Note 7 - Stock-based Compensation - Stock Option Activity (Details) - USD ($)	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Options outstanding, number (in shares)	2,240,204	309,276
Options outstanding, weighted-average exercise price (in dollars per share)	$ 8.28	$ 55.78
Granted (in shares)	1,815,767	1,931,100
Granted, weighted-average exercise price (in dollars per share)	$ 0.89	$ 0.68
Expired (in shares)		(172)
Expired, weighted-average exercise price (in dollars per share)		$ 142.50
Options outstanding, number (in shares)	3,626,223	2,240,204
Options outstanding, aggregate intrinsic value		$ 289,067
Forfeited (in shares)	(429,748)
Forfeited, weighted-average exercise price (in dollars per share)	$ 1.37
Options outstanding, number (in shares)	3,626,223	2,240,204
Options outstanding, weighted-average exercise price (in dollars per share)	$ 5.40	$ 8.28
Options outstanding, weighted-average remaining contractual life (Year)	8 years 6 months 7 days
Exercisable (in shares)	2,140,524
Exercisable, weighted-average exercise price (in dollars per share)	$ 8.58
Exercisable, weighted-average remaining contractual life (Year)	8 years 1 month 2 days
Vested and expected to vest (in shares)	3,626,223
Vested and expected to vest, weighted-average exercise price (in dollars per share)	$ 5.40
Vested and expected to vest, weighted-average remaining contractual life (Year)	8 years 6 months 7 days