Masada – Ein Gedi – Dead Sea

I am planning a day trip to Masada, Ein Gedi and the Dead Sea from Tel Aviv. Is it possible to visit all 3 places using public transportation?

If by public transportation, you mean the buses, no. Even if the connections were possible, why would you want to do it. The whole day would be spent riding, or waiting for a bus, and you'd have to walk in from the main road.

It's a full day tour from Jerusalem, so from Tel Aviv, a tour or taxis would be the only way to comfortably get to all three places and actually spend time there. In my educated opinion.

I would disagree. If you go to Trip Advisor you will find people who have done it. Personally, I would never recommend it. Buses do not reach certain stops at an exact time. THe schedule is an "about" time and the bus may be earlier or later. You have to be there earlier to make sure you make the bus. Take a tour or rent a car.

The OP wants to do a DAY trip from TEL-AVIV ! This is absolutely impossible !!!!! Even from Jerusalem it is extremely difficult to do all three in the same day using the bus. Either stay overnight at the Dead Sea (look at http://www.iyha.org.il/eng/ ) or take a tour. Only the Abraham Hostel tour (from Jerusalem) goes to Massada AND Ein Gedi:
http://abrahamtours.com/theme/israel-tours/