Valter SERGO | Università degli Studi di Trieste (original) (raw)

Papers by Valter SERGO

Colloids and Surfaces B: Biointerfaces, 2010

Hybrid bilayer lipid membranes (HBMs) were built on roughened silver electrodes exhibiting surfac... more Hybrid bilayer lipid membranes (HBMs) were built on roughened silver electrodes exhibiting surfaceenhanced Raman scattering (SERS) activity. The HBM consisted of a first layer of octadecanethiol (ODT) directly bound to the electrode surface, on which a second layer of 1,2-diphytanoyl-snglycero-3-phosphocholine (DPhPC) was obtained by self-assembled phospholipid vesicle fusion. The electrochemical properties of the HBM were investigated in situ by cyclic voltammetry (CV), AC voltammetry and electrochemical impedance spectroscopy (EIS). The results indicate that our HBMs are well-formed, and their insulating properties are comparable to those observed for HBM supported by smooth metal substrates. The interaction between the bilayer and the human enzyme cytochrome P450 2D6 (CYP2D6) was investigated. Surface-enhanced resonance Raman scattering (SERRS) measurements in combination with AC and EIS, performed on the same electrode sample, proved that the CYP2D6 is immobilized on the HBM without evident alterations of its active site and without significant perturbations of the bilayer architecture. This study yields novel insights into the properties of HBMs built on roughened surfaces, providing in situ electrochemical characterization of a substrate which is suitable for studying peripheral membrane proteins with SERRS spectroscopy.

The stress dependence of the Raman bands of β-silicon nitride, β-SiâNâ, has been investigated. ... more The stress dependence of the Raman bands of β-silicon nitride, β-SiâNâ, has been investigated. In the stress range examined (from -200 to +200 MPa), low-frequency shift bands (namely the 183, 205, and 226 cm⁻¹ lines) do not show any frequency change with the stress, whereas the high-frequency shift bands (862, 925, and 936 cm⁻¹) have been found to have a linear stress dependence. The pertinent piezo-spectroscopic coefficients have been determined and are found to depend strongly on the additives used to promote densification presumably being taken in solid solution into the β-SiâNâ phase.

ABSTRACT The stress dependence of the Raman bands of silicon nitride (β-Si3N4) have been investig... more ABSTRACT The stress dependence of the Raman bands of silicon nitride (β-Si3N4) have been investigated and applied to indentation experiments. Seven high-frequency bands have been found to have linear and negative stress dependencies. On the other hand, low frequency bands (namely 183, 205 and 226 cm-1 bands) showed small positive correlations with the stress. The piezospectroscopic (PS) coefficients of all the observed Raman bands have been determined. As an application, one of the PS coefficients has been used to determine the stress distribution around a triangular indentation.

ABSTRACT The effect of systematic modifications in the chemistry of the phase-boundary film on th... more ABSTRACT The effect of systematic modifications in the chemistry of the phase-boundary film on the macroscopic mechanical properties of Si3N4-matrix composites was investigated. Model composite materials, containing SiC or WC platelets, were prepared and only the bulk anion composition of the glassy-SiO2 intergranular phase was varied by adding increasing amounts of fluorine to the material. Detailed material characterizations by high-resolution electron microscopy (HREM) and Raman spectroscopy on both undoped and F-doped composites allowed to derive a structural model of the phase-boundary film as well as to evaluate the average microscopic stresses acting on it. In addition, high-temperature internal friction measurements provided an estimate of the grain-boundary relaxation temperature as a function of the F content. Noticeable variations of both elastic modulus and fracture energy of the composite were detected upon F addition, which were related to a spontaneous process of phase-boundary microcracking upon cooling. A threshold of the F-content was found for microcrack formation and its existence is theoretically explained according to a percolation process of non-bridged SiO4-tetrahedra, which arises from the incorporation of F into the intergranular film network.

