Detection Of Pentachlorophenol With Fluorescent Molecularly Imprinted Matrix And Surface Enhanced Raman Spectroscopy Substrates

As an organochlorine pesticide, pentachlorophenol (PCP) has been widely used as fungicides, algicides, herbicides and wood preservatives. Because of its chemical stability, high toxicity and mutagenicity, PCP has been listed as strictly controlled envioremental pollutants in China. Envioremental Protection Agency in U.S. also classified it as a priority pollution. Common methods for PCP detection in lab include gas chromatography (GC), high performance liquid chromatography (HPLC), colcorimetry and gas chromatography-mass spectrometry (GC-MS). However, drawbacks exist in the methods. In colorimetry method, specificity and sensitivity are relatively poor. Although GC-MS method is able to give a high sensitivity, accuracy and resolution detection, such a method needs expensive equipments and cumbersome, time-consuming routine sample extraction, purification, derivatization, making it not suitable to large-scale sample testing. As PCP existence condition is relatively complex, it is an important issue to detect PCP quickly without interface of the other co-existant substances. In this paper, two proposals were chosen to sense PCP with high selectivity. This is the main objective of this paper. One way is using molecular imprinting technique. Molecular imprinting technique is a progress to prepare a matrix with specific selectivity to a particular target molecule. Molecularly imprinted polymers (MIPs) are complentary in spatial structure and functionality to template and promising in enrichment and analysis indentically. MIPs of PCP can be synthesized to adsorb and seprate selectively. However, MIPs cannot give the output signal. Quantum dots (QDs) were introduced to MIPs, making it possible to monitor the adsorption. In analytical testing, the most direct and accurate method for detection is using the output signal of the analyte. Surface enhanced Raman scattering (SERS) can provide the fingerprint information of analyte, with potential application in the detection of chemicals and biological molecules for the characterization of high sensitivity and selectivity. Therefore, the second proposal to detect PCP is using SERS. In this paper, fluorescent molecularly imprinted matrix and SERS substrates were synthesized for the detection of PCP with fluorescent and Raman spectra. The main contents can be summarized as follows:1. An imprinted silica matrix of PCP co-loaded with FeO4nanoparticles and ZnS:Mn2+QDs was fabricated. The introduction of Fe3O4nanoparticles to the imprinted matrix provided an easy way to separate PCP under an external magnetic field. ZnS:Mn2+QDs offered a readout signal to monitor the amount of PCP bound to the imprinted matrix and evaluate the efficiency of imprinting. X-ray diffraction, transmission electron microscopy, Fourier transform infrared spectroscopy were used to characterize the imprinted matrix. The low angle X-ray diffraction and N2adsorption-desorption analysis indicated a periodic mesoporous structure. The adsorption of magnetic imprinted matrix was studied. The adsorption reached equilibrium quickly because of the mesoporous structure. The as-synthesized imprinted matrix preferred to adsorb PCP rather than the other aromatic compounds like2,4-dichlorophenoxy acetic acid,2,4-dichlorophenol and phenol. The common ions like K+, Na+, Ca2+, Mg2+, Cl-,CO32-interfaced little to the detection. The recoveries of spiked PCP in spring water and tap water with Fe3O4-ZnS:Mn2+co-loaded MIPsare101%and97%, respectively.2. The two emissions of ZnS:Mn2+QDs exhibited different responces when PCP was added. A ratiometric fluorescent method was established to detect PCP. In this work, water soluble ZnS:Mn2+QDs were synthesized with defect-related emission (467nm) and impurity emission (595nm). When PCP was added, impurity emission was quenched whileas defect-related emission changed little. The fluorescent lifetimes of the two emissions were measured. A possible reason was deduced for this phenomenane. The lifetime of impurity emission is about6magnitudes longer than defect-related emission, which affect the quenching efficiency. To improve the selectivity to PCP, surface imprinting was fabricated on ZnS:Mn2+QDs. PCP was preassembled with the functional monomer3-aminopropyltriethoxysilane (APTES) and copolymerized with cross-linkers tetraethoxysilane (TEOS). The as synthesized fluorescent imprinted matrix was characterized with XRD, TEM and FTIR. The ratio of two emission bands (F467/F595) was employed to evalue the efficiency of the imprinting. The ratio (F467/F595) exhibited a linearship with PCP concentration range of0-5μmol L-1. Compared with the other structural analogues, fluorescent imprinted matrix exhibited more affinity to PCP. Great recoveries were obtained in real sample detection with this approach.3. Silver structures were obtained on copper foil by the galvanic displacement reaction between copper and silver nitrate in the presence of hydrogen fluoride for the detection of PCP. The electrode potential of copper changed from0.3419V to0.2353V in the presence of fluoride ions. The electric potential difference of copper and silver nitrate (0.7996V) became larger, promoting the reaction. Experimental conditions like the concentration of silver nitrate, ratio of silver ion and fluoride ion and reaction time were optimized to obtain substrates with high enhancement factor. Substrates prepared with10m mol L-1silver nitrate, ratio of silver ion and fluoride ion1:10and reaction time of60s were used for the SERS detection of PCP.