DNA-programmed nanogap 3D SERS aptasensor via silica monoliths for ultrasensitive detection of BPA leaching from microplastics

The environmental risks of microplastics are exacerbated by the leaching of endocrine-disrupting additives such as bisphenol A (BPA). Effective monitoring requires analytical methods that are ultrasensitive, specific, and suitable for on-site application, requirements that remain challenging for conventional techniques. Herein, we develop an integrated capillary-based SERS aptasensor for the rapid and specific detection of BPA leached from microplastics. The sensor core is a three-dimensional hierarchical porous silica monolith (3D-PSM) anchored inside a quartz capillary. A DNA-programmed nanogap SERS hotspot matrix is constructed on the 3D-PSM by immobilizing cDNA-modified Au nanoparticles, followed by hybridization with aptamer-conjugated Au@4-MBN@Ag nanotags. This design utilizes the cDNA-aptamer duplex as a programmable molecular spacer to create a uniform sub-10-nm gap, generating an intense initial SERS signal (“signal-on”). Competitive binding of BPA triggers nanotag release and quantifiable signal attenuation (“signal-off”). Benefiting from convective mass transport within the 3D architecture, the platform achieves a limit of detection (LOD) of 1.24 pM for BPA, exhibiting a linear range spanning five orders of magnitude (1.0 pM to 0.1 μM), with a recognition time of 10 min. Practical utility was demonstrated by analyzing BPA thermally liberated (70 °C) from polycarbonate microplastics (PC-MPs, 100 and 1000 mesh) in environmental water matrices. The method exhibited high specificity and satisfactory recoveries (93.7 ± 3.6% to 102.0 ± 7.6%) in spiked river water samples, demonstrating a positive correlation between leached BPA amounts and MP contamination levels. This work provides a reliable tool for the direct assessment of hazardous chemical leaching from microplastics.