Marianna Pannico

Time-resolved Fourier transform infrared spectroscopy, gravimetry, and thermodynamic modeling for a molecular level description of water sorption in poly(ε-caprolactone).

Sorption of water in poly(ε-caprolactone) (PCL), with specific focus on the hydrogen-bonding interactions, has been analyzed by combining ab initio calculations, macroscopic thermodynamics modeling, and relevant features emerging from spectroscopic and gravimetric measurements. Fourier transform infrared (FTIR) data, analyzed by difference spectroscopy, two-dimensional correlation spectroscopy, and least-squares curve-fitting analysis associated with gravimetric determination of water sorption isotherm provided information on the systems behavior and on the molecular interactions established between the polymer and the penetrant. A consistent physical picture emerged pointing to the presence of two spectroscopically discernible water species (first-shell and second-shell layers) that have been quantified. Water molecules are present in the form of dimers within the polymer equilibrated with water vapor up to a relative humidity of 0.65. At higher humidities, clustering of water sorbed molecules starts to take place. The multicomponent ν(OH) band representative of absorbed water has been interpreted with the aid of ab initio calculations performed on suitably chosen model systems. The outcomes of spectroscopic analyses were interpreted at a macroscopic level by modeling the thermodynamics of water sorption in PCL based on a nonrandom compressible lattice theory accounting for hydrogen-bonding (HB) interactions. Starting from the fitting of the gravimetric sorption isotherm, the model provided quantitative estimates for the amount of self- and cross-HBs which compare favorably with the FTIR results.

Skin transport of PEGylated poly(ε-caprolactone) nanoparticles assisted by (2-hydroxypropyl)-β-cyclodextrin

The aim of this work was to investigate the potential of small nanoparticles (NPs) made of a poly(ethylene glycol)-poly(ε-caprolactone)-amphiphilic diblock copolymer (PEG-b-PCL, PEG=2kDa and PCL=4.2kDa) as drug carrier system through the skin. Zinc(II) phthalocyanine (ZnPc), selected as lipophilic and fluorescent model molecule, was loaded inside NPs by a melting/sonication procedure. Loaded NPs with a hydrodynamic diameter around 60nm, a slightly negative zeta potential and a ZnPc entrapment dependent on polymer/ZnPc ratio were obtained. Spectroscopic investigations evidenced that ZnPc was entrapped in monomeric form maintaining its emission properties. The transport of ZnPc through porcine ear skin was evaluated on Franz-type diffusion cells after treatment with different vehicles (water or PEG 0.4kDa) containing free ZnPc or ZnPc-loaded NPs without and with (2-hydroxypropyl)-β-cyclodextrin (HPβCD) as permeation enhancer. Independently of the sample tested, ZnPc was transported in the skin without reaching receptor compartment. On the other hand, ZnPc was found in the skin in large amount and also in the viable epidermis when delivered through NPs associated with HPβCD, especially in conditions limiting water evaporation. Fluorescence images of skin samples after 24h of permeation were in line with ZnPc dosage in the skin and demonstrated the ability of NPs covalently tagged with rhodamine to penetrate the skin and to locate in the intercellular spaces. Insight into skin chemical properties upon application of NPs by confocal Raman spectroscopy demonstrated that HPβCD caused an alteration of water profile in the skin, highly reducing the degree of hydration at stratum corneum/viable epidermis interface which can promote NP transport. Taken together, these results highlight PEG-b-PCL NPs coupled with HPβCD as a novel vehicle for the skin delivery of highly lipophilic compounds paving the way to several applications.

Electroless Gold-Modified Diatoms as Surface-Enhanced Raman Scattering Supports.

Porous biosilica from diatom frustules is well known for its peculiar optical and mechanical properties. In this work, gold-coated diatom frustules are used as low-cost, ready available, functional support for surface-enhanced Raman scattering. Due to the morphology of the nanostructured surface and the smoothness of gold deposition via an electroless process, an enhancement factor for the p-mercaptoaniline Raman signal of the order of 105 is obtained.

