Note 6 - Stock-based Compensation - Stock-based Compensation Expense (Details) - USD ($)	3 Months Ended	6 Months Ended
Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Stock-based compensation expense	$ 319,769	$ 315,066	$ 644,436	$ 681,449
Research and Development Expense [Member]
Stock-based compensation expense	16,274	24,072	32,646	67,404
General and Administrative Expense [Member]
Stock-based compensation expense	$ 303,495	$ 290,994	$ 611,790	$ 614,045

Represents the expense recognized during the period arising from equity-based compensation arrangements (for example, shares of stock, unit, stock options or other equity instruments) with employees, directors and certain consultants qualifying for treatment as employees.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
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Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
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