122 research outputs found
Electrochemical and theoretical investigation of the silver nanoparticles/TiO2 interface: the “silver-ion electrode”
No full textA sandwich-like structure electrode of silver nanoparticles embedded in a titania (anatase polymorph) photoactive layer was prepared [1-2] and electrochemically characterized by cyclic voltammetry and electrochemical impedance spectroscopy.
In comparison with literature data on bare silver nanoparticles-modified electrodes [3-5], the new device features a pronounced electrocatalytic effect on the silver oxidation peak (Fig. a) together with a great increase in the current intensity. Plane-wave DFT calculations, performed using the VASP code, described the composite junction as a distorted bulk Ag structure, commensurate with the periodicity of the (101) face of the I41/amd TiO2 polymorph. The silver atoms close to the semiconductor were found to gain a partially positive charge, quickly decreasing with the distance from the TiO2 surface.
These joint theoretical and experimental evidences demonstrate that the device could be considered as a “positively charged silver nanoparticles-based electrode”, with positively ionized surface silver atoms protected by the titania layer, which holds a partial negative charge. This peculiar electrode structure shows interesting properties, among which self-cleaning ability, to be conveniently used for sensor applications.
References
[1] G. Soliveri, V. Pifferi, G. Panzarasa, S. Ardizzone, G. Cappelletti, D. Meroni, K. Sparnacci, L. Falciola, Analyst, 140, (2015), 1486 – 1494.
[2] V. Pifferi, G. Soliveri, G. Panzarasa, S. Ardizzone, G. Cappelletti, D. Meroni, L. Falciola, RSC Advances, 5, (2015), 71210 – 71214.
[3] O. S. Ivanova, F. P. Zamborini, J. Am. Chem. Soc., 132, (2010), 70–72.
[4] G. Chang, J. Zhang, M. Oyama, K. Hirao, J. Phys. Chem. B, 109, (2005), 1204-1209.
[5] S.E. Ward Jones, F.W. Campbell, R. Baron, L. Xiao, R.G. Compton, J. Phys. Chem. C, 112, (2008), 17820–17827.
Acknowledgements
This work has been supported by Fondazione Cariplo (Milano, Italy), grant no. 2014-1285. We acknowledge the CINECA and the Regione Lombardia award under the LISA initiative (grant SURGREEN) for the availability of high performance computing resources. We also thank the Chemistry Department for funding through the Development Plan of Athenaeum grant – line B1 (UNIAGI 17777)
Silver cations electroanalytical sensor: sensitivity and selectivity iIn the detection of neurotransmitters
No full textA composite electrode with a sandwich structure combining the properties of silver nanoparticles and a titania (anatase polymorph) photoactive layer was prepared [1-2] and electrochemically characterized by cyclic voltammetry and electrochemical impedance spectroscopy. A pronounced electrocatalytic effect was observed along with a great increase in the current intensity of the silver oxidation peak (Figure 1). Results are compared with literature data on bare silver nanoparticles [3-5].
Theoretical DFT calculations, performed using the VASP code [6], described the composite junction as a distorted bulk Ag structure, commensurate with the periodicity of the (101) face of the I41/amd TiO2 polymorph. The silver atoms close to the semiconductor gain a partially positive charge [7], which quickly decreases with the distance from the TiO2 surface.
This joint theoretical and experimental study allows us to conclude that the device could be considered as a “silver cations electrode”, with silver ions protected by the titania layer, which holds a partial negative charge. This peculiar electrode structure can be conveniently used for sensor applications. For example, we successfully applied our device for the determination of neurotransmitters such as dopamine, norepinephrine and serotonin in simulated biological matrices (liquor, serum and urine). Our optimized analytical methodology is not only characterized by high sensitivity and low detection limits (around 0.03 μM) but also by high selectivity in the presence of high concentrations of conventional interferents (uric and ascorbic acids).
Moreover, the device shows under UV light self-cleaning properties of its titania overlayer, with complete removal of fouling, originated by the chemisorption of analytes and byproducts. Irradiating the device with UVA light, the initial sensor sensitivity was restored, making it reusable and suggesting its employment in integrated monitoring systems.
Acknowledgements
This work has been supported by MIUR (Ministero dell’Istruzione, dell’Università e della Ricerca) in the framework of the PRIN 2012 Project (20128ZZS2H).
References
[1] G. Soliveri, V. Pifferi, G. Panzarasa, S. Ardizzone, G. Cappelletti, D. Meroni, K. Sparnacci, L. Falciola, Analyst 140, 2015, pp 1486 – 1494.
[2] V. Pifferi, G. Soliveri, G. Panzarasa, S. Ardizzone, G. Cappelletti, D. Meroni, L. Falciola, RSC Advances 5, 2015, pp 71210 – 71214.
