Stockholders' equity (Details) - shares	9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014
Shares
Outstanding, beginning balance		7,977,990
Outstanding, ending balance	33,077,886	25,795,553
Warrant [Member]
Shares
Outstanding, beginning balance	23,933,922	7,977,990
Issued in connection with sales of common and preferred stock		17,918,675
Issued during the year in connection with issuance of convertible notes	1,983,340
Expired or cancelled during the year	(160,894)	(158,450)
Outstanding, ending balance	25,756,368	25,738,215
Options [Member]
Shares
Outstanding, beginning balance	8,807,667	1,566,667
Issued during the year in connection with issuance of convertible notes	600,000	5,918,000
Expired or cancelled during the year	(740,834)	(110,000)
Outstanding, ending balance	8,666,833	7,374,667