Convergence and Performance Analysis of a Particle Swarm Optimization Algorithm for Optical Tuning of Gold Nanohole Arrays.

Gold nanohole arrays, hybrid metal/dielectric metasurfaces composed of periodically arranged air holes in a thick gold film, exhibit versatile support for both localized and propagating surface plasmons. Leveraging their capabilities, particularly in surface plasmon resonance-oriented applications, demands precise optical tuning. In this study, a customized particle swarm optimization algorithm, implemented in Ansys Lumerical FDTD, was employed to optically tune gold nanohole arrays treated as bidimensional gratings following the Bragg condition. Both square and triangular array dispositions were considered. Convergence and evolution of the particle swarm optimization algorithm were studied, and a mathematical model was developed to interpret its outcomes.

Refractive Index Dependence of Fluorescence Enhancement in a Nanostructured Plasmonic Grating.

Plasmonic gratings are attracting huge interest in the context of realizing sensors based on surface-enhanced fluorescence. The grating features control the plasmonic modes and consequently have a strong effect on the fluorescence response. Within this framework, we focused on the use of a buffer solution flowing across the grating active surface to mimic a real measurement. The refractive index of the surrounding medium is therefore altered, with a consequent modification of the resonance conditions. The result is a shift in the spectral features of the fluorescence emission accompanied by a reshaping of the fluorescence emission in terms of spectral weight and direction.

Plasmonic Modes and Fluorescence Enhancement Coupling Mechanism: A Case with a Nanostructured Grating.

The recent development and technological improvement in dealing with plasmonic metasurfaces has triggered a series of interesting applications related to sensing challenges. Fluorescence has been one of the most studied tools within such a context. With this in mind, we used some well characterized structures supporting plasmonic resonances to study their influence on the emission efficiency of a fluorophore. An extended optical analysis and a complementary investigation through finite-difference time-domain (FDTD) simulations have been combined to understand the coupling mechanism between the excitation of plasmonic modes and the fluorescence absorption and emission processes. The results provide evidence of the spectral shape dependence of fluorescence on the plasmonic field distribution together with a further relationship connected with the enhancement of its signal. It has made evident that the spectral region characterized by the largest relative enhancement closely corresponds to the strongest signatures of the plasmonic modes, as described by both the optical measurements and the FDTD findings.

Semiconductor nanowire arrays for optical sensing: a numerical insight on the impact of array periodicity and density.

Recent advances in the nanofabrication and modeling of metasurfaces have shown the potential of these systems in providing unprecedented control over light-matter interactions at the nanoscale, enabling immediate and tangible improvement of features and specifications of photonic devices that are becoming always more crucial in enhancing everyday life quality. In this work, we theoretically demonstrate that metasurfaces made of periodic and non-periodic deterministic assemblies of vertically aligned semiconductor nanowires can be engineered to display a tailored effective optical response and provide a suitable route to realize advanced systems with controlled photonic properties particularly interesting for sensing applications. The metasurfaces investigated in this paper correspond to nanowire arrays that can be experimentally realized exploiting nanolithography and bottom-up nanowire growth methods: the combination of these techniques allow to finely control the position and the physical properties of each individual nanowire in complex arrays. By resorting to numerical simulations, we address the near- and far-field behavior of a nanowire ensemble and we show that the controlled design and arrangement of the nanowires on the substrate may introduce unprecedented oscillations of light reflectance, yielding a metasurface which displays an electromagnetic behavior with great potential for sensing. Finite-difference time-domain numerical simulations are carried out to tailor the nanostructure parameters and systematically engineer the optical response in the VIS-NIR spectral range. By exploiting our computational-methods we set-up a complete procedure to design and test metasurfaces able to behave as functional sensors. These results are especially encouraging in the perspective of developing arrays of epitaxially grown semiconductor nanowires, where the suggested design can be easily implemented during the nanostructure growth, opening the way to fully engineered nanowire-based optical metamaterials.

Fluorescence Spectroscopy Study of Protoporphyrin IX in Optical Tissue Simulating Liquid Phantoms.

Fluorescence spectroscopy has been extensively investigated for disease diagnosis. In this framework, optical tissue phantoms are widely used for validating the biomedical device system in a laboratory environment outside of clinical procedures. Moreover, it is fundamental to consider that there are several scattering components and chromophores inside biological tissues and the interplay between scattering and absorption may result in a distortion of the emitted fluorescent signal. In this work, the photophysical behaviour of a set of liquid, tissue-like phantoms containing different compositions was analysed: phosphate buffer saline (PBS) was used as the background medium, low fat milk as a scatterer, Indian ink as an absorber and protoporphyrin IX (PpIX) dissolved in dimethyl formamide (DMF) as a fluorophore. We examined the collected data in terms of the impact of surfactant Tween-20 on the background medium, scattering effects and combination of scattering and absorption within a luminescent body on PpIX. The results indicated that the intrinsic emission peaks are red shifted by the scattering particles or surfactant, whilst the scattering agent and the absorbent can alter the emission intensity substantially. We corroborated that phantoms containing higher surfactant content (>0.5% Tween 20) are essential to prepare stable aqueous phantoms.

