Fair value measurement (Details - Fair value of warrants) - Warrant [Member]	12 Months Ended
	Dec. 31, 2021
Measurement Input, Expected Term [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair Value Measurement	5 years
Measurement Input, Risk Free Interest Rate [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair Value Measurement	0.58%-0.77%
Measurement Input, Price Volatility [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair Value Measurement	82.20%-82.36%
Measurement Input, Expected Dividend Rate [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair Value Measurement	0