Detection of molecules in samples

A method of detecting the presence in a sample of a polypeptide exogenously administered to a mammalian subject from whom the sample is obtained, and distinguishing between such an exogenously administered polypeptide and a naturally-occurring endogenous polypeptide present in the sample;

• the method comprising obtaining a sample of body fluid from the subject;
• and subjecting the sample to analysis of fluorescence at a suitable wavelength;
• wherein the sample is subjected to processing, prior to analysis, by one or more of the following:
• centrifugation;
• HPLC;
• FPLC;
• affinity chromatography;
• immunoaffinity chromatography;
• denaturation or heat treatment, so as to enrich or purify the exogenous polypeptide thereby to improve the signal:noise ratio;
• and wherein the exogenously administered polypeptide has a greater or lesser amount of fluorescence activity, relative to the endogenous polypeptide, at the wavelength(s) analysed, wherein the greater or lesser amount of fluorescence activity is due to the respective presence or absence in the exogenously administered polypeptide, relative to the endogenous polypeptide, of a fluorescent amino acid residue or a synthetic amino acid derivative in the amino acid backbone of the polypeptide, the synthetic amino acid derivative having the formula
• wherein R1 comprises the fluorophore and R2 is H, OH, halide or substituted or unsubstituted lower alkyl;
• and wherein the exogenously administered polypeptide comprises human, bovine or porcine growth hormone.