Polystyrene nanoplastics demonstrate high structural stability in vivo: A comparative study with silica nanoparticles via SERS tag labeling

Nanoplastics are regarded as inert particulate pollutants pose potential threat to organisms. It has been verified that they can penetrate biological barriers and accumulate in organisms; however, there is still a knowledge gap on the in vivo stability and degradation behaviors due to the lack of ideal analytical methods. Herein, a surface-enhanced Raman scattering (SERS) tag labeling technique was developed to study the in vivo behaviors of polystyrene (PS) nanoplastics by comparison with silica (SiO2) nanoparticles (NPs). The labeled NPs were composed of gold NP core, attached Raman reporters as well as PS and silica shell, respectively, demonstrating strong SERS signals which were responsive to the compactness of the shells. The labeled NPs enabled the probing of in vivo structural stability of PS and silica in the liver, spleen and lung of mice after intravenous injection via the time-dependent evolution of SERS signal intensity and gold element content in the organs. The results indicated that both PS and silica model NPs retained in these organs without apparent excretion within 28 d. However, the structural stabilities of PS and silica differed dramatically as reflected by the SERS signal and tissue slice characterization. The silica shell completely degraded whereas the PS shell was still compact. Our results verified the long-term accumulation and in vivo inert property of nanoplastics, hinting that they were distinct from natural NPs and probably induce higher health risks from the aspect of the non-degradation property.