Note 3 - Sale of Stock for Cash (Details Textual) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022	Dec. 31, 2022
Proceeds from Issuance of Common Stock			$ 1,497,000	$ 3,267,000
Warrants Issued with 2020 Unit Offering [Member] | Minimum [Member]
Warrants and Rights Outstanding, Term (Month)	6 months	6 months	6 months	6 months
Warrants Issued with 2020 Unit Offering [Member] | Maximum [Member]
Warrants and Rights Outstanding, Term (Month)	5 years	5 years	5 years	5 years
The 2020 Unit Offering [Member]
Stock Issued During Period, Shares, New Issues (in shares)	0	3,766,126	5,234,948	13,568,524
Proceeds from Issuance of Common Stock		$ 632,000	$ 995,000	$ 2,364,000
Lincoln Park Capital Fund, LLC [Member]
Stock Purchase Agreement, Maximum Amount of Common Stock					$ 10,000,000
Stock Issued During Period, Shares, New Issues (in shares)	1,190,223	2,440,958	2,833,846	4,353,919
Proceeds from Issuance of Common Stock	$ 203,000	$ 485,000	$ 502,000	$ 903,000