Intangible assets - Narrative (Details) (USD $)	12 Months Ended
Intangible assets - Narrative (Details) (USD $)	Dec. 31, 2014	Dec. 31, 2013
Acquired Finite-Lived Intangible Assets [Line Items]
Amortization expense	$ 83,986us-gaap_AmortizationOfIntangibleAssets	$ 56,643us-gaap_AmortizationOfIntangibleAssets
Product Certifications
Acquired Finite-Lived Intangible Assets [Line Items]
Capitalized finited lived intangible assets	68,638	171,224
Patents
Acquired Finite-Lived Intangible Assets [Line Items]
Capitalized finited lived intangible assets	73,321	226,726
Patents \| Minimum
Acquired Finite-Lived Intangible Assets [Line Items]
Finited lived intangible assets, estimated useful life	7 years
Patents \| Maximum
Acquired Finite-Lived Intangible Assets [Line Items]
Finited lived intangible assets, estimated useful life	10 years
Developed Technology
Acquired Finite-Lived Intangible Assets [Line Items]
Capitalized finited lived intangible assets	$ 240,000
Finited lived intangible assets, estimated useful life	15 years