A system and an apparatus for use in detecting a target microorganism or agent is disclosed which involves a solid support carrying a binding partner specific for the particular microorganism or agent and the solid support being characterised in that it defines means for protecting the binding partner from being dislodged or scraped off the solid support by physical means. The provision of protection against the binding partner being dislodged from or scraped off the solid support improves the reliability of tests such as immunoassays being conducted with the solid support and also enables such tests to be automated. Modules and machines for use with the solid support, and the automated conduct of tests are also disclosed.