Blue light emitting graphene quantum dots/ Rhodamine B doped gold nanostars for ratiometric detection of methotrexate

In this work, an innovative ratiometric sensing platform was developed for the determination of methotrexate (MTX), an antifolate drug, a chemotherapy agent, and an immune system suppressant based on blue emission graphene quantum dots/Rhodamine B doped gold nanostars (B-GQDs/Au NSt-RB). The developed sensor was a dual-emission fluorescent probe with two major emission peaks at 440 nm (B-GQDs) and 580 nm (Au NSt-RB) by exciting at 330 nm. Based on the inhibiting effect of MTX on the system's fluorescence density, the stable ratiometric fluorescent probe was used for the rapid determination of MTX in aquatic solutions and spiked human serum samples. The results indicated good linear correlations over the logarithmic concentration range of 0.3 nM-50.0 μM. In addition, B-GQDs/Au NSt-RB can further realize highly sensitive detection of MTX with a low LOD value of 2.28 × 10^-10 M. The RSD% values obtained for the intra-day and inter-day precision were 0.63-3.86 %. With recoveries of 98.2-100.1 % and 98.7-100.5 %, respectively. The short-term temperature and freeze-thaw tests confirmed the higher stability of the developed sensor. In addition, the calculated recoveries for MTX recognition in real samples were in the range of 98-102 %. These findings suggested the excellent potential of the ratiometric fluorescence B-GQDs/Au NSt-RB sensor for detecting MTX in real plasma samples.