▎ 摘　　要

NOVELTY - Biossensor comprises a gold working electrode with immobilized specific DNA probe to detect microRNA (miRNA) 184 in patient samples. USE - Biossensor for diagnosis of major depressive disorder in elderly patients. ADVANTAGE - The biosensor is highly sensitive, requiring a low amount of sample, specific, is capable of differentiating healthy and depressed elderly patients with real samples and excellent capacity for regeneration and stability. DETAILED DESCRIPTION - An INDEPENDENT CLAIM is included for a method for constructing biossensor involves: (A) carrying out immobilization of the DNA probe DEP1S having a nucleotide sequence comprising 22 nucleobases of (SEQ ID NO: Not defined), that is 5'(HS) acccttatcagttctccgtccg-3, on the working electrodes, by chemosorption; (B) pre-treating the plasma to be used in the biosensor, by exposure to high temperature at 100 degrees C for 30 minutes and under ultra-violet light for 30 minutes; (C) detecting the complementary target DEP2 of the nucleotide sequence comprising 22 nucleobases of (SEQ ID NO: Not defined), that is 5'-cggacggagaacugauaagggu-3 ', indirectly in real time, using the intercalating ethidium bromide through the technique of differential pulse voltammetry; and (D) detecting miRNA 184 in samples of total miRNA extracted from patients, indirectly in real time, using the ethidium bromide indicator using the differential pulse voltammetry technique.