Note 11 - Warrant Transactions (Tables)

3 Months Ended

Mar. 31, 2014

Warrants [Abstract]

Schedule of Warrant Summary [Table Text Block]

					Weighted-average			Balance sheet
	Warrants as of				exercise			classification
	March 31, 2014		December 31, 2013		price per share		Expiration	March 31, 2014	December 31, 2013
Venture Lending & Leasing VI, Inc.		170,919		255,102	$	1.96	2/28/2024	Liability	Liability
Venture Lending & Leasing VII, Inc.		170,919		255,102		1.96	2/28/2024	Liability	Liability
Allen, F. Stephen Series #2		500,000		500,000		3.55	3/21/2016	Equity	Equity
Allen, F. Stephen Series #3		500,000		500,000		3.55	3/21/2016	Equity	Equity
Stearns, Robert		200,000		200,000		3.55	3/21/2016	Equity	Equity
MATT Series #1		270,576		401,486		2.75	9/19/2016	Equity	Equity
MATT Series #2		1,000,000		1,000,000		2.75	9/19/2016	Equity	Equity
All warrants		2,812,414		3,111,690

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

	March 31, 2014
Risk-free interest rate:		2.73	%
Expected term (years):		9.92
Expected dividend yield:		-
Expected volatility:		90.59	%

Risk-free interest rate:	3.24	%
Expected term (years):	6.08
Expected dividend yield:	—
Expected volatility:	94.07	%

Risk-free interest rate:	2.81	%
Expected term (years):	8.73
Expected dividend yield:	-
Expected volatility:	100.75	%

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

Warrants	Number of Warrants			Weighted- Average Exercise Price
Outstanding at December 31, 2013		3,111,690		$	2.61
Granted		-			-
Exercised		(168,366	)		1.96
Forfeited or expired		(130,910	)		2.75
Outstanding at March 31, 2014		2,812,414		$	3.00
Exercisable at March 31, 2014		2,812,414		$	3.00