Analytical and Bioanalytical Chemistry, 2015

In this contribution, we investigated whether surface-enhanced Raman scattering (SERS) of serum c... more In this contribution, we investigated whether surface-enhanced Raman scattering (SERS) of serum can be a candidate method for detecting "luminal A" breast cancer (BC) at different stages. We selected three groups of participants aged over 50 years: 20 healthy women, 20 women with early localized small BC, and 20 women affected by BC with lymph node involvement. SERS revealed clear spectral differences between these three groups. A predictive model using principal component analysis (PCA) and linear discriminant analysis (LDA) was developed based on spectral data, and its performance was estimated with cross-validation. PCA-LDA of SERS spectra could distinguish healthy from BC subjects (sensitivity, 92 %; specificity, 85 %), as well as subjects with BC at different stages, with a promising diagnostic performance (sensitivity and specificity, ≥80 %; overall accuracy, 84 %). Our data suggest that SERS spectroscopy of serum, combined with multivariate data analysis, represents a minimally invasive, easy to use, and fast approach to discriminate healthy from BC subjects and even to distinguish BC at different clinical stages.

MRS Proceedings, 2009

The role of thermal annealing and of CdCl 2 as a main source of electrically active but vaporizab... more The role of thermal annealing and of CdCl 2 as a main source of electrically active but vaporizable chlorine doping in chemical bath deposited CdS thin films is studied. The films were deposited on glass substrates from aqueous solution of either CdCl 2 , NH 4 Cl, NH 4 OH, and thiourea, or CdSO 4 , (NH 4 ) 2 SO 4 , NH 4 OH, and thiourea. Films deposited in the presence of CdCl 2 and annealed in H 2 atmosphere at 310 and 420 °C show a resistivity lower than 10 Ω·cm, one order of magnitude less than for identically annealed films deposited in absence of CdCl 2 . Annealing at 420 °C in closed ampoules, where a counter pressure of CdCl 2 builds up, leads to a lower resistivity on the order of 10 -1 Ω·cm, confirming the key role of chlorine on the electronic properties. However, further characterization via photoluminescence raises new questions about chlorine-related defects and their role in the mechanisms that govern film resistivity.

Analytical and Bioanalytical Chemistry, 2015

In clinical practice there is a trend to obtain diagnostic information minimizing the invasivenes... more In clinical practice there is a trend to obtain diagnostic information minimizing the invasiveness of the tests and the pain for the patients. In this sense, tests based on the interaction of light with readily available biofluids such as blood, urine or saliva are highly desirable. In this review we examine the state of art on the use of Surface Enhanced Raman Spectroscopy (SERS) to investigate biofluids, focusing on diagnostic applications. To start with, a critical evaluation of the experimental aspects involved in the collection of SERS spectra is presented; different substrate types are introduced with a clear distinction between colloidal and non-colloidal metal nanostructures. Then, the role of the excitation wavelength is discussed, along with anomalous bands and artifacts which might affect SERS spectra of biofluids. The central part of the review examines the literature available on the SERS spectra of blood, plasma, serum, urine, saliva, tears and semen. Finally, diagnostic applications are critically discussed in light of the published evidence; this part clearly shows that SERS of biofluids holds its most promising asset as a rapid, cheap, non-invasive tool for mass screening for cancer diseases.

Nanoscale Imaging, Sensing, and Actuation for Biomedical Applications VI, 2009

Mechanical forces and living cells are closely related, in particular in connections, named Focal... more Mechanical forces and living cells are closely related, in particular in connections, named Focal Adhesions (FAs), between cells and extracellular matrix. FAs are mechanosensors and regulate physiological processes. The aim of this contribution is to explore the possibility of performing micrometric and submicrometric protein pattern in order to study FAs on different materials. Typical substrates for microelectromechanical systems (MEMS) are tested and the results are reported. A laser is used to produce a pattern of extracellular matrix proteins, like fibronectin. A new use of a Raman microprobe is described. Cells arrange in a regular shape, following the geometry of the pattern. Protein spots last for more than 24 hours. It is very important to have a complete control on FAs and the technique proposed is a suitable solution.

