In a recent study, researchers conducted an investigation on the use of microfluidic paperbased solution sampling coupled with Pb2+-ISEs for the analysis of heavy metals in samples with low volumes and/or high solid-to-liquid contents. They found that acidification of paper substrates prior to use was effective in eliminating the super-Nernstian response of Pb2+-ISEs observed otherwise. To determine the optimal pH range of the potentiometric sensors when coupled with acidified paper substrates, 3D approximate analyses of the Pb2+-ISEs responses were carried out. The results showed that the acceptable operational pH range for the paper substrate containing the sample solution was found to be between 3 and 4. In order to simplify the analytical protocol for heavy metal sensing using Pb2+-ISEs coupled with microfluidic paper-based solution sampling, a colour-coded matching graph was proposed to match the appropriate acidified paper substrate to the pH of the unbuffered sample solution. This approach was then tested in various complex environmental samples with small volumes of solution and/or high solid-to-liquid ratios, such as wet soil, street runoff, chemical spillage, and plant dew. The use of acidified paper substrates was found to be reliable in the determination of lead(II) in complex sample matrices, with results comparable to those obtained using potentiometry and ICP-OES. The study demonstrated that acidification of microfluidic paper-based solution sampling substrates, when coupled with Pb2+-ISEs in potentiometric cell design, is useful for samples containing low volumes and/or high solidto-liquid content. The optimized acidified paper substrates effectively eliminated the super-Nernstian response of Pb2+-ISEs, which would otherwise be present when unmodified paper was used. Although the ultimate detection limit of the sensor was not improved, the developed approach was utilized for the determination of Pb2+ in various samples, where Pb2+-ISEs were coupled with acidified microfluidic paper-based solution sampling substrates to analyze lead concentrations in rainwater and ash leachate samples. The researchers suggest that future work could focus on pH optimization with paper substrates to eliminate the super-Nernstian response for other metal ions. Overall, this study provides a new method for paper modification in direct paper-based potentiometric heavy metal detection and has significant potential for use in environmental monitoring and analysis.