Note 4 - Stockholders' Equity, Stock Options and Warrants - Schedule of Listing of Stock Options and Warrants (Details) - $ / shares	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Shares, options (in shares)	981,060
Shares, warrants (in shares)	36,328,731	31,699,885	7,353,376
Warrants issued, exercise price (in dollars per share)	$ 1.13	$ 1.66	$ 1.99
Stock Options 2022 [Member]
Shares, options (in shares)	20,406
Minimum [Member]
Price, options (in dollars per share)	$ 0.40
Warrants issued, exercise price (in dollars per share)	0.70
Minimum [Member] | Stock Options 2022 [Member]
Price, options (in dollars per share)	0.26
Maximum [Member]
Price, options (in dollars per share)	5,962.50
Warrants issued, exercise price (in dollars per share)	13.13
Maximum [Member] | Stock Options 2022 [Member]
Price, options (in dollars per share)	$ 0.7361
Warrants 2018 [Member]
Shares, warrants (in shares)	196,946
Warrants 2018 [Member] | Minimum [Member]
Warrants issued, exercise price (in dollars per share)	$ 8.36
Warrants 2018 [Member] | Maximum [Member]
Warrants issued, exercise price (in dollars per share)	$ 13.13
Warrants 2019 [Member]
Shares, warrants (in shares)	1,690,286
Warrants 2019 [Member] | Minimum [Member]
Warrants issued, exercise price (in dollars per share)	$ 0.85
Warrants 2019 [Member] | Maximum [Member]
Warrants issued, exercise price (in dollars per share)	$ 11.80
Warrants 2020 [Member]
Shares, warrants (in shares)	1,311,731
Warrants 2020 [Member] | Minimum [Member]
Warrants issued, exercise price (in dollars per share)	$ 0.85
Warrants 2020 [Member] | Maximum [Member]
Warrants issued, exercise price (in dollars per share)	$ 2.99
Warrants 2021 [Member]
Shares, warrants (in shares)	12,067,054
Warrants 2021 [Member] | Minimum [Member]
Warrants issued, exercise price (in dollars per share)	$ 0.80
Warrants 2021 [Member] | Maximum [Member]
Warrants issued, exercise price (in dollars per share)	$ 2.44
Warrants 2022 [Member]
Shares, warrants (in shares)	21,062,714
Warrants 2022 [Member] | Minimum [Member]
Warrants issued, exercise price (in dollars per share)	$ 0.70
Warrants 2022 [Member] | Maximum [Member]
Warrants issued, exercise price (in dollars per share)	$ 0.75
Stock Options 2013 [Member]
Shares, options (in shares)	123
Stock Options 2013 [Member] | Minimum [Member]
Price, options (in dollars per share)	$ 1.54
Stock Options 2013 [Member] | Maximum [Member]
Price, options (in dollars per share)	$ 5,962.50
Stock Options 2014 [Member]
Shares, options (in shares)	84
Stock Options 2014 [Member] | Minimum [Member]
Price, options (in dollars per share)	$ 1.54
Stock Options 2014 [Member] | Maximum [Member]
Price, options (in dollars per share)	$ 3,468.75
Stock Options 2015 [Member]
Shares, options (in shares)	239
Stock Options 2015 [Member] | Minimum [Member]
Price, options (in dollars per share)	$ 1.54
Stock Options 2015 [Member] | Maximum [Member]
Price, options (in dollars per share)	$ 862.50
Stock Options 2016 [Member]
Shares, options (in shares)	6,641
Stock Options 2016 [Member] | Minimum [Member]
Price, options (in dollars per share)	$ 1.54
Stock Options 2016 [Member] | Maximum [Member]
Price, options (in dollars per share)	$ 42.50
Stock Options 2017 [Member]
Shares, options (in shares)	214,555
Stock Options 2017 [Member] | Minimum [Member]
Price, options (in dollars per share)	$ 1.54
Stock Options 2017 [Member] | Maximum [Member]
Price, options (in dollars per share)	$ 21.00
Stock Options 2018 [Member]
Shares, options (in shares)	57,868
Stock Options 2018 [Member] | Minimum [Member]
Price, options (in dollars per share)	$ 1.54
Stock Options 2018 [Member] | Maximum [Member]
Price, options (in dollars per share)	$ 13.50
Stock Options 2019 [Member]
Shares, options (in shares)	306,663
Stock Options 2019 [Member] | Minimum [Member]
Price, options (in dollars per share)	$ 1.54
Stock Options 2019 [Member] | Maximum [Member]
Price, options (in dollars per share)	$ 7.50
Stock Options 2020 [Member]
Shares, options (in shares)	297,669
Stock Options 2020 [Member] | Minimum [Member]
Price, options (in dollars per share)	$ 0.73
Stock Options 2020 [Member] | Maximum [Member]
Price, options (in dollars per share)	$ 3.48
Stock Options 2021 [Member]
Shares, options (in shares)	76,812
Stock Options 2021 [Member] | Minimum [Member]
Price, options (in dollars per share)	$ 0.72
Stock Options 2021 [Member] | Maximum [Member]
Price, options (in dollars per share)	$ 1.47