Income taxes (Details) - USD ($)	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Total taxable income (loss)	$ 1,691,003	$ 758,130
UNITED STATES
Total taxable income (loss)	(50,029)	758,130
HONG KONG
Total taxable income (loss)	(59,027)
CHINA
Total taxable income (loss)	$ 1,800,059