Marta Valledor

The influence of surface coating on the properties of water-soluble CdSe and CdSe/ZnS quantum dots

It is well-known that ligands coating the surface of luminescent semiconductor nanocrystals (quantum dots [QDs]) play an important role in the preparation, stability and physical properties of the colloidal QDs in both organic and aqueous media. Here we report on the synthesis and characterization of core (CdSe QDs) and core–shell structured QDs (CdSe/ZnS QDs), both of them stabilized in aqueous medium through different mechanisms of modification of their surface chemistry. The approaches evaluated for QDs transfer to aqueous media were ligand exchange and polymer coating. Experiments were performed using two typical thioalkyl acids as ligands, namely mercaptoacetic acid (QDs-MAA) and 2-mercaptoethanesulphonic acid (QDs-MES), and an amphiphilic polymer (PQDs) based on poly(maleic anhydride) functional groups. The effects of pH (buffer solution), illumination and the presence of ions in the QD environment on the spectroscopic properties of the different synthesized QDs are reported. The stability of the prepared QDs has been comparatively evaluated aimed to elucidate which surface chemistry provides the suitable properties to be employed as fluorescence labels in distinct types of applications. The experimental results and conclusions will be useful for the development of sensitive sensors or assays adopting QDs as fluorescence labels.

Low-cost system based on electro-oculography for communication of disabled people

This paper describes a new low-cost real-time communication assistive system for disabled people, especially those with only eye-motor coordination. The retinal resting potential causes an electric field around the eyeball, centred on the optical axis, which can be measured by placing electrodes near to the eye. An acquisition system was implemented for measuring this potential in order to detect the movement of the eyes and to provide a relative gaze position, making it possible to codify ocular actions as commands. A human-computer interface (HCI) to control the mouse and a virtual screen keyboard, that offers simple setup combined with high performance, have also been developed. This device has multiple applications, especially in assistive research, where control is governed by means of the ocular position (eye displacement in its orbit). The theory behind the device and the hardware and software design of the system are presented.

Amplitude and Phase Fluorescence-Spectroscopy Methods for Dissolved Oxygen Concentration Evaluation: Comparative Practical Results

This paper shows the practical results from a detailed comparative study of amplitude and phase fluorescence-spectroscopy methods for dissolved oxygen concentration evaluation. These results were obtained with an implemented optoelectronic measurement system that guarantees near-optimal operation conditions for both methods and a commercial fluorescence optical-fiber sensor, which is excited by a continuous-regulated sinusoidal-amplitude modulated light beam. The comparison was made through the analysis of the time dependence of the fluorescent signal and the values of DC voltages proportional to amplitude and phase shift of the fluorescent emitted signal obtained for a constant dissolved oxygen concentration water sample at a controlled temperature

A low-cost open-source data acquisition system

Data acquisition is present in several laboratory, test and production applications. In this paper, an USB controlled data acquisition device, especially suitable for use in both industrial and academic environments, is presented. It is a powerful learning tool, practical, easy to use, and low cost. Unlike other devices, it provides all the information about its inner design, both at hardware and software levels, and can be used without any restrictions as additional teaching material. We present an example of use.

EOG-based system for mouse control

The fact that the oculomotor system is one of the last capabilities that people suffering from neurodegenerative diseases or trauma retain allows us to develop a system to provide a means of communication for this particular target group. The retinal resting potential causes an electric field around the eyeball, centred on the optical axis, which can be measured by placing electrodes near to the eye. An acquisition system and a LabVIEW application were implemented for measuring these biopotentials in order to detect the movement of the eyes and to provide a relative gaze position, making it possible to control the computer mouse. Several techniques are implemented to denoise the EOG signal obtained in noisy environments for use in biomedical diagnosis.

