*4.2. Cylindrospermopsin*

Cylindrospermopsin (CYN), a tricyclic alkaloid with a molecular mass of 415 Da, is a common cyanotoxin, and is produced by cyanobacteria including *Cylindrospermopsis*, *Anabaena*, *Umezakia,* and *Aphanizomenon* [160–166]. Cylindrospermopsin can cause DNA/RNA strand breakage and promote hepatotoxicity, cytoxicity, and genotoxicity through inhibiting protein translation and binding to DNA. The Falconer recommends a tentative guideline value of 1 ug L−<sup>1</sup> for cylindrospermopsin [166]. Recently, we fabricated a label-free impedimetric aptasensor based on a GO-thionine (TH-GO) nanocomposite for detection of CYN by covalent binding of the amino-terminated aptamer of CYN to TH-GO nanocomposite-modified GCE via glutaraldehyde (as shown in Figure 10) [167]. Using [Fe(CN)6]<sup>4</sup>−/3− as an electrochemically active probe, CYN can be detected as low as 0.117 ng mL−<sup>1</sup> in water. The as-proposed aptasensor has been employed for detecting CYN in spiked lake water samples, and satisfactory recoveries were obtained. With its superior performance characteristics combined with long-term stability (it retained approximately 74.7% of its initial value after being stored at 4 ◦C for 30 days) and excellent reusability (RSD = 2.1% within 10 reacting cycles), the as-developed aptasensor is a potential candidate for on-site CYN analysis.

**Figure 10.** Schematic representation of the label-free impedimetric aptasensor for detecting cylindrospermopsin (adapted from Zhao et al. 2015 [167], Copyright 2015 The Royal Society of Chemistry and reproduced with permission).