Colloids and surfaces. B, Biointerfaces, 2015

The development of nanotechnological devices and their clinical application in medicine has becom... more The development of nanotechnological devices and their clinical application in medicine has become increasingly important, especially in the context of targeted and personalized therapy. This is particularly important in cancer therapy, where antitumor drugs are highly cytotoxic and often exert their therapeutic effect at concentrations close to systemic toxicity. In the last years a growing number of studies has started to report the use of plasmonic nanoprobes in the field of theranostics, broadening the application of vibrational spectroscopies like Raman scattering and surface enhanced Raman scattering (SERS) in biomedicine. The present work aims to identify and characterize the vibrational profiles of a widely used anticancer drug, irinotecan (CPT-11). With a rational approach, SERS experiments have been performed on this analyte employing both Au and Ag colloids, starting from simple aqueous solutions up to albumin mixtures. A major step forward for drug detection in albumin s...

IFMBE Proceedings, 2009

The aim of this contribution is to demonstrate the possibility of performing macrometric and micr... more The aim of this contribution is to demonstrate the possibility of performing macrometric and micrometric protein patterns in order to study focal adhesions of human cells on different materials. A laser is used to produce a pattern of extracellular matrix protein (e. g. fibronectin) as in photolithographic techniques. Maskless lithography is performed, using a common instruments such as Raman spectroscopy

Journal of applied biomaterials & biomechanics : JABB

Bioactive glasses in the Na2 O-K2 O-MgO-CaO-B2 O3 -P2 O5 -SiO2 system characterized by an unusual... more Bioactive glasses in the Na2 O-K2 O-MgO-CaO-B2 O3 -P2 O5 -SiO2 system characterized by an unusually large working range were used for the production of fiber porous scaffolds. In vitro tests were carried out by immersing the scaffolds in simulated body fluid (SBF) solution; soaking time and glass composition effects on the degradation of the material are the principal subject of this investigation. Raman spectroscopy and scanning electron microscopy (SEM) were used as the main investigative methods. The study demonstrates the importance of the network modifiers and, in particular, of the amount of alkaline and al-kaline earths in the different stages of the material degradation and in the development of the hydroxyl-carbonate-apatite (HCA) layer.

Key Engineering Materials, 2004

... The powders were added separately to the two components (isocyanate and polyalcohol in volume... more ... The powders were added separately to the two components (isocyanate and polyalcohol in volumetric ratio 1:1) of commercially available, closed cell polyurethane (ESPAK) in order to have different volumetric ratios (11, 16 and 22% vol) of the powder with respect to the total ...

Volume 2: Aircraft Engine; Ceramics; Coal, Biomass and Alternative Fuels; Controls, Diagnostics and Instrumentation; Environmental and Regulatory Affairs, 2006

Thermally Grown Oxide (TGO) layer develops and grows subjected to very high compressive residual ... more Thermally Grown Oxide (TGO) layer develops and grows subjected to very high compressive residual stresses at the interface between metallic bond coat and EB-PVD thermal barrier coating. A significant decrease of such stress level is a useful indicator of incipient local ...

Materials Science Forum, 1998

Spectroscopy, 2006

... gynecological screening for cervical dysplasia and malignancies. The initial work of Wong and... more ... gynecological screening for cervical dysplasia and malignancies. The initial work of Wong and coworkers on FTIR spectroscopy of cervical cancer started the field of “FTIR diagnostics” [162]. Since then most FTIR studies have ...

Key Engineering Materials, 1991

Analytical and Bioanalytical Chemistry, 2014

Hierarchical cluster analysis (HCA) is extensively used for the analysis of hyperspectral data. I... more Hierarchical cluster analysis (HCA) is extensively used for the analysis of hyperspectral data. In this work, hyperspectral data sets obtained from Raman maps were analyzed using an alternative mode of cluster analysis, clustering "images" instead of spectra, under the assumption that images showing similar spatial distributions are related to the same chemical species. Such an approach was tested with two Raman maps: one simple "test map" of micro-crystals of four different compounds for a proof of principle, and a map of a biological tissue (i.e. cartilage) as an example of chemically complex sample. In both cases, the "image-clustering" approach gave similar results as the traditional HCA, but at lower computational effort. The alternative approach proved to be particularly helpful in cases, as for the cartilage tissue, where concentration gradients of chemical composition are present. Moreover, with this approach yielded information about correlation between bands in the average spectrum, making band assignment and spectral interpretation easier.

