Preferred Stock – Our authorized preferred stock consists of 10,000,000 shares of preferred stock with a par value of $0.001, of which no shares have been issued or are outstanding.

Common Stock – Our authorized common stock consists of 200,000,000 shares of common stock with a par value of $0.001, of which 18,689,807 and 18,413,419 shares were issued and outstanding as of March 31, 2021 and December 31, 2020, respectively.

Employee Stock Purchase Plan – On September 17, 2014, our stockholders approved our 2014 Employee Stock Purchase Plan (“ESPP”). We recorded expense of $4,224 and $6,667 related to the ESPP for the three months ended March 31, 2021 and 2020, respectively.

	Warrants
						Weighted-
						Average
	Number			Exercise Price		Exercise Price
	of Shares			per Share		Per Share
Outstanding at December 31, 2020		1,021,060		$1.15 — $3.88		$	1.56
Exercised		(181,834	)	$1.15 — $3.88		$	1.23
Canceled/Forfeited		(339,226	)	$1.15 — $3.88		$	1.83
Outstanding at March 31, 2021		500,000			$1.50	$	1.50

The following table summarizes the warrants issued and outstanding as of March 31, 2021:

Date of

Shares of

Description

Issuance

Expiration

Exercise Price

Common Stock

Exercisable Warrants

10/19/2020

03/19/2028

1.50

500,000

Stock Options – We recorded stock option expense of $216,958 and $294,661 for the three months ended March 31, 2021 and 2020, respectively. The following table summarizes the stock option activity for the three months ended March 31, 2021:

	Stock Options
					Weighted-
				Exercise	Average
	Number			Price Per	Exercise Price
	of Shares			Share	Per Share
Outstanding at December 31, 2020		3,177,942		$1.17 — $23.20	$	2.78
Granted		193,000		$3.83 — $3.01	$	3.82
Exercised		(94,554	)	$3.10 — $1.48	$	2.68
Cancelled/Forfeited		(6,250	)	$5.44	$	5.44
Outstanding at March 31, 2021		3,270,138		$1.17 — $23.20	$	2.84

Deferred Stock Units – Effective September 1, 2019, nonemployee directors can elect to receive all or a portion of their annual retainers in the form of deferred stock units (“DSUs”). The DSUs are recognized at their fair value on the date of grant. Each DSU represents the right to receive one share of our common stock following the completion of a director’s service. During the three months ended March 31, 2021, we granted 2,845 DSUs and recorded director compensation expense of $8,661 related to the grants. In addition, during the three months ended March 31, 2021 we granted 13,333 DSUs to executive employees and recorded compensation expense of $79,768, which includes an accrual of anticipated bonus expense to be paid in DSUs for certain executive employees. We had 89,409 and 73,231 DSUs outstanding at March 31, 2021 and December 31, 2020, respectively.