Previously published optoelectronic device, encompassing a flexible graphene array biointerface compatible with optical sensing and actuation. (A) Schematic of graphene device compatible with dual optical mapping [voltage (Vm) and calcium (Ca²⁺)]. (B) Traditional electrocardiogram (ECG) and fluorescent voltage (rh237) and Ca²⁺ (rhod-2-AM) signals acquired by dual optical mapping of ex vivo mouse hearts during pacing by unipolar, transparent graphene electrode. (C) Schematic of graphene array device compatible with optogenetics in ex vivo mouse hearts with channelrhodopsin 2 (ChR2) cardiomyocyte-specific expression. (D) Traditional ECG and graphene electrogram recordings during sinus rhythm. (E) Traditional ECG and graphene electrogram recordings during optogenetic pacing at 125 ms cycle length. Figure reprinted and adapted with permission from¹³⁹ by Lin et al.