Detection method for polycyclic aromatic hydrocarbons based on the Au nanoparticles liquid film SERS substrate
[Objective]Rapid on-site testing of polycyclic aromatic hydrocarbons(PAHs)is essential for effective prevention and control of environmental pollution.However,many traditional detection methods,including those set by national standards,are complex and time-consuming.They offen involve lengthy pretreatment processes and require expensive and bulky instruments,thus being impractical for rapid on-site testing.Considering the advantages of surface-enhanced Raman spectroscopy(SERS),a simple and reliable SERS method was proposed for detecting PAHs in water.The gold nanoparticle(Au NP)liquid film(MeLLFs)SERS method was developed using Au NP liquid-film SERS substrates.[Methods]First,Au NPs with a particle size of 60 nm were successfully prepared by reducing HAuCl4 solution using sodium citrate.The characteristics of Au NPs were determined using a UV-vis spectrometer(MAYA2000Pro,Ocean Optics,USA)and a scanning electron microscope.SERS measurements were performed using a custom Raman microscope equipped with a Pixis-100BR CCD(Princeton Instruments),an Acton SP-2500i spectrometer,and a He-Nelaser(20 mW).The excitation wavelength was 633 nm,and the objective lens was 50×(NA=0.60),with integration times of 5 and 10 s.To prepare Au NP MeLLFs,the addition sequence of Au NPs,oil phase,and accelerator were explored.Then,the concentration of tetrabutylammonium nitrate on the SERS spectra of pyrene(Pyr)was investigated.Subsequently,the preparation time of the substrates was investigated by heating.Next,the effect of KBr on the SERS signal intensity of Pyr was explored.Based on the above-optimized conditions,the working curves were plotted for the detection of three PAHs,phenanthrene(Phe),Pyr,and anthracene(Ant),using liquid-film SERS substrates modified with Au NPs and KBr.To verify the feasibility,the proposed method was used in the SERS detection of PAH mixtures in spiked water samples.[Results]The experimental results showed the following:1)The SERS substrate prepared by mixing gold nano ions(Au NPs)with the oil phase(hexane)followed by the addition of a promoter(tetrabutylammonium nitrate)showed the best activity;2)the SERS signal obtained at a promoter concentration of 10 mmol/L was the strongest;3)the preparation time was shortened from 12 h to 40 min by increasing the heating temperature from room temperature to 80 ℃,without affecting the SERS signal;4)the modification by adding 20 mmol/L KBr was beneficial for enhancing the SERS signal;5)the detection limits were 4 397,613.6,and 2 919 pg/L,and the recoveries of Phe,Pyr,and Ant were in the ranges of 83％-110％,82％-114％,and 83％-118％,respectively.[Conclusions]The key to the assembly of SERS substrates in Au NP liquid films is the interaction between NPs on the interface and ions with opposite charges in the oil phase.By optimizing the detection conditions,the detection methods for Phe,Pyr,and Ant were established.The proposed method achieves the detection of PAHs in tap,lake,and river water,with recovery rates ranging from 82％to 118％.This research offers significant technical support for the rapid on-site detection of PAHs in real water samples.
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