[3] O. S. Ivanova, F. P. Zamborini, J. Am. Chem. Soc. 132, 2010, pp 70–72.
[4] G. Chang, J. Zhang, M. Oyama, K. Hirao, J. Phys. Chem. B 109, 2005, pp 1204-1209.
[5] S.E. Ward Jones, F.W. Campbell, R. Baron, L. Xiao, R.G. Compton, J. Phys. Chem. C 112, 2008, pp 17820–17827.
[6] G. Kresse, D. Joubert, Phys. Rev. B: Condens. Matter 59, 1999, pp 1758−1775.
[7] W. Tang, E. Sanville, and G. Henkelman, J. Phys. Condens. Matter 2009, 21, 084204
Capgras delusion for animals and inanimate objects in Parkinson’s Disease: a case report
No full textBackground: Capgras delusion is a delusional misidentification syndrome, in which the patient is convinced that someone that is well known to them, usually a close relative, has been replaced by an impostor or double. Although it has been frequently described in psychotic syndromes, including paranoid schizophrenia, over a third of the documented cases of Capgras delusion are observed in patients with organic brain lesions or neurodegenerative disease, including Parkinson's Disease. Variants of Capgras involving animals or inanimate objects have also been described. The etiology of Capgras in Parkinson's remains unclear, but may arise from a combination of factors, such as frontal lobe dysfunction and dopaminergic medication. Case presentation: We present the case of a 53-year old right-handed female with Parkinson's disease who developed Capgras delusion during treatment with dopamine agonists and Levodopa/Carbidopa. She became convinced that her pet dogs and the plants in her garden had been substituted by identically looking ones. Our patient was initially treated with Quetiapine, with no improvement, and subsequently treated with Clozapine, which lead to partial regression of her symptoms. Neuropsychological Evaluation showed Mild Cognitive Impairment in Executive Functions. Conclusions: Given the clinical history, onset and evolution of symptoms we believe our patient's delusion resulted from the overlap of dopaminergic medication and Mild Cognitive Impairment in executive functions. Zoocentric Capgras, the variant we describe, has been rarely described in scientific literature, and we believe it is of interest due to its unusual characteristics
Photo-renewable electroanalytical sensor for neurotransmitters detection: The role of silver ion nanoparticles
No full textA sandwich-like structure electrode of silver nanoparticles embedded in a titania (anatase polymorph) photoactive layer was prepared [1-2] and electrochemically characterized by cyclic voltammetry and electrochemical impedance spectroscopy.
In comparison with literature data on bare silver nanoparticles-modified electrodes [3-5], the new device features a pronounced electrocatalytic effect on the silver oxidation peak together with a great increase in the current intensity (Figure a).
Theoretical DFT calculations, performed using the VASP code [6], described the composite junction as a distorted bulk Ag structure, commensurate with the periodicity of the (101) face of the I41/amd TiO2 polymorph. The silver atoms close to the semiconductor were found to gain a partially positive charge [7], quickly decreasing with the distance from the TiO2 surface.
These joint theoretical and experimental studies demonstrated that the device could be considered as a “charged silver nanoparticles-based electrode”, with positively ionized surface silver atoms protected by the titania layer, which holds a partial negative charge. This peculiar electrode structure was found to be of a highly convenient use for sensor applications.
As a proof-of-concept, this device performed efficiently for the determination of neurotransmitters such as dopamine, norepinephrine and serotonin in simulated biological matrices (liquor, serum and urine). Moreover, this optimized analytical methodology is not only characterized by high sensitivity and low detection limits (around 0.03 μM, which makes it appealing for clinical purposes), but also by high selectivity in the presence of high concentrations of conventional interferents (uric and ascorbic acids). Furthermore, the fouling of the electrode surface, typical which is unavoidable for this kind of analytes, could be easily overcome by irradiating the device with UVA-light, which restored the initial sensor sensitivity. This feature allows the possibility to reactivate the sensor on site, i.e. directly in solution, to yield a system capable of working in continuous, able to be used in an integrated monitoring system.
References
[1] G. Soliveri, V. Pifferi, G. Panzarasa, S. Ardizzone, G. Cappelletti, D. Meroni, K. Sparnacci, L. Falciola, Analyst 140, 2015, pp 1486 – 1494.
[2] V. Pifferi, G. Soliveri, G. Panzarasa, S. Ardizzone, G. Cappelletti, D. Meroni, L. Falciola, RSC Advances 5, 2015, pp 71210 – 71214.
[3] O. S. Ivanova, F. P. Zamborini, J. Am. Chem. Soc. 132, 2010, pp 70–72.
