Method and apparatus for therapeutic drug monitoring using an acoustic device

A method for detecting one or more immunosuppressants in a sample, the method comprising the steps of:

• a) introducing a fluid comprising a sample, a plurality of magnetic particles and a competitor molecule into a fluid chamber, said magnetic particles being coated with a first capture agent capable of binding an immunosuppressant, wherein at least one surface of the fluid chamber comprises a flexural plate wave device that has been coated with a second capture agent capable of binding to the competitor molecule, wherein the flexural plate wave device has a membrane that is capable of vibrating, and wherein the second capture agent is bound to the membrane;
• b) applying a retractable source of magnetic flux positioned external to the fluid chamber close to the membrane to create a significant magnetic field gradient to attract the magnetic particles in the fluid toward the membrane;
• c) monitoring a first signal output by the flexural plate wave device, wherein the first signal output is monitored in the presence of a magnetic flux;
• d) after removing the retractable source of magnetic flux, flowing a solution through the fluid chamber to remove magnetic particles not bound to the membrane;
• e) monitoring a second signal output by said flexural plate wave device, wherein the second signal output is monitored in the absence of the magnetic flux;
• and
• f) comparing the first and the second signal output to a control signal, thereby detecting the immunosuppressant.