Strong Modulations of Optical Reflectance in Tapered Core-Shell Nanowires.

Random assemblies of vertically aligned core-shell GaAs-AlGaAs nanowires displayed an optical response dominated by strong oscillations of the reflected light as a function of the incident angle. In particular, angle-resolved specular reflectance measurements showed the occurrence of periodic modulations in the polarization-resolved spectra of reflected light for a surprisingly wide range of incident angles. Numerical simulations allowed for identifying the geometrical features of the core-shell nanowires leading to the observed oscillatory effects in terms of core and shell thickness as well as the tapering of the nanostructure. The present results indicate that randomly displaced ensembles of nanoscale heterostructures made of III-V semiconductors can operate as optical metamirrors, with potential for sensing applications.

Self-Assembled InAs Nanowires as Optical Reflectors.

Subwavelength nanostructured surfaces are realized with self-assembled vertically-aligned InAs nanowires, and their functionalities as optical reflectors are investigated. In our system, polarization-resolved specular reflectance displays strong modulations as a function of incident photon energy and angle. An effective-medium model allows one to rationalize the experimental findings in the long wavelength regime, whereas numerical simulations fully reproduce the experimental outcomes in the entire frequency range. The impact of the refractive index of the medium surrounding the nanostructure assembly on the reflectance was estimated. In view of the present results, sensing schemes compatible with microfluidic technologies and routes to innovative nanowire-based optical elements are discussed.

Demonstration of fluorescence enhancement via Bloch surface waves in all-polymer multilayer structures.

An all-polymer photonic structure constituted by a distributed Bragg reflector topped with an ultrathin fluorescent polymer film has been studied. A Bloch surface wave resonance has been exploited to improve pumping efficiency. A strongly polarization and angle dependent fluorescence signal is found with respect to the light pumping beam and the emitted wavelength. Matching the most favorable condition for the pump coupling and the collection geometry, the signal obtained from the structure appears to be two orders of magnitude larger than the one of the bare emitting film.

Parkinsonism and dementia are negative prognostic factors for the outcome of subdural hematoma.

To determine, among a population with subdural hematoma (SH), whether patients affected by neurodegenerative disorders (parkinsonism and dementia) have a worse clinical outcome. We reviewed the data of patients diagnosed with fall-related SH discharged from the Departments of Neurology/Stroke unit, Neurosurgery, Intensive Care Unit at Brotzu General Hospital (Cagliari, Italy) between January 2010 and December 2013. Patients with severe traumatisms, evidence of spontaneous intracerebral bleeding or aged less than 50 were excluded. 332 patients were selected: 69 with a neurodegenerative parkinsonism or dementia (N-group), 217 with history of chronic non-neurological medical conditions with significant disability, previous falls and/or balance problems (NND-group) and 46 with a history of "minor" chronic non-neurological disorder. (NN-group). The clinical status at admission and discharge was assessed by modified Rankin Scale (mRS). The time-span between trauma and hospital admission was also calculated. At hospital admission we found a significantly longer delay in SH's diagnosis (χ (2) test p < 0.001) and a worse mRS score (Kruskal Wallis p < 0.001) in the N-group compared to both NN and NND-groups. During hospital stay we observed the lack of significant variation in mRS score in N-group (Wilcoxon test p = 0.86), in contrast with NN and NND-groups who significantly improved (Wilcoxon test p < 0.001). Our results demonstrate that the consequences of SH are more severe in the N-group compared to NN and NND-groups. The longer interval between trauma and hospital admittance plays a critical role in worsening the outcome of patients with parkinsonism and dementia compared to subjects without neurodegenerative disorders.

Synergic combination of the sol-gel method with dip coating for plasmonic devices.

Biosensing technologies based on plasmonic nanostructures have recently attracted significant attention due to their small dimensions, low-cost and high sensitivity but are often limited in terms of affinity, selectivity and stability. Consequently, several methods have been employed to functionalize plasmonic surfaces used for detection in order to increase their stability. Herein, a plasmonic surface was modified through a controlled, silica platform, which enables the improvement of the plasmonic-based sensor functionality. The key processing parameters that allow for the fine-tuning of the silica layer thickness on the plasmonic structure were studied. Control of the silica coating thickness was achieved through a combined approach involving sol-gel and dip-coating techniques. The silica films were characterized using spectroscopic ellipsometry, contact angle measurements, atomic force microscopy and dispersive spectroscopy. The effect of the use of silica layers on the optical properties of the plasmonic structures was evaluated. The obtained results show that the silica coating enables surface protection of the plasmonic structures, preserving their stability for an extended time and inducing a suitable reduction of the regeneration time of the chip.

