Stockholders' equity (deficit) (Tables)

9 Months Ended

12 Months Ended

Sep. 30, 2019

Dec. 31, 2018

Stockholders' Equity Note [Abstract]

Schedule of Company Recognized Stock-Based Compensation Expense

For the three and nine months ended September 30, 2019 and 2018, the Company recognized stock-based compensation expense as follows:

	Three Months Ended September 30,					Nine Months Ended September 30,
	2019		2018			2019		2018
Cost of services	$	584	$	(2,807	)	$	1,146	$	924
Research and development		20,175		56,961			55,635		187,512
General and administrative		65,318		141,974			202,696		434,314
Sales and marketing		5,090		10,523			15,694		35,981
	$	91,167	$	206,651		$	275,171	$	658,731

For the years ended December 31, 2018 and 2017, the Company recognized stock compensation expense as follows:

	Year Ended December 31,
	2018		2017
Cost of services	$	964	$	13,776
Research and development		241,122		237,103
General and administrative		574,244		603,787
Sales and marketing		45,951		56,732
	$	862,281	$	911,398

Schedule of Warrants to Purchase Shares of Common Stock

At September 30, 2019 and December 31, 2018, the following warrants to purchase shares of common stock were outstanding:

							Outstanding at
Issuance			Exercise Price		Expiration		September 30, 2019 (1)		December 31, 2018 (1)
	November 2009		$	3,955.00		November 2019		17		17
	January 2010		$	3,955.00		January 2020		17		17
	March 2010		$	3,955.00		March 2020		7		7
	November 2011		$	3,955.00		November 2021		15		15
	December 2011		$	3,955.00		December 2021		2		2
	March 2012		$	54,950.00		March 2019		—		8
	February 2015		$	3,300.00		February 2025		451		451
	May 2015		$	3,300.00		May 2020		6,555		6,555
	May 2016		$	656.00		May 2021		9,483		9,483
	June 2016		$	656.00		May 2021		4,102		4,102
	June 2017		$	390.00		June 2022		938		938
	July 2017		$	345.00		July 2022		318		318
	July 2017		$	250.00		July 2022		2,501		2,501
	July 2017		$	212.60		July 2022		50,006		50,006
	February 2018		$	81.20		February 2023		9,232		9,232
	February 2018		$	65.00		February 2023		92,338		92,338
								175,982		175,990
	(1)	Warrants to purchase fractional shares of common stock resulting from the reverse stock split on August 29, 2019 were rounded up to the next whole share of common stock on a holder by holder basis.

At December 31, 2018 and 2017, the following warrants to purchase shares of common stock were outstanding:

				Outstanding at December 31,
Issuance	Exercise Price		Expiration	2018 (1)		2017 (1)
March 2008	$	19,763.50	March 2018		—		2
November 2009	$	197.75	November 2019		270		270
January 2010	$	197.75	January 2020		270		270
March 2010	$	197.75	March 2020		55		55
November 2011	$	197.75	November 2021		212		212
December 2011	$	197.75	December 2021		27		27
March 2012	$	2,747.50	March 2019		165		165
February 2015	$	165.00	February 2025		9,001		9,001
May 2015	$	165.00	May 2020		138,310		138,310
May 2016	$	32.81	May 2021		189,577		189,577
June 2016	$	32.81	May 2021		82,035		82,035
June 2017	$	19.50	June 2022		18,754		18,754
July 2017	$	17.25	July 2022		6,350		6,350
July 2017	$	12.50	July 2022		50,000		50,000
July 2017	$	10.625	July 2022		1,000,003		1,000,003
February 2018	$	4.06	February 2023		184,615		—
February 2018	$	3.25	February 2023		1,846,153		—
					3,525,797		1,495,031

Summary of Status of Options Granted

A summary of the status of options granted is presented below as of and for the years ended December 31, 2018 and 2017:

	Number of Options			Weighted- Average Exercise Price		Weighted- Average Remaining Contractual Life (in years)		Aggregate Intrinsic Value
Outstanding at January 1, 2017		119,106		$	44.00		8.6	$	663,298
Granted		58,324		$	17.58
Exercised		(1,167	)	$	7.01			$	11,256
Forfeited		(24,538	)	$	36.31
Expired		(12,330	)	$	83.49
Outstanding at December 31, 2017		139,395		$	31.16		8.3	$	37,339
Granted		95,800		$	3.84
Exercised		—			—
Forfeited		(18,812	)	$	11.98
Expired		(4,824	)	$	56.12
Outstanding at December 31, 2018		211,559		$	20.58		7.6	$	522
Vested and expected to vest		211,559		$	20.58		7.6	$	522
Exercisable at December 31, 2018		10,445		$	1.25		5.3	$	522

Schedule of Fair Value of Option Grant Estimated Using Black-Scholes Option Pricing Model

The fair value of each option grant was estimated at the date of grant using the Black-Scholes option pricing model based on the assumptions below:

	Year Ended December 31,
	2018		2017
Annual dividend		—		—
Expected life (in years)	5.25 - 6.25		5.25 - 6.25
Risk free interest rate	2.5 - 2.9%		1.8 - 2.3%
Expected volatility	46.0 - 49.6%		44.2 - 53.0%

Summary of Status of Restricted Stock Unit Granted

A summary of the status of restricted stock units granted is presented below as of and for the years ended December 31, 2018 and 2017:

	Number of Options			Weighted- Average Grant Date Fair Value
Unvested at January 1, 2017		750		$	42.50
Granted		11,175		$	6.93
Vested		(6,025	)	$	8.01
Forfeited		—			—
Unvested at December 31, 2017		5,900		$	31.16
Granted		—			—
Vested		(5,650	)	$	8.93
Forfeited		—			—
Unvested at December 31, 2018		250		$	42.50