- 4 publications
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Graphene-Based Pressure Sensor Application in Non-Invasive Pulse Wave Velocity Continuous Estimation
Irene Buraioli, Stefania Vitale, Andrea Valerio, Alessandro Sanginario, Dario Leone, Sabrina Conoci, Artur Ciesielski, Alberto Milan, Danilo Demarchi, Paolo Samorì
Adv. Mater. Technol., 2024, in press (open access). Featured in Advanced Materials Technologies Editors’ Choice, Hot Topic: Carbon, Graphite, and Graphene, and Hot Topic: Wearable Sensors.
Monitoring the cardiovascular health of patients and early diagnosis of heart diseases are highly sought after as they can represent a true cornerstone in tomorrow's healthcare surveillance. Here, an unprecedented non-invasive device prototype is reported for pulse wave velocity (PWV) measurement based on a piezoelectric graphene pressure sensor. PWV is a critical health indicator that estimates arterial stiffness by measuring the velocity of arterial pulse flow through the circulatory system. The sensor incorporates advanced electronic components and data analysis tools, enabling the measurement of pulse transit time (PTT), that is the time required for the pulse wave to travel between carotid and femoral artery sites. Significantly, the outcomes obtained through the novel method, which involved monitoring 10 patients within clinical environment, show statistical similarity to results obtained using established technology for the PWV estimation such as SphygmoCor. In particular, the mean difference between measurements done with the two techniques resulted in 0.1 m s−1, that is <2%, underscoring the reliability of the novel device. The technology holds big promise for enhancing cardiovascular healthcare delivery: it is wearable, potentially exploitable by a non-expert user, and it needs to be powered with just 0.2 V, thus it can become compatible even with applications in point-of-care settings.
Reduced Graphene Oxide-Based Flexible Pressure Sensor for Biomedical Applications
A. Sanginario, I. Buraioli, M. Boscherini, S. Vitale, S. Conoci, D. Botto, D. Leone, A. Milan, A. Ciesielski, P. Samorì, D. Demarchi
IEEE Sens. J., 2024, 24, 37090–37103. Link to article (open access).
Pressure sensing is a crucial technique for various biomedical applications, where it can provide valuable information about the health and function of different organs and systems. This article reports the development of a novel integrated pressure sensor based on modified reduced graphene oxide (rGO), a graphene-derivative material with enhanced piezoresistive properties. The sensor is fabricated on a flexible printed circuit board (PCB) substrate and conditioned by a smart current-based Wheatstone bridge circuit, which enables high sensitivity, wide detection range, fast response and recovery, and good stability under cyclic loading. The sensor achieves a measured sensitivity of 0.281 kPa−1 (at 0.5 kPa load). A mechanical system is also designed to adapt the sensor to different anatomical sites and improve its elastic recovery. The sensor’s functionality is initially demonstrated through its response to controlled mechanical stimulation, achieving a signal-to-noise ratio (SNR) of 25 dB. Subsequently, in a practical application, physiological signals from the carotid and femoral arteries of volunteers were acquired. The system effectively captured the pulse waveforms with high fidelity and accuracy (23.5-dB SNR) and measured the pulse transit time, an important parameter for estimating the pulse wave velocity (PWV) and arterial stiffness. The sensor is not limited to this specific application and can be easily extended to other domains where pressure sensing is required. In conclusion, it offers a low-cost, flexible, and user-friendly solution for noninvasive biomedical monitoring and diagnosis.
Quantifying the effect of nanosheet dimensions on the piezoresistive response of printed graphene nanosheet networks
E. Caffrey, J. M. Munuera, T. Carey, J. N. Coleman
Nanoscale Horiz., 2024, 9, 1774–1784. Link to article (open access).
Printed networks of 2D nanosheets have found a range of applications in areas including electronic devices, energy storage systems and sensors. For example, the ability to print graphene networks onto flexible substrates enables the production of high-performance strain sensors. The network resistivity is known to be sensitive to the nanosheet dimensions which implies the piezoresistance might also be size-dependent. In this study, the effect of nanosheet thickness on the piezoresistive response of nanosheet networks has been investigated. To achieve this, we liquid-exfoliated graphene nanosheets which were then subjected to centrifugation-based size selection followed by spray deposition onto flexible substrates. The resultant devices show increasing resistivity and gauge factor with increasing nanosheet thickness. We analyse the resistivity versus thickness data using a recently reported model and develop a new model to fit the gauge factor versus thickness data. This analysis allowed us to differentiate between the effect of strain on inter-nanosheet junctions and the straining of the individual nanosheets within the network. Surprisingly, our data implies the nanosheets themselves to display a negative piezo response.
Defect Engineering of MoTe2 via Thiol Treatment for Type III van der Waals Heterojunction Phototransistor
Y. Jeong, B. Han, A. Tamayo, N. Claes, S. Bals, P. Samorì
ACS Nano, 2024, 18, 18334–18343. Link to article (open access).
Molybdenum ditelluride (MoTe2) nanosheets have displayed intriguing physicochemical properties and opto-electric characteristics as a result of their tunable and small band gap (Eg ∼ 1 eV), facilitating concurrent electron and hole transport. Despite the numerous efforts devoted to the development of p-type MoTe2 field-effect transistors (FETs), the presence of tellurium (Te) point vacancies has caused serious reliability issues. Here, we overcome this major limitation by treating the MoTe2 surface with thiolated molecules to heal Te vacancies. Comprehensive materials and electrical characterizations provided unambiguous evidence for the efficient chemisorption of butanethiol. Our thiol-treated MoTe2 FET exhibited a 10-fold increase in hole current and a positive threshold voltage shift of 25 V, indicative of efficient hole carrier doping. We demonstrated that our powerful molecular engineering strategy can be extended to the controlled formation of van der Waals heterostructures by developing an n-SnS2/thiol-MoTe2 junction FET (thiol-JFET). Notably, the thiol-JFET exhibited a significant negative photoresponse with a responsivity of 50 A W–1 and a fast response time of 80 ms based on band-to-band tunneling. More interestingly, the thiol-JFET displayed a gate tunable trimodal photodetection comprising two photoactive modes (positive and negative photoresponse) and one photoinactive mode. These findings underscore the potential of molecular engineering approaches in enhancing the performance and functionality of MoTe2-based nanodevices as key components in advanced 2D-based optoelectronics.
