Search

Scuola di dottorato"Archimede" Scienza e Tecnologia dei Sistemi Complessi, Ciclo XXVII a.a. 2014 Università della Calabria

International audience; Sine wave signals are widely used in electronic applications such as digital oscilloscopes calibration, speech analysis and electrochemical sensors. In particular, impedance based microbial biosensors detect bacterial concentration by stimulating the sample with a sinusoidal test signal and measuring its electrical characteristics. Thus, for reliable microbial biosensing, fast and accurate sine wave analysis is mandatory. Many algorithms for the estimation of sinusoidal parameters exist that provide accurate estimate but are based on time consuming iterative procedures and/or need good starting values for the sine parameters. In this paper a linear non iterative algorithm based on the least squares method is presented that allows sinusoidal voltages analysis in a fast and efficient manner. The algorithm has been tested either with simulation analysis either with real impedances and the results proved to be accurate enough for reliable bacterial concentration measurement.

International audience; Microbial screening is a primary concern for many products. Traditional techniques based on standardplate count (SPC) are accurate, but time consuming. Furthermore, they require a laboratory environmentand qualified personnel. The impedance technique (IT) looking for changes in the electrical characteristicsof the sample under test (SUT) induced by bacterial metabolism represents an interesting alternative toSPC since it is faster (3–12 h vs. 24–72 h for SPC) and can be easily implemented in automatic form.With this approach, the essential parameter is the time for bacteria concentration to reach a criticalthreshold value (about 107 cfu mL−1) capable of inducing significant variations in the SUT impedance,measured by applying a 100 mV peak-to-peak 200 Hz sinusoidal test signal at time intervals of 5 min.The results of this work show good correlation between data obtained with the SPC approach and withimpedance measurements lasting only 3 h, in the case of highly contaminated samples (106 cfu mL−1).Furthermore, this work introduces a portable system for impedance measurements composed of anincubation chamber containing the SUT, a thermoregulation board to control the target temperature andan impedance measurement board. The mix of cheap electronics and fast detection time provides a usefultool for microbial screening in industrial and commercial environments.

This paper presents novel read-out electronic systems for a fast DNA label-less detection. The capacitive shift due to the hybridisation effect is monitored by means of a Charge Sensitive Amplifier (CSA) and a differential stage. The systems provide an A/D conversion and an evaluation of the capacitive shift amount with a resolution of 11 bit. The read-out solutions demonstrate the ability to identify a 0.01% variation on the capacitive value of the sensor. The investigated techniques are suitable for monolithic systems or for a micro-fabricated array of sensors.

Organic Thin-Film Transistors (OTFTs) in top-contact configuration and Metal-Insulator-Semiconductor (MIS) structures with different organic dielectrics as the gate insulator have been fabricated using the same organic semiconductor layer, pentacene, in order to investigate the changes in the electrical behavior by varying the interface properties. A gold bottom gate electrode was sputtered on a glass substrate whereas gold source and drain were thermally evaporated onto the pentacene layer. Several organic dielectrics have been tested as insulating layers, namely were poly(vinyl alcohol) (PVA), polyvinyl alcohol with ammonium dichromate (PVAad) as a cross-linking agent, poly (4-vinyl phenol) (PVP), poly(dimethylsiloxane) (PDMS) and poly(methylsilsesquioxane) (pMSSQ). The interesting differences found out by varying the interface confirm that the chemical-physical interaction between semiconductor and dielectric is crucial for the conduction mechanisms of the charge carriers. In particular we observed that the electron traps can influence not only the electron transport, therefore allowing a more or less marked ambipolar behavior, but also affect the hole transport.

We report a microscopic investigation of the spectrum of voltage fluctuations in nanometric n-Si layers. Theory makes use of a Monte Carlo simulator self-consistently coupled with a two-dimensional Poisson solver. We consider layers of variable thickness W in the range of 2–100 nm and variable length L in the range of 10–1000 nm embedded in an external dielectric medium. Calculations are performed at T=300 K for different doping levels and in the presence of an applied voltage of increasing strength. The spectra are found to exhibit peaks centered on the terahertz region. For W≥100 nm and carrier densities of 5×1017 and 5×1018 cm−3, the frequency peaks agree with the value of the three dimensional plasma frequency. For W≤100 nm, the results exhibit a plasma frequency that depends on L, thus implying that the oscillation mode is dispersive. The corresponding frequency covers a wide range of values of 0.2–10 THz and is in agreement with the values of the two-dimensional plasma frequency predicted by existin...