Application of cadmium sulfide nanoparticles as oligonucleotide labels for the electrochemical detection of NOS terminator gene sequences

A mercaptoacetic acid (MAA)-modified cadmium sulfide (CdS) nanoparticle was synthesized in aqueous solution and used as an oligonucleotide label for the electrochemical detection of nopaline synthase (NOS) terminator gene sequence. The carboxyl groups on the surface of the CdS nanoparticle can be easily covalently linked with NH₂-modified NOS oligonucleotide probe sequences. The target ssDNA sequence was fixed onto the electrode surface by covalently linking to a mercaptoethanol self-assembled gold electrode, and the DNA hybridization of target ssDNA with probe ssDNA was accomplished on the electrode surface. The CdS nanoparticles anchored on the hybrids were dissolved in the solution by the oxidation with HNO₃ and further detected by a sensitive differential pulse anodic stripping voltammetric method. The detection results can be used for monitoring the hybridization, and the NOS target sequence was satisfactorily detected in the approximate range from 8.0 × 10⁻¹² to 4.0 × 10⁻⁹ mol L⁻¹ with a detection limit of 2.75 × 10⁻¹² mol L⁻¹ (3σ). The established method extended the nanoparticle-labeled electrochemical DNA analysis to genetically modified organisms (GMOs) specific sequence samples with higher sensitivity and selectivity.