Fig. 2

A NIR (808 nm, 0.53 W cm⁻²) separately induced photocurrent responses of Ti₃C₂T_x Mxene and Cu₂O/Ti₃C₂T_x nanosheets in sodium sulfate solution (Na₂SO₄, 0.1 M) at − 0.25 V. Incubation of Ti₃C₂T_x Mxene with 10, 25, 50 or 100 μg mL⁻¹ of CuCl₂ for 1 h at room temperature to prepare Cu₂O/Ti₃C₂T_x nanosheets. The ‘on’ and ‘off’ time interval in A is 20 s. B Fluorescence intensity of AR (50.0 μM) dispersed in PBS solution (pH 7.4) containing MXene or Cu₂O/Ti₃C₂T_x nanosheets with HRP (0.1 unit mL⁻¹) after incubation for 10 min. C ESR spectra of DMPO (10 mM) with Cu₂O/MXene recorded immediately (red), and after 5 min (blue), and with the catalase (pink; 1.5 mg mL⁻¹ equ. 12,000 U mL⁻¹) in PBS solution, upon NIR irradiation (808 nm, 0.54 W cm⁻², 10 min). The black rhombus (◆), triangle (▼), and dots (●) represent the signals of DMPO–⋅OOH (a_N = 1.42 G \({\mathrm{a}}_{\mathrm{H}}^{\upbeta }\) = 1.135 G), DMPO–⋅OH (a_N = a_H^β = 14.9 G), and DMPO–H₃C⋅ (a_N = 16.4 G, a^β_H = 23.3 G), respectively. Concentration of Ti₃C₂T_x nanosheets or Cu₂O/Ti₃C₂T_x nanosheets in A–C was fixed at 50 μg mL⁻¹ (in terms of Ti₃C₂T_x). D CV response of Cu₂O/Ti₃C₂T_x nanosheets measured at Da positive and Db negative potential at a scan rate of 10 mV s^–1 in the presence of an inert (i.e., ionic liquid) electrolyte solution. The Cu₂O/Ti₃C₂T_x nanosheets prepared at 50 μg mL⁻¹ of CuCl₂ were used in B–D, Proposed energy band diagram of Cu₂O/Ti₃C₂T_x nanosheets and possible reaction mechanisms for the enhanced production of ROS upon photoirradiation. The error bars in B represent the standard deviation of three repeated experiments. Asterisks in B indicate a statistically significant difference of the AR + HRP + Cu₂O/Ti₃C₂T_x groups compared to those of AR + HRP + MXene groups (***p < 0.0001)