Note 3 - Sale of Stock for Cash (Details Textual) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Proceeds from Issuance of Common Stock			$ 2,150,000	$ 3,520,000
Warrants Issued with 2020 Unit Offering [Member] | Minimum [Member]
Warrants and Rights Outstanding, Term (Month)		6 months		6 months
Warrants Issued with 2020 Unit Offering [Member] | Maximum [Member]
Warrants and Rights Outstanding, Term (Month)		5 years		5 years
The 2020 Unit Offering [Member]
Stock Issued During Period, Shares, New Issues (in shares)	4,605,430	2,556,547	9,802,398	3,431,547
Proceeds from Issuance of Common Stock	$ 876,000	$ 400,000	$ 1,732,000	$ 505,000
Lincoln Park Capital Fund, LLC [Member]
Stock Issued During Period, Shares, New Issues (in shares)	406,140	6,070,690	1,912,961	18,526,309
Proceeds from Issuance of Common Stock	$ 72,000	$ 1,014,000	$ 418,000	$ 3,015,000