Langmuir, 2012

Positively charged nanoparticles to be used as substrates for surface-enhanced Raman scattering (... more Positively charged nanoparticles to be used as substrates for surface-enhanced Raman scattering (SERS) were prepared by coating citrate-reduced silver nanoparticles with the cationic polymer poly-L-lysine. The average diameter of the coated nanoparticles is 75 nm, and their zeta potential is +62.3 ± 1.7 mV. UV-vis spectrophotometry and dynamic light scattering measurements show that no aggregation occurs during the coating process. As an example of their application, the soobtained positively charged coated particles were employed to detect nanomolar concentrations of the anionic chromophore bilirubin using SERS. Because of their opposite charge, bilirubin molecules interact with the coated nanoparticles, allowing SERS detection. The SERS intensity increases linearly with concentration in a range from 10 nM to 200 nM, allowing quantitative analysis of bilirubin aqueous solutions.

Wear, 2005

The outstanding performances of the Al 2 O 3 cutting tools in terms of potential cutting speed ca... more The outstanding performances of the Al 2 O 3 cutting tools in terms of potential cutting speed can lead to substantial economies in the machining of metallic materials.

Thermochimica Acta, 1988

ABSTRACT The redox behaviour of ceria zirconia alloy (50 mol %) has been investigated by thermoan... more ABSTRACT The redox behaviour of ceria zirconia alloy (50 mol %) has been investigated by thermoanalytical methods under controlled atmospheres (air, oxygen and argon with 5% hydrogen). The supposed non-stoichiometry (CeOx-ZrO2, x being a function of oxygen pressure and temperature) is proved by weight changes which are accompanied by volume variations investigated via thermodilatoiiietry. These phenomena are attributed to the redox equilibrium of Ce(+3)-Ce(+4) associated with oxygen vacancies. The reduced material is characterized by a cubic unit cell, larger than that previously reported for the tetragonal structure of the same oxidized sample.

Colloids and Surfaces B: Biointerfaces, 2010

Hybrid bilayer lipid membranes (HBMs) were built on roughened silver electrodes exhibiting surfac... more Hybrid bilayer lipid membranes (HBMs) were built on roughened silver electrodes exhibiting surfaceenhanced Raman scattering (SERS) activity. The HBM consisted of a first layer of octadecanethiol (ODT) directly bound to the electrode surface, on which a second layer of 1,2-diphytanoyl-snglycero-3-phosphocholine (DPhPC) was obtained by self-assembled phospholipid vesicle fusion. The electrochemical properties of the HBM were investigated in situ by cyclic voltammetry (CV), AC voltammetry and electrochemical impedance spectroscopy (EIS). The results indicate that our HBMs are well-formed, and their insulating properties are comparable to those observed for HBM supported by smooth metal substrates. The interaction between the bilayer and the human enzyme cytochrome P450 2D6 (CYP2D6) was investigated. Surface-enhanced resonance Raman scattering (SERRS) measurements in combination with AC and EIS, performed on the same electrode sample, proved that the CYP2D6 is immobilized on the HBM without evident alterations of its active site and without significant perturbations of the bilayer architecture. This study yields novel insights into the properties of HBMs built on roughened surfaces, providing in situ electrochemical characterization of a substrate which is suitable for studying peripheral membrane proteins with SERRS spectroscopy.

The stress dependence of the Raman bands of β-silicon nitride, β-SiâNâ, has been investigated. ... more The stress dependence of the Raman bands of β-silicon nitride, β-SiâNâ, has been investigated. In the stress range examined (from -200 to +200 MPa), low-frequency shift bands (namely the 183, 205, and 226 cm⁻¹ lines) do not show any frequency change with the stress, whereas the high-frequency shift bands (862, 925, and 936 cm⁻¹) have been found to have a linear stress dependence. The pertinent piezo-spectroscopic coefficients have been determined and are found to depend strongly on the additives used to promote densification presumably being taken in solid solution into the β-SiâNâ phase.

