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Chemical nanosensors based on nanoparticles (NPs) of pure tin dioxide (SnO2) and graphene-decorated tin dioxide were developed and characterized for the detection of pollutant gases. Sensitive layers were prepared by a drop casting method. The photoactivation of the sensors allows for the detection of ultra-low NO2 concentrations (50 ppb) at room temperature. The sensors show strong responses to NO2 and weak ones to the other tested polluting gases (CO, CH4 and CO2). The effect of humidity and the presence of graphene on the sensors’ response were studied.

This work reports on two-dimensional MoS 2 nanomaterial-based resistive gas sensors and their response to sub-ppm NO 2 concentrations. The sensitive material was prepared by drop-casting MoS 2 nanosheet dispersions on silicon nitride suspended membranes. The sensor response was studied at operating temperatures up to 300 °C. The fabricated sensors provided good responses to NO 2 concentrations as low as 20 ppb at room temperature. The n-type MoS 2 sensing mechanism is here discussed.

En las últimas décadas se ha observado un incremento de personas que sufren diferentes enfermedades crónicas, debido a diversos factores como el estilo de vida, la alimentación, el estrés, la contaminación ambiental o el aumento de la esperanza de vida. En este tipo de enfermedades, un diagnóstico precoz y un buen control de la afección es muy importante para aumentar la calidad de vida del paciente y evitar posteriores exacerbaciones de la patología. Por ello, se hace necesario el desarrollo de dispositivos económicos y que de forma no invasiva se pueda realizar un diagnóstico eficaz y un control mucho más exhaustivo. Además, esta tecnología puede contribuir a una disminución del gasto sanitario a largo plazo en el tratamiento de estos pacientes, así como una mejora en la gestión de los recursos. Esta tesis doctoral está enfocada en el estudio y desarrollo de nanosensores químicos selectivos para la detección en el aliento de compuestos de interés como marcadores de enfermedades respiratorias. Debido a la complejidad de la composición del aire exhalado se han seleccionado diferentes compuestos gaseosos de interés como el monóxido de carbono (CO), óxido nítrico (NO), dióxido de nitrógeno (NO2), acetona o etanol. Estos son biomarcadores de diferentes enfermedades crónicas como el asma, la diabetes, la fibrosis quística o la enfermedad pulmonar obstructiva crónica, así como de infecciones respiratorias que puede contribuir en gran medida a un agravamiento de las afecciones anteriores. Dichas enfermedades han sido seleccionadas debido al eleva donúmero de pacientes que las padecen, y al infradiagnóstico y deficiente control existente en la actualidad..., In recent decades there has been an increase in the number of people suffering from various chronic diseases due to various factors such as lifestyle, diet, stress,environmental pollution, and increased life expectancy. Early diagnosis and effective control of the condition are essential in this type of disease to increase the patient's quality of life and avoid subsequent pathology exacerbations. For this reason, it is necessary to develop inexpensive, non-invasive devices that can provide adequate diagnosis and much more exhaustive monitoring. In addition, this technology can contribute to a decrease in long-term healthcare costs for these patients and an improvement in resource management. This doctoral thesis is focused on the study and development of selective chemical nanosensors for breath detection of compounds of interest as markers of respiratory diseases. Due to the complexity of the composition of exhaled air, different gaseous compounds of interest such as carbon monoxide (CO), nitric oxide (NO), nitrogendioxide (NO2), acetone or ethanol were selected. These are biomarkers for different chronic diseases such as asthma, diabetes, cystic fibrosis or chronic obstructive pulmonary disease, and respiratory infections that significantly aggravate the above conditions. These diseases were selected because of the high number of patients suffering from them and the current under-diagnosis and poor management...

In this communication, we present a versatile, home-developed, and portable electronic nose used to discriminate biomarkers of different diseases through the breath. The electronic nose is equipped with embedded control, support 16 different micro-sensors (8 commercial sensors and 8 home-made sensors), instrumentation electronics, rechargeable batteries, pump and electrovalve to control the way of the sampling gas, touch screen and IEEE 802.11 transceiver for wireless communication. We have used samples corresponding with different levels of gravity of illnesses. Several measurements were made to check the performance of the prototype in the discrimination of different biomarkers of diseases.

In this work, ZnO nanoparticle resistive sensors decorated with rare earths (REs; including Er, Tb, Eu and Dy) were used at room temperature to detect atmospheric pollutant gases (NO, CO and CH). Sensitive films were prepared by drop casting from aqueous solutions of ZnO nanoparticles (NPs) and trivalent RE ions. The sensors were continuously illuminated by ultraviolet light during the detection processes. The effect of photoactivation of the sensitive films was studied, as well as the influence of humidity on the response of the sensors to polluting gases. Comparative studies on the detection properties of the sensors showed how the presence of REs increased the response to the gases detected. Low concentrations of pollutant gases (50 ppb NO, 1 ppm CO and 3 ppm CH) were detected at room temperature. The detection mechanisms were then discussed in terms of the possible oxidation-reduction (redox) reaction in both dry and humid air atmospheres.

This work presents a device, “dropcaster”, developed to automate and optimize the deposition process of the sensitive layer of gas sensors using the drop–casting technique. It is designed to development sensors in the research phase of different materials and the study of their behavior and response to different gaseous compounds.

This work presents the development of tin oxide nanofibers (NFs) and nanoribbons (NRs) sensors with graphene as a dopant for the detection of volatile organic compounds (VOCs) corresponding to different chronic diseases (asthma, chronic obstructive pulmonary disease, cystic fibrosis or diabetes). This research aims to determine the ability of these sensors to differentiate between gas samples corresponding to healthy people and patients with a disease. The nanostructures were grown by electrospinning and deposited on silicon substrates with micro-heaters integrated. The morphology of NFs and NRs was characterized by Scanning Electron Microscopy (SEM). A gas line was assembled and programmed to measure a wide range of gases (ethanol, acetone, NO and CO) at different concentrations simulating human breath conditions. Measurements were made in the presence and absence of humidity to evaluate its effect. The sensors were able to differentiate between the concentrations corresponding to a healthy person and a patient with one of the selected diseases. These were sensitive to biomarkers such as acetone and ethanol at low operating temperatures (with responses above 35%). Furthermore, CO and NO response was at high temperatures (above 5%). The sensors had a rapid response, with times of 50 s and recovery periods of about 10 min.