Nanoparticle-Assisted Nuclear Relaxation-Based Detection of Oligonucleotides

Nuclear relaxation-based techniques rely on the capability of paramagnetic center to affect the transverse relaxation time (T₂) of the water protons. These changes are sensitive to the microenvironment of the paramagnetic center, which can be used to detect a variety of targets. In this work, we present an "on-off" oligonucleotide detection scheme in aqueous solutions, which uses gadolinium phthalocyanine (GdTcPc)-grafted silica nanoparticles as the paramagnetic centers. A probe oligonucleotide strand was conjugated to the GdTcPc to act as a recognition element. In the presence of the target oligonucleotide, which was complementary to the probe, an increase in the ΔT₂ value, which was measured by subtracting the characteristic T₂ value of the background solution from that of the sample using a benchtop relaxometer, was observed. The magnitude of this increase was proportional to the target oligonucleotide concentration. A linear range was obtained from 30 to 140 nM, with a detection limit of 15 nM. The developed nuclear relaxation-based detection scheme is shown to be a simple, fast, and selective method to detect oligonucleotide and could be useful in point-of-care diagnostic applications.