Octupolar Metastructures for a Highly Sensitive, Rapid, and Reproducible Phage-Based Detection of Bacterial Pathogens by Surface-Enhanced Raman Scattering

The development of fast and ultrasensitive methods to detect bacterial pathogens at low concentrations is of high relevance for human and animal health care and diagnostics. In this context, surface-enhanced Raman scattering (SERS) offers the promise of a simplified, rapid, and high-sensitive detection of biomolecular interactions with several advantages over previous assay methodologies. In this work, we have conceived reproducible SERS nanosensors based on tailored multilayer octupolar nanostructures which can combine high enhancement factor and remarkable molecular selectivity. We show that coating novel multilayer octupolar metastructures with proper self-assembled monolayer (SAM) and immobilized phages can provide label-free analysis of pathogenic bacteria via SERS leading to a giant increase in SERS enhancement. The strong relative intensity changes of about 2100% at the maximum scattered SERS wavelength, induced by the Brucella bacterium captured, demonstrate the performance advantages of the bacteriophage sensing scheme. We performed measurements at the single-cell level thus allowing fast identification in less than an hour without any demanding sample preparation process. Our results based on designing well-controlled octupolar coupling platforms open up new opportunities toward the use of bacteriophages as recognition elements for the creation of SERS-based multifunctional biochips for rapid culture and label-free detection of bacteria.

Plasmonic octagonal quasicrystals for surface enhanced Raman sensing

Abstract Surface enhanced Raman scattering (SERS) on eight-fold quasicrystal arrays with precisely controlled size and spacing fabricated via electron beam lithography was investigated. This SERS substrate shows high efficiency at 785 nm excitation in the detection of p-mercaptoaniline (pMA), and a SERS enhancement factor (EF ) of 107 is achieved. SERS behavior of the realized engineered SERS substrate indicates that the present engineered metamaterial may be used as an ultrasensitive Raman probe and could open up interesting new opportunities in biosensing.

Diffusion and molecular interactions in a methanol/polyimide system probed by coupling time-resolved FTIR spectroscopy with gravimetric measurements.

In this contribution the diffusion of methanol in a commercial polyimide (PMDA-ODA) is studied by coupling gravimetric measurements with in-situ, time-resolved FTIR spectroscopy. The spectroscopic data have been treated with two complementary techniques, i.e., difference spectroscopy (DS) and least-squares curve fitting (LSCF). These approaches provided information about the overall diffusivity, the nature of the molecular interactions among the system components and the dynamics of the various molecular species. Additional spectroscopic measurements on thin film samples (about 2 μm) allowed us to identify the interaction site on the polymer backbone and to propose likely structures for the H-bonding aggregates. Molar absorptivity values from a previous literature report allowed us to estimate the population of first-shell and second-shell layers of methanol in the polymer matrix. In terms of diffusion kinetics, the gravimetric and spectroscopic estimates of the diffusion coefficients were found to be in good agreement with each other and with previous literature reports. A Fickian behavior was observed throughout, with diffusivity values markedly affected by the total concentration of sorbed methanol.

Hyperspectral Raman imaging of human prostatic cells: An attempt to differentiate normal and malignant cell lines by univariate and multivariate data analysis

Hyperspectral Raman images of human prostatic cells have been collected and analysed with several approaches to reveal differences among normal and tumor cell lines. The objective of the study was to test the potential of different chemometric methods in providing diagnostic responses. We focused our analysis on the ν(CH) region (2800-3100cm-1) owing to its optimal Signal-to-Noise ratio and because the main differences between the spectra of the two cell lines were observed in this frequency range. Multivariate analysis identified two principal components, which were positively recognized as due to the protein and the lipid fractions, respectively. The tumor cells exhibited a modified distribution of the cytoplasmatic lipid fraction (mainly localized alongside the cell boundary) which may result very useful for a preliminary screening. Principal Component analysis was found to provide high contrast and to be well suited for image-processing purposes. Self-Modelling Curve Resolution made available meaningful spectra and relative-concentration values; it revealed a 97% increase of the lipid fraction in the tumor cell with respect to the control. Finally, a univariate approach confirmed significant and reproducible differences between normal and tumor cells.

