Several methods are presently being developed to sense the presence of a target molecule in small or modest concentration in a fluid. However, estimation of the concentration of the target molecule is unavailable where the fluid is substantially motionless relative to the sensor, in part because the fluid in equilibrium will have substantially the same concentration everywhere.
This innovation provides a nanostructure that has known mechanical properties, and one, two, or more spaced-apart beams partly coated with a selected chemical substance that binds to, or has an affinity for, the target molecule. The fluid is encouraged to move relative to the nanostructure, and to interact with the chemical substance. In the absence of the target molecule, the microchannel has one or more predictable resonant frequencies of longitudinal vibration.
Where the target molecule becomes attached to the beam, the resonant frequency of vibration changes to another predictable value, according to one or more dispersion relations. Where two or more spaced apart beams are provided, the variation in number of target molecules attached to each of the two or more beams allows one to estimate the concentration of the target molecule in the fluid. The invention allows the fluid to move relative to different sensor components to enable sensing of the presence of, and estimation of the concentration of, the target molecule. From knowledge of the maximum concentration of the target molecule attached to the beam(s), the invention can also indicate whether the target molecule is saturated so that an estimate of the concentration of the fluid may be inaccurate.
The innovation is constructed of a sequence of one or more substantially identical, thin, rectangular parallelepiped beams, each attached at both ends to a non-moveable wall of solid material with known properties, and having a longitudinal axis in the x-direction. On the beam, a selected chemical substance (a thin coating of a selected antibody) is applied in an orientation that is substantially along the longitudinal axis. A fluid, having a known density, is allowed to flow across the beam and the chemical substance. Initially, the fluid is absent, and one or more resonant frequencies of each reference beam is estimated before the fluid is introduced.