Table 1.

Comparative study of the properties of the three commonly used biorecepters.

Property	Enzyme	Antibody	Aptamer
Acquisition	In vitro process no animals are involved	In vivo process -animals are involved	In vitro process no animals are involved
	All the toxins don't inhibit enzymatic activity or not substrate of enzyme	Difficult to obtain antibodies against targets that are non-immunogenic or toxic	Possible to obtain aptamers against targets that are non-immunogenic or toxic
	Manipulation is not possible Physiological conditions obligatory	Manipulation of selection hardly or not possible Physiological conditions obligatory	Manipulate selection to obtain binding and kinetic properties desirable for specific assays Non-physiological conditions acceptable
		Difficult to expose different epitopes of the same target for selection Identification laborious the immunogen must be the major fraction in the immunization reagent	Expose different epitopes of the same target for selection Identification easy and rapid process performed on automated platform the target used for selection can be a small portion in the target preparation
Stability	Increased by modifications	Cannot be increased by modification	Increased by modifications
	Loss activity over time Narrow stability in terms of pH, ionic strength and temperature	Relatively stable over time Narrow stability in terms of pH, ionic strength and temperature	Relatively stable over time Stability over a wide range of pH, ionic strength and temperature
	Unstable at room temperature	Unstable at room temperature	Long room temperature shelf lives
Specificity and selectivity	Less selective and specific Can be engineered	Binding constants for target species comparable with aptamers	Binding constants for target species comparable with antibodies
Modifications	Can be engineered	Biological and hardly engineered	Chemically easy to engineer Side specific attachment
			Efficient and exact modification -of reporter molecule -of spacers -of functional groups
			Homogeneous product
Denaturation	Enzyme accelerates the reaction and does not consume	Mild conditions needed to prevent irreversible denaturation	Regeneration after denaturation possible
		Sometimes difficult to separate from antibody-target-complex	Easy to separate from aptamer-target-complex
Sensors	Immobilization at defined densities and locations difficult	Immobilization at defined densities and locations sometimes difficult	Immobilization at defined densities at precise locations on solid surfaces (microarrays)
	Immobilization can denature enzyme	Molecular recognition functionalities hardly possible	Conformational changes on binding providing molecular-recognition functionalities Irreversible
		Irreversible cross-linking usually not possible	cross-linking with target protein possible-second legand for detection not needed