Optical Sensitivity Gain in Silica-Coated Plasmonic Nanostructures.

Ultrathin films of silica realized by sol-gel synthesis and dip-coating techniques were successfully applied to predefined metal/polymer plasmonic nanostructures to spectrally tune their resonance modes and to increase their sensitivity to local refractive index changes. Plasmon resonance spectral shifts up to 100 nm with slope efficiencies of ∼8 nm/nm for increasing layer thickness were attained. In the ultrathin layer regime (<10 nm), which could be reached by suitable dilution of the silica precursors and optimization of the deposition speed, the sensitivity of the main plasmonic resonance to refractive index changes in aqueous solution could be increased by over 50% with respect to the bare plasmonic chip. Numerical simulations supported experimental data and unveiled the mechanism responsible for the optical sensitivity gain, proving an effective tool in the design of high-performance plasmonic sensors.

The bowel cleansing for colonoscopy. A randomized trial comparing three methods.

INTRODUCTION: Colonoscopy is the procedure of choice for the detection and ablation of small lesions o the colonic mucosa. A proper bowel cleansing is mandatory. So far several regimens have been proposed but rather none has shown a clear-cut advantage over the others. Aim of this study was to compare cleansing ability and patients' compliance of three oral regimens. PATIENTS AND METHODS: Two-hundred and seventy-three patients were block randomised into three groups. Group A (92 patients) received tablets containing senna 12 mg and Magnesium Sulphate 15 mg the day before colonoscopy. Group B (98 patients) received a Polyethylene Glycol-based solution of two litres plus 4 tablets of Bisacodyl the day before the exam. Group C (83 patients) received Sodium Phosphate 40 milliliters the day before and the day of colonoscopy. Results of 265 patients were available for the analysis. Eight patients were excluded because inability to follow prescription. The lower incidence of constipation in group C was not significant. The other parameters were homogeneously distributed in the three groups. RESULTS: The 79 patients of the group C achieved a better bowel cleansing as compared with the 90 of group A (p = 0.0003) and the 96 of group B (p = 0.034). Constipated patients had a significantly better cleansing with Sodium Phosphate preparation compared with senna plus Magnesium Sulphate (p = 0.017), but not significantly better compared with Golytely solution. Compliance and rate of total colonoscopy performed were not statistically different in the three groups. CONCLUSIONS: Sodium Phosphate solution gave better bowel preparation, with the same compliance, than either senna or Polyethylene solution. In constipated patients Sodium Phosphate showed good efficacy resulting in good cleansing rates similar to that of non-constipated patients. The poor results obtained by Polyethylene were related to the little amount of solution taken even if associated to Bisacodyl.

Imaging of early postoperative complications after polypropylene mesh repair of inguinal hernia.

PURPOSE: We report our experience with the use of US and CT in postoperative complications of inguinal hernioplasty using a prosthetic polypropylene mesh. MATERIALS AND METHODS: This study was divided into two parts. In the first we evaluated the in-vitro sonographic and CT appearance of a fragment of prosthetic mesh. In the second, we retrospectively reviewed the imaging findings in 31 patients (aged 42 to 75 years) examined after inguinal hernia repair between December 2000 and December 2002. Seventeen hernias had been repaired with a laparoscopic approach, and the others with the anterior tension-free technique proposed by Lichtenstein (12 cases) and Trabucco (2 cases). Sonography was performed to assess suspected complications between the second and the fourth postoperative day. Both high-resolution 7.5-10 MHz linear transducers and a 3.5 MHz convex probe were employed to ensure complete evaluation of superficial and deep structures. Eight obese patients also underwent CT for confirmation of the US results. RESULTS: At sonography the prosthetic mesh appeared as a linear hyperechoic image measuring about 2 mm in thickness, with posterior acoustic shadow and a finely irregular surface. Only one of the 17 patients examined after laparoscopic inguinal hernioplasty had a seroma; in the other 14 repaired with the anterior tension-free technique we identified 2 abscesses, 3 seromas, 2 "foldings" of the prosthetic mesh, and 2 mesh displacements with associated recurrence of hernia. CT confirmed the US results as to the presence of fluid collections, and visualised the prosthetic mesh in only 2/8 cases. CONCLUSIONS: Sonography is a useful means of assessing postoperative changes in laparoscopic and in anterior tension-free hernia repair. It can differentiate these complications from recurrences of hernia. Colour-Doppler US can also correctly detect normal blood flow of the testes. Sonography is the only technique that can easily demonstrate the prosthetic mesh in the abdominal wall.