There are four types of bioconjugation. 

Biopolymer Labeling: a large biopolymer is labeled or conjugated with a small molecule. The small molecule can be linked directly or indirectly to the biopolymer. Typical examples are fluorescent labeling and biotinylation.

Biopolymer Conjugation: two molecules linked together through a linker. The two molecules generally have distinct properties and may function independently after conjugation.   

Biopolymer and Small Molecule Immobilization: biopolymers or small molecules covalently linked to a solid support.

Biopolymer Modification: modification of a biopolymer. For example, introduction of functional groups or small molecule labeling.

The diagram on the right illustrates the relationship among the four types of bioconjugation. Biopolymers may need to be modified prior to being labeled with other small molecules, immobilized on a solid surface, or conjugated to another biopolymer.