Microplastics are persistent pollutants that accumulate in the environment and can cause serious toxicity to mammals. At present, few technologies are able to quantitatively detect chemicals and provide morphological information simultaneously. Herein, we developed a dragonfly-wing-mimicking ZnO nanorod array decorated with AgNPs on polydimethylsiloxane (PDMS) as a surface-enhanced Raman spectroscopy (SERS) and photo-induced enhanced Raman spectroscopy (PIERS) substrate for trace analysis of microplastics. The Ag/ZnO@PDMS hybrid nanorod array endows the sensor with high sensitivity and signal repeatability (RSD ∼ 5.89%), ensuring the reliable quantitative analysis of microplastics. Importantly, when the noble metal−semiconductor substrate was preradiated with ultraviolet light, a surprising PIERS was attained, achieving an additional enhancement of 11.3-fold higher than the normal SERS signal. By combining the PIERS technology with the "coffee ring effect", the sensor successfully discerned microplastics of polyethylene (PE) and polystyrene (PS) at a trace level of 25 μg/mL even with a portable Raman device. It was capable of identifying PS microspheres in contaminated tap water, lake water, river water, and seawater with detection limits of 25, 28, 35, and 60 μg/mL, respectively. The recovery rates of PS microspheres in four water environments ranged from 94.8 to 102.4%, with the RSD ranging from 2.40 to 6.81%. Moreover, quantitative and visualized detection of microplastics was readily realized by our sensor. This portable PIERS sensor represents a significant step toward the generalizability and practicality of quantitative and visual sensing technology.

Figure 6. SERS spectra collected from different concentrations of a) triazophos and d) diquat of honeysuckle leaves using our SERS platform. b,e) Corresponding linear relationship between Raman intensity and detected concentrations. SERS spectra of c) three components and f) four components.