Principles, performance and emerging trends for optical detection of environmental microplastics: A review

Microplastics (MPs), as emerging contaminants, originate from diverse sources and accumulate across various environmental media, posing potential risks to both ecosystems and human health. Optical detection techniques have emerged as a primary and efficient approach for MPs analysis due to their high sensitivity, accuracy, environmental friendliness, efficient, non-destructiveness and high specificity. This review systematically summarizes recent advances in optical methods for MPs detection, with a focus on two major methodological pathways: spectroscopic detection and fluorescence-based detection methods. For spectroscopic methods, the principles, advantages, limitations and practical applications of Raman spectroscopy and infrared spectroscopy are discussed specifically. Additionally, the significant contributions of machine learning (ML)-enhanced spectroscopic methods in improving MPs identification accuracy and spectral data processing efficiency were highlighted. For fluorescence-based detection, a comprehensive overview is provided on detection strategies employing fluorescent staining like Nile red (NR) for MPs in diverse environmental settings, as well as recent improvements in novel dyes designed to enhance sensitivity and anti-interference capabilities. The unique advantages of carbon dots (CDs) and carbon nitride materials as fluorescent labels for specific MPs identification and environmental behavior tracing are also critically evaluated. Through Comparing the detection principles, practical performance, strengths and limitations of various methods, theoretical support and methodological guidance are provided for the continual optimization of MPs detection technologies and the precision of environmental monitoring.