SQL Backup error in c sharp

Question

dbMDFName = C:\main\ext\AssetTrackingExt.mdf;
dbLDFName = C:\main\ext\AssetTrackingExt.ldf;

string str = "use master \n GO \n sp_attach_db 'ATT'" + "," + "'" + dbMDFName + "'" + "," + "'" + dbLDFName + "'";
this is my backup database code but an error occur

"Incorrect sysnat near Go"

what is solution for this error