Enzyme formulations, their advantages, challenges, and some examples in different solvent systems. GMO: genetically modified organism. More information, examples and literature is shown in the ESI†.

Enzyme formulation	Advantages	Challenges	Selected examples in the different reaction systems
Crude cell extract	• High activity	• Likely unstable in organic solvents	Cosolvent67
	• Relatively easy and cheap to produce	• Hard to retain in continuous systems	Biphasic80
	• Cofactors potentially already present in extract	• Hard to recycle for reuse
		• Possible interfering native background reactions
Soluble purified enzyme	• No native background reactions	• Laborious and expensive to produce	Cosolvent67
	• High activity	• Likely unstable in organic solvents	Biphasic33,81
	• No GMO license needed	• Hard to recycle for reuse	MARS30
		• Hard to separate from reaction mixture	Neat58
Immobilized enzyme	• No native background reactions	• Laborious and expensive to produce	Cosolvent82
	• No GMO licence needed	• Additional material needed	Biphasic83
	• Easy to retain and reuse	• Not always biodegradable	MARS33,83,84
	• Possible enhanced stability in organic solvents	• Unpredictable effect on enzyme activity and stability possible	Neat56,57,83
Whole cells	• Easy and cheap to produce	• Possible interfering native background reactions	Cosolvent85,86
	• Possible enhanced stability in organic solvents	• Viable cells can be susceptible to reaction components	Biphasic55,87
	• Easy to separate from reaction mix	• Often GMO licence needed	MARS48,88
			Neat45
Immobilized whole cells	• Relatively cheap to produce	• Possible interfering native background reactions	Biphasic89
	• Potentially stable in organic media	• Viable cells can be susceptible to reaction components	MARS55,90,91
	• Easy to retain in continuous systems	• Possibly laborious to produce	Neat76
	• Easy to separate from reaction mixture	• Often GMO licence needed