Note 9 - Stockholders' Equity - Summary of Option Activity for Employees and Non-employees (Details) - Share-based Payment Arrangement, Option [Member] - USD ($)	9 Months Ended		12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020	Dec. 31, 2019
Share-based Payment Arrangement, Employee [Member]
Number of options (in shares)	1,953,443	1,212,442	1,212,442
Weighted average exercise price, outstanding (in dollars per share)	$ 1.88	$ 1.61	$ 1.61
Weighted average remaining contractual life, outstanding (Year)	7 years 1 month 20 days	1 year 7 months 2 days	3 years 1 month 2 days	2 years
Aggregate intrinsic value, outstanding	$ 35,776	$ 114,570	$ 476,964	$ 0
Number of options granted (in shares)	2,032,175	80,000
Weighted average exercise price, granted (in dollars per share)	$ 2.48	$ 0
Number of options exercised (in shares)	(485,247)	0
Weighted average exercise price, exercised (in dollars per share)	$ 1.59	$ 0
Number of options forfeited and expired (in shares)	(351,759)	(289,464)
Weighted average exercise price, forfeited or expired (in dollars per share)	$ 1.99	$ 3.89
Number of options exercisable (in shares)	604,817	828,370
Weighted average exercise price, exercisable (in dollars per share)	$ 1.95	$ 1.55
Weighted average remaining contractual life, exercisable (Year)	1 year 10 months 24 days	1 year 4 months 17 days
Aggregate intrinsic value, exercisable	$ 35,776	$ 88,983
Common stock issued to employee for stock options exercised (in shares)	485,247	(0)
Number of options (in shares)	3,148,612	1,002,978	1,953,443	1,212,442
Weighted average exercise price, outstanding (in dollars per share)	$ 2.30	$ 1.56	$ 1.88	$ 1.61
Share-based Payment Arrangement, Nonemployee [Member]
Number of options (in shares)	74,997	49,998	49,998
Weighted average exercise price, outstanding (in dollars per share)	$ 1.41	$ 1.43	$ 1.43
Weighted average remaining contractual life, outstanding (Year)	3 years 1 month 2 days	2 years 10 months 9 days	3 years 2 months 4 days	2 years 11 months 8 days
Aggregate intrinsic value, outstanding	$ 38,082	$ 19,333	$ 54,748
Number of options granted (in shares)	16,666	24,999
Weighted average exercise price, granted (in dollars per share)	$ 3.94	$ 1.70
Number of options exercised (in shares)	(8,333)	0
Weighted average exercise price, exercised (in dollars per share)	$ 2.34	$ 0
Number of options exercisable (in shares)	55,553	52,776
Weighted average exercise price, exercisable (in dollars per share)	$ 1.09	$ 1.57
Weighted average remaining contractual life, exercisable (Year)	2 years 2 months 8 days	2 years 2 months 26 days
Aggregate intrinsic value, exercisable	$ 32,860	$ 14,666
Common stock issued to employee for stock options exercised (in shares)	8,333	0
Number of options (in shares)	83,330	74,997	74,997	49,998
Weighted average exercise price, outstanding (in dollars per share)	$ 1.83	$ 1.52	$ 1.41	$ 1.43