Note 4 - Stockholders' Equity, Stock Options and Warrants - Summary of Status of Options and Warrants Outstanding (Details)	12 Months Ended
	Dec. 31, 2021 $ / shares shares
Shares, options (in shares) | shares	1,062,871
Shares, warrants (in shares) | shares	31,699,885
Minimum [Member]
Warrants issued, exercise price (in dollars per share)	$ 0.80
Maximum [Member]
Warrants issued, exercise price (in dollars per share)	$ 22.50
Warrant One [Member]
Shares, warrants (in shares) | shares	21,468,599
Weighted average remaining life, warrants (Year)	3 years 3 months 21 days
Warrant One [Member] | Minimum [Member]
Warrants issued, exercise price (in dollars per share)	$ 80
Warrant One [Member] | Maximum [Member]
Warrants issued, exercise price (in dollars per share)	$ 1.72
Warrant Two [Member]
Shares, warrants (in shares) | shares	8,451,287
Weighted average remaining life, warrants (Year)	4 years 6 months
Warrant Two [Member] | Minimum [Member]
Warrants issued, exercise price (in dollars per share)	$ 1.80
Warrant Two [Member] | Maximum [Member]
Warrants issued, exercise price (in dollars per share)	$ 2.18
Warrant Three [Member]
Shares, warrants (in shares) | shares	1,555,778
Weighted average remaining life, warrants (Year)	3 years 4 months 13 days
Warrant Three [Member] | Minimum [Member]
Warrants issued, exercise price (in dollars per share)	$ 2.25
Warrant Three [Member] | Maximum [Member]
Warrants issued, exercise price (in dollars per share)	$ 10.00
Warrant Four [Member]
Shares, warrants (in shares) | shares	224,221
Weighted average remaining life, warrants (Year)	2 years 11 months 8 days
Warrant Four [Member] | Minimum [Member]
Warrants issued, exercise price (in dollars per share)	$ 10.71
Warrant Four [Member] | Maximum [Member]
Warrants issued, exercise price (in dollars per share)	22.50
Stock Options One [Member]
Options, lower limit (in dollars per share)	0.72
Options, upper limit (in dollars per share)	$ 1.10
Shares, options (in shares) | shares	335,876
Weighted average remaining life, options (Year)	9 years 3 months 21 days
Stock Options Two [Member]
Options, lower limit (in dollars per share)	$ 1.15
Options, upper limit (in dollars per share)	$ 1.64
Shares, options (in shares) | shares	356,673
Weighted average remaining life, options (Year)	8 years 4 months 9 days
Stock Options Three [Member]
Options, lower limit (in dollars per share)	$ 2.610
Options, upper limit (in dollars per share)	$ 8.41
Shares, options (in shares) | shares	214,937
Weighted average remaining life, options (Year)	8 years 1 month 24 days
Stock Options Four [Member]
Options, lower limit (in dollars per share)	$ 10.10
Options, upper limit (in dollars per share)	$ 5,962.50
Shares, options (in shares) | shares	155,385
Weighted average remaining life, options (Year)	5 years 11 months 26 days