Label-Free Extended Gate Field-Effect Transistor for Sensing Microcystin-LR in Freshwater Samples

In this study, we developed a label-free biosensor based on aptamer-modified multi-walled carbon nanotube extended gate field-effect transistor (MWCNT-EG-FET) for easy and selective detection of microcystin-LR (MC-LR), a prominent cyanotoxin associated with liver damage, bleeding, and necrosis. EG-FET had two parts: a MOSFET and an extended-gate Au/SiO₂ electrode, which serves as the sensitive membrane. A custom-designed DNA oligonucleotide (5-NH₂-C₆-AN6) was used as MC-LR-targeting aptamer (MCTA). MWCNTs were functionalized with MCTA and then stably fixed on the sensitive membrane. The detection of MC-LR in freshwater was effectively achieved within 5 min by assessing the variations in electrical resistance that occur due to the selective interactions between MC-LR and MCTA. The detection limit and analytical sensitivity of the biosensor for MC-LR were found to be 0.134 ng/mL and 0.024 ng/mL, respectively. The sensitive membrane could be readily discarded if damaged, eliminating the need to replace the main transducer MOSFET. The developed sensor exhibits features such as straightforward preparation, swift response, potential for miniaturization, and ease of use, making it an attractive candidate for future integrated lab-on-chip systems for MC-LR detection in freshwater environments.