The person you should be suing is your ex-wife.
The DA does not get the case until after you have been arrested. Based on the facts you provided, it sounds like the police arrested you and the DA refused to prosecute for lack of evidence. Thus, the DA probably helped you. However, even if the DA chose to prosecute you, you still would not be able to sue because the DA has immunity for any official acts.
The police only need probable cause to arrest you. Thus, even if there was not enough evidence to convict you that does not mean the police did not have enough evidence to arrest you.
You did not specify what makes you believe that the police acted based on race. If the police were motivated by race and the arrest was made without probable cause, then you would have a good case. But based on the facts you provided, I am not sure race was a factor. And if race was a factor, I suspect the cops also had probable cause to arrest you.
If you have specific facts to suggest that the arrest was motivated by race, I would suggest you consult an attorney.