Rapid Detection of Saxitoxin Using a Nucleic Acid Aptamer Biosensor Based on Graphene Oxide as a Fluorescence Quencher

Saxitoxin (STX) is a toxin with paralyzing and lethal properties, necessitating the development of a simple analytical method. This study developed a nucleic acid aptamer biosensor using graphene oxide (GO) as a fluorescence quencher for STX detection. GO was combined with M30-f, an STX nucleic acid aptamer modification with 5-carboxyfluorescein, which can produce fluorescence absorption under the conditions of an excitation wavelength of 408 nm and emission wavelength of 515 nm. Based on the principle of fluorescence resonance energy transfer, the fluorescence of M30-f was quenched. In the presence of STX, M30-f specifically binds to STX and dissociates from the GO surface, thereby restoring fluorescence. The STX content can be quantitatively detected through differences in fluorescence absorption. The influence of ultrasonic time on the fluorescence quenching ability of GO was investigated. The aqueous solution of graphene oxide, 30GO, optimized by ultrasound treatment for a duration of 30 min, demonstrated excellent fluorescence quenching capability. 30GO was analyzed utilizing various characterization techniques, including SEM, FT-IR, UV, XPS, XRD, AFM, and contact angle measurements. The methodological validation showed that the established STX sensor exhibits excellent linearity within a concentration range of 10–100,000 ng/L, with a limit of detection (LOD) as low as 0.098 μg/L. In addition, the results further demonstrated the sensor’s high specificity for detecting neurotoxic shellfish toxin STX. The recovery rate for clam samples ranged from 89.12% to 104.71%, while that for oyster samples ranged from 91.20% to 109.65%, with relative standard deviations (RSDs) all below 3%. This aptamer sensor is characterized by its simplicity, high sensitivity, and broad detection range, providing significant technical support for advancing marine biotoxin research.