs deform along the direction of the external applied magnetic field. Solving the relevant magnetostatic equations, we present a theoretical model to explain the ML deformations by analyzing the forces exerted by the magnetic field over the surface of the spheroidal liposome. Tangential magnetic forces acting on the ML surface result in a press force deforming MLs. The type of deformations will depend on the magnetic properties of the mediums inside and outside the MLs. The model predicts a coexistence region of oblate–prolate deformation in the zone where χ = 1. We can understand the chain formation in terms of a dipole–dipole interaction of SNP.
The fringe projection (FP) method is an outstanding tool for reconstructing painted surfaces. This technique, which has been used for conservation and digitization, does not damage the artwork and can reach sub-millimeter accuracy. To carry out this type of analysis, it is necessary to achieve the most accurate measurements possible. Measuring the precision that a projector-camera-object arrangement can achieve is a complex task. In this paper, we show an experimental method used to measure the accuracy of this technique with instrumentation within the reach of most conservation laboratories. The method consists of capturing, as a reference model, a stepped cylindrical Nylamid® pyramid, as a construction whose shape, size, and manufacturing accuracy are known with high precision. The pyramid has eight well-defined steps, which are fashioned with an accuracy more exact than that of the fringe projection method. The height of each step was measured, obtaining the mean and variance of the height measurements fitted to a Gaussian distribution. In this work, we show the measured heights of the steps, obtained by varying the period of the fringes. The smallest detectable step height was less than 44.1 µm; however, this was obtained with a variance in the order of the step height. The smallest detectable step height with a small variance was 0.1008 mm. In addition to this accuracy measurement, a qualitative evaluation of a painting was carried out, finding the presence of possible superimposed thin layers, fabric, and microcracks, which commonly occur in the drying and aging processes. Further research would provide an experimental measurement of the method’s accuracy and its variance as essential for obtaining a confidence criterion that could then be applied to the model of the painting’s surface.
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