Dottorato in INGEGNERIA ELETTRICA, DEI MATERIALI E DELLE
NANOTECNOLOGIE

Titolo della tesi: DEVELOPMENT OF GRAPHENE-BASED SENSORS TO BE INTEGRATED INTO A SMART TEXTILE

In most of the countries (developed and developing) the life expectancy has been increasing over the years with reference to taking of health care and timely diagnosis, thanks to novel inventions in medicine, public health sector and environmental hygiene. However, the death rate is also increased and it expected to continue in same level and causing a significant burden on the socio-economic structure of these countries and already life expectancy is considerably less in undeveloped nations. Therefore, it is quite necessary to develop cost-effective, easy-to-use systems to improve the health conditions of human-being. The solution would be remote health monitoring which is based on non-invasive and wearable sensors, actuators and modern communication systems and these systems should be available at low cost- and handy (compatible), it allows the human beings to improve, monitor and maintain the health conditions at comfort while doing their regular daily activities instead of expensive healthcare facilities. The main objective of this research activity is to Develop and Characterize Novel Graphene-based Polymer Nanocomposites for Anti-bacterial coatings, Health Monitoring Sensors, and Flexible electrodes for Energy generation applications. In particular, this thesis discusses and presents two types of healthcare sensors: (a) Sweat detection; and (b) Respiration monitoring. Apart of developing wearable sensors it is also necessary to look after the power management and thus the research activity also focused on the power supply and so a Flexible Battery has developed. Recently, personalized healthcare devices are attracting an increasing interest due to their ability to provide rapid, easy detection and off-site diagnosis. Among them, wearable sweat sensors enable a non-invasive and continuous tracking of individuals’ health status. Yet, the development of these sensors is facing several challenges including wearability, easy-to-use, and cost-effectiveness. In order to overcome these bottlenecks, developing a flexible, light-weight graphene-based polymer nanocomposite sensor for sweat detection is proposed. The main idea is to realize a self-powered membrane able to provide a voltage signal in presence of sweat with signal amplitude depending on sweat salt concentration. The produced sensor membrane is chemically and morphologically well characterized. Then, its wettability properties and electrochemical performances are assessed. The obtained results indicated that the proposed graphene-based membrane is a promising candidate for next-generation wearable sweat sensing devices. Later, the research activity has carried out on sensorized face mask for respiration monitoring. In fact, the most crucial vital sign of the human body is respiration. In particular, wearable strain-based sensors have become critical for real-time monitoring of human respiration. However, there are some problems related to present sensors, including incompatibility, low durability, complexity, low sensitivity, inconvenience and high fabrication cost. In this research work to overcome the respiration sensors issues a cost-effective solution to produce a graphene-based sensorized face mask has been developed, which is antimicrobial, biocompatible for non-invasive tracking of respiration signals. Taking advantage of the durability and sensitivity of wearable graphene-based sensors promotes its application for practical monitoring in the healthcare system. Sensor performance is assessed by a simulated real test in which experimental results show an immediate response and an excellent reproducibility with clear differentiation between various signals, which makes it a potential candidate for respiration monitoring to assist person’s state of health. Additionally, the power supply to the above discussed wearable sensors was identified as a major concern and it is another challenge. The complex fabrication of battery (power source) strategies utilized by recent wearable sensing systems significantly limit their applications for continuous monitoring of health indicators. Therefore, a novel flexible battery is produced through a cost-effective procedure for low energy generation applications. In addition, the electrodes are produced through an easy process, without the use of any chemical or physical doping agent. The flexible electrodes are morphologically and chemically characterized and their applicability as polymeric electrodes is investigated through electrochemical tests. Furthermore, an equivalent circuit model (ECM) is adapted to simulate the discharge characteristics of the developed flexible battery under two different loads. Specifically, the discharge characteristics of the battery under resistive loads ranging from 20 to 1000 Ω and current loads ranging from 0.2 to 0.5 mA were investigated. In summary, the major findings from this research activity on anti-bacterial coatings for hospital appliances have shown that using the synergistic combination of graphene nanoplatelets (GNP) and zinc oxide (ZnO) nanostructures exhibits hydrophobic (CA = 94.84 ± 1.70⁰) and water resistance properties. In the case of healthcare sensors, the novel sweat sensor is proven for its simple detection of salt concentration with a response time of less than 10 s. The output voltage is proportional with a correlation coefficient (R2) greater than 0.98, and a generated voltage above ⁓280 mV indicates dehydration or chronic disorders. And, the respiration monitoring sensors report high sensitivity with GF = 4.2 under applied strain (ε) of 0.9% and measured ΔR/R0 ⁓6.8% higher for abnormal breath signals. Furthermore, a novel battery (OCV=1.1V) is developed with the aim of flexible and portable power source for wearable health monitoring devices. These results indicate that the developed graphene-based coatings, sensors and batteries have a potential application in advanced healthcare systems, eventually reducing burden of health expenses and improving quality of life.