ABSTRACT The stress dependence of the Raman bands of silicon nitride (β-Si3N4) have been investig... more ABSTRACT The stress dependence of the Raman bands of silicon nitride (β-Si3N4) have been investigated and applied to indentation experiments. Seven high-frequency bands have been found to have linear and negative stress dependencies. On the other hand, low frequency bands (namely 183, 205 and 226 cm-1 bands) showed small positive correlations with the stress. The piezospectroscopic (PS) coefficients of all the observed Raman bands have been determined. As an application, one of the PS coefficients has been used to determine the stress distribution around a triangular indentation.

ABSTRACT The effect of systematic modifications in the chemistry of the phase-boundary film on th... more ABSTRACT The effect of systematic modifications in the chemistry of the phase-boundary film on the macroscopic mechanical properties of Si3N4-matrix composites was investigated. Model composite materials, containing SiC or WC platelets, were prepared and only the bulk anion composition of the glassy-SiO2 intergranular phase was varied by adding increasing amounts of fluorine to the material. Detailed material characterizations by high-resolution electron microscopy (HREM) and Raman spectroscopy on both undoped and F-doped composites allowed to derive a structural model of the phase-boundary film as well as to evaluate the average microscopic stresses acting on it. In addition, high-temperature internal friction measurements provided an estimate of the grain-boundary relaxation temperature as a function of the F content. Noticeable variations of both elastic modulus and fracture energy of the composite were detected upon F addition, which were related to a spontaneous process of phase-boundary microcracking upon cooling. A threshold of the F-content was found for microcrack formation and its existence is theoretically explained according to a percolation process of non-bridged SiO4-tetrahedra, which arises from the incorporation of F into the intergranular film network.

Analytical and Bioanalytical Chemistry, 2015

In this contribution, we investigated whether surface-enhanced Raman scattering (SERS) of serum c... more In this contribution, we investigated whether surface-enhanced Raman scattering (SERS) of serum can be a candidate method for detecting "luminal A" breast cancer (BC) at different stages. We selected three groups of participants aged over 50 years: 20 healthy women, 20 women with early localized small BC, and 20 women affected by BC with lymph node involvement. SERS revealed clear spectral differences between these three groups. A predictive model using principal component analysis (PCA) and linear discriminant analysis (LDA) was developed based on spectral data, and its performance was estimated with cross-validation. PCA-LDA of SERS spectra could distinguish healthy from BC subjects (sensitivity, 92 %; specificity, 85 %), as well as subjects with BC at different stages, with a promising diagnostic performance (sensitivity and specificity, ≥80 %; overall accuracy, 84 %). Our data suggest that SERS spectroscopy of serum, combined with multivariate data analysis, represents a minimally invasive, easy to use, and fast approach to discriminate healthy from BC subjects and even to distinguish BC at different clinical stages.

MRS Proceedings, 2009

The role of thermal annealing and of CdCl 2 as a main source of electrically active but vaporizab... more The role of thermal annealing and of CdCl 2 as a main source of electrically active but vaporizable chlorine doping in chemical bath deposited CdS thin films is studied. The films were deposited on glass substrates from aqueous solution of either CdCl 2 , NH 4 Cl, NH 4 OH, and thiourea, or CdSO 4 , (NH 4 ) 2 SO 4 , NH 4 OH, and thiourea. Films deposited in the presence of CdCl 2 and annealed in H 2 atmosphere at 310 and 420 °C show a resistivity lower than 10 Ω·cm, one order of magnitude less than for identically annealed films deposited in absence of CdCl 2 . Annealing at 420 °C in closed ampoules, where a counter pressure of CdCl 2 builds up, leads to a lower resistivity on the order of 10 -1 Ω·cm, confirming the key role of chlorine on the electronic properties. However, further characterization via photoluminescence raises new questions about chlorine-related defects and their role in the mechanisms that govern film resistivity.

