In this paper we present a study and evaluation of a custom single differential sensor design for ECG data acquisition, recurring to electro-textile electrodes as the interface between the sensor and the skin. Our work is focused on improving current signal acquisition methods for ECG biometrics, targeting wearable, continuous and unobtrusive applications. A circuit with virtual ground was also devised for enhanced usability. The purpose is to build upon and further extend the state-of-the-art in the field, improving existing signal acquisition conditions by: minimizing the number of electrical contact points with the subject's body; eliminating the need of gel in the interface with the skin; and devising a non-intrusive design that can be easily integrated into wearable devices. Experimental analysis has been performed to compare the proposed approach with a reference acquisition sensor, and results validate the potential of our method.