Note 10 - Stockholders' Equity (Tables)

6 Months Ended

Jun. 30, 2019

Notes Tables

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

	June 30, 2019		December 31, 2018
Options issued and outstanding		2,166,800		865,163
Available for future grants of equity awards		186,410		223,377
Common stock warrants		12,832,188		10,914
Total		15,185,398		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	1,646,364	$	0.10	April 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	12,832,188