Analytical and Bioanalytical Chemistry, 2015

In clinical practice there is a trend to obtain diagnostic information minimizing the invasivenes... more In clinical practice there is a trend to obtain diagnostic information minimizing the invasiveness of the tests and the pain for the patients. In this sense, tests based on the interaction of light with readily available biofluids such as blood, urine or saliva are highly desirable. In this review we examine the state of art on the use of Surface Enhanced Raman Spectroscopy (SERS) to investigate biofluids, focusing on diagnostic applications. To start with, a critical evaluation of the experimental aspects involved in the collection of SERS spectra is presented; different substrate types are introduced with a clear distinction between colloidal and non-colloidal metal nanostructures. Then, the role of the excitation wavelength is discussed, along with anomalous bands and artifacts which might affect SERS spectra of biofluids. The central part of the review examines the literature available on the SERS spectra of blood, plasma, serum, urine, saliva, tears and semen. Finally, diagnostic applications are critically discussed in light of the published evidence; this part clearly shows that SERS of biofluids holds its most promising asset as a rapid, cheap, non-invasive tool for mass screening for cancer diseases.

Nanoscale Imaging, Sensing, and Actuation for Biomedical Applications VI, 2009

Mechanical forces and living cells are closely related, in particular in connections, named Focal... more Mechanical forces and living cells are closely related, in particular in connections, named Focal Adhesions (FAs), between cells and extracellular matrix. FAs are mechanosensors and regulate physiological processes. The aim of this contribution is to explore the possibility of performing micrometric and submicrometric protein pattern in order to study FAs on different materials. Typical substrates for microelectromechanical systems (MEMS) are tested and the results are reported. A laser is used to produce a pattern of extracellular matrix proteins, like fibronectin. A new use of a Raman microprobe is described. Cells arrange in a regular shape, following the geometry of the pattern. Protein spots last for more than 24 hours. It is very important to have a complete control on FAs and the technique proposed is a suitable solution.

Colloids and surfaces. B, Biointerfaces, 2015

The development of nanotechnological devices and their clinical application in medicine has becom... more The development of nanotechnological devices and their clinical application in medicine has become increasingly important, especially in the context of targeted and personalized therapy. This is particularly important in cancer therapy, where antitumor drugs are highly cytotoxic and often exert their therapeutic effect at concentrations close to systemic toxicity. In the last years a growing number of studies has started to report the use of plasmonic nanoprobes in the field of theranostics, broadening the application of vibrational spectroscopies like Raman scattering and surface enhanced Raman scattering (SERS) in biomedicine. The present work aims to identify and characterize the vibrational profiles of a widely used anticancer drug, irinotecan (CPT-11). With a rational approach, SERS experiments have been performed on this analyte employing both Au and Ag colloids, starting from simple aqueous solutions up to albumin mixtures. A major step forward for drug detection in albumin s...

IFMBE Proceedings, 2009

The aim of this contribution is to demonstrate the possibility of performing macrometric and micr... more The aim of this contribution is to demonstrate the possibility of performing macrometric and micrometric protein patterns in order to study focal adhesions of human cells on different materials. A laser is used to produce a pattern of extracellular matrix protein (e. g. fibronectin) as in photolithographic techniques. Maskless lithography is performed, using a common instruments such as Raman spectroscopy

Journal of applied biomaterials & biomechanics : JABB

Bioactive glasses in the Na2 O-K2 O-MgO-CaO-B2 O3 -P2 O5 -SiO2 system characterized by an unusual... more Bioactive glasses in the Na2 O-K2 O-MgO-CaO-B2 O3 -P2 O5 -SiO2 system characterized by an unusually large working range were used for the production of fiber porous scaffolds. In vitro tests were carried out by immersing the scaffolds in simulated body fluid (SBF) solution; soaking time and glass composition effects on the degradation of the material are the principal subject of this investigation. Raman spectroscopy and scanning electron microscopy (SEM) were used as the main investigative methods. The study demonstrates the importance of the network modifiers and, in particular, of the amount of alkaline and al-kaline earths in the different stages of the material degradation and in the development of the hydroxyl-carbonate-apatite (HCA) layer.

