Neuromorphic devices utilizing atomically thin 2D materials show promise for large-scale computing by emulating biological neural networks. Floating gate transistors (FGTs) typically fall into two categories based on the selection of the semiconductor channel layer material. One category involves unipolar semiconductors that transmit only one type of majority carrier, while the second category consists of ambipolar semiconductors, tunable to switch the type of majority carrier. This flexibility enables devices to switch modes and respond to specific stimulation, such as molybdenum ditelluride (MoTe₂), proven to be valid as a channel material [1]. Here, MoTe₂, hexagonal boron nitride (h-BN), and graphene (Gr) were applied to construct the ambipolar FGT (AFGT). Additionally, access regions (ARs) were introduced in the AFGT to fabricate AR-based AFGT (AR-AFGT), altering the transmission mechanism of carriers in the channel layer compared with the AFGT device [2].2D van der Waal materials were stacked in the order of Gr/h-BN/MoTe₂ to fabricate AFGTs with source/drain electrodes overlapping the Gr, serving as the floating gate (FG), with a channel length of about 2 µm. Gr/h-BN/MoTe₂ AR-AFGTs were fabricated by placing ARs, which do not overlap with FG, in proximity to source/drain electrodes with a channel length of 10 µm. We measured and compared the transfer characteristic of AFGT and AR-AFGT devices. The AFGT exhibited obvious ambipolar behavior with dominant n-branch and p-branch. However, in the case of AR-AFGT, a significant n-branch portion was observed. These phenomena may arise from the AR increasing the distance from the electrode to the storage layer, indicating that MoTe₂ acts as a unipolar material. Our study compared AFGT and AR-AFGT devices, highlighting their unique traits. While AFGT exhibited significant ambipolar behavior, AR-AFGT, influenced by the increased distance, displayed a dist

The neurotransmitter acetylcholine (ACh) is hydrolyzed by acetylcholinesterase (AChE) into acetic acid and choline to terminate synaptic transmission (1). Organophosphorus (OPs) found in pesticides induce toxicity in organisms by irreversibly binding to AChE, leading to the phosphorylation of the serine residue at the active site. ACh cannot undergo hydrolysis by the phosphorylated enzyme, resulting in excessive stimulation of nerves and muscles, akin to a nerve agent (2). Our objective is to develop a rapid detection tool for determining the levels of pesticide residues in dairy products. In this study, we measured the release of hydrogen ions (H⁺) resulting from the hydrolysis of ACh by AChE, serving as an indirect method to evaluate the inhibitory effect of OPs on AChE. To detect the signals of H⁺ released during ACh decomposition, we used ITO-coated nanostructures modified with 3-aminopropyl trimethoxysilane (APTMS) as a sensing substrate integrated into the extended gate of a field-effect transistor (EGFET) biosensor. The amino group at the end of APTMS can bond with H⁺. By monitoring the changes in electrical signal from the EGFET biosensor, it is possible to know the concentration of H⁺ in the solution. The output characteristics (I_d-V_d) of the APTMS-modified ITO-VASiNW EGFET were measured using ACh solutions at different concentrations. A correlation was observed between I_d and ACh concentration within the tested range, exhibiting a sensitivity of 0.016 mA^1/2 / mM and an R² value of 0.9. A lower concentration of H⁺ indicates a more pronounced inhibitory effect on AChE by OPs and suggests higher levels of pesticide residues.

References

(1) Colović, M. B., Krstić, D. Z., Lazarević-Pašti, T. D., Bondžić, A. M., & Vasić, V. M. (2013). Acetylcholinesterase inhibitors: pharmacology and toxicology. Curr Neuropharmacol,