Very simple and ultra-sensitive fluorescence resonance energy transfer aptasensor for turn-on C-reactive protein detection in biological matrices.

In the present study, an ultra-sensitive, very simple, and specific fluorescence resonance energy transfer (FRET)-based aptasensor was developed to detect C-reactive protein (CRP). CRP is a critical clinical biomarker and a sensitive indicator of inflammation, tissue damage, and infectious illnesses. Our turn off-on aptasensor system utilizes 6-carboxyfluorescein (5-FAM) dye-labeled aptamer assembled on graphene oxide (GO). The noncovalent assembly between the aptamer and GO initially quenches the fluorescence of the dye through FRET, creating a "turn-off" state. Upon addition of CRP protein, the aptamer binds to CRP, causing the dye to separate from GO, thereby recovering the fluorescence signal and creating a "turn-on" state. Under optimal conditions, the aptasensor exhibits two linear ranges (33-82 fg/ml and 114-207 fg/ml) and an exceptional limit of detection (LOD) of 2.27 fg/ml. This ultra-sensitive aptasensor demonstrates excellent selectivity, as potential interference from other substances was negligible. Compared to other methods, our proposed turn off-on aptasensor-assembled GO offers a more extensive detection range and significantly higher sensitivity. Additionally, it yields satisfactory results by applying 1 µl of real positive and negative serum samples, showcasing its potential for practical applications in clinical diagnostics.