G4S Linker is a commonly used flexible amino acid linker that plays a significant role in antibody expression and design. The sequence of this linker is (Gly-Gly-Gly-Gly-Ser)n, where "n" represents the number of repetitions. By altering the value of "n," the length of the GS amino acid chain can be optimized to achieve appropriate separation of antibody or protein domain functions or to maintain necessary inter-domain interactions. G4S Linker is typically used in single-chain variable fragments (scFv) and chimeric antigen receptors (CARs) to connect the variable heavy (VH) and variable light (VL) domains for the recognition of target antigens. The length of this linker is crucial for controlling the stability of scFv and the non-covalent association between the VH and VL domains. In CAR structures, the G4S Linker is located in the extracellular domain of the scFv, helping to maintain the structure and function of the CAR. Additionally, G4S Linker is used to detect CAR cells designed with G4S Linker, which offers high specificity and sensitivity.