Cyclic GMP recognition using ratiometric QD-fluorophore conjugate nanosensors.

Novel luminescent ratiometric nanosensors (QD-NAPTHs) were prepared based on cadmium telluride (CdTe655) quantum dots as luminescent nanoscaffolds with naphthyridine dyes as fluorescent receptors. This biosensing bifluorophoric nanosystem has been designed to achieve detection of guanosine 3',5'-cyclic monophosphate (cyclic GMP) in buffered media. Cyclic GMP is a secondary messenger that is an important factor for detecting cancer, diabetes and, cardiovascular diseases. Due to low concentration levels, even in pathological conditions, sensitive cGMP detection remains a challenge for modern biomedical diagnostics. Here, QD-NAPTH nanosensors were tested in the presence of a target nucleotide and with various structural cGMP analogues. Steady-state fluorescence spectroscopy was used to monitor a change in the nucleotide concentration. A 5-fold increase in naphthyridine fluorescence with a simultaneous decrease in QD luminescence was observed after adding 50 μM of cGMP. Using this novel nanosystem with ratiometric detection, it was possible to recognize cGMP with limit of detection (3σ) equal to 70 ng/ml. Moreover, the enhancement in fluorescence upon interaction with the target nucleotide constitutes a favourable approach towards the detection of cGMP in buffered media. These bifluorophoric nanosensors have a potential for application in fluorescence microscopy imaging and in-vitro assays.