**1. Introduction**

Tremendous achievements have been made in industrial, agricultural and medical fields in the last several decades, which also led much pressure on our living environment. The uncontrollable releasing of various toxic and potentially harmful chemicals and/or biological products into the environment results in serious damages to ourselves. The pollution in water, soil and air is becoming main threat to ecosystem and health, and the pollutants include inorganic gases, irons, pathogenic organisms and organic pollutants such as persistent organic pollutants (POPs),

© 2017 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2017 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

antibiotics and pesticides [1, 2]. It is urgent to develop rapid and sensitive strategy to classify, quantify and assess them from the environment, which is the basic information to early warning for their threats and getting the precondition for solving these problems. Environmental monitoring requires the analysis of pollutants at (very) low concentrations since many of the pollutants have serious consequence at even extremely low levels. In addition, the methods to be used should also be simple and rapid for their operations in the real application.

Different techniques including chromatography, spectroscopy, mass‐spectra methods are well established in environmental analysis [3–5], but most of these methods require sophisticated instruments and some of them are lack of sufficiently recognition capacity, which limit their wide applications for infield application. Recently, advanced nanomaterial‐based methods have contributed a lot to this area, such as microfluidics, electrochemical sensor, surface plasmon resonance (SPR) method, single‐molecule spectroscopy and hyperspectroscopy [6– 8]. Among these methods, surface‐enhanced Raman spectroscopy (SERS) is one of the most promising methods for environmental monitoring. As a molecular vibrational spectroscopy, SERS holds several outstanding advantages compared to the traditional techniques. Firstly, by making use of the SPR‐induced strong electromagnetic field to enhance signals of the analytes, SERS has high sensitivity which enables detection at low concentrations, even as low as to single molecule level [9]. Secondly, the obtained Raman spectra contains abundant molecular information of the analytes, and the finger‐print information is valuable for identification and classification [10]. Thirdly, the Raman character peaks have very narrow width, which enables multiple detection or complex identification. Unlike other vibrational spectroscopy such as infrared spectroscopy, SERS can be applied directly in solution since water has little back‐ ground signal. SERS technique is also compatible with different sample conditions including aqueous, solidary and even gaseous state, and it needs less sample preparation and preoper‐ ation. This technique can get the character signal within seconds to minutes, which is suitable for rapid signal readout. SERS is also very convenient and cost‐effective to be combined with miniaturized Raman spectrometers and offers good practical utility for real application, even for infield detection.

The above‐mentioned remarkable advantages have led many significant achievements of SERS in the environmental detection [11]. Recently, several review articles have covered different considerations, such as facing various targets such as organics, [12] ions [13] or pathogens [14]. Considering the real condition when performing SERS in environmental application, we believe that special attention should be paid to the following aspect in order to fully realize the potential of SERS method. (1) SERS phenomenon only takes effect when the analyte is near the surface of the SERS substrate, which usually needs to be within several nanometers [15]. While for most of the environmental targets, their interaction with the bare substrate is not strong enough to get them close to the substrate; thus, it is important to shorten the distance between them. (2) The matrix of the environmental samples is complex, which will interrupt the effective interaction between the substrate and the analytes, and hence, the proposed method should have specific selectivity to the interested targets. (3) In many cases, the proposed method should have the ability to concentrate the target in order to meet the demands of sensitivity. (4) For most of infield detections, a strategy is required to be compatible with portable instruments (or miniaturized devices). In this chapter, therefore, we mainly focus on the recent achievements with the goal of developing target-specific SERS-based methods for pollutant detection, the strategies for realizing selective target capture, concentration and separation. We also summarize detection systems that are compatible with specific complex matrix and newly proposed devices suitable for infield application. This review further covers the current challenge and future prospect for better application of SERS in environmental protection.
