Note 5 - Fair Value Measurements and Financial Instruments (Tables)

6 Months Ended

Jun. 30, 2018

Notes Tables

Fair Value, Liabilities Measured on Recurring Basis [Table Text Block]

	Fair value measurement using inputs
	Level 1		Level 2		Level 3
Financial instruments:
Series 2023 Note Derivative	$	-0-	$	-0-	$	748,417
Series A Note Derivative	$	-0-	$	-0-	$	8,000,101

Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Table Text Block]

Balance at December 31, 2017	$	2,047,264	Balance at December 31, 2016	$	2,176,552
Issuance of additional Series 2023 Notes		- 0 -	Issuance of additional Series 2023 Notes		25,038
Issuance of additional Series A Notes		122,750	Issuance of additional Series A Notes		- 0 -
Net unrealized gain (loss) included in operations		6,578,504	Net unrealized gain (loss) included in operations		(1,636,841	)
Balance at June 30, 2018	$	8,748,518	Balance at June 30, 2017	$	564,749

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

Series 2023 Note derivative liability	Fair Value Measurements
	Using Inputs
	June 30,			December 31,
	2018			2017
Market price and estimated fair value of stock	$	0.17		$	0.05
Exercise price (1)	$	0.59		$	0.59
Term (years)		5.08			5.58
Dividend yield		-0-			-0-
Expected volatility		130.4	%		115.3	%
Risk-free interest rate		2.73	%		2.24	%

Series A Note derivative liability	Fair Value Measurements
	Using Inputs
	June 30,			December 31,
	2018			2017
Market price and estimated fair value of stock	$	0.17		$	0.05
Exercise price (1)	$	0.40		$	0.40
Term (years)		5.09			5.58
Dividend yield		-0-			-0-
Expected volatility		130.4	%		115.3	%
Risk-free interest rate		2.73	%		2.24	%