A projectile, either a crossbow bolt or an arrow, having a compressible nock. The fuel injector has a nozzle member and a needle valve member slidingly disposed with the nozzle member. Temperature is sensed from a first position and a second position along the inserted guide member. For example, the amino acid at position 447 can be alanine, isoleucine, valine, phenylalanine, tryptophan, or methionine. The invention also relates to a method for producing these derivatives and to their use in pairing andor testing systems. Methods of the present invention may comprise immobilizing a plurality of analyte molecules or particles to form a plurality of complexes, releasing at least a portion of some of the plurality of complexes, determining at least a portion of the plurality of complexes released, and determining a measure of the concentration of the analyte molecules or particles in a fluid sample.