The COVID-19 pandemic has taught us valuable lessons, especially the urgent need for a widespread, rapid and sensitive diagnostic tool. To this, the integration of bidimensional nanomaterials, particularly graphene, into point-of-care biomedical devices is a groundbreaking strategy able to potentially revolutionize the diagnostic landscape. Despite advancements in the fabrication of these biosensors, the relationship between their surface biofunctionalization and sensing performance remains unclear. Here, we demonstrate that the combination of careful sensor fabrication and its precise surface biofunctionalization is crucial for exalting the sensing performances of 2D biosensors. Specifically, we have biofunctionalized Graphene Field-Effect Transistor (GFET) sensors surface through different biochemical reactions to promote either random/heterogeneous or oriented/homogeneous immobilization of the Anti-SARS-CoV-2 spike protein antibody. Each strategy was thoroughly characterized by in-silico simulations, physicochemical and biochemical techniques and electrical characterization. Subsequently, both biosensors were tested in the label-free direct titration of SARS-CoV-2 virus in simulated clinical samples, avoiding sample preprocessing and within short timeframes. Remarkably, the oriented GFET biosensor exhibited significantly enhanced reproducibility and responsiveness, surpassing the detection sensitivity of conventional non-oriented GFET by more than twofold. This breakthrough not only involves direct implications for COVID-19 surveillance and next pandemic preparedness but also clarify an unexplored mechanistic dimension of biosensor research utilizing 2D-nanomaterials.

In this work, a functional Z2-FET DRAM memory matrix is experimentally demonstrated for the first time. Word-level operation with simultaneous reading and programming accesses is successfully proved. Disturbance is also explored, and the results demonstrate bitline disturbance immunity. Furthermore, the fabricated memory matrix, which includes only one selector per word-line, facilitates the scalability of the memory for increasing array dimensions.

Molybdenum disulfide (MoS ₂ ) MOSFETs have been widely reported to exhibit hysteresis behavior, which is usually attributed to charge trapping effects due to defective/sub-stoichiometric compositions in the material, or defects near, or at, the oxide/channel interfaces. It is also suggested that defective MoS ₂ transistors show current limitations caused by the Schottky barrier junctions formed at the contacts. Here, we report on the static and dynamic device response of back-gated MoS ₂ transistors directly fabricated on a SiO ₂ /Si substrate using chemical vapor deposition synthesis, without film transfer, and standard CMOS optical lithography. The devices exhibit an atypical hysteresis in the transfer characteristics, as well as a delayed response in the formation of the conducting channel in response to voltage pulses applied to the back gate. Analysis of the output characteristic is consistent with two back-to-back Schottky diodes, allowing the Fermi level pinning position at the Ni/MoS ₂ source and drain contacts and blocking the MoS ₂ hole channel. Capacitance-voltage characterization demonstrates that the grown MoS ₂ thin film is p-type, resulting in a nominally-off, inversion mode, n-channel device. Analysis of the transient response and hysteresis as a function of device temperature, illumination and ambient conditions indicates that the dynamic response of the device is determined by the net charge in the MoS ₂ film combined with the minority carrier generation lifetime in the underlying silicon substrate. The work demonstrates the strong dependence of the device response time on substrate, temperature, illumination, and net charge in the MoS ₂ layer opening the possibility of applications in photo-detectors and sensors.