[4] G. Chang, J. Zhang, M. Oyama, K. Hirao, J. Phys. Chem. B 109, 2005, pp 1204-1209.
[5] S.E. Ward Jones, F.W. Campbell, R. Baron, L. Xiao, R.G. Compton, J. Phys. Chem. C 112, 2008, pp 17820–17827.
[6] G. Kresse, D. Joubert, Phys. Rev. B: Condens. Matter 59, 1999, pp 1758−1775.
[7] W. Tang, E. Sanville, and G. Henkelman, J. Phys. Condens. Matter 2009, 21, 084204.
Acknowledgements
This work has been supported by Fondazione Cariplo (Milano, Italy), grant no. 2014-1285. We acknowledge the CINECA and the Regione Lombardia award under the LISA initiative (grant SURGREEN) for the availability of high performance computing resources. We also thank the Chemistry Department for funding through the Development Plan of Athenaeum grant – line B1 (UNIAGI 17777)
Discriminant function analysis of Fuld's formula and WAIS subtests in different types of dementia
No full textSilver nanoparticles/nanostructured TiO2 interface: a photo-renewable “silver-ions electrode” for neurotransmitters detection
No full textSilver nanoparticles were embedded in a TiO2 (anatase polymorph) photoactive layer in a sandwich-like nanostructured electrode. [1-2]
The device was (photo)electrochemically characterized by cyclic voltammetry and electrochemical impedance spectroscopy.
In comparison with literature data on electrodes modified with silver nanoparticles [3-5], the new sensor presents a pronounced electrocatalytic effect on the silver oxidation peak together with a great increase in the current intensity.
Parallel plane-wave DFT calculations, performed using the VASP code [6], described the composite junction as a distorted bulk Ag structure, commensurate with the periodicity of the (101) face of the I41/amd TiO2 anatase polymorph. The silver atoms close to the semiconductor were found to gain a partially positive charge, quickly decreasing with the distance from the TiO2 surface.
Comparing the theoretical and experimental results it could be concluded that the device may be considered as a “positively charged silver nanoparticles-based electrode”, with positively ionized surface silver atoms protected by the titania layer, which holds a partial negative charge.
The final sensor performed efficiently in the electroanalytical determination of some neurotransmitters (e.g. dopamine, norepinephrine and serotonin) in simulated biological matrices (liquor, serum and urine). The optimized analytical methodology is not only characterized by high sensitivity and low detection limits (around 0.03 μM, which makes it appealing for clinical purposes), but also by high selectivity in the presence of high concentrations of conventional interferents (uric and ascorbic acids).
Last but not least, the fouling and passivation of the electrode surface, an unavoidable drawback during the detection of this kind of analytes, could be easily overcome by irradiating the device with UVA-light, which restored the initial sensor sensitivity. The photo-renewability allows to reactivate the sensor on site, i.e. directly in solution, to yield a system capable of working in continuous, able to be used in an integrated monitoring system.
References
[1] G. Soliveri, V. Pifferi, G. Panzarasa, S. Ardizzone, G. Cappelletti, D. Meroni, K. Sparnacci, L. Falciola, Analyst, 140, (2015), 1486 – 1494.
[2] V. Pifferi, G. Soliveri, G. Panzarasa, S. Ardizzone, G. Cappelletti, D. Meroni, L. Falciola, RSC Advances, 5, (2015), 71210 – 71214.
[3] O. S. Ivanova, F. P. Zamborini, J. Am. Chem. Soc., 132, (2010), 70–72.
[4] G. Chang, J. Zhang, M. Oyama, K. Hirao, J. Phys. Chem. B, 109, (2005), 1204-1209.
[5] S.E. Ward Jones, F.W. Campbell, R. Baron, L. Xiao, R.G. Compton, J. Phys. Chem. C, 112, (2008), 17820–17827.
[6] G. Kresse, J. Furthmüller, Phys. Rev. B, 54:11169, (1996).
Acknowledgements
This work has been supported by Fondazione Cariplo (Milano, Italy), grant no. 2014-1285. We acknowledge the CINECA and the Regione Lombardia award under the LISA initiative (grant SURGREEN) for the availability of high performance computing resources. We also thank the Chemistry Department for funding through the Development Plan of Athenaeum grant – line B1 (UNIAGI 17777)
The Potential of Sound Analysis to Reveal Hemodynamic Conditions of Arteriovenous Fistulae for Hemodialysis
No full textPurpose: Arteriovenous fistula (AVF), the preferred vascular access for hemodialysis, is associated with high failure rate. The aim of this study was to investigate the potential of AVF sound auscultation in providing quantitative information on AVF hemodynamic conditions.
