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 15,403,111 and 15,372,905 shares were issued and outstanding as of June 30, 2020 and December 31, 2019, respectively.

Employee Stock Purchase Plan – On September 17, 2014, our stockholders approved our 2014 Employee Stock Purchase Plan (“ESPP”). On May 14, 2020, we issued 30,206 shares to employees for $30,040 under our ESPP for options that vested and were exercised. We recorded expense of $20,867 and $13,827 related to the ESPP for the six months ended June 30, 2020 and 2019, respectively.

Warrants – At June 30, 2020, we had outstanding exercisable warrants to purchase 521,060 shares of common stock.

The following table summarizes the warrants issued and outstanding as of June 30, 2020:

Date of

Exercise

Shares of

Description

Issuance

Expiration

Price

Common Stock

Exercisable Warrants

3/30/2016

03/30/2021

3.88

521,060

Total warrants issued and outstanding

521,060

See Note 14. Subsequent Events for further information regarding certain exercisable warrants.

Stock Options – We recorded stock option expense of $621,032 and $459,405 for the six months ended June 30, 2020 and 2019, respectively. The following table summarizes the stock option activity for the six months ended June 30, 2020:

	Stock Options
					Weighted-
				Exercise	Average
	Number			Price Per	Exercise Price
	of Shares			Share	Per Share
Outstanding at December 31, 2019		2,445,453		$1.17 — $23.20	$	3.37
Granted		918,052		$1.35 — $2.32	$	1.53
Canceled/Forfeited		(17,458	)	$1.51 — $16.40	$	3.18
Outstanding at June 30, 2020		3,346,047		$1.17 — $23.20	$	2.86

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 six months ended June 30, 2020, we granted 35,166 DSUs and recorded director compensation expense of $51,974 related to the grants. In addition, during the six months ended June 30, 2020 we granted 39,684 DSUs to executive employees and recorded compensation expense of $83,805, which includes an accrual of anticipated bonus expense to be paid in DSUs for certain executive employees.