Note 6 - Stock-based Compensation - Stock-based Compensation Expense (Details) - USD ($)	3 Months Ended	6 Months Ended
Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Stock-based compensation expense	$ 113,444	$ 149,080	$ 304,824	$ 240,284
Research and Development Expense [Member]
Stock-based compensation expense	91,896	13,577	188,426	27,173
General and Administrative Expense [Member]
Stock-based compensation expense	$ 21,548	$ 135,503	$ 116,398	$ 213,111

Amount of expense for award under share-based payment arrangement. Excludes amount capitalized.

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