Note 8 - Stock-based Compensation (Tables)

12 Months Ended

Dec. 31, 2019

Notes Tables

Share-based Payment Arrangement, Expensed and Capitalized, Amount [Table Text Block]

	Year ended December 31,
	2019		2018
Research and development	$	54,155	$	62,161
General and administrative		461,607		1,159,430
Total stock-based compensation expense	$	515,762	$	1,221,591

Share-based Payment Arrangement, Option, Activity [Table Text Block]

	Number of Options			Weighted average exercise price per share		Weighted average remaining contractual life (in years)		Aggregate Intrinsic Value
Balance at January 1, 2018		170,461		$	109.74
Granted		44,005			15.37
Forfeited		(10,583	)		131.25
Expired		(147	)		256.50
Balance at January 1, 2019		203,736		$	88.14		6.70	$	143
Granted		117,270			2.62
Forfeited		(11,583	)		83.81
Expired		(147	)		276.00
Outstanding at December 31, 2019		309,276		$	55.78		6.98	$	—
Exercisable at December 31, 2019		235,415		$	71.75		6.34	$	—
Vested and expected to vest at December 31, 2019		309,276		$	55.78		6.98	$	—

Schedule of Share-based Payment Award, Stock Options, Valuation Assumptions [Table Text Block]

	2019						2018
Expected term (in years)		5.25		—	5.77			5.27		—	5.66
Risk-free interest rate		1.9	%	—	2.5	%		2.3	%	—	2.8	%
Expected volatility		112.4	%	—	114.4	%		113.6	%	—	115.0	%
Dividend yield		—		—	—			—		—	—