Note 7 - Shareholders' Equity - Stock Option Activity (Details) - USD ($)	6 Months Ended	12 Months Ended
	Jun. 30, 2020	Dec. 31, 2019
Balance, number of shares (in shares)	1,544,826
Balance, weighted average exercise price (in dollars per share)	$ 2.74
Balance, weighted average remaining contractual life (Year)	8 years 54 days	7 years 171 days
Balance, aggregate intrinsic value	$ 418,539	$ 46,582
Granted, number of shares (in shares)	567,900
Granted, weighted average exercise price (in dollars per share)	$ 1.02
Exercised, number of shares (in shares)
Exercised, weighted average exercise price (in dollars per share)
Forfeited, number of shares (in shares)	(109,656)
Forfeited, weighted average exercise price (in dollars per share)	$ 1.72
Expired, number of shares (in shares)	(172,898)
Expired, weighted average exercise price (in dollars per share)	$ 4.82
Balance, number of shares (in shares)	1,830,172	1,544,826
Balance, weighted average exercise price (in dollars per share)	$ 2.07	$ 2.74
Vested and expected to vest, number of shares (in shares)	1,540,412
Vested and expected to vest, weighted average exercise price (in dollars per share)	$ 2.20
Vested and expected to vest, weighted average remaining contractual life (Year)	7 years 343 days
Vested and expected to vest, aggregate intrinsic value	$ 320,836
Exercisable, number of shares (in shares)	529,497
Exercisable, weighted average exercise price (in dollars per share)	$ 3.63
Exercisable, weighted average remaining contractual life (Year)	5 years 186 days
Exercisable, aggregate intrinsic value	$ 6,100