Note 6 - Stock-based Compensation - Stock-based Compensation Expense (Details) - USD ($)	3 Months Ended	9 Months Ended
Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Stock-based compensation expense	$ 164,392	$ 279,473	$ 642,952	$ 584,297
Research and Development Expense [Member]
Stock-based compensation expense	18,811	19,838	111,378	136,236
General and Administrative Expense [Member]
Stock-based compensation expense	$ 145,581	$ 259,635	$ 531,574	$ 448,061

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

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