Vol.:(0123456789) 1 3 Journal of the Iranian Chemical Society https://doi.org/10.1007/s13738-020-02035-5 ORIGINAL PAPER A novel G‑quadruplex DNA‑based biosensor for sensitive electrochemical determination of thallium(I) ions Nastaran Ebrahimi 1  · Jahan Bakhsh Raoof 1  · Reza Ojani 1  · Maryam Ebrahimi 1 Received: 12 February 2020 / Accepted: 10 August 2020 © Iranian Chemical Society 2020 Abstract We used electroactive label crystal violet (CVi) as a G-quadruplex (G4) DNA intercalator for sensitive electrochemical sensing of Tl + . Diferential pulse voltammetry (DPV) and cyclic voltammetry (CV) techniques were applied for electro- chemical determination of Tl + at the surface of carbon paste electrode as working electrode. Under optimized conditions, the diference in the DPV reduction peak currents of CVi before and after its intercalation into the formed G4 (ΔI) used an analytical signal for determination of Tl + was linearly related to the concentration of Tl + over the ranges of 0.4–50.0 nM and 0.1–10 μM. Limit of detection was calculated 0.341 nM (S/N = 3). The biosensor showed good selectivity and satisfactory results in real sample analysis of Tl + . Keywords Thallium(I) ions · Intramolecular G-quadruplex · Crystal violet · DNA biosensor Introduction Among several sources of environmental pollutants, heavy metal ions such as Pb 2+ , Mn 2+ and Hg 2+ are serious ones. Heavy metals can generate polymorphism in genes and cause many diseases [1, 2]. Thallium is one of the most important heavy metals with diferent monovalent and trivalent forms that its toxicity nature is known. Tl + is more toxic than Cu 2+ , Cd 2+ , Ni 2+ , Mn 2+ , Sn 2+ , As 3+ and Pb 2+ , while its toxicity is similar to Hg 2+ [3, 4]. Therefore, it is important to develop sensitive and selective analytical methods for determination of this toxic ion. Among the various analytical techniques used for the detection of thallium ions, such as electrochemical method [5], electrothermal atomic absorption spectrometry [6], cathode glow discharge-atomic emission spectrometer [7] and ICP-OES [8] methods, electrochemical methods have attracted great attentions because of their excellent proper- ties, such as high selectivity and sensitivity, price, simplicity and short analytical time. Recently, several G-quadruplex DNA (G4)-based biosen- sors have been reported for determination of some heavy metal ions [1, 9, 10]. Nucleic acids with guanine-rich sequences are known as G4, stabilized in the presence of some metal ions such as K + , Na + , Pb 2+ and Tl + [11–13]. Some electroactive molecules are able to intercalate into this structure and used as G4-selective probes for sensitive electrochemical sensing of metal ions [9, 10, 14]. CVi as a triarylmethane dye was proven to be an efective G4 binder [14, 15] and was used for Pb 2+ sensing as a G4 intercalator [14]. We used this electroactive dye for voltammetric sens- ing of Tl + ions according to its ability to be as a G4 binder, too. To the best our knowledge, the electrochemical determi- nation of Tl + based on G4 DNA using CVi as an intercala- tor electroactive label has not been reported. Therefore, we developed a new G4-based biosensor for electrochemical detection of thallium(I) ions. We investigated the selectiv- ity of proposed biosensor and its ability to analyze of real sample. * Jahan Bakhsh Raoof j.raoof@umz.ac.ir 1 Electroanalytical Chemistry Research Laboratory, Department of Analytical Chemistry, Faculty of Chemistry, University of Mazandaran, Babolsar, Iran