Deoxyribonucleic acid (DNA) and ribonucleic acid (RNA) play important roles in the storage of genetic information and protein biosynthesis. Nucleobases, which are nitrogenous bases, are the functional units of these nucleic acids. It is very important to detect changes in the sequence of DNA/RNA, as any mutations in them may cause harm to the organism. Our aim is to verify the use of (CdSe)3 Quantum Dots (QDs), owing to their distinctive optical and electronic properties, for sensing changes in DNA/RNA. Hence, in this work, we have focused on studying the interaction between (CdSe)3 QDs and the five nucleobases (adenine, guanine, cytosine, thymine and uracil) at various probable sites by means of density functional calculations. Several structural, electronic and optical properties, and charge transfer on interaction between the two, have been discussed. The present band gap and charge transfer calculations indicate that binding of (CdSe)3 to guanine is strongest and is weakest with uracil. The vibrational spectral analysis indicates that the intensities of the peaks due to (CdSe)3 enhance on interacting with the nucleobase, and a blue shift is observed in all the interactions. The presence of both the frontier orbitals (HOMO and LUMO) on the QD indicates that (CdSe)3 acts as a guardian of DNA and prevents it from damage. Hence, our studies direct that CdSe QDs can be successfully employed as sensors for these nucleobases.