Note 4 - Equity (Details Textual) | | | | | | | | | | | | | 1 Months Ended | 3 Months Ended | 12 Months Ended | | |
Mar. 21, 2024 USD ($) $ / shares shares | Feb. 02, 2024 | Jan. 19, 2024 | Jan. 02, 2024 shares | Jan. 01, 2024 shares | Dec. 31, 2023 USD ($) $ / shares shares | Dec. 13, 2023 | Jul. 21, 2023 USD ($) $ / shares shares | Mar. 01, 2023 USD ($) $ / shares shares | Jan. 01, 2023 shares | Nov. 18, 2022 USD ($) | Jan. 01, 2022 shares | Mar. 31, 2024 USD ($) | Mar. 28, 2024 USD ($) shares | Dec. 31, 2023 USD ($) $ / shares shares | Dec. 31, 2022 USD ($) $ / shares shares | Dec. 31, 2021 $ / shares shares | Apr. 03, 2018 shares |
Class of Warrant or Right, Number of Securities Called by Warrants or Rights (in shares) | | | | | | 346,440 | | | | | | | | | 346,440 | | | |
Warrants and Rights Outstanding, Term (Year) | | | | | | 5 years | | | | | | | | | 5 years | | | |
Class of Warrant or Right, Exercise Price of Warrants or Rights (in dollars per share) | $ / shares | | | | | | $ 57.79 | | | | | | | | | $ 57.79 | $ 172.81 | $ 175.65 | |
Proceeds from Issuance of Common Stock | $ | | | | | | | | | | | | | | | $ 10,593,377 | $ 6,426 | | |
Stock Issued During Period, Value, Issued for Services | $ | | | | | | | | | | | | | | | $ 19,010 | $ 163,232 | | |
Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Exercises in Period (in shares) | | | | | | | | | | | | | | | 500 | 2,925 | | |
Stock Issued During Period, Shares, Exercise of Cashless Warrants (in shares) | | | | | | | | | | | | | | | | 342 | | |
Preferred Stock, Shares Authorized (in shares) | | | | | | 10,000,000 | | | | | | | | | 10,000,000 | | | |
Preferred Stock, Par or Stated Value Per Share (in dollars per share) | $ / shares | | | | | | $ 0.001 | | | | | | | | | $ 0.001 | | | |
Preferred Stock, Shares Outstanding (in shares) | | | | | | 0 | | | | | | | | | 0 | | | |
Common Stock, Shares Authorized (in shares) | | | | | | 200,000,000 | | | | | | | | | 200,000,000 | 200,000,000 | | |
Common Stock, Par or Stated Value Per Share (in dollars per share) | $ / shares | | | | | | $ 0.001 | | | | | | | | | $ 0.001 | $ 0.001 | | |
Common Stock, Shares, Outstanding (in shares) | | | | | | 1,485,902 | | | | | | | | | 1,485,902 | 1,202,677 | | |
Class of Warrant or Right, Issued in Period (in shares) | | | | | | | | | | | | | | | 296,273 | 2,575 | | |
Class of Warrant or Right, Cancelled During Period (in shares) | | | | | | | | | | | | | | | 3,528 | 3,659 | | |
Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Outstanding, Number (in shares) | | | | | | 285,883 | | | | | | | | | 285,883 | 284,377 | 214,370 | |
Share-based Compensation Arrangement by Share-based Payment Award, Expiration Period (Year) | | | | | | | | | | | | | | | 10 years | | | |
Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Outstanding, Weighted Average Exercise Price (in dollars per share) | $ / shares | | | | | | $ 121.11 | | | | | | | | | $ 121.11 | $ 123.19 | $ 134.14 | |
Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Grants in Period, Gross (in shares) | | | | | | | | | | | | | | | 8,251 | 74,600 | | |
Share-Based Compensation Arrangements by Share-Based Payment Award, Options, Grants in Period, Weighted Average Exercise Price (in dollars per share) | $ / shares | | | | | | | | | | | | | | | $ 30.14 | $ 86.45 | | |
Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Forfeitures and Expirations in Period (in shares) | | | | | | | | | | | | | | | 6,245 | 1,668 | | |
Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Forfeitures and Expirations in Period, Weighted Average Exercise Price (in dollars per share) | $ / shares | | | | | | | | | | | | | | | $ 104.42 | $ 101.88 | | |
Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Outstanding, Weighted Average Remaining Contractual Term (Year) | | | | | | | | | | | | | | | 6 years 1 month 17 days | 7 years 29 days | | |
Class of Warrant or Right, Outstanding (in shares) | | | | | | 346,440 | | | | | | | | | 346,440 | 53,695 | 55,121 | |
Options and Warrants [Member] | | | | | | | | | | | | | | | | | | |
Share-Based Payment Arrangement, Expense | $ | | | | | | | | | | | | | | | $ 5,400,000 | | | |
Options and Warrants [Member] | General and Administrative Expense [Member] | | | | | | | | | | | | | | | | | | |
Share-Based Payment Arrangement, Expense | $ | | | | | | | | | | | | | | | 4,400,000 | | | |
Options and Warrants [Member] | Research and Development Expense [Member] | | | | | | | | | | | | | | | | | | |
Share-Based Payment Arrangement, Expense | $ | | | | | | | | | | | | | | | 1,000,000 | | | |
Time-Based Stock Option Awards, RSUs, and Warrants [Member] | | | | | | | | | | | | | | | | | | |
Share-Based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Amount | $ | | | | | | $ 4,700,000 | | | | | | | | | $ 4,700,000 | | | |
Share-Based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Period for Recognition (Year) | | | | | | | | | | | | | | | 3 years | | | |
Time-Based Stock Option Awards, RSUs, and Warrants [Member] | Related to General and Administrative Expense [Member] | | | | | | | | | | | | | | | | | | |
Share-Based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Amount | $ | | | | | | 3,800,000 | | | | | | | | | $ 3,800,000 | | | |
Time-Based Stock Option Awards, RSUs, and Warrants [Member] | Related to Research and Development Expense [Member] | | | | | | | | | | | | | | | | | | |
Share-Based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Amount | $ | | | | | | $ 900,000 | | | | | | | | | $ 900,000 | | | |
Performance Shares [Member] | | | | | | | | | | | | | | | | | | |
Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Outstanding, Number (in shares) | | | | | | 0 | | | | | | | | | 0 | | | |
Share-Based Payment Arrangement, Option [Member] | | | | | | | | | | | | | | | | | | |
Share-Based Payment Arrangement, Expense | $ | | | | | | | | | | | | | | | | $ 4,700,000 | | |
Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Vested in Period, Fair Value | $ | | | | | | | | | | | | | | | | $ 4,600,000 | | |
The 2018 Equity Incentive Plan [Member] | | | | | | | | | | | | | | | | | | |
Share Based Compensation Arrangement By Share Based Payment Award, Percentage Applied on Outstanding Shares of Common Stock For Automatically Increase on Each Year | | | | | | | | | | | | | | | | | | 5% |
Share-Based Compensation Arrangement by Share-Based Payment Award, Number of Additional Shares Authorized (in shares) | | | | | | 74,294 | | | | 60,132 | | 59,843 | | | | | | |
Share-Based Compensation Arrangement by Share-Based Payment Award, Number of Shares Available for Grant (in shares) | | | | | | 11,686 | | | | | | | | | 11,686 | | | |
The 2018 Employee Stock Purchase Plan [Member] | | | | | | | | | | | | | | | | | | |
Share Based Compensation Arrangement By Share Based Payment Award, Percentage Applied on Outstanding Shares of Common Stock For Automatically Increase on Each Year | | | | | | | | | | | | | | | | | | 2% |
Share-Based Compensation Arrangement by Share-Based Payment Award, Number of Shares Authorized (in shares) | | | | | | | | | | | | | | | | | | 5,202 |
Excluding the 2018 Equity Incentive Plan [Member] | | | | | | | | | | | | | | | | | | |
Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Outstanding, Number (in shares) | | | | | | 25,417 | | | | | | | | | 25,417 | | | |
