Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	Common stock	Additional paid-in capital	Accumulated deficit	Convertible Preferred Stock Preferred stock
Beginning balance (in shares) at Dec. 31, 2019		21,018,663			3,704,288
Beginning balance at Dec. 31, 2019	$ 20,015	$ 21	$ 431,305	$ (411,315)	$ 4
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock upon exercise of options (in shares)		6,842
Issuance of common stock upon exercise of options	5		5
Issuance of common stock upon exercise of warrants (in shares)		1,038,970
Issuance of common stock upon exercise of warrants	692	$ 1	691
Issuance of common stock upon vesting of restricted stock units (in shares)		75,384
Issuance of common stock, preferred stock and warrants from private placement, net of offering costs (in shares)		24,341,607			272,970
Issuance of common stock, preferred stock and warrants from private placement, net of offering costs	18,166	$ 25	18,141
Stock-based compensation expense	2,614		2,614
Issuance of common stock under Employee Stock Purchase Plan (in shares)		4,998
Issuance of common stock under Employee Stock Purchase Plan	2		2
Issuance of common stock through ATM (in shares)		492,268
Issuance of common stock through ATM	262		262
Conversions of convertible preferred stock (in shares)		20,453,980			(2,045,398)
Conversions of convertible preferred stock	0	$ 20	(18)		$ (2)
Net loss	(15,730)			(15,730)
Ending balance (in shares) at Dec. 31, 2020		67,432,712			1,931,860
Ending balance at Dec. 31, 2020	26,026	$ 67	453,002	(427,045)	$ 2
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock upon exercise of options (in shares)		27,728
Issuance of common stock upon exercise of options	26		26
Issuance of common stock upon exercise of warrants (in shares)		2,668,681
Issuance of common stock upon exercise of warrants	832	$ 3	829
Issuance of common stock upon vesting of restricted stock units (in shares)		33,751
Issuance of common stock, preferred stock and warrants from private placement, net of offering costs (in shares)		58,923,352			3,725,720
Issuance of common stock, preferred stock and warrants from private placement, net of offering costs	32,360	$ 59	32,298		$ 3
Stock-based compensation expense	2,923		2,923
Issuance of common stock under Employee Stock Purchase Plan (in shares)		11,619
Issuance of common stock under Employee Stock Purchase Plan	$ 7		7
Issuance of common stock through ATM (in shares)	11,619	16,017,131
Issuance of common stock through ATM	$ 20,592	$ 16	20,576
Conversions of convertible preferred stock (in shares)		856,210			(85,621)
Conversions of convertible preferred stock		$ 1	(1)
Net loss	(27,808)			(27,808)
Ending balance (in shares) at Dec. 31, 2021		145,971,184			5,571,959
Ending balance at Dec. 31, 2021	$ 54,958	$ 146	$ 509,660	$ (454,853)	$ 5