Many methods for early diagnosis of the cancer are using biomarkers, measuring indicators of some biological state. However, there is no proper detection kits because of low sensitivity and specificity of the biomarkers. This problem can be solved if very small amount of them can be detected effectively. Therefore, we have developed human albumin-based nanoparticle that encapsulates an excess of horseradish peroxidase (HRP) which is used extensively for ELISA assay. If it is applied to complementary principle of antigen-antibody reaction, it shows higher optical signal than many HRP-conjugated antibodies commercialized on the market. More specifically, it is detectable from 10fM to 1nM range of the probe. As a result, this research verifies that this albumin nanoparticle containing excess HRP enhances signal strength of probe detection contributing to more accurate and early diagnosis for breast cancer.