Note 12 - Stockholders' Equity (Tables)

12 Months Ended

Dec. 31, 2020

Notes Tables

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

	December 31, 2020		December 31, 2019
Options issued and outstanding		6,813,033		1,811,652
Available for future grants of equity awards		1,230,863		295,180
Common stock warrants		1,244,974		43,370,162
Total		9,288,870		45,476,994

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		5,000	$	0.30	September 2024
Common Stock		224,797	$	0.375	September 2024
Common Stock		225,966	$	1.10	April 2024
Common Stock		111,931	$	1.375	April 2024
Common Stock		316,584	$	2.50	March 2025
Common Stock		269,496	$	3.125	February 2025
Common Stock		80,286	$	3.125	March 2024
Common Stock		10,914	$	22.99	December 2026
Total		1,244,974

Fair Value of Warrants, Assumptions [Table Text Block]

Offering	March 2019			April 2019			September 2019			March 2020
Aggregate valuation on issuance date	$	100,000		$	333,000		$	497,000		$	453,000
Number of warrants issued		84,000			636,364			2,115,738			280,000
Exercise price	$	3.125		$	1.375		$	0.375		$	3.125
Closing stock price	$	2.08		$	0.89		$	0.36		$	2.34
Risk-free interest rate		2.34	%		2.31	%		1.55	%		0.88	%
Expected term (In Years)		5.00			5.00			5.00			4.99
Expected volatility		80	%		83	%		83	%		98	%
Dividend yield		—	%		—	%		—	%		—	%