Construction Of Molecular Imprinting-based Surface-enhanced Raman Sensor And Its Application In Rapid Detection Of Environmental Pollutants

Surface enhanced Raman scattering（SERS）,as an emerging analytical technology,can quickly obtain molecular"fingerprint"spectra with high detection sensitivity.The instrument is portable and suitable for on-site rapid detection of environmental pollutants.However,since the actual sample matrix is often very complicated,there are many structural analogs of the target pollutant,or the concentration of the sample is very low,so the analytical method is required to have better anti-interference ability and higher sensitivity.Molecularly imprinted polymer（MIP）has highly selective recognition characteristics for template molecules.When the template molecule is combined with the polymer,it will form multiple action sites and be"memorized",which can specifically separate and recognize the target in the complex matrix.This research combines the advantages of MIP and SERS to develop a new method for detecting trace environmental pollutants and prepares a variety of molecularly imprinted SERS sensors that can effectively improve separation,enrichment capabilities and detection selectivity.In addition,we also combine the MIP-SERS sensor with electrochemical preconcentration（EP）to quickly pull the analyte to the surface of SERS substrate by electrostatic force,which can play the role of in-situ separation and enrichment,and significantly increase the analyte content of SERS enhanced regional.Combined with portable Raman spectrometer,the prepared sensor can meet the requirements of high selectivity,high sensitivity and rapid detection of pollutants in complex environment.The main contents and conclusions are as follows:（1）A new MIP-SERS nanoprobe is fabricated by a convenient electrochemical method.Single-layered Mo S₂ is electrochemically reduced on a screen-printed electrode（SPE）as the scaffold.Functional monomers o-phenylenediamine（o PD）,template theophylline（THP）,and SERS-active Au nanoparticles（AuNPs）are then one-step electropolymerized on the scaffold.The morphology of the nanoprobe（AuNPs-MIP/r Mo S₂/SPE）is found to be a three-dimensional and porous structure.After the template molecules in the probe are eluted,the recognition sites matching the spatial configuration of the template molecules can be formed.The nanoprobe displays a strong SERS effect for THP with a detection limit（LOD）of 0.01 nmol·L^-1.The SERS peak intensity at 1487 cm^-1 increases linearly with the concentration of THP in the range from1.0×10^-10 mol·L^-1 to 1.0×10^-4 mol·L^-1,and exhibits low SERS interference for structural analogues theobromine（THB）and caffeine（CAF）.（2）A bio-inspired polydopamine（PDA）molecularly imprinted substrate is fabricated by one-step oxidative self-polymerization of dopamine and template molecules in weakly alkaline medium on screen-printed electrode（SPE）.Through the catechol and amine groups on PDA surface,Au nanoparticles（AuNPs）can be easily anchored and growth on PDA-MIP coating,thereby forming a three-dimensional architecture.By adjusting the reaction conditions,the particle size and distribution of PDA and AuNPs can be well controlled.Benefting from the“hot spots”generated by AuNPs and recognition sites produced by MIP,the AuNP/PDA-MIP nanocomposite can serve as excellent SERS substrate enabling selective enrichment and identifcation of phthalate plasticizers（PAEs）.Using this substrate,an enhancement factor（EF）up to 1.7×10⁷ mol·L^-1 for dimethyl phthalate（DMP）is achieved with a detection limit as low as 1.0×10^-10 mol·L^-1.This green and environmental-friendly fabrication method is promising for synthesis of highly performance sensing.（3）MIP-based core-shell AuNP@polydopamine（AuNP@PDA-MIP）nanoparticles are designed and immobilized on an electrochemically reduced Mo S₂-modified SPE（AuNP@PDA-MIP/r Mo S₂/SPE）.This portable electrochemical-Raman interface offers the dual functions of electrokinetic pre-separation（EP）and MIP trapping of charged molecules so that a reliable SERS recognition with molecular selectivity and high sensitivity can be achieved.The introduction of electric field enables the autonomous exclusion and separation of similarly charged molecules as well as attraction and concentration of the oppositely charged molecules by electrostatic attraction.Subsequently,the specific MIP recognition cavities allow selective adsorption of targets on the interface without the interference of analogues.As a proof-of-concept study,when the template molecule is DMP（-）,applying a potential of+0.2 V for 400s has the best enrichment effect on DMP（-）,and the detection limit is as low as 2.7×10^-12 mol·L^-1.When the template molecule is bis（2-ethylhexyl）phthalate（DEHP（+））,applying a potential of-0.1 V 360s has the best enrichment effect on DEHP（+）,and the detection limit is as low as2.3×10^-11 mol·L^-1.This sensing strategy for in situ SERS analysis of charged pollutants or toxins holds vast promises for a wide range of in-field applications.