Engineered plasmonic Thue-Morse nanostructures for LSPR detection of the pesticide Thiram

Abstract In this paper, the size- and shape-dependent spectral characteristics of plasmonic nanostructures based on the Thue-Morse (ThMo) sequence are investigated in theory and experiment. We designed, fabricated, and characterized nine different Au nanopillars (NPs) lattices to evaluate their use as nanosensors based on localized surface plasmon resonances (LSPR). The extinction spectra and the bulk refractive index sensitivity (m) are compared to three selected shapes of the NPs (square, circular, and triangular) with different minimum interparticle distance. The maximum m of 275 nm/RIU is obtained for a ThMo pattern with square NPs. Finally, a detection limit of 260 pM (62 pg/ml) of Thiram pesticide has been achieved using an LSPR nanosensor based on an optimized ThMo pattern with triangular NPs employing a phase-sensitive setup to increase the figure-of-merit (FOM) of the sensor.

Raman Line Imaging of Poly(ε-caprolactone)/Carbon Dioxide Solutions at High Pressures: A Combined Experimental and Computational Study for Interpreting Intermolecular Interactions and Free-Volume Effects

In the present study, a Raman line-imaging setup was employed to monitor in situ the CO2 sorption at elevated pressures (from 0.62 to 7.10 MPa) in molten PCL. The method allowed the quantitative measurement of gas concentration in both the time-resolved and the space-resolved modes. The combined experimental and theoretical approach allowed a molecular level characterization of the system. The dissolved CO2 was found to occupy a volume essentially coincident with its van der Waals volume and the estimated partial molar volume of the probe did not change with pressure. Lewis acid-Lewis base interactions with the PCL carbonyls was confirmed to be the main interaction mechanism. The geometry of the supramolecular complex and the preferential interaction site were controlled more by steric than electronic effects. On the basis of the indications emerging from Raman spectroscopy, an equation of state thermodynamic model for the PCL-CO2 system, based upon a compressible lattice fluid theory endowed with specific interactions, has been tailored to account for the interaction types detected spectroscopically. The predictions of the thermodynamic model in terms of molar volume of solution have been compared with available volumetric measurements while predictions for CO2 partial molar volume have been compared with the values estimated on the basis of Raman spectroscopy.

Surface-enhanced Raman spectroscopy on engineered plasmonic metamaterials for “label free” biosensing

The last decade has been characterized by artificial electromagnetic (EM) materials, including photonic crystals (PCs) and photonic quasi-crystals (PQCs), making these very attractive given that there are new possibilities to control the EM field in innovative way. Quasiperiodic crystals (QCs) are a new class of materials that have fascinating optical properties lying somewhere between those of disordered and period structures. With the use of PCs and PQCs, it is possible to synthesize novel artificial structures characterized by selective EM responses, which, in turn, undergo significant frequency shifts, in presence of biological material. In the present work we studied artificial EM nanomaterials to develop innovative plasmonic nanobiosensors based on Surface Enhanced Raman Scattering (SERS) substrates and working in the visible and NIR frequency bands. A fabricated gold PQC in a Thue Morse arrangement is proposed for the engineering of reproducible SERS substrates. Structural characterization of this surface is performed by SEM and AFM. Optical properties of this plasmonic nanostructure are evaluated via UV/ Vis absorption spectroscopy and surface–enhanced Raman spectroscopy (SERS). Using a molecular monolayer of pMA (p-mercaptoaniline) as a Raman reporter, we show that a high value of SERS enhancement factor (measured up to 1.4 x 107) can be achieved in a properly optimized photonic structure, in good agreement with FDTD calculations. SERS enhancement factor is dependent on the plasmon absorption wavelength and laser wavelength used in these experiments.