REVENUE - Revenue by customer type and geographic area (Details) - USD ($)
 3 Months Ended 12 Months Ended
Dec. 31, 2021
Sep. 30, 2021
Jun. 30, 2021
Mar. 31, 2021
Dec. 31, 2020
Sep. 30, 2020
Jun. 30, 2020
Mar. 31, 2020
Dec. 31, 2019
Sep. 30, 2019
Jun. 30, 2019
Mar. 31, 2019
Dec. 31, 2021
Dec. 31, 2020
Dec. 31, 2019
Product sales:                              
Total revenue $ 10,782,195 $ 9,760,416 $ 12,024,069 $ 10,598,847 $ 11,955,776 $ 10,546,612 $ 9,794,903 $ 8,707,310 $ 7,430,311 $ 6,095,007 $ 6,232,526 $ 5,191,629 $ 43,165,527 $ 41,004,601 $ 24,949,473
Product                              
Product sales:                              
Total revenue                         40,108,567 39,452,502 22,765,854
Grant                              
Product sales:                              
Total revenue                         3,056,960 1,552,099 2,183,619
United States | Product                              
Product sales:                              
Total revenue                         1,689,867 1,341,200 220,100
United States | Grant                              
Product sales:                              
Total revenue                         3,056,960 1,552,099 2,183,619
Germany | Product                              
Product sales:                              
Total revenue                         21,006,432 20,257,410 14,396,418
All other countries | Product                              
Product sales:                              
Total revenue                         17,412,268 17,853,892 8,149,336
Direct                              
Product sales:                              
Total revenue                         27,041,855 26,681,329 17,764,047
Direct | Product                              
Product sales:                              
Total revenue                         27,041,855 26,681,329 17,764,047
Direct | United States | Product                              
Product sales:                              
Total revenue                         189,167 1,148,300 220,100
Direct | United States | Grant                              
Product sales:                              
Total revenue                         0 0 0
Direct | Germany | Product                              
Product sales:                              
Total revenue                         21,006,432 20,257,410 14,396,418
Direct | All other countries | Product                              
Product sales:                              
Total revenue                         5,846,256 5,275,619 3,147,529
Distributors/Strategic Partners                              
Product sales:                              
Total revenue                         13,066,712 12,771,173 5,001,807
Distributors/Strategic Partners | Product                              
Product sales:                              
Total revenue                         13,066,712 12,771,173 5,001,807
Distributors/Strategic Partners | United States | Product                              
Product sales:                              
Total revenue                         1,500,700 192,900 0
Distributors/Strategic Partners | United States | Grant                              
Product sales:                              
Total revenue                         0 0 0
Distributors/Strategic Partners | Germany | Product                              
Product sales:                              
Total revenue                         0 0 0
Distributors/Strategic Partners | All other countries | Product                              
Product sales:                              
Total revenue                         11,566,012 12,578,273 5,001,807
United States Government Agencies                              
Product sales:                              
Total revenue                         3,056,960 1,552,099 2,183,619
United States Government Agencies | Product                              
Product sales:                              
Total revenue                         0 0 0
United States Government Agencies | United States | Product                              
Product sales:                              
Total revenue                         0 0 0
United States Government Agencies | United States | Grant                              
Product sales:                              
Total revenue                         3,056,960 1,552,099 2,183,619
United States Government Agencies | Germany | Product                              
Product sales:                              
Total revenue                         0 0 0
United States Government Agencies | All other countries | Product                              
Product sales:                              
Total revenue                         $ 0 $ 0 $ 0