Detection units and methods for detecting a target analyte

A method of detecting a target analyte in a sample, the method comprising:

• a) providing a complex formed from:
• i) a first probe coupled to a particle and bound to said analyte if present, and
• ii) a second probe coupled to a solid support and bound to said analyte if present, so that if the target analyte is present in the sample, the particle is indirectly coupled to the solid support via a complex formed by the target analyte and the first and second probes, and wherein the complex comprises an elongated region;
• and
• b) either i) applying a force to the indirectly coupled particle or to the complex comprising the elongated region and measuring the amount of particle displacement or the length of the complex, wherein the amount of displacement or length of the complex indicates whether or not the target analyte is present in the sample, or ii) measuring the Brownian motion of the indirectly coupled particle, wherein the amount of Brownian motion indicates whether or not the target analyte is present in the sample.