A sensitive MWCNT-OH/PDDA/B-GQDs nanocomposite biosensor for toxicity assessment of nanoplastics and bisphenols in water: Mechanistic insights into cellular toxicity

Nanoplastics and bisphenols (including bisphenol A and its alternatives) are emerging co-contaminants in aquatic ecosystems, yet their combined toxicological effects remain poorly understood. To address this gap, we developed a novel electrochemical biosensor using HepG2 cells and a nanocomposite of hydroxylated multi-walled carbon nanotubes, poly(diallyldimethylammonium chloride), and boron-doped graphene quantum dots (MWCNT-OH/PDDA/B-GQDs). This unique composite design, verified by density functional theory (DFT) calculations, revealed strong adsorption energies for cellular electroactive substances (xanthine: −1.12 eV; guanine: −1.56 eV), confirming the sensor's superior detection capability. The biosensor was used to assess the cytotoxicity of polystyrene nanoplastics (PS 25 nm ) and five bisphenols individually; their mixture exhibited an additive combined effect. Beyond rapid toxicity screening, we further conducted comprehensive mechanistic investigations through oxidative stress analysis, apoptosis assessment, and transcriptome sequencing. Results indicated that exposure to PS 25 nm and bisphenols, either individually or in combination, induced oxidative stress, as evidenced by decreased glutathione (GSH) levels and reduced superoxide dismutase (SOD) activity. Transcriptome analysis revealed substantial enrichment of differentially expressed genes in the pathways related to protein synthesis, oxidative stress response, and liver disease. This study not only establishes a rapid and sensitive approach for evaluating the toxicity of nanoplastics and bisphenols in aquatic environments but also provides a comprehensive understanding of the underlying mechanisms through integrated multi-level analysis, thereby providing essential mechanistic data to support their comprehensive biosafety assessment and regulatory management.