Copper ions (Cu 2+ ), as a crucial trace element, play a vital role in living organisms. Thus, the detection of Cu 2+ is of great significance for disease prevention and diagnosis. Nanochannel devices with an excellent nanoconfinement effect show great potential in recognizing and detecting Cu 2+ ions. However, these devices often require complicated modification and treatment, which not only damages the membrane structure, but also induces nonspecific, low-sensitivity and non-repeatable detection. Herein, a 2D MXene-carboxymethyl chitosan (MXene/CMC) freestanding membrane with ordered lamellar channels was developed by a super-assembly strategy. The introduction of CMC provides abundant space charges, improving the nanoconfinement effect of the nanochannel. Importantly, the CMC can chelate with Cu 2+ ions, endowing the MXene/CMC with the ability to detect Cu 2+ . The formation of CMC-Cu 2+ complexes decreases the space charges, leading to a discernible variation in the current signal. Therefore, MXene/CMC can achieve highly sensitive and stable Cu 2+ detection based on the characteristics of nanochannel composition. The linear response range for Cu 2+ detection is 10 -9 to 10 -5 M with a low detection limit of 0.095 nM. Notably, MXene/CMC was successfully applied for Cu 2+ detection in real water and fetal bovine serum samples. This work provides a simple, highly sensitive and stable detection platform based on the properties of the nanochannel composition.