# Recent Advances in Spectroscopy Technology for Trace Analysis of Persistent Organic Pollutants
## 2 Applications of Spectroscopy Technology in Detection of POPs
### SPR Sensors  
SPR is wave sensing technique that can detect biochemical reactions in the near-field region [61; 62; 63]. The SPR phenomenon was first discovered in 1900s by [PERSON]. As he measured the reflection of metallic gratings, he found that some optical power of polarized incident light was absorbed by metal because of the excitation of surface plasma waves (SPW) [64]. Subsequently, the investigation of SPR sensing was motivated after the introduction of attenuated total internal reflection (ATR) by [PERSON] and [PERSON] in 1968 [65; 66]. However, the original investigation, bringing SPR technique into the biochemical sensing field and detailing the application of the SPR sensor, was published in the 1980s by [PERSON] and [PERSON] [67]. They first employed the SPR technique for gas detection and demonstrated that the method was able to monitor low-concentrations of anesthetic gas, which made the pioneering work practical for applications of the SPR sensor in the biochemical field. Since then SPR sensors have become a valuable platform for low-level detection of environmental pollutants [68]. SPR sensors are one of the favorable strategies in determination of POPs, due to their many advantages, such as high sensitivity and selectivity, label-free detection, rapid response [69; 70; 71]. Conventional SPR sensors with dense sensing films cannot directly detect small molecules, due to the extremely small depth between the evanescent field and surface-bound molecules. Thus, abundant biorecognition elements can be immobilized on the surface of the sensing film to fabricate SPR biosensors that show a high specificity for targeted molecules. Some typical strategies for functionalization of sensing surfaces are illustrated in Figure 3[72]. Any of these methods could greatly improve the amounts of target molecules anchored on the sensing surface and amplify the SPR signal. [PERSON] et al. investigated the detection of BaP by SPR immunosensors with the indirect inhibition method in 2002 [73]. They immobilized BaP conjugated with bovine serum albumin (BSA) on a dense gold surface of a sensing film as BaP has a low-molecular weight. The experimental results indicated that the incident angle changed as the samples of antibodies against BaP at different concentrations were injected into, and flowed through, the sensor chip. The detection limit of this method was up to 0.1 ppb. A similar strategy was employed by [PERSON] et al. who detected PCB using the SPR technique in 2008 [38]. The detection mechanism was based on PCB-induced conformational changes of Cytochrome c (Cyt c) immobilized on the dense gold film, altering the local dielectric function of the supported Cyt c, which can be detected by SPR (Figure 4a). The confirmations of Cyt c sensitively varied with the changes of PCB concentrations, and the reflectance \(R\) at the SPR angle of the supported  
Figure 2: (**A**) Schematic of the plasmonic hot spots formed on Fe\({}_{3}\)O\({}_{4}\)@Au NPs(nanoparticles) (a), calculated electric field intensity distribution induced by localized surface plasmon resonance (LSPR) on the Fe\({}_{3}\)O\({}_{4}\)@Au system (b–e). (**B**) Diagram of the construction of AgNPs assembled bi-nanoring arrays (a–c). Lower-right panel is a schematic for one cycle of glancing angle sputtering. (**C**) Illustration of the pesticide hosting in the dithiol layer organized in interparticle gaps between metal NPs. (**D**) Surface enhanced Raman spectroscopy (SERS) spectra of aldrin, endosulfan, lindane, and dieldrin on DTS(1,8-octanedithiol)-functionalized citrate AgNPs exciting at 785 nm. Republished with permission from [31; 41; 48] (Copyright © 2016, Elsevier; Copyright © 2014, American Chemical Society). Cyt c increased with increasing PCB concentrations. The detection limit was as low as 0.1 ppb and the responses could be finished in less than 10 min.