Later, Doflamingo was shown to be well capable of cutting a Logia type as he brutally injured Chaser Smoker by combining his Haki with his strings. ... Doflamingo has completely mastered his powers of the String-String Fruit and has thus managed to achieve the rare phenomenon of "awakening".

Does String fruit have Logia?

The String fruit is a bad fruit for grinding due to no Logia protection (if you know how to use it wisely, it can be good at grinding), also it is an excellent fruit for PVP (due to the large hitboxes of the awakened String).

Does doflamingo have a devil fruit?

Devil Fruit

Doflamingo uses his strings. Doflamingo ate the Ito Ito no Mi, a Paramecia-type Devil Fruit which allows him to create and control strings.