Developing a fluorometric aptasensor based on carbon quantum dots and silver nanoparticles for the detection of adenosine

A new simple fluorometric aptasensor was developed for the determination of adenosine (AD) in human urine samples. A mixture of new and green nitrogen and sulfur co-doped carbon quantum dots (N,S-CQDs) as fluorescents and silver nanoparticles (AgNPs) as quenchers were utilized for aptasensing. The binding of AD to anti AD aptamer (AP) provided greater protection for unmodified AgNPs against salt-induced aggregation than AP alone. In this case, the fluorescence signal of N,S-CQDs was quenched by the dispersed AgNPs based on the inner filter effect. In the absence of AD, AgNPs tended to aggregate in a high salt solution. Hence, the fluorescence spectrum of N,S-CQDs no longer overlapped with the absorption spectrum of the aggregated AgNPs, and consequently N,S-CQDs did not quench. The linear range of the method was in the range of 50-200 nM, and the limit of detection was 13 nM. The relative standard deviations ranged from 5.2 to 7.3% (n = 6). In addition, the method had high selectivity toward AD in the presence of other interferences. The applicability of the method was examined by the quantitation of AD in urine samples of two patients through the standard addition method with recoveries in the range of 89-93%.