Scientific Advisory Board Chairman [Member] | | | | | | | | | | | | | | | | | | |
Stock Issued During Period, Shares, Issued for Services (in shares) | | | | | | | | | | | | | | | 500 | 500 | | |
Stock Issued During Period, Value, Issued for Services | $ | | | | | | | | | | | | | | | $ 19,200 | $ 42,400 | | |
Consultant [Member] | | | | | | | | | | | | | | | | | | |
Stock Issued During Period, Shares, Issued for Services (in shares) | | | | | | | | | | | | | | | | 1,919 | | |
Stock Issued During Period, Value, Issued for Services | $ | | | | | | | | | | | | | | | | $ 99,010 | | |
Former Board Member [Member] | | | | | | | | | | | | | | | | | | |
Shares Issued, Price Per Share (in dollars per share) | $ / shares | | | | | | $ 11.92 | | | | | | | | | $ 11.92 | | | |
Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Exercises in Period (in shares) | | | | | | | | | | | | | | | 500 | | | |
Company Executives [Member] | | | | | | | | | | | | | | | | | | |
Shares Issued, Price Per Share (in dollars per share) | $ / shares | | | | | | | | | | | | | | | | $ 0.6 | | |
Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Exercises in Period (in shares) | | | | | | | | | | | | | | | | 2,925 | | |
Maximum [Member] | | | | | | | | | | | | | | | | | | |
Class of Warrant or Right, Exercise Price of Warrants or Rights (in dollars per share) | $ / shares | | | | | | 288.8 | | | | | | | | | $ 288.8 | | | |
Warrants or Rights, Fair Value Per Share (in dollars per share) | $ / shares | | | | | | 185 | | | | | | | | | $ 185 | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period (Month) | | | | | | | | | | | | | | | 48 months | | | |
Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Outstanding, Weighted Average Exercise Price (in dollars per share) | $ / shares | | | | | | 140 | | | | | | | | | $ 140 | | | |
Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Vested, Weighted Average Grant Date Fair Value (in dollars per share) | $ / shares | | | | | | | | | | | | | | | 98.84 | | | |
Share-Based Compensation Arrangements by Share-Based Payment Award, Options, Grants in Period, Weighted Average Exercise Price (in dollars per share) | $ / shares | | | | | | | | | | | | | | | 60.4 | $ 140 | | |
Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Forfeitures and Expirations in Period, Weighted Average Exercise Price (in dollars per share) | $ / shares | | | | | | | | | | | | | | | 142 | 146.4 | | |
Minimum [Member] | | | | | | | | | | | | | | | | | | |
Class of Warrant or Right, Exercise Price of Warrants or Rights (in dollars per share) | $ / shares | | | | | | 26 | | | | | | | | | 26 | | | |
Warrants or Rights, Fair Value Per Share (in dollars per share) | $ / shares | | | | | | 13.85 | | | | | | | | | $ 13.85 | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period (Month) | | | | | | | | | | | | | | | 12 months | | | |
Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Outstanding, Weighted Average Exercise Price (in dollars per share) | $ / shares | | | | | | 18 | | | | | | | | | $ 18 | | | |
Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Vested, Weighted Average Grant Date Fair Value (in dollars per share) | $ / shares | | | | | | | | | | | | | | | 12.62 | | | |
Share-Based Compensation Arrangements by Share-Based Payment Award, Options, Grants in Period, Weighted Average Exercise Price (in dollars per share) | $ / shares | | | | | | | | | | | | | | | 18 | 50.8 | | |
Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Forfeitures and Expirations in Period, Weighted Average Exercise Price (in dollars per share) | $ / shares | | | | | | | | | | | | | | | $ 50.8 | $ 80 | | |
