Note 4 - Stockholders' Equity, Stock Options and Warrants - Summary of Transactions for Stock Options and Warrants (Details) - $ / shares	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Number of Shares Outstanding (in shares)	1,062,871
Warrant [Member]
Number of Shares Outstanding (in shares)	7,353,376	2,171,610
Average Exercise Price Outstanding (in dollars per share)	$ 1.99	$ 15.26
Number of Shares Issued (in shares)	29,640,801	8,097,468
Average Exercise Price Issued (in dollars per share)	$ 1.44	$ 1.55
Number of Shares Forfeited (in shares)	0	(128,710)
Average Exercise Price Forfeited (in dollars per share)	$ 0	$ 95.11
Number of Shares Exercised (in shares)	(5,269,059)	(2,786,992)
Average Exercise Price Exercised (in dollars per share)	$ 0.86	$ 0.79
Expired (in shares)	(25,233)
Expired (in dollars per share)	$ 10.00
Number of Shares Outstanding (in shares)	31,699,885	7,353,376
Average Exercise Price Outstanding (in dollars per share)	$ 1.66	$ 1.99
Share-based Payment Arrangement, Option [Member]
Number of Shares Outstanding (in shares)	1,013,547	766,424
Average Exercise Price Outstanding (in dollars per share)	$ 5.41	$ 11.34
Number of Shares Issued (in shares)	147,230	319,851
Average Exercise Price Issued (in dollars per share)	$ 1.06	$ 1.03
Number of Shares Forfeited (in shares)	(92,593)	(72,728)
Average Exercise Price Forfeited (in dollars per share)	$ 8.64	$ 10.58
Number of Shares Exercised (in shares)	(5,313)	0
Average Exercise Price Exercised (in dollars per share)	$ 0.74	$ 0
Expired (in shares)	0
Expired (in dollars per share)	$ 0
Number of Shares Outstanding (in shares)	1,062,871	1,013,547
Average Exercise Price Outstanding (in dollars per share)	$ 4.83	$ 5.41