Note 10 - Stockholder's Equity - Outstanding Warrants (Details) - $ / shares	Dec. 31, 2022	Aug. 04, 2022	Jan. 14, 2022	Dec. 31, 2021
Total outstanding and exercisable (in shares)	51,185,758			26,456,895
Underlying shares of common stock (in shares)	8,255,148			132,265
Series 1 February 2018 Warrants [Member]
Total outstanding and exercisable (in shares)	8,979,000			8,979,000
Underlying shares of common stock (in shares)	44,895			44,895
Exercise price per share (in dollars per share)	$ 400.00			$ 400.00
Series 2 February 2018 Warrants [Member]
Total outstanding and exercisable (in shares)	8,709,500			8,709,500
Underlying shares of common stock (in shares)	43,548			43,548
Exercise price per share (in dollars per share)	$ 400.00			$ 400.00
November 2018 Warrants [Member]
Total outstanding and exercisable (in shares)	8,768,395			8,768,395
Underlying shares of common stock (in shares)	43,842			43,842
Exercise price per share (in dollars per share)	$ 80.00			$ 80.00
Placement agent warrants issued in the January 2022 financing [Member]
Total outstanding and exercisable (in shares)	1,330,000
Underlying shares of common stock (in shares)	66,500		66,500
Exercise price per share (in dollars per share)	$ 10.00		$ 10.00
Warrants Issued in the January 2022 Financing [Member]
Total outstanding and exercisable (in shares)	16,150,000
Underlying shares of common stock (in shares)	807,500
Exercise price per share (in dollars per share)	$ 9.60
Pre-funded Warrants Issued in August 2022 Financing [Member]
Total outstanding and exercisable (in shares)	1,369,864
Underlying shares of common stock (in shares)	1,369,864
Exercise price per share (in dollars per share)	$ 0.0001	$ 0.0001
Series A Private Investment Options Issued in August 2022 Financing [Member]
Total outstanding and exercisable (in shares)	2,853,883
Underlying shares of common stock (in shares)	2,853,883
Exercise price per share (in dollars per share)	$ 1.502
Series B Private Investment Options Issued in August 2022 Financing [Member]
Total outstanding and exercisable (in shares)	2,853,883
Underlying shares of common stock (in shares)	2,853,883
Exercise price per share (in dollars per share)	$ 1.502
Placement Agent Private Investment Options Issued in August 2022 Financing [Member]
Total outstanding and exercisable (in shares)	171,233
Underlying shares of common stock (in shares)	171,233
Exercise price per share (in dollars per share)	$ 2.19