Two-Dimensional Double Transition Metal MXenes in Electrochemical Biosensors

MXenes have been used in many sensing and biosensing platforms because of their excellent electrochemical characteristics 1. Ordered double-transition metal MXenes (DTMs) are composed of two distinct transition metals, differentiated by Mʹ and Mʺ. Control of the transition metal pairs in DTM MXenes, combined with different surface terminations, provides tunable optical, electric, catalytic and electrochemical properties 2. In this work, we investigated the applicability of two ordered DTM MXenes, Mo₂Ti₂C₃T_x and Mo₂Nb₂C₃T_x, in electrochemical biosensing. Two immunosensors were designed for the electrochemical detection of RSV (respiratory syncytial virus) and Zika virus. 

The first immunosensor was constructed by immobilizing the RSV antibody on screen-printed carbon electrodes (SPCE) modified with graphene-oxide and Mo₂Ti₂C₃T_x DTM MXene. By using the Mo₂Ti₂C₃T_x MXene-based immunosensor, we achieved excellent linearity for quantifying RSV within the wide range of 0.01 pg/mL to 10 µg/mL, and a high sensitivity with the low limit of detection of 0.015 pg/mL 3. For testing Zika, the surface of graphene-modified SPCEs was covered with Mo₂Nb₂C₃T_x MXene, then functionalized with a monoclonal antibody specific to Zika virus. The resulting immunosensor was employed for voltametric detection of Zika virus from 0.01 pg/mL to 1 µg/mL with the low detection limit of 21.57 pg/mL. 

Both the DTM MXenes showed selectivity for the tested immunosensors, against other bacterial and viral pathogens, including Coronavirus and Herpes.  Finally, the applicability of Mo₂Ti₂C₃T_x and Mo₂Nb₂C₃T_x MXene-based immunosensors was demonstrated in spiked serum samples, with excellent recovery percentages ranging from 95.48 to 98.59 and was compared to that of the widely explored Ti₃C₂T_x MXene as a control. In this work, we demonstrated that Mo₂Ti₂C₃T_x and Mo₂Nb₂C₃T_x MXenes provide a higher active surface area and better electron transfer than the commonly used Ti₃C₂T_x MXene for the electrochemical detection of RSV (respiratory syncytial virus) and Zika virus.