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Semiconductor quantum dots have been recently employed as luminescent probes for the detection of hazardous nitroaromatic compounds. Despite the high sensitivity, such detection systems involve laboratory procedures and employ complex instrumentation. Here, we demonstrate the use of colloidal PbS quantum dots as the main component of a chemiresistor for the detection of nitroaromatic compounds. The proposed device is low-cost, reusable, and produces an electric signal that can be acquired with off-the-shelf electronic components. In this paper, we demonstrate the operation of the proposed device and we discuss its sensing mechanism. We also show the sensor’s response to nitrobenzene in the 65 ppb–16 ppm range, estimating a theoretical detection limit of 2 ppb.

Colloidal quantum dots (CQDs) have been recently investigated as promising building blocks for low-cost and high-performance gas sensors due to their large effective surface-to-volume ratio and their suitability for versatile functionalization through surface chemistry. In this work we report on lead sulphide CQDs based sensors for room temperature NO2 detection. The sensor response has been measured for different pollutant gases including NO2, CH4, CO and CO2 and for different concentrations in the 2.8–100 ppm range. For the first time, the influence of the QDs film thickness on the sensor response has been investigated and optimized. Upon 30 ppm NO2 release, the best room temperature gas response is about 14 Ω/Ω, with response and recovery time of 12 s and 26 min, respectively. A detection limit of about 0.15 ppb was estimated from the slope of the sensor response and its electric noise. The gas sensors exhibit high sensitivity to NO2, remarkable selectivity, repeatability and full recovery after exposure.

In case of serious environmental disasters, such as floods, landslides and earthquakes, the first activity that an emergency management system must carry out is the detection, recognition and report of anomalous events. In order to be able to automatically perform these actions, it is necessary to have an efficient sensor network within the building. By means of a well- organized and high-performance sensor network, data from the field are acquired and processed to produce usable information at a high level. The Building Management System (BMS) therefore has information available on the occurrence of an anomalous event, whether caused by natural or intentional causes. The purpose of our work is to design and implement a cost-effective sensorized device, managed by an ATmega microcontroller and equipped with a Wi-Fi module for easier integration, able to detect and report potentially dangerous situations within a building. In particular, fires, floods, gas leaks and earthquakes were considered. Thanks to the integration of simple data analysis and data fusion algorithms, the platform is able to recognize and report the occurrence of emergency events within a building.

PbS colloidal quantum dots (CQDs) are attractive materials for the realization of simple, low-cost, high responsivity near-infrared photodetectors due to the large tunability of their optical properties together with their solution processability. In this work we propose multiple PbS CQD photoconductive devices with different spectral sensitivity realized on silicon substrates. We characterized the devices in terms of dark current, responsivity and response speed. Eventually, we discuss an algorithm for wavelength measurement of a quasi-monochromatic radiation based on linear combination of photocurrents from different photodetectors.

We demonstrated an optical method to evaluate the state of asphalt due to the presence of atmospheric agents using the measurement of the polarization/depolarization state of near infrared radiation. Different sensing geometries were studied to determine the most efficient ones in terms of performance, reliability and compactness. Our results showed that we could distinguish between a safe surface and three different dangerous surfaces, demonstrating the reliability and selectivity of the proposed approach and its suitability for implementing a sensor.

Germanium-based photodetectors represent the state-of-the-art in Near Infrared (NIR) detection systems when it comes to the monolithic integration with silicon electronics and CMOS compatibility. Germanium-on-silicon devices have been widely studied and several different photodetection schemes have been employed, such as Shottky junctions, pn diodes and phototransistors. Typically, germanium-based photodetectors provide a sensitivity spectrum ranging from the visible to the near infrared (NIR) and their responsivity at shorter wavelengths can be slightly tuned by the applied bias due to the varying extension of the electric field inside the Ge film. In this paper we propose a novel Ge-on-Si photodetector architecture whose spectral response can be completely switched from the visible to the NIR with the application of a proper bias. We provide Technology Computer Aided Design (TCAD) simulations of the device showing how the photodetection performance depend on different fabrication parameters. Finally, we show preliminary results obtained on sample devices.

Designs and results for a low-power and economical fingerprint visible light positioning (VLP) system are discussed in this paper. A system using four white LEDs and one photodiode was deployed. The LEDs are independently controlled and modulated by individual transmitter circuits, removing the requirement for a large, expensive signal generator. The receiver circuit filters and converts the received signal to DC, allowing a simple microcontroller to save the received signal. We propose the creation of a fingerprint database by recording signal data, fitting a two-dimensional Gaussian distribution to the data, and then generating the fingerprint database for all positions in the evaluation system. System positioning accuracy of 13.44 + / − 0.36 mm was observed, corresponding to a relative error of 2.8% with respect to the system dimensions. This result presents an improvement on positioning accuracy for fingerprint positioning VLP systems, which build their own transmitters.