Design of Aptamer-Gold Nanoparticles Based Colorimetric Assay for the Early Diagnosis of Breast Tumor

Combinatorial chemistry techniques based on the SELEX methodology were used for the identification of the specific aptamers. We have developed a highly specific colorimetric assay for breast tumor antigen (CA 15-3) that uses aptamer-gold nanoparticles (Apt-GNPs) conjugate, to combine the selectivity and affinity of aptamers and the spectroscopic advantages of gold nanoparticles to allow for the sensitive detection of CA 15-3. We have synthesized an Apt-GNPs conjugate that is specific to CA 15-3 and we used this conjugate system to detect CA 15-3 by monitoring the changes in the color and UV-vis extinction spectra of the Apt-GNPs that occur due to the aggregation of Goldnanoparticles. In this colorimetric assay we found, at very low concentration of CA 15-3 i. e.30 units the red color of Apt-GNPs conjugate turned purple and at higher concentration of CA 15-3 i. e. greater than500 units there were very less extent of aggregation, which is not visible as a change in color. We have checked the change in flocculation intensity in the presence of different concentration of CA 15-3 by UV-vis extinction spectra. The results obtained in this assay would be much helpful in the practical applications of Apt-GNPs conjugate and breast tumor diagnosis.