1,721,045 research outputs found
ELECTROCHEMICAL SENSORS BASED ON SINGLE-WALLED CARBON NANOTUBES FOR BIOLOGICAL DETECTION
Full text linkIn this work thesis we aim at discussing electrochemical biosensors based on single-walled carbon nanotubes for biological detection. The main strategy is to obtain modified electrodes with carbon nanotubes with two different classes of strategy. This can be realized in two ways: a surface modification strat- egy and a bulk modification strategy. The first one concerns the modification of patterned gold electrodes in which the tridimensionality is assured by the creation of a controlled forest of single-walled carbon nanotubes. The second strategy proposed is the modification of electrodes by means of a bulk doping of materials. We realized carbon nanotubes doped polyacrylamide hydrogels (HYs) acting as biosensors for glucose detection.
Finally examples for the integration of biosensing and microfluidic environ- ments are proposed. Electrochemical measurements (EIS, CV and CA) were performed in order to characterize samples and substrates. Also morphological measurements (AFM and SEM) were conducted to study topographic features of samples. Biocom- patibility tests and electrical measurements were performed when treating with living systems.In questo lavoro di tesi vogliamo discutere biosensori elettrochimici modificati con nanotubi di carbonio a parete singola. La strategia principale è di ottenere elettrodi modificati con nanotubi di carbonio attraverso due classi diverse di modificazione. Ciò può essere realizzato in due modi: attraverso una modifica della superficie dell’elettrodo oppure attraverso una modifica della struttura del materiale. Per quanto riguarda la prima si tratta di una modificazione di elettrodi d’oro disegnati in cui la tridimensionalità è assicurata dalla creazione di una forest controllata di nanotubi di carbonio a parete singola. La seconda strategia proposta è la modifica di elettrodi per mezzo di doping di materiali. Si sono realizzati hydrogel (HYs) di poliacrilammide drogati con nanotubi di carbonio a parete singola in modo da funzionare come biosensori per il rilevamento di glucosio.
Infine vengono proposti esempi per l’integrazione dei biosensori in piattaforme mifcrofluidiche. La caratterizzazione dei substrati e dei campioni è stata condotta per mezzo di misure elettrochimiche (EIS, CV e CA). Vengono eseguite inoltre misure di caratterizzazione morfologica (AFM e SEM) per studiare le proprietà topografiche dei campioni in esame. Nei casi in cui si è avuto a che fare di sistemi viventi sono state condotte prove di biocompatibilità e prove per il riconoscimento del segnale elettrico dalla superficie delle cellule
Electrochemical sensing with carbon nanotubes
No full textIn this chapter we aim at reviewing the most relevant contributions in the development of electrochemical sensors and biosensors based on carbon nanotubes (CNTs). Particular attention will be focused on the different strategies to modified the electrodes for sensing application.
First, we will discuss about the electrochemical properties of nanotubes, their peculiar physical-chemical features that make them very useful for sensing. For instance, CNTs have been incorporated in electrochemical sensors to decrease overpotential and to improve sensitivity. In addition, concerning biosensing, the use of nanotubes enhancing the electrochemical reactivity of important biomolecules by promoting the electron-transfer reactions of biomolecules with catalytic activity.
Different ways of integrating nanotubes and electrodes will be presented: from a bulk modification to a more sensible surface one. After a survey of bulk modification strategies, we will show an in-depth study of the surface modification technique developing the random and oriented choice to modify the surface, especially focusing on the vertical alignment. A structured methodological point of view will be given in this latter section.
We will review the state of the art of sensing and biosensing with CNTs. In the first part of this section we will present how CNTs modified electrodes can act as sensors without any further modification of their structure. In the latter we will first focalize the attention to the functionalization techniques required in order to make CNTs able to detect biological substrates. Therefore we will review how CNTs modified electrodes will detect biological species such as neurotransmitters, proteins, enzymes and proteins enhancing the detection limits obtained using other techniques.
Finally a future perspectives section is provided in which we will analyze the possibility to integrate the CNTs electrochemical devices in microfluidic platforms in order to diminish the average dimensions of the substrates, to enhance the selectivity and other appreciable advantages
Coordinated local reactive power control in smart distribution grids for voltage regulation using sensitivity method to maximize active power
No full textDistributed generation (DG) integrated into Smart grid is the future of distribution systems. The expected impact is wide in terms of control, management, supply and use. In particular, in
order to integrate DG based on renewable sources in distribution networks without
compromising the integrity of the grid, it needs to develop proper control techniques to allow power delivery to customers in compliance with power quality and reliability standards. This
paper proposes a coordinate local control approach based on a mixed distribution network (DN)
sensitivity analysis to maintain voltage levels within regulatory limits. The proposed control is based on a reactive/active power regulation able to offer voltage regulation as ancillary services
to the DN, and to maximize the produced active power of the DGs. The validation of the
proposed control technique has been conducted through a several number of simulations on a
real MV Italian distribution system
BIOSENSING WITH ELECTROCONDUCTIVE BIOMIMETIC SOFT MATERIALS
Full text linkElectrochemical sensors based on microstructured electrodes represent one of the most promising technological solutions for biological monitoring because of the amount of possibilities that electrical signaling offers and the possibility of realizing microstructured systems with high specificity and sensitivity.
The development of these devices may be improved by the availability of soft biocompatible electroactive materials. The latter are an innovative answer in this context because of they can be manipulated, doped or functionalized in order to realize a biological transducer.
