SELEX-derived DNA aptamer utilized for sensitive electrochemical biosensing of Toxoplasma gondii surface antigen 1

Toxoplasma gondii (T. gondii) is a global parasitic pathogen with significant health implications. Effective diagnosis is crucial, especially for vulnerable populations like immunocompromised individuals and pregnant women. Here, we developed a novel electrochemical aptasensor for detecting Surface Antigen 1 (SAG1), a key biomarker for acute T. gondii infections. New high-affinity aptamers (SOK3, SOK14, and SOK18) specific to SAG1 were identified using SELEX method. The aptamers were then immobilized onto screen-printed carbon electrodes (SPE) modified with graphene quantum dots (GQDs). Physicochemical characterization confirmed successful aptasensor fabrication. SOK14 was identified as optimal for SAG1 detection due to its lower dissociation constant and distinct current response upon protein binding. Square wave voltammetry (SWV) showed a linear response from 0.01 to 100 nM SAG1 (n = 3), correlating with [Fe(CN)₆]^3-/4- oxidation peak current changes and achieving a low detection limit of 11.5 pM with relative standard deviations ranging from 3.3 to 4.9 %. Selectivity studies against other nonspecific biomarkers for other pathogens validated the aptasensor's specificity. Application of the aptasensor in spiked serum samples indicated its efficiency in complex biological samples. This platform enables rapid, on-site detection of T. gondii with high sensitivity, selectivity, and reliability in serum samples, supporting early diagnosis and timely treatment to prevent complications.