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  The spacer is an integral part of the FSL Kode construct and gives it several important characteristics including water dispersibility.
  * Length – the spacer can be varied in length, for example 1.9 nm (Ad), 7.2 nm (CMG2), 11.5 nm (CMG4), allowing for enhanced presentation of Functional groups at the biosurface.
  * Optimizes F presentation – The presentation of the bioactive (functional group) on a spacer reduces steric hindrance and increases the bioactive surfaces exposed and available for interactions
  * Rigidity – the spacer can be modified to be either flexible or rigid depending upon desired characteristics
  * Substitutions (represented by the leaves on the stalk) – the spacer can be modified both in charge, and polarity.
  * Branches – usually the spacer is linear, but it can also be branched including specific spacing of the branches to optimize presentation and interaction of the F group.
  * Inert – important to the design of FSL Kode constructs is the biologically inert nature of the spacer. Importantly this feature means the S-L components of the constructs are unreactive with undiluted serum. Consequently, the constructs are compatible in vivo use, and can improve diagnostic assay sensitivity by allowing for the use of undiluted serum.