Condensed Consolidated Statements of Cash Flows - USD ($)	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018
Operating activities
Net loss	$ (10,168,116)	$ (9,482,676)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	603,480	778,344
Accretion of discount on NuvoGen obligation	(6,483)	(6,006)
Provision for excess inventory	45,000	23,533
Amortization of Growth Term Loan discount and issuance costs		62,951
Loss on extinguishment of Growth Term Loan		105,064
Amortization of QNAH Convertible Note issuance costs	6,727	6,727
Amortization of MidCap Credit Facility discount and issuance costs	81,096	48,092
Stock-based compensation expense	528,578	1,385,378
Employee stock purchase plan expense	33,589	28,906
Amortization of operating lease right-of-use assets	194,232
Amortization of incentive from landlord		(71,000)
Accrued interest on available-for-sale securities investments	(178,165)	(187,946)
Changes in operating assets and liabilities:
Accounts receivable	1,031,575	2,874,274
Inventory	100,927	191,836
Prepaid expenses and other	(501,474)	(402,102)
Deferred offering costs		2,953
Accounts payable	1,172,992	(656,645)
Accrued liabilities	(1,784,860)	(1,319,010)
Contract liabilities	344,494	(389,172)
Operating lease liabilities	(270,477)
Net cash used in operating activities	(8,766,885)	(7,006,499)
Investing activities
Purchase of property and equipment	(319,425)	(829,186)
Sales, redemptions and maturities of available-for-sale securities	22,400,000	3,300,000
Purchase of available-for-sale securities	(9,290,341)	(38,079,329)
Net cash provided by (used in) investing activities	12,790,234	(35,608,515)
Financing activities
Proceeds from MidCap Credit Facility		7,000,000
MidCap Credit Facility lender fees		(422,390)
Payments on Growth Term Loan		(1,684,626)
Payments for extinguishment of Growth Term Loan		(4,276,988)
Proceeds from public offering, net of underwriting discounts, commissions and costs of $2.6 million		37,724,316
Proceeds from ATM Offering, net		556,706
Payments on NuvoGen obligation	(655,855)	(435,093)
Payments on financing leases	(25,227)	(40,017)
Proceeds from exercise of stock options	120,954	69,513
Taxes paid for net share settlement of restricted stock awards	(20,837)	(133,513)
Proceeds from shares purchased under stock purchase plans	82,345	62,862
Payment of deferred offering costs	(139,058)
Net cash (used in) provided by financing activities	(637,678)	38,420,770
Effect of exchange rates on cash	(4,682)
Increase (decrease) in cash, cash equivalents and restricted cash	3,380,989	(4,194,244)
Cash, cash equivalents and restricted cash at beginning of period	11,702,847	9,968,600
Cash, cash equivalents and restricted cash at end of period	15,083,836	5,774,356
Supplemental disclosure of noncash investing and financing activities
Fixed asset purchases payable and accrued at period end	374,202	2,730
Adoption of ASC 842, Leases	694,352
Operating lease right-of-use assets obtained in exchange for operating lease liabilities	894,544
Equipment purchased through capital leases		45,896
Carrying value of demonstration units transferred from property and equipment to inventory		49,245
MidCap Term Loan fees and warrant discount		389,000
Supplemental cash flow information
Cash paid for interest	348,130	202,573
Cash paid for taxes	$ 6,848	$ 3,545