Note 6 - Stock-based Compensation (Tables)

6 Months Ended

Jun. 30, 2021

Notes Tables

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

	Three Months Ended June 30,				Six Months Ended June 30,
	2021		2020		2021		2020
Research and development	$	59,567	$	91,896	$	92,567	$	188,426
General and administrative		237,713		21,548		385,993		116,398
Total stock-based compensation expense	$	297,280	$	113,444	$	478,560	$	304,824

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, 2021		2,240,204		$	8.28
Granted		924,115			1.10
Forfeited		(111,432	)		0.91
Outstanding at June 30, 2021		3,052,887		$	6.37		8.8	$	219,228
Exercisable at June 30, 2021		1,563,224		$	11.54		8.1	$	195,252
Vested and expected to vest at June 30, 2021		3,052,887		$	6.37		8.8	$	219,228

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

	2021			2020
Expected term (in years)		10			5.59
Risk-free interest rate		1.5	%		1.3	%
Expected volatility		124.5	%		115.1	%
Dividend yield		—	%		—	%