Nanoscale optical characterization of two-dimensional (2D) materials and heterostructures is important for the design of novel optoelectronic flexible nano-devices. Nano-optical photoluminescence (PL) and Raman imaging of bilayer 2D materials has been a challenging problem due to weak signals. The exciton-dominated light emission of two-dimensional (2D) transition metal dichalcogenide (TMDC) materials is affected by the formation of defects and doping states. Previous studies have shown that chemical treatment modifies the defect and doping states of chemical vapor deposition (CVD)-grown monolayers of MoS₂ and WS₂, which provides a promising possibility for engineering the optoelectronic properties of these 2D TMDCs. Here, near-field spectroscopy and imaging were used to study the effect of superacid treatment to improve the optical properties of bilayer MoS₂-WS₂ lateral heterostructures. CVD-grown bilayer MoS₂-WS₂ lateral heterostructures were treated with bis-(trifluoromethane)-sulfonamide (TFSI), and photoluminescence (PL)/Raman signals of the non-treated and chemically treated samples were obtained with 20 nm resolution. The enhancement factors of the PL/Raman signals were obtained, revealing the synergistic effect of the TFSI and tip enhancement.