Christian Falconi

Quantifying the Traction Force of a Single Cell by Aligned Silicon Nanowire Array

The physical behaviors of stationary cells, such as the morphology, motility, adhesion, anchorage, invasion and metastasis, are likely to be important for governing their biological characteristics. A change in the physical properties of mammalian cells could be an indication of disease. In this paper, we present a silicon-nanowire-array based technique for quantifying the mechanical behavior of single cells representing three distinct groups: normal mammalian cells, benign cells (L929), and malignant cells (HeLa). By culturing the cells on top of NW arrays, the maximum traction forces of two different tumor cells (HeLa, L929) have been measured by quantitatively analyzing the bending of the nanowires. The cancer cell exhibits a larger traction force than the normal cell by approximately 20% for a HeLa cell and approximately 50% for a L929 cell. The traction forces have been measured for the L929 cells and mechanocytes as a function of culture time. The relationship between cells extending area and their traction force has been investigated. Our study is likely important for studying the mechanical properties of single cells and their migration characteristics, possibly providing a new cellular level diagnostic technique.

Piezoelectric potential in vertically aligned nanowires for high output nanogenerators

In this work we analyze the coupled piezoelectric and semiconductive behavior of vertically aligned ZnO nanowires under uniform compression. The screening effect on the piezoelectric field caused by the free carriers in vertically compressed zinc oxide nanowires (NWs) has been computed by means of both analytical considerations and finite element calculations. We predict that, for typical geometries and donor concentrations, the length of the NW does not significantly influence the maximum output piezopotential because the potential mainly drops across the tip, so that relatively short NWs can be sufficient for high-efficiency nanogenerators, which is an important result for wet-chemistry fabrication of low-cost, CMOS- or MEMS-compatible nanogenerators. Furthermore, simulations reveal that the dielectric surrounding the NW influences the output piezopotential, especially for low donor concentrations. Other parameters such as the applied force, the sectional area and the donor concentration have been varied in order to understand their effects on the output voltage of the nanogenerator.

Piezo‐Semiconductive Quasi‐1D Nanodevices with or without Anti‐Symmetry

The piezopotential in floating, homogeneous, quasi-1D piezo-semiconductive nanostructures under axial stress is an anti-symmetric (i.e., odd) function of force. Here, after introducing piezo-nano-devices with floating electrodes for maximum piezo-potential, we show that breaking the anti-symmetric nature of the piezopotential-force relation, for instance by using conical nanowires, can lead to better nanogenerators, piezotronic and piezophototronic devices.

Feature Extraction of chemical sensors in phase space

In this paper a sensor phase space is introduced and the analysis of trajectories in this space is proposed as a method to evaluate the sensor response. The phase space gives the opportunity to introduce a novel feature describing the area spanned by the trajectory during adsorption and/or desorption of chemicals from the sensor. A comparison with the usual features resulted in a better accuracy and a shortest measurement time.

Development of a ChemFET sensor with molecular films of porphyrins as sensitive layer

The interaction of chemical species with molecular films of porphyrins causes variations of the work function of the film itself, as it has been recently demonstrated by using the Kelvin probe technique. This characteristic makes porphyrins films suitable to be used as sensitive layers in ChemFET sensors. In this paper, we present a preliminary report about the fabrication and testing of such gas sensitive devices. The technological solutions towards an optimised device are also illustrated and discussed.

Detection and identification of cancers by the electronic nose

INTRODUCTION The early determination of serious pathologies has so far been an important issue in both the medical and social fields. The search for an instrument able to detect cancers has led to the consideration of the usage of chemicals of the human body, which carry, through its volatile compounds, information coming from or related to defined pathologies. AREAS COVERED The electronic nose (EN) seems to represent a good solution for the detection of cancers of different types. Recent results showed the utility of an EN to smell chemicals related to lung, melanoma, prostatic, breast and pancreatic cancers. The results obtainable from ENs are chemical images and, as it will be shown in this paper, the probability of cancer recognition is rather high. Main results obtained at international level and by the authors of this paper will be commented upon. EXPERT OPINION A personal opinion is given trying to foresee future developments of the olfaction strategy. To this purpose, two main aspects are considered: looking for better overall stability of the EN and for a new use of ENs in detecting alterations between blood and pathology components.

Comparison and integration of arrays of quartz resonators and metal-oxide semiconductor chemoresistors in the quality evaluation of olive oils

Abstract Olive oil analysis is considered as a promising application of electronic noses. In this paper, two electronic noses, based on different sensor technologies (quartz resonators and metal-oxides chemoresistors) are applied to the measure of samples of olive oils of different qualities and values. Among them, samples of oil produced from organically farmed olives have also been measured. While both the sensor systems provided very similar images for the commercial oils defining a sort of quality growing direction in their principal component analysis score plots, the organically farmed product has been differently interpreted by the two arrays. Merging of data, both at high and low abstraction level, shown that the co-operation of the two sensor arrays identified the organically farmed product different from the commercial samples. Details about the single sensors behavior, and the option of sensors data fusion will be illustrated and discussed.

Current-Mode High-Accuracy High-Precision CMOS Amplifiers

In low-voltage, deep sub- mum analog CMOS circuits, the accuracy and precision can be limited by the finite gain as well as by the input offset and 1/f noise voltages of opamps. Here, we show how to design high-accuracy high-precision CMOS amplifiers by properly applying dynamic element matching to a second-generation current conveyor (CCII); if all of the critical, nominally identical transistor pairs are dynamically matched, the resulting amplifier has low residual input offset and noise voltages. When compared with chopper or traditional dynamic element-matching amplifiers, the proposed approach alleviates the tradeoff between output swing and output resistance and is more robust against the finite opamp gain. Transistor-level simulations confirm theoretical results.

Lateral bending of tapered piezo-semiconductive nanostructures for ultra-sensitive mechanical force to voltage conversion

Quasi-1D piezoelectric nanostructures may offer unprecedented sensitivity for transducing minuscule input mechanical forces into high output voltages due to both scaling laws and increased piezoelectric coefficients. However, until now both theoretical and experimental studies have suggested that, for a given mechanical force, lateral bending of piezoelectric nanowires results in lower output electric potentials than vertical compression. Here we demonstrate that this result only applies to nanostructures with a constant cross-section. Moreover, though it is commonly believed that the output electric potential of a strained piezo-semiconductive device can only be reduced by the presence of free charges, we show that the output piezopotential of laterally bent tapered nanostructures, with typical doping levels and very small input forces, can be even increased up to two times by free charges.Our analyses confirm that, though not optimal for piezoelectric energy harvesting, lateral bending of tapered nanostructures with typical doping levels can be ideal for transducing tiny input mechanical forces into high and accessible piezopotentials. Our results provide guidelines for designing high-performance piezo-nano-devices for energy harvesting, mechanical sensing, piezotronics, piezo-phototronics, and piezo-controlled chemical reactions, among others.

Low Voltage CMOS Current and Voltage References without Resistors

The authors describe low voltage current and voltage references which only use MOSFETs in strong inversion and pnp substrate transistors; both the references exhibit very good performance in terms of power supply rejection and do not require compensation capacitances; the minimum supply voltage is about 0.8V for the current reference and 1.2V for the voltage reference.