Methods: This single-center prospective study involved six patients with native radio-cephalic AVFs who underwent multiple follow-up visits. Doppler Ultrasound blood flow volume (BFV) assessment and electronic stethoscope-based sound recordings were performed during each visit, whereas MRIs were acquired 3 days, 3 weeks and 1 year after surgery. Computational fluid dynamic (CFD) simulations were performed on patient-specific MRI-derived geometrical models.
Results: Higher values of median peak amplitudes ratios (high-low peak ratio-HLPR) were found to be associated with complex blood flow and velocity streamlines recirculation at systolic peak, and corresponding extended regions of high oscillatory shear index (OSI). On the contrary, lower values of HLPR were associated with laminar flow pattern and low values of OSI. Significant differences were observed in HLPR between subgroups with extended or limited areas with OSI > 0.1 (0.67 vs 0.31, respectively). Significant relationships were found between AVF sound intensity and brachial BFV (slope = 0.103, p < 0.01) as well as between longitudinal changes in brachial BFV and HLPR (slope = − 0.001, p < 0.01).
Conclusion: Our results show that AVF sound can be exploited to extract fundamental information on AVF hemodynamic conditions, providing indication of the presence of complex hemodynamic and adequate BFV to perform hemodialysis. Sound analysis has therefore the potential to improve clinical AVF surveillance and to ameliorate outcom
The silver nanoparticles/TiO2 interface: a combined electrochemical and theoretical investigation
No full textA modified electrode, made by silver nanoparticles covered with a thin layer of titanium dioxide (anatase polymorph) was prepared and electrochemically characterized by cyclic voltammetry and electrochemical impedance spectroscopy. Previously synthesized silver nanoparticles (mean diameter 10 ± 2 nm) were immobilized on an inert support (aminosiloxane-functionalized fluorine-doped tin oxide) and subsequently covered with a 100 nm-thick layer of titania using our previously reported methodology [1].
Electrochemical studies showed a pronounced electrocatalytic effect and an increase in the current intensity of the silver oxidation peak in comparison with the results reported in the literature for uncovered silver nanoparticles [2-4]. Moreover, the resulting composite showed a strong UV light response: complete restoration of the silver oxidation current peak was observed when the composite was irradiated after performing a voltammetric scan, thanks to the UV-assisted reduction of the passivating oxide layer.
These results are explained by theoretical DFT calculations, performed using the VASP code [5-10]. Namely, an interface of silver on the (101) cut of anatase TiO2 was grown and characterized. A commensurate Ag structure was found, showing an interaction in the region of the junction between silver atoms and TiO2. The interaction was justified by the Ag-O distances and the atomic charges computed using a special code [11-13], which takes in input the outputs of VASP. The silver atoms close to the semiconductor gain a partially positive charge, while the oxygens of TiO2 host the negative ones. The charge transfer decreases with the distance from TiO2 and characterizes the metal-semiconductor junction. This theoretical picture allowed us to find a very good agreement between theory and experiment, shining light on a system of both great theoretical and applicative interest.
REFERENCES
[1] G. Soliveri, V. Pifferi, G. Panzarasa, S. Ardizzone, G. Cappelletti, D. Meroni, K. Sparnacci, L. Falciola, Analyst, (2015), 140, 1486 – 1494.
[2] O. S. Ivanova, F. P. Zamborini, J. Am. Chem. Soc., (2010), 132, 70–72
[3] G. Chang, J. Zhang, M. Oyama, K. Hirao, J. Phys. Chem. B, (2005), 109, 1204-1209
[4] S.E. Ward Jones, F.W. Campbell, R. Baron, L. Xiao, R.G. Compton, J. Phys. Chem. C, (2008), 112, 17820–17827.
[5] G. Kresse, J. Hafner, Phys. Rev. B: Condens. Matter, (1993), 47, 558−561.
[6] G. Kresse, J. Furthmuller, Phys. Rev. B: Condens. Matter, (1996), 54, 11169−11186. [7] P.E. Blöchl, Phys. Rev. B: Condens. Matter, (1994), 50, 17953−17979. [8] G. Kresse, D. Joubert, Phys. Rev. B: Condens. Matter, (1999), 59, 1758−1775. [9] J. P. Perdew, K. Burke, M. Ernzerhof, Phys. Rev. Lett., (1996), 77, 3865−3868. [10] G. Kresse, J. Hafner, Phys. Rev. B: Condens. Matter, (1994), 49, 14251−14269. [11] W. Tang, E. Sanville, G. Henkelman, J. Phys. Condens. Matter, (2009), 21, 084204. [12] E. Sanville, S. D. Kenny, R. Smith, G. Henkelman, J. Comp. Chem., (2007), 28, 899. [13] G. Henkelman, A. Arnaldsson, H. Jónsson, Comput. Mater. Sci., (2006), 36, 254
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