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Note 7 - Stockholders' Equity and Common Stock Warrants (Tables) | 12 Months Ended
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Dec. 31, 2020
Notes Tables |
Schedule of Stockholders' Equity Note, Warrants or Rights [Table Text Block] |
|  | Outstanding |  |  | Range of exercise price per share |  | Expiration dates
Common stock warrants issued in 2017 related to Series A convertible preferred stock offering |  |  | 903,870 |  |  |  | $33.30 |  |  | March 2022
Common stock warrants issued in 2018 related to the January 2018 common stock offering |  |  | 1,181,421 |  |  | $12.00 | - | $15.00 |  | January 2023
Common stock warrants issued related to the May 2019 Offering |  |  | 1,382,913 |  |  | $5.00 | - | $6.11875 |  | May and December 2024
Common stock warrants issued related to the November 2019 Offering |  |  | 497,140 |  |  | $0.35 | - | $0.4375 |  | May 2024
Common stock warrants issued related to the December 2019 Offering |  |  | 313,339 |  |  | $0.4335 | - | $0.6981 |  | December 2024 and June 2025
Common stock warrants issued related to the May 2020 Offering |  |  | 571,429 |  |  |  | $1.31 |  |  | March 2025
Common stock warrants issued related to the May 2020 Investor Warrant Exercise |  |  | 4,250,000 |  |  | $0.5263 | - | $0.5938 |  | November 2025
|  |  | 9,100,112 |  |  |  |  |  |  |

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- Definition Tabular disclosure of warrants or rights issued. Warrants and rights outstanding are derivative securities that give the holder the right to purchase securities (usually equity) from the issuer at a specific price within a certain time frame. Warrants are often included in a new debt issue to entice investors by a higher return potential. The main difference between warrants and call options is that warrants are issued and guaranteed by the company, whereas options are exchange instruments and are not issued by the company. Also, the lifetime of a warrant is often measured in years, while the lifetime of a typical option is measured in months. Disclose the title of issue of securities called for by warrants and rights outstanding, the aggregate amount of securities called for by warrants and rights outstanding, the date from which the warrants or rights are exercisable, and the price at which the warrant or right is exercisable. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 1 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5047-113901 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 505 -SubTopic 50 -Section S99 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6784392&loc=d3e188667-122775 + Details
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