The biosensor was applied to spiked untreated human serum and saliva, and was able to analyze the endogenous TP53 status in only 50 ng of cDNA, synthetized by reverse transcriptase from total RNA (RNAt), which was extracted from one non-tumorigenic epithelial (MCF-10A) and two cancer (MCF-7 and SK-BR-3) human breast cells. The gene discussed is TP53; the disease is cancer.