# Plasmonic Nanomaterials for Micro- and Nanoplastics Detection
## 4 SERS-Based MNPs Detection
### Detection of MNP Using SERS-Based Techniques
#### 4.2.3 Hybrid SERS System Capable of Simultaneous Detection and Remediation of MNPs
The use of membranes to filtrate and separate micro- and nanoplastics is widely popular thanks to its numerous advantages (high efficiency, easy operation, maintenance of the original morphology of the particles, and the ability to retain particles of different sizes). Figure 8: Panel (**a**) is a schematic representation of the work in ref. [74] with the synthesis of gold-modified sponges and the subsequent capture, pre-concentration, and SERS detection of microplastics. Reprinted from [74]. Copyright 2021, with permission from Elsevier. In the second part (**b**), the graphical abstract of [PERSON] et al. [67] is reported, schematizing the preconcentration and analysis of nanoplastics using their hyphenated method of pre-concentration and detection using membrane filtration and SERS. Reprinted with permission from [67]. Copyright 2022, American Chemical Society. AgNW membranes were tested with 500 nm PS nanoplastics (see Figure 8b), showing increasing retention rates with the increase in the loaded volume of AgNW solution. Under the optimal conditions, 98.9% of PSNPs was trapped in the membrane. Some tests were also conducted with PSNPs of other dimensions (50 nm, 100 nm, 300-1000 nm), which always obtained a retention rate above 86%, suggesting that the AgNW membrane is suitable for enriching PSNPs of different sizes in water. Before the detection of nanoplastics, the SERS performances of the AgNW membranes were tested using 4-aminothiophenol (PATP) as the probe molecule, evaluating this system for its:  
* Sensitivity, by comparing the SERS spectra of PATP solutions with different concentrations;
* Time stability, by comparing the SERS spectra of samples newly prepared with those of one-day and one-week-old samples;
* Uniformity, where the AgNW membranes showed a good relative standard deviation of 3.68%;
* Laser irradiation stability, by using 10\({}^{-6}\) M PATP, resulting in a relative standard deviation of 7.18%. Another significant aspect of this work was the use of potassium iodide to clean the background signal of the SERS substrate: iodide helps to reduce the interference signals of the AgNW membrane, being a competitive adsorption agent for removing impurities on the surface of silver nanostructures. After the treatment with KI, the characteristic SERS peaks of the plastics were stronger, whereas on the other hand, the signals of PVP and the other impurities disappeared. The amount of KI was another important parameter that has to be evaluated, since it affects the enhancement performance of the substrate. In the last part of the paper, they focused on the detection of nanoplastics; in more detail, they worked with PSNPs of different dimensions (50 nm, 100 nm, 300 nm, 500 nm, and 1 \(\upmu\)m) and 500 nm PMMA-NPs: for 50 nm PSNPs, they registered a LOD of 10\({}^{-4}\)\(\upmu\)g/mL, while for 500 nm PMMA-NPs, a LOD of 10\({}^{-3}\)\(\upmu\)g/mL was obtained. The detection of nanoplastics in environmental water samples was also tested, specifically working with seafood market water, seawater, and river water. The 500 nm PSNPs, with a concentration of 10\({}^{-3}\)\(\upmu\)g/mL, were detected in seafood market water and seawater, while in river water, the same concentration was not detectable. In summary, both the hybrid SERS systems reported here resulted in very low LODs, but [PERSON] et al. [67], who worked with silver nanostructures that are known to have a higher SERS effect than the gold ones, obtained the best result, reaching a LOD of 10\({}^{-4}\)\(\upmu\)g/mL for 50 nm PSNPs, the lowest of all the works examined in this review.