Note 12 - Stockholders' Equity (Tables)

12 Months Ended

Dec. 31, 2019

Notes Tables

Schedule of Common Stock Reserved for Issuance [Table Text Block]

	December 31, 2019		December 31, 2018
Options issued and outstanding		1,811,652		865,163
Available for future grants of equity awards		295,180		223,377
Common stock warrants		43,370,162		10,914
Total		45,476,994		1,099,454

Schedule of Stockholders' Equity Note, Warrants or Rights [Table Text Block]

Securities into which warrants are convertible	Warrants outstanding	Exercise Price		Expiration Date
Common Stock	30,068,600	$	0.30	September 2024
Common Stock	2,115,738	$	0.375	September 2024
Common Stock	10,454,546	$	1.10	April 2024
Common Stock	636,364	$	1.375	April 2024
Common Stock	84,000	$	3.125	March 2024
Common Stock	10,914	$	22.99	December 2026
Total	43,370,162

Fair Value of Warrants, Assumptions [Table Text Block]

Offering		March 2019		April 2019		September 2019
Aggregate valuation on issuance date	$	100,000	$	333,000	$	497,000
Number of warrants issued		84,000		636,364		2,115,738
Exercise price	$	3.125	$	1.375	$	0.375
Closing stock price	$	2.08	$	0.89	$	0.36
Risk-free interest rate		2.34%		2.31%		1.55%
Expected term		5.0 Years		5.0 Years		5.0 Years
Expected volatility		80%		83%		83%
Dividend yield		—%		—%		—%