Weighted Average [Member] | Time-Based Stock Option Awards, RSUs, and Warrants [Member] | | | | | | | | | | | | | | | | | | |
Share-Based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Period for Recognition (Year) | | | | | | | | | | | | | | | 1 year 1 month 13 days | | | |
Warrants Issued with Registered Direct Offering [Member] | | | | | | | | | | | | | | | | | | |
Class of Warrant or Right, Number of Securities Called by Warrants or Rights (in shares) | | | | | | | | 185,644 | 95,239 | | | | | | | | | |
Warrants and Rights Outstanding, Term (Year) | | | | | | | | 5 years | 5 years | | | | | | | | | |
Class of Warrant or Right, Exercise Price of Warrants or Rights (in dollars per share) | $ / shares | | | | | | | | $ 35.4 | $ 44 | | | | | | | | | |
Class of Warrant or Right, Issued in Period (in shares) | | | | | | | | 185,644 | 95,239 | | | | | | | | | |
Placement Agent Warrants [Member] | | | | | | | | | | | | | | | | | | |
Class of Warrant or Right, Number of Securities Called by Warrants or Rights (in shares) | | | | | | | | 11,140 | | | | | | | | | | |
Class of Warrant or Right, Exercise Price of Warrants or Rights (in dollars per share) | $ / shares | | | | | | | | $ 50.5 | | | | | | | | | | |
Class of Warrant or Right, Issued in Period (in shares) | | | | | | | | 11,140 | | | | | | | | | | |
Class of Warrant or Right, Cancelled During Period (in shares) | | | | | | | | | | | | | | | 960 | | | |
Warrants Issued for Services [Member] | | | | | | | | | | | | | | | | | | |
Class of Warrant or Right, Issued in Period (in shares) | | | | | | | | | | | | | | | 4,250 | | | |
Class of Warrant or Right, Cancelled During Period (in shares) | | | | | | | | | | | | | | | 2,568 | | | |
Warrants Issued for Services [Member] | Maximum [Member] | | | | | | | | | | | | | | | | | | |
Class of Warrant or Right, Exercise Price of Warrants or Rights (in dollars per share) | $ / shares | | | | | | 66 | | | | | | | | | $ 66 | | | |
Warrants Issued for Services [Member] | Minimum [Member] | | | | | | | | | | | | | | | | | | |
Class of Warrant or Right, Exercise Price of Warrants or Rights (in dollars per share) | $ / shares | | | | | | $ 26 | | | | | | | | | $ 26 | | | |
Vesting of Warrants For Service Provider [Member] | | | | | | | | | | | | | | | | | | |
Share-Based Payment Arrangement, Expense | $ | | | | | | | | | | | | | | | $ 133,558 | | | |
Warrant For Service Provider [Member] | | | | | | | | | | | | | | | | | | |
Class of Warrant or Right, Number of Securities Called by Warrants or Rights (in shares) | | | | | | | | | | | | | | | | 1,250 | | |
Class of Warrant or Right, Exercise Price of Warrants or Rights (in dollars per share) | $ / shares | | | | | | | | | | | | | | | | $ 55.2 | | |
Warrant For Service Provider 2 [Member] | | | | | | | | | | | | | | | | | | |
Class of Warrant or Right, Number of Securities Called by Warrants or Rights (in shares) | | | | | | | | | | | | | | | | 1,250 | | |
Class of Warrant or Right, Exercise Price of Warrants or Rights (in dollars per share) | $ / shares | | | | | | | | | | | | | | | | $ 59.6 | | |
Warrant for Services Provided at IPO [Member] | | | | | | | | | | | | | | | | | | |
Class of Warrant or Right, Number of Securities Called by Warrants or Rights (in shares) | | | | | | | | | | | | | | | | 75 | | |
Class of Warrant or Right, Exercise Price of Warrants or Rights (in dollars per share) | $ / shares | | | | | | | | | | | | | | | | $ 200 | | |
Class of Warrant or Right, Cancelled During Period (in shares) | | | | | | | | | | | | | | | | 257 | | |
Warrants from Prior Service Providers [Member] | | | | | | | | | | | | | | | | | | |
