Deoxyribonucleic acid (DNA) detection is essential for the accurate and early diagnosis of a disease. In this study, a femtomolar DNA detection method based on the exploitation of the localized surface plasmon (LSP) resonance of gold nanoparticles (AuNPs) was developed. We prepared Poly Ethylen Glycol (PEG) functionalized AuNPs with a specific DNA capture probe (CP) directly modified on the gold surface. Two strategies are proposed using different kinds of CP to detect the target DNA (tDNA). In the first strategy, CP is the complementary of the complete sequence of the DNA (CCP method). For the second strategy, we used two CPs, which were half complementary to tDNA, and these were hybridized with tDNA to form sandwich structures (MIX method). The results showed that our detection methods are highly sensitive and that the limits of detection of 124 a m and 2.54 f m tDNA can be reached when using the CCP and MIX methods, respectively. In addition, the specificity of our two strategies is also demonstrated with mismatched DNAs. The proposed method provides a simple, fast, sensitive and specific DNA biosensor, which has the potential to be used for point‐of‐care tests (POCT).