Epidermal growth factor receptor (EGFR) mutation status is pivotal in predicting the efficacy of tyrosine kinase inhibitor treatments against tumors. Among EGFR mutations, the E746–A750 deletion is particularly common and accurately quantifying it can guide targeted therapies. This study introduces a novel visual sensing technology using the clustered regularly interspaced short palindromic repeats (CRISPR)/Cas12a system guided by ligation-initiated loop-mediated isothermal amplification (LAMP) to detect the del E746–A750 mutation in EGFR. Conventional LAMP primers were simplified by designing a pair of target-specific stem-loop DNA probes, enabling selective amplification of the target DNA. The CRISPR/Cas12a system was employed to identify the target nucleic acid and activate Cas12a trans-cleavage activity, thereby enhancing the specificity of the assay. Furthermore, the biosensor utilized high-performance nanomaterials such as triangular gold nanoparticles and graphdiyne, known for their large specific surface area, to enhance sensitivity effectively as a sensing platform. The proposed biosensor demonstrated outstanding specificity, achieving a low detection limit of 17 fM (S/N=3). Consequently, this innovative strategy not only expands the application scope of CRISPR/Cas12a technology but also introduces a promising approach for clinical diagnostics in modern medicine.