Warrants or Rights, Cancelled During Period (in shares) | | | | | | | | | | | | | | | | 3,402 | | |
Performance-based Warrant [Member] | | | | | | | | | | | | | | | | | | |
Class of Warrant or Right, Outstanding (in shares) | | | | | | 1 | | | | | | | | | 1 | | | |
Warrant, Nonvested Award, Cost Not yet Recognized, Amount | $ | | | | | | $ 300,000 | | | | | | | | | $ 300,000 | | | |
Registered Direct Offering [Member] | | | | | | | | | | | | | | | | | | |
Stock Issued During Period, Shares, New Issues (in shares) | | | | | | | | | 95,239 | | | | | | | | | |
Equity Offering, Combined Purchase Price (in dollars per share) | $ / shares | | | | | | | | | $ 42 | | | | | | | | | |
Proceeds from Issuance or Sale of Equity | $ | | | | | | | | | $ 3,600,000 | | | | | | | | | |
Payments of Stock Issuance Costs | $ | | | | | | | | | $ 400,000 | | | | | | | | | |
July 2023 Registered Direct Offering [Member] | | | | | | | | | | | | | | | | | | |
Stock Issued During Period, Shares, New Issues (in shares) | | | | | | | | 185,644 | | | | | | | | | | |
Proceeds from Issuance or Sale of Equity | $ | | | | | | | | $ 6,700,000 | | | | | | | | | | |
Payments of Stock Issuance Costs | $ | | | | | | | | $ 800,000 | | | | | | | | | | |
Shares Issued, Price Per Share (in dollars per share) | $ / shares | | | | | | | | $ 40.4 | | | | | | | | | | |
The 2022 ATM Facility [Member] | | | | | | | | | | | | | | | | | | |
Stock Issued During Period, Shares, New Issues (in shares) | | | | | | | | | | | | | | | 1,342 | | | |
Brokerage Commissions, Percentage of Gross Proceeds | | | | | | | | | | | 3% | | | | | | | |
Proceeds from Issuance of Common Stock | $ | | | | | | | | | | | | | | | $ 78,355 | | | |
The 2022 ATM Facility [Member] | Maximum [Member] | | | | | | | | | | | | | | | | | | |
Common Stock, Shares Authorized, Value | $ | | | | | | | | | | | $ 50,000,000 | | | | | | | |
The 2023 ATM Facility [Member] | | | | | | | | | | | | | | | | | | |
Stock Issued During Period, Shares, New Issues (in shares) | | | | | | | | | | | | | | | 0 | | | |
Proceeds from Issuance or Sale of Equity | $ | | | | | | | | | | | | | | | $ 881,946 | | | |
Brokerage Commissions, Percentage of Gross Proceeds | | | | | | | 3% | | | | | | | | | | | |
Subsequent Event [Member] | The 2018 Equity Incentive Plan [Member] | | | | | | | | | | | | | | | | | | |
Share-Based Compensation Arrangement by Share-Based Payment Award, Number of Additional Shares Authorized (in shares) | | | | | 74,294 | | | | | | | | | | | | | |
Subsequent Event [Member] | Scientific Advisory Board Chairman [Member] | | | | | | | | | | | | | | | | | | |
Stock Issued During Period, Shares, Issued for Services (in shares) | | | | 125 | | | | | | | | | | | | | | |
Subsequent Event [Member] | Registered Direct Offering [Member] | | | | | | | | | | | | | | | | | | |
Stock Issued During Period, Shares, New Issues (in shares) | 165,000 | | | | | | | | | | | | | | | | | |
Equity Offering, Combined Purchase Price (in dollars per share) | $ / shares | $ 4.215 | | | | | | | | | | | | | | | | | |
Proceeds from Issuance or Sale of Equity | $ | $ 5.8 | | | | | | | | | | | | $ 5.8 | | | | | |
Subsequent Event [Member] | The 2023 ATM Facility [Member] | | | | | | | | | | | | | | | | | | |
Stock Issued During Period, Shares, New Issues (in shares) | | | | | | | | | | | | | | 158,474 | | | | |
Proceeds from Issuance of Common Stock | $ | | | | | | | | | | | | | | $ 881,946 | | | | |
Subsequent Event [Member] | Reverse Stock Split [Member] | | | | | | | | | | | | | | | | | | |
Stockholders' Equity Note, Stock Split, Conversion Ratio | | 40 | 40 | | | | | | | | | | | | | | | |