Consolidated Statements of Cash Flows - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Operating activities
Net loss	$ (19,297,664)	$ (16,453,918)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	1,259,015	1,468,121
Accretion of discount on NuvoGen obligation	(13,821)	(12,480)
Provision for excess inventory	153,729	83,218
Amortization of Growth Term Loan discount and issuance costs		62,951
Loss on extinguishment of Growth Term Loan		105,064
Write-off of ATM offering costs	108,883
Amortization of QNAH Convertible Note issuance costs	13,454	13,453
Amortization of MidCap Credit Facility discount and issuance costs	183,002	133,963
Stock-based compensation expense	1,156,567	1,888,055
Employee stock purchase plan expense	66,238	58,959
Amortization of operating lease right-of-use assets	476,789
Amortization of incentive from landlord		(142,000)
Accrued interest on available-for-sale securities investments	(325,666)	(412,436)
Loss on disposal of assets	9,051	8,104
Changes in operating assets and liabilities:
Accounts receivable	1,848,502	1,332,030
Inventory	(116,787)	(171,909)
Prepaid expenses and other	(177,307)	(113,581)
Deferred offering costs		2,953
Accounts payable	(155,974)	(150,176)
Accrued liabilities	(1,440,065)	(447,351)
Contract liabilities	188,507	(426,938)
Operating lease liabilities	(632,389)
Net cash used in operating activities	(16,695,936)	(13,173,918)
Investing activities
Purchase of property and equipment	(1,103,176)	(949,514)
Sales, redemptions and maturities of available-for-sale securities	32,200,000	31,700,000
Purchase of available-for-sale securities	(34,601,208)	(53,970,921)
Net cash used in investing activities	(3,504,384)	(23,220,435)
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 2018 underwritten public offering, net of underwriting discounts, commissions and issuance costs of $2.6 million		37,724,316
Proceeds from 2019 underwritten public and private offerings, net of underwriting discounts, commissions and issuance costs of $1.7 million	20,758,940
Proceeds from ATM Offering, net		556,706
Payments on NuvoGen obligation	(1,327,922)	(1,012,122)
Payments on financing leases	(44,043)	(62,085)
Proceeds from exercise of stock options	120,954	316,767
Taxes paid for net share settlement of restricted stock awards	(30,904)	(150,748)
Proceeds from shares purchased under stock purchase plans	104,952	140,915
Payment of deferred offering costs	(190,173)
Net cash provided by financing activities	19,391,804	38,129,745
Effect of exchange rates on cash	(4,336)	(1,145)
(Decrease) increase in cash, cash equivalents and restricted cash	(812,852)	1,734,247
Cash, cash equivalents and restricted cash at beginning of year	11,702,847	9,968,600
Cash, cash equivalents and restricted cash at end of year	10,889,995	11,702,847
Supplemental disclosure of noncash investing and financing activities
Fixed asset purchases payable and accrued at period end	8,299	39,265
Adoption of ASC 842, Leases	694,352
Operating lease right-of-use assets obtained in exchange for operating lease liabilities	1,005,085
Financing lease right-of-use assets obtained in exchange for financing lease liabilities	63,406
Equipment purchased through capital leases		71,709
Carrying value of demonstration units transferred from property and equipment to inventory		49,245
Debt issuance costs payable and accrued at period end		59,030
MidCap Term Loan fees and warrant discount		389,000
Supplemental cash flow information
Cash paid for interest	686,042	553,070
Cash paid for taxes	$ 3,379	$ 3,545