Consolidated Statements of Cash Flows - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Operating activities
Net loss	$ (16,453,918)	$ (18,960,017)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	1,468,121	1,241,873
Accretion of discount on NuvoGen obligation	(12,480)	195,248
Provision for excess inventory	83,218	366,963
Amortization of Growth Term Loan discount and issuance costs	62,951	404,462
Loss on extinguishment of Growth Term Loan	105,064
Amortization of QNAH Convertible Note issuance costs	13,453	1,269
Amortization of MidCap Credit Facility discount and issuance costs	133,963
Stock-based compensation expense	1,888,055	1,376,969
Employee stock purchase plan expense	58,959	59,118
Accretion of incentive from landlord	(142,000)	(142,000)
Accrued interest on available-for-sale securities investments	(412,436)
Loss on disposal of assets	8,104	81,539
Changes in operating assets and liabilities:
Accounts receivable	1,332,030	(4,978,827)
Inventory	(171,909)	77,176
Prepaid expenses and other	(113,581)	(3,749)
Deferred offering costs	2,953	49,630
Accounts payable	(150,176)	1,225,954
Accrued liabilities	(447,351)	2,076,500
Contract liabilities	(426,938)	355,584
Net cash used in operating activities	(13,173,918)	(16,572,308)
Investing activities
Purchase of property and equipment	(949,514)	(1,020,531)
Sales, redemptions and maturities of available-for-sale securities	31,700,000	4,300,000
Purchase of available-for-sale securities	(53,970,921)
Net cash (used in) provided by investing activities	(23,220,435)	3,279,469
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)	(6,389,782)
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	(231,476)
Proceeds from ATM Offering, net	556,706	19,908,954
Proceeds from issuance of convertible note to QNAH, a related party		3,000,000
QNAH Convertible Note financing costs		(40,509)
Payments on NuvoGen obligation	(1,012,122)	(800,000)
Payments on capital leases	(62,085)	(69,142)
Proceeds from exercise of stock options	316,767	112,138
Taxes paid for net share settlement of restricted stock awards	140,915
Proceeds from shares purchased under stock purchase plans		266,549
Payment of deferred offering costs	(150,748)	(2,952)
Net cash provided by financing activities	38,129,745	15,753,780
Effect of exchange rates on cash	(1,145)
Increase in cash, cash equivalents and restricted cash	1,734,247	2,460,941
Cash and cash equivalents at beginning of year	9,968,600	7,507,659
Cash, cash equivalents and restricted cash at end of year	11,702,847	9,968,600
Supplemental disclosure of noncash investing and financing activities
Fixed asset purchases payable and accrued at period end	39,265	477,966
Carrying value of demonstration units transferred from property and equipment to inventory	49,245	113,607
Equipment purchased through capital lease	71,709
Debt issuance costs payable and accrued at period end	59,030
MidCap Term Loan fees and warrant discount	389,000
Retirement of treasury stock		75,000
Supplemental cash flow information
Cash paid for interest	553,070	698,065
Cash paid for taxes	$ 3,545	$ 1,967