In our work we have investigated the possibility of using polyacrylamide hydrogels (HYs) doped with Single-Walled Carbon Nanotubes (SWCNTs) in order to achieve the electroconduction, then loaded with a specific enzyme for glucose detection (Glucose Oxidase, GOx).
The electrical analysis was performed by means of Electrochemical Impedance Spectroscopy (EIS) characterization of polarization resistance of the equivalent circuit model. Although GOx-doped hydrogels do not exhibit any electrical activity to glucose in measurements, GOx-SWNT doped hydrogels show glucose-concentration linear response in the range between 0.1 mM to 1.6 mM; all together this result show high sensitivity (up to 15 uM) of glucose detection. In addition, dielectrophoresis (DEP) was applied to doped HYs in order to align SWCNTs in the materials as a proof of concept for increasing the sensitivity of the organic biosensor. The results and the possibility of HY functionalization allow the device to be integrated in cell culture systems in order to allow the detection and the acquisition of electrochemical associated biological phenomena
Enhancement of heterogeneous electron transfer dynamics tuning single-walled carbon nanotube forest height and density
Full text linkElectrochemical sensors are growing in number and importance. Surface modifications could enhance charge transfer properties occurring at the interfaces and carbon nanoassemblies is one of the most used strategy to improve sensitivity to measurements. However, well defined protocols of surface modification are needed in order to fabricate electrochemically effective nanostructured sensors.
Therefore, we aim at investigating the electrochemical properties of single-walled carbon nanotube (SWCNT) forests as a function of height and nanotube surface density. Height of the forests is accurately controlled tuning the oxidation temperatures in the range of 293–313 K of SWCNTs. The surface density of carbon nanotubes was adjusted developing cysteamine/2-mercaptoethanol (CYS/ME) self-assembled monolayers (SAMs) on gold surfaces at different ratios (1:0, 1:3, 1:10, 1:100, 0:1).
Apparent electron transfer rate was analyzed with electrochemical impedance spectroscopy (EIS) and experimental data show that transfer rate constant, kapp, increases from 1 × 10−4 cm/s to 6 × 10−4 cm/s rising oxidation temperatures (i.e. lowering forest height); therefore forests with reduced height show higher electron transfer rate without significant difference in electrodic reversibility. On the other hand, tuning SWCNT surface density, forests obtained with no ME show optimal Δpeak value of 0.087 ± 0.015 V and highest kapp value of 9.15 × 10−3 cm/s. Surprisingly, electrochemical surface area analysis shows that samples with lower amount of cysteamine have an active surface area three times bigger than samples with 1:3 CYS/ME ratio. Low electrochemical efficiency associated with high active surface may be related to unwanted SWCNT bundles adsorbed on the surface for 1:10 and 1:100 CYS/ME ratio samples as confirmed by AFM morphological characterization. Further investigation shows that a transition from a semi-infinite planar diffusion mechanism to a radial diffusion one takes place when SAMs with low chemical affinity to nanotubes are used. Wettability analysis confirms the robustness of the surface chemical modification during the forest development. Altogether these results show that optimal electrochemical properties of carbon modified electrodes require an accurate control of forest fabrication in terms of carbon nanotube structural assembling
Massive data analysis to assess PV/ESS integration in residential unbalanced LV networks to support voltage profiles
Full text linkThe integration of energy storage systems (ESSs), co-located with distributed photovoltaic (PV) units in low voltage (LV) networks, offers new opportunities to support distribution system operator (DSO) in distribution network operations and management. The deepening penetration of renewable resources exacerbates the challenge to maintain demand–supply equilibrium. ESSs can tackle this challenge making PV resources dispatchable. Here, we apply a Monte Carlo analysis considering different residential load profiles and PV/ESS characteristics (e.g., penetration levels, locations, and capabilities) to assess the impact that two different control strategies have in supporting the DSO in improving the power quality of the distribution network
A smart strategy for voltage control ancillary service in distribution networks
Full text linkThe expected impact of distributed generation (DG) into Smart Grid represents a great challenge of the future for power systems. In particular, the integration of DG based on renewable energy sources (RESs) in distribution networks, without compromising the integrity of the grid, requires the development of proper control techniques to allow power delivery to customers in compliance with power quality and reliability standards. This paper proposes a coordinated local control approach that allows distribution system operator (DSO) and independent power producers (IPPs) to obtain benefits offering the voltage regulation ancillary service to DSO and maximizing allowable active power production for each RES unit belonging to the same IPP. The control is based on a cooperation of data transfer between DSO and IPPs. In order to realize such cooperation, a nonlinear constrained optimization problem is formulated and solved by sequential quadratic programming (SQP) method. The validation of the proposed control technique has been conducted through several time series simulations on a real MV Italian distribution system
Nanotubes oxidation temperature controls the height of single-walled carbon nanotube forests on gold micropatterned thin layers
No full textWe developed a simple methodology for a direct control of the height of carboxylated single-walled carbon nanotube (SWNT) forests. We found that the important step is a good control of the oxidation temperature of the nanotubes. SWNTs oxidation at different temperature was followed by Raman and X-ray photoelectron spectroscopies. Atomic force microscopy images showed that micropatterned self-assembled monolayers forests have average height from 20 to 80 nm using SWNTs oxidized in the temperature ranging from 323 to 303 K, respectively
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