Condensed Statements of Cash Flows - USD ($)	6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016
Operating activities
Net loss	$ (11,657,176)	$ (13,878,027)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	587,466	728,828
Accretion of discount on NuvoGen obligation	99,377	104,467
Provision for excess inventory	244,026	149,763
Amortization of Growth Term Loan discount and issuance costs	231,319	267,047
Stock-based compensation expense	814,583	322,136
Employee stock purchase plan expense	29,223
Accretion of incentive from landlord	(71,000)	(59,165)
Accrued interest on available-for-sale securities investments	5,991	125,138
Changes in operating assets and liabilities:
Accounts receivable	(173,427)	(1,195,148)
Inventory	(19,673)	(161,570)
Prepaid expenses and other	(35,103)	(228,723)
Deferred offering costs	49,630
Accounts payable	480,025	799,786
Accrued liabilities	(456,675)	(42,404)
Deferred revenue	278,310	136,231
Net cash used in operating activities	(9,593,104)	(12,931,641)
Investing activities
Purchase of property and equipment	(152,339)	(1,620,946)
Sales, redemptions and maturities of available-for-sale securities	4,300,000	18,700,000
Purchase of available-for-sale securities		(3,381,271)
Net cash provided by investing activities	4,147,661	13,697,783
Financing activities
Payment of offering costs	(201,475)
Proceeds from Growth Term Loan		5,000,000
Payments on Growth Term Loan	(3,126,629)	(1,450,576)
Proceeds from ATM offering	14,907,245
Payments on capital leases	(24,796)	(66,706)
Proceeds from exercise of stock options	109,786	2,142
Proceeds from shares purchased under the stock purchase plan	71,689	146,758
Payments on NuvoGen obligation	(400,000)	(181,250)
Net cash provided by financing activities	11,335,820	3,450,368
Increase in cash and cash equivalents	5,890,377	4,216,510
Cash and cash equivalents at beginning of period	7,507,659	3,293,983
Cash and cash equivalents at end of period	13,398,036	7,510,493
Noncash investing and financing activities
Fixed asset purchases payable and accrued at period end	72,224	214,033
Offering costs payable at period end	30,000
Carrying value of demonstration units transferred from property and equipment to inventory	26,807
Stock issued for settlement of accrued bonus		(364,910)
Purchase of property and equipment under capital lease		209,588
Incentive from landlord		710,000
Retirement of treasury stock	75,000
Supplemental cash flow information
Cash paid for interest	$ 417,782	$ 559,832