Biocompatible magnetic nanosensors have been designed to detect molecular interactions in biological media. Upon target binding, these nanosensors cause changes in the spin-spin relaxation times of neighboring solvent molecules of a sample, which can be detected by magnetic resonance (NMR) techniques. Thus, by using these nanosensors in a liquid sample, it is possible to detect the presence of an analyte at very low concentration—for example, small molecules, specific DNA, RNA, proteins, carbohydrates, organisms, and pathogens (e.g. viruses)—with sensitivity in the low femtomole range (from about 0.5 to about 30 fmol).
In general, magnetic nanosensors are derivatized superparamagnetic nanoparticles that form clusters (aggregates) or nanoassemblies as a function of the presence or concentration of their intended molecular target. It is thought that when superparamagnetic nanoparticles assemble into clusters and the effective cross sectional area becomes larger, the nanoassembly becomes more efficient at dephasing the spins of surrounding water (or other solvent) protons, leading to the measurable change of the relaxation rates (1/T2).
Additionally, nanoassembly formation can be designed to be reversible (e.g., by temperature shift, chemical cleavage, pH shift, etc.) so that “forward” or “reverse” assays can be developed for detection of specific analytes. Forward (clustering) and reverse (declustering) types of assays can be used to detect a wide variety of biologically relevant materials. Furthermore, the spin-lattice relaxation time (T1) is considered independent of nanoparticle assembly formation and can be used to measure concentration in both nano-assembled and dispersed states within the same solution.
Examples of magnetic nanosensors are described in Perez et al., “Use of Magnetic Nanoparticles as Nanosensors to Probe for Molecular Interactions,” Chem Bio Chem, 2004, 5, 261-264, and in U.S. Patent Application Publication No. US2003/0092029 (Josephson et al.), the texts of which are incorporated by reference herein, in their entirety.
Current diagnostic systems involve, for example, microarray technology, polymerase chain reaction (PCR), in situ hybridization, antibody-based immunoassays (e.g. enzyme-linked immunosorbant assays), chemiluminescence, nephelometry, and/or photometry. Generally, these systems cannot perform the diversity of assays at high sensitivity that is possible with an NMR-based nanosensor system.
Various non-NMR-based point of care bio-assays have been developed, such as portable blood glucose meters that operate using test strips impregnated with glucose oxidase. However, these systems generally lack the sensitivity, calibration, and maintenance that a laboratory setting provides. These portable systems also lack the sensitivity that is possible with NMR-based nanosensor systems, and they cannot be easily adapted for multiple analyte detection.
The above-cited Josephson et al. and Perez et al. documents describe applications of NMR relaxation methods with nanosensors using off-the-shelf relaxometers and MRI units. However, these units require large RF coils and magnets and are bulky and expensive.
There is a need for NMR-based analyte detection systems capable of in vivo use.
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