A sensor assembly probe may include a fluorescent semi-conductive nanoparticle. A sensor assembly probe may include a hydrophobic substrate for a predetermined enzyme, associated with the fluorescent semi-conductive nanoparticle by a non-covalent electrostatic interaction. A sensor assembly probe may include a hydrophilic group bonded to the hydrophobic substrate.

Provided are recombinant amebocyte clotting factors, their formulation and use in determining the presence and/or amount of a microbial endotoxin in a sample. Also provided is a cartridge containing the recombinant amebocyte clotting factors for determining the presence and/or amount of a microbial endotoxin in a sample.