Graphene is considered for different technological applications, particularly biosensing, due to its unique electrical and electronic properties, such as its ambipolar transport and ballistic electron dynamics. Thus, graphene-based setups that allow fast and simple access to its quantum properties are required to advance in the design of high-performance devices. Non-destructive methodologies based on small electrical perturbations offer the possibility of accessing graphene's electronic structure (V-shaped DOS) in mild experimental conditions. Here, we present a device comprising 20 graphene functionalized channels per chip operated in two modes: a 3-terminal DC transistor and a 2-terminal AC electrochemical setup. Both setups resolved the graphene electronic structure, used as a transduction signal to detect four brain tumor single-stranded DNA biomarkers with a single genetic mutation. The device detected the four cancer biomarkers in the attomolar range (~ 10 aM) in DC transistor mode. A detection limit of 1 aM was achieved in the AC electrochemical mode for the DNA mutation studied. We present a CMOS integrated circuit for fast readout of the multiplexed graphene sensor arrays.