Fair value measurements (Narrative) (Details) € in Millions	1 Months Ended	3 Months Ended		9 Months Ended
	Jun. 30, 2019 EUR (€)	Sep. 30, 2021 USD ($)	Sep. 30, 2020 USD ($)	Sep. 30, 2021 USD ($)	Sep. 30, 2020 USD ($)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impairment of right-of-use asset				$ 170,714
Fair Value on Non-Recurring Basis [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impairment of non-financial assets and liabilities at fair value			$ 0		$ 750,596
Impairment of right-of-use asset				$ 170,714
Fair Value on Recurring Basis [Member] | Curetis GmbH [Member] | European Investment Bank [Member] | Share-based Payment Arrangement, Tranche One [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Drew down amount | €	€ 5.0
Participation percentage interest	2.10%
Additional payment percentage	2.10%
Fair Value on Recurring Basis [Member] | Curetis GmbH [Member] | European Investment Bank [Member] | Share-based Payment Arrangement, Tranche One [Member] | Minimum [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cumulative equity capital raised | €	€ 15.0
Fair Value on Recurring Basis [Member] | OpGen's Equity [Member] | European Investment Bank [Member] | Share-based Payment Arrangement, Tranche One [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Participation percentage interest	0.30%
Maturity period				mid-2024 and mid-2025