Income taxes - Net long-term deferred tax liability (Details) - USD ($)	Dec. 31, 2024	Dec. 31, 2023
Deferred tax assets:
Net operating loss carryforwards	$ 80,285	$ 130,911
Accruals and reserves	209,549	146,057
Operating lease liabilities	425,797	501,397
Capitalized research expenditures	316,937	326,178
Others	88,750	29,094
Valuation allowances	0	0
Deferred tax assets	1,121,318	1,133,637
Deferred tax liabilities:
Property and equipment	239,830	325,473
Intangible assets	672,973	847,450
Operating lease right-of-use assets	419,408	491,494
Deferred Tax Liabilities, Gross	1,332,211	1,664,417
Net deferred tax liability	210,893	530,780
Discontinued Operations
Deferred tax assets:
Valuation allowances	0	(15,678,994)
Operating loss carryforwards - Mexico	0	5,844,847
Land basis difference - Mexico	0	2,818,663
Start-up costs - Mexico	0	7,015,484
Deferred tax assets	$ 0	$ 0