Ratiometric Methods For Optical Fiber Instrumentation Based On Luminescence Sensors

The optical fiber instruments in analytical applications are usually based on a luminescence chemical sensor. Direct intensity measurements of the luminescence emission are, due to their simplicity, a very common measuring principle. Consequently, many optical fiber devices are based on the intensity measurement of the luminescence emission. Unfortunately, direct luminescent intensity measurements suffer from a series of non-analyte fluctuations, which make them inappropriate for the development of precise instrumentation. An alternative for solvents this trouble is to measure the lifetime of luminescence emission. In that case the drawback is an increase in the complexity of the measurement. A ratiometric measurement can solve many of the trouble previously exposed. When the excitation light interacts with a luminescence chemical sensor different optical emissions take place. Some of these emissions are analyte dependent and they are employed to extract the quantitative information required. The rest of emissions are usually considered like noise that can reduce the accuracy. With a ratiometric scheme this noise, or background light, is converted in a useful signal that can improve the accuracy of the measurement. In this paper we proposed two new ratiometric methods specially designed to be implemented with optical fiber instrumentation. The potential of our proposed ratiometric methods to overcome such problems of accuracy in luminescent sensing will be evaluated. The correct election of the methodologies with respect to the analytical performance of the chemical sensor will be also analyzed.

A Ratiometric Method for Oxygen Measurement Using a Luminescent Sensor

A great variety of methods for oxygen sensing using luminescent sensors have been proposed in recent years based on intensity or in lifetime quenching. Like lifetime measurements, ratiometric techniques are insensitive to the variations of the excitation light, optical path and photo-bleaching. In this work, we present a ratiometric method based on the phosphorescence-fluorescence spectral overlap emission of a phosphorescent chemical sensor. This dual emission makes ratiometric measurements possible without need of adding a reference luminophore. The ratio is calculated by measuring the phase shift between the excitation and the emission signal at two different frequencies. Theoretical aspects of the proposed methodology and the design and construction of a fiber-optical measuring system are discussed. Finally, the performance of the proposed measurement method has been assessed using the metal chelate Al-Ferron immobilized in an inorganic sol-gel support (an oxygen indicator which displays a strong fluorescence emission overlapping significantly with the measured phosphorescence emission)

A study on electrode placement in EOG systems for medical applications

The eye acts as a dipole between the cornea (positive potential) and the retina (negative potential) which causes an electric field around the eyeball. Therefore, when humans make saccadic eye movements, they generate signals relative to this potential called electrooculography (EOG) signals. These signals can be measured by placing electrodes near the eye. Different electrode configurations can be employed to acquire the EOG signals. The properties of these signals change depending on the number and placement of the electrodes. Therefore, this paper presents a comparative study of electrode placement used to measure EOG signals. In order to support this study a low-cost signal acquisition hardware was developed. It enables the comparison of different electrode placements while showing the particularities of each one. The aim of this study is to analyse which electrode configuration could be best for medical applications.

EOG signal processing module for medical assistive systems

Electrooculography (EOG) is one of the occulography methods used for the estimation of eye orientation. These signals, generated by eye movements, can be used in an efficient way as input in different control systems. So, the signal processing of the EOG signal is a key point when performing complex tasks, for instance, in a Human-Machine Interface (HMI). In this sense machine learning algorithms allow patterns in data to be identified, and then, to predict future actions using those patterns that have been learned. This paper presents a signal processing module for EOG signals, applying Wavelets Transform (WT) as a denoising procedure and AdaBoost as a machine learning algorithm.

An Electronic Instrumentation Course as Part of a Multidisciplinary Learning Project

This paper describes a final year undergraduate course on electronic Instrumentation. This course is part of multidisciplinary collaboration that involves several assignments of a last year undergraduate course in Electrical Engineering: Computers, Electronic Instrumentation, Automatic Control and Business Administration. The students must propose a new product, elaborate a market survey, etc. to create a new enterprise following the same steps than in a real case. As respect to the assignment of Electronic Instrumentation, the students must design a prototype of the electronic system or subsystem of the product they propose. The main goal of this course is to cover and to integrate the disciplines involved in instrumentation within a framework that provides highly motivating work and to integrate this learning with other assignments of the same course. The proposed solutions to achieve this goal, the laboratory support, extra work, course costs are described in this paper.