ACh is a crucial neurotransmitter present in cholinergic neurons scattered across various regions in the brain and spinal cord. These neurons are responsible for a range of functions such as motor activity and cognitive processing. When ACh is released by a cholinergic neuron, it attaches to specific receptors located on the neighboring neuron's surface. These receptors serve as the conduit for signal transmission between cells. In Alzheimer's disease, the brain typically experiences a decline in cholinergic neurons located in the basal forebrain, resulting in decreased levels of ACh and a reduction in the enzyme responsible for synthesizing ACh, choline acetyltransferase, in the cerebral cortex. Kim et al. presented receptor-modified carbon nanotube sensors for the detection of acetylcholine (ACh), an important neurotransmitter. They successfully expressed the M1 muscarinic acetylcholine receptor (M1 mAChR), which belongs to a family of G protein-coupled receptors (GPCRs), in E. coli and coated single-walled carbon nanotube (SWCNT)-field effect transistors (FETs) with a lipid membrane including the receptor. This enabled the highly selective and sensitive detection of ACh. The sensor was capable of detecting ACh at a concentration of 100 pM, which is very low. The sensor was also able to selectively detect ACh among other neurotransmitters. This is the first instance of real-time detection of ACh using specific binding between ACh and M1 mAChR. The researchers believe that this could lead to breakthroughs in various applications such as disease diagnosis and drug screening. The team developed ACh sensors using swCNT-FETs functionalized with lipid membranes incorporating M1 mAChR, a specific bio-recognition receptor of ACh molecules. The sensors could detect ACh in real-time at a concentration of 100 pM, which is a significant improvement in sensitivity compared to existing methods. The sensors were also selective in responding only to ACh among other neurotransmitters. The highly sensitive and selective sensors for neurotransmitters could be useful for various biomedical applications such as research on disease mechanism and rapid diagnostics.