Key Engineering Materials, 2004

... The powders were added separately to the two components (isocyanate and polyalcohol in volume... more ... The powders were added separately to the two components (isocyanate and polyalcohol in volumetric ratio 1:1) of commercially available, closed cell polyurethane (ESPAK) in order to have different volumetric ratios (11, 16 and 22% vol) of the powder with respect to the total ...

Volume 2: Aircraft Engine; Ceramics; Coal, Biomass and Alternative Fuels; Controls, Diagnostics and Instrumentation; Environmental and Regulatory Affairs, 2006

Thermally Grown Oxide (TGO) layer develops and grows subjected to very high compressive residual ... more Thermally Grown Oxide (TGO) layer develops and grows subjected to very high compressive residual stresses at the interface between metallic bond coat and EB-PVD thermal barrier coating. A significant decrease of such stress level is a useful indicator of incipient local ...

Materials Science Forum, 1998

Spectroscopy, 2006

... gynecological screening for cervical dysplasia and malignancies. The initial work of Wong and... more ... gynecological screening for cervical dysplasia and malignancies. The initial work of Wong and coworkers on FTIR spectroscopy of cervical cancer started the field of “FTIR diagnostics” [162]. Since then most FTIR studies have ...

Key Engineering Materials, 1991

Analytical and Bioanalytical Chemistry, 2014

Hierarchical cluster analysis (HCA) is extensively used for the analysis of hyperspectral data. I... more Hierarchical cluster analysis (HCA) is extensively used for the analysis of hyperspectral data. In this work, hyperspectral data sets obtained from Raman maps were analyzed using an alternative mode of cluster analysis, clustering "images" instead of spectra, under the assumption that images showing similar spatial distributions are related to the same chemical species. Such an approach was tested with two Raman maps: one simple "test map" of micro-crystals of four different compounds for a proof of principle, and a map of a biological tissue (i.e. cartilage) as an example of chemically complex sample. In both cases, the "image-clustering" approach gave similar results as the traditional HCA, but at lower computational effort. The alternative approach proved to be particularly helpful in cases, as for the cartilage tissue, where concentration gradients of chemical composition are present. Moreover, with this approach yielded information about correlation between bands in the average spectrum, making band assignment and spectral interpretation easier.

Langmuir, 2012

Positively charged nanoparticles to be used as substrates for surface-enhanced Raman scattering (... more Positively charged nanoparticles to be used as substrates for surface-enhanced Raman scattering (SERS) were prepared by coating citrate-reduced silver nanoparticles with the cationic polymer poly-L-lysine. The average diameter of the coated nanoparticles is 75 nm, and their zeta potential is +62.3 ± 1.7 mV. UV-vis spectrophotometry and dynamic light scattering measurements show that no aggregation occurs during the coating process. As an example of their application, the soobtained positively charged coated particles were employed to detect nanomolar concentrations of the anionic chromophore bilirubin using SERS. Because of their opposite charge, bilirubin molecules interact with the coated nanoparticles, allowing SERS detection. The SERS intensity increases linearly with concentration in a range from 10 nM to 200 nM, allowing quantitative analysis of bilirubin aqueous solutions.

Wear, 2005

The outstanding performances of the Al 2 O 3 cutting tools in terms of potential cutting speed ca... more The outstanding performances of the Al 2 O 3 cutting tools in terms of potential cutting speed can lead to substantial economies in the machining of metallic materials.

Thermochimica Acta, 1988

ABSTRACT The redox behaviour of ceria zirconia alloy (50 mol %) has been investigated by thermoan... more ABSTRACT The redox behaviour of ceria zirconia alloy (50 mol %) has been investigated by thermoanalytical methods under controlled atmospheres (air, oxygen and argon with 5% hydrogen). The supposed non-stoichiometry (CeOx-ZrO2, x being a function of oxygen pressure and temperature) is proved by weight changes which are accompanied by volume variations investigated via thermodilatoiiietry. These phenomena are attributed to the redox equilibrium of Ce(+3)-Ce(+4) associated with oxygen vacancies. The reduced material is characterized by a cubic unit cell, larger than that previously reported for the tetragonal structure of the same oxidized sample.