How to check when Db was last used in order to remove them from server.

I am using SQL Server 2008R2 & i have 50 DB's in this instance.

my Question is how to Identify , when a DB's was last accessed. Based on the last date of access I can decide which DB's to keep and which have to be deleted.

I got plenty of Queries in google, but the problem but none accurate, daily sql full backup job & diff back up are executing, so when i execute the query's from google, its showing yesterdays date, i.e the last day when the sql backups are  executed,

i need a solution apart from this method , so i request you to help me.

NJPA