7.3.3. Nucleic Acids

One of the most important biomolecules is deoxyribonucleic acid (DNA), which is responsible for determining inherited traits and storing genetic information necessary for the replication of living organisms. The sensors that use DNA molecules are a grea<sup>t</sup> tool not only to detect individual DNA or RNA molecules but also molecules belonging to other classes of biomolecules [83–86]. Nucleic acids do not have properties that would be useful for their direct detection, so their detection requires the use of, e.g., fluorescent markers [14,87]. Table 5 shows an exemplary QDs-based sensors for nucleic acids determination.



Nejdl et al. reported a systematic study of the self-assembly of CdTe QDs stabilized by mercaptosuccinic acid (MSA) These QDs were used for the preparation of a fluorescent (off–on) probe based on methylene blue as a quencher for the specific determination of nucleic acid from urine. Using this technique, it was possible to determine the DNA isolated from the urine and decide whether the amount of DNA was in an acceptable range. The LOD was calculated as 0.003 <sup>μ</sup>g·mL−<sup>1</sup> DNA. Such constructed sensing systems can be used for very sensitive detection of DNA [83].

Mohammadinejad group has prepared mercaptosuccinic acid-capped CdTe quantum dots, which were successfully fabricated as a simple synthesized and sensitive fluorescence sensor for tandem determination of mitoxantrone and ribonucleic acid and also monitoring their interaction. Due to the adsorption of positively-charged mitoxantrone on the surface of negatively-charged quantum dots through electrostatic interactions, the fluorescence intensity of mercaptosuccinic acid-capped CdTe QDs can be effectively quenched by mitoxantrone. After addition of ribonucleic acid to mitoxantrone–QDs solution, mitoxantrone mainly bound to the uracil (C=O) and adenine (C=N) sites of ribonucleic acid. A complex which was formed between mitoxantrone and ribonucleic acid, prevented more interactions between quantum dots and anticancer drug resulted in enhancing of fluorescence intensity. Quantitative results were obtained for all combinations with a linear range of 20–10,000 pM and a LOD of 3–52 pM [87].
