What are the types of recombinant antibody fragments?

Recombinant antibodies (rAbs) are monoclonal antibodies that are generated in vitro using synthetic genes. There are three types of recombinant antibody fragments - Fab, Single-chain fragment variable (scfv), and Bispecific antibodies. 

• FAB fragments - Fab fragment recombinant antibodies are composed of 2 sets of constant and variable components that create 2 stable polypeptide chains. Fab fragments have an inhibitory function. They bind directly to the paratope of the target antibody, where they compete with the drug for binding site. Fab fragment antibodies can be used in the detection of unbound drugs in the serum. 
• Single-chain fragment variable (scfv) – With a molecular weight of approximately 27kDa, scfv is the smallest of the recombinant antibody formats that is capable of antigen binding. They are formed by two chains – a light and heavy chain – of an immunoglobulin’s variable region. A flexible peptide linker, which consists of short sequence repetition, links the two chains in scfv. The main function of the sequence is to stabilize the fragment. 
• Bispecific recombinant antibodies – Bispecific recombinant antibodies are also known as diabodies. They combine two different antigen binding specificities within one molecule and are used to crosslink the molecules of interest with 2 different cells and facilitate direct cytotoxicity.