Optimizing the ratio of Coomassie and Methylene blue dyes for a cost-effective and rapid staining of PET, PVC, PP, PS, LLDPE, LDPE, and HDPE

<title>Abstract</title> The ubiquitous presence of plastic brought on by the extensive use of plastic products calls for efficient and rapid plastic detection methods for the detection and evaluation of pollution. The commonly used Nile red dye takes many hours and is expensive while also not equally efficient across all the common plastic waste. To address this, we investigated the staining efficiency and optimized the ratio of a combined dye of Coomassie brilliant blue and Methylene blue. In the optimisation process, Methanol-based Coomassie and Methylene blue dyes effectively stained the PET, PP, PS, LLDPE, LDPE, and HDPE plastics without compromising the plastic's integrity. Image analysis showed a generally better staining efficacy compared to Nile red. Given the cost-effectiveness, efficiency, and accessibility of the blue dyes in labs, the optimized ratio of the blue dyes makes it suitable for large-scale plastic staining across the six tested types of plastic, replacing Nile red.