Note 8 - Stock-based Compensation - Stock Option Activity (Details) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Options outstanding, number (in shares)	309,276	203,736
Options outstanding, weighted-average exercise price (in dollars per share)	$ 55.78	$ 88.14
Granted (in shares)	1,931,100	117,270
Granted, weighted-average exercise price (in dollars per share)	$ 0.68	$ 2.62
Forfeited (in shares)		(11,583)
Forfeited, weighted-average exercise price (in dollars per share)		$ 83.81
Expired (in shares)	(172)	(147)
Expired, weighted-average exercise price (in dollars per share)	$ 142.50	$ 276
Options outstanding, weighted-average remaining contractual life (Year)	8 years 328 days	6 years 357 days
Options outstanding, aggregate intrinsic value	$ 289,067
Options outstanding, number (in shares)	2,240,204	309,276
Options outstanding, weighted-average exercise price (in dollars per share)	$ 8.28	$ 55.78
Options outstanding, weighted-average remaining contractual life (Year)	8 years 328 days	6 years 357 days
Exercisable (in shares)	1,129,733
Exercisable, weighted-average exercise price (in dollars per share)	$ 15.64
Exercisable, weighted-average remaining contractual life (Year)	8 years 102 days
Exercisable, aggregate intrinsic value	$ 219,010
Vested and expected to vest (in shares)	2,240,204
Vested and expected to vest, weighted-average exercise price (in dollars per share)	$ 8.28
Vested and expected to vest, weighted-average remaining contractual life (Year)	8 years 328 days
Vested and expected to vest, aggregate intrinsic value	$ 289,067