Diagnosis of breast cancer by analysis of sialic acid concentrations in human saliva by surface-enhanced Raman spectroscopy of silver nanoparticles

Breast cancer is the most common type of malignant tumor among women and their second leading cause of cancer-related deaths. The most common method for screening and diagnosis is mammography. Nonetheless, two main problems have been identified. First, the dose of radiation received during the test prevents the method from the use on women who are < 40 years old. Second, there can be mammogram failure owing to the lack of tumor contrast with the fibrous tissue. Therefore, there is a need for screening methods that will help to identify high-risk cases. We developed a biological marker test that can help to identify them. Increased levels of sialic acid (SA) in saliva are known to correlated with breast cancer. In this study, we evaluated the feasibility of Raman spectroscopy as a method for quantification of SA in saliva, using citrate-reduced silver nanoparticles (cit-Ag-NPs) as a surface-enhanced Raman spectroscopy (SERS) substrate. Quantification of SA was accomplished by measuring its intensity in saliva and comparing it with a calibration curve of SA standards. The mean SA concentration in saliva was found to be significantly higher among 100 breast cancer patients (18.3 +/- 9.4 mg.dL(-1); mean +/- SD) than among 106 healthy controls (3.5 +/- 1.0 mg.dL(-1)). The SERS test showed sensitivity of 94% and specificity 98% for detection of patients with breast cancer, assuming that SA concentration > 7 mg.dL(-1) is a cutoff for positive test results. Our findings prove the usefulness of this SERS technique as a simple, convenient, and highly sensitive method of quantitative analysis of SA in saliva. The simplicity of this nanotechnological test may help to substantially reduce the mortality among patients with breast cancer by providing women with a simple, noninvasive screening test that can be applied regardless of age or density of breast tissue.