Note 10 - Summary of Deferred Tax Assets (Details) - USD ($)	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Net operating loss carryforwards	$ 34,488,000	$ 29,217,000	$ 26,304,000
Federal and state tax credits	$ 16,404,000	$ 12,126,000	9,941,000
Deferred revenue			1,147,000
Accrued expenses	$ 27,000	$ 478,000	332,000
Patents	443,000	531,000	$ 612,000
Stock-based compensation	596,000	92,000
Other	276,000	8,000	$ 300,000
	52,234,000	42,452,000	38,636,000
Valuation allowance	(52,234,000)	(42,452,000)	(38,636,000)
Net deferred tax asset	$ 0	$ 0	$ 0