Serotonin is a principal neurotransmitter that actively takes part in our behavioral as well as biological activities. Hence, its detection plays a vital role in understanding the intricate connections between this neurotransmitter and various physiological processes. Consequently, the development of sensitive and reliable electrochemical sensors for serotonin detection is of paramount importance. In this study, we present a different approach for synthesizing a highly stable composite of Nb2CTx and protonated carbon nitride (Nb2CTx/PCN) utilizing the electrostatic interaction between them. The synthesized Nb2CTx/PCN composite was utilized for the construction of an electrochemical sensor dedicated to serotonin analysis. The developed sensor exhibits remarkable performance, offering enhanced sensitivity, selectivity and detection limits of 63.24 nM over a concentration range of 1-100 μM for serotonin detection in human serum. A versatile thread-based sensing platform is made to validate the sensor performance. Our findings pave the way for significant advancements in the field of MXene-based composites for neurotransmitter analysis, enabling researchers and clinicians to gain deeper insights into the role of serotonin in human health and diseases. © 2023 American Chemical Society.