Development of new sensors using nanomaterials and molecularly imprinted polymer modified electrodes for diagnostic and food safety monitoring

In this work, the development of new sensors based on electrochemical sensors and quartz crystal microbalance (QCM) were investigated. The electrochemical sensors consist of 2 parts including chemical sensor and biosensor. The chemical sensor was developed for dopamine (DA) and uric acid (UA) determination in the pharmaceutical and urine samples. The development electrode was constructed based on ferrocence polyaniline and carbon nanotubes modified CPE (p(Fc-Ani)-CNTs/CPE). After that, Nafion (Nf) was coated onto p(Fc-Ani)-CNTs/CPE surface to obtain Nf/p(Fc-Ani)-CNTs/CPE. The oxidations of DA, UA and AA were measured by differential pulse voltammetry (DPV). The results revealed that the Nf/p(Fc-Ani)-CNTs/CPE exhibit the oxidation peaks at +0.3 and +0.45 V for the DA and UA, respectively, whereas the oxidation peak of AA does not appear. These results shows that the developed Nf/p(Fc-Ani)-CNTs/CPE provides high selectivity and good repeatability. The oxidation peaks current from DPV varied linearly with the concentrations of 1-150, and 5-250 µM for DA and UA, respectively. The estimated detection limit (3S/N) are 0.21 and 0.58 µM for DA and UA, respectively. The proposed electrode was successfully applied to determine DA and UA in pharmaceutical and urine samples with good performance.
Biosensor was developed for the determination of sulfite in wine and picked foods. The biosensor was constructed based on immobilized sulfate oxidase (SOx) enzyme onto Fe3O4@Au-Cys-FA nanocomposites which prepared using Fe3O4@Au core encased within a conjugated cysteine (Cys) as a bi-functional linker. The cysteine was attached to gold surface through thiol group. Then, amino-terminated from cysteine was conjugated to folic acid (FA) with an amide-linkage formation to obtain Fe3O4@Au-Cys-FA. The biosensor was fabricated using mixture of polydimethylsiloxane and mineral oil as binder to enhances the physical stability and sensitivity of the electrode. Cyclic voltammetry was used to investigate electrocatalytic behavior at the Fe3O4@Au-Cys-FA/CPE. The amperometric detection in FIA system was performed applying a potential at +0.35 V. Linear concentration dependence is observed in the range between 0.1 to 200 mg L-1. The regression equation is given by y=1.086x-1.147 (r2=0.998), when y and x are the area of peak current (µA) and sulfite concentration (mg L-1). The detection limit (3 ơ) was 10 µg L-1. The developed biosensor also provided good precision (RSD=3.1%) for sulfite signal (15 mg L-1, n=20) with a rapid sample throughput (109 samples h-1). The developed method was applied to the determination of sulfite content in wines and pickled food extracts with the high efficiency and accuracy with good agreement with the standard iodometric method.
The QCM sensor based on molecular imprinted polymer (MIP) to enhance the selectivity of the sensor for CBF and PFF determination pesticides. The CBF-MIP were prepared using methacrylic acid as a functional monomer, ethylene glycol dimenthacrylate as a crosslinker, and azodiisobutyronitrile as an initiator. The PFF-MIP was synthesized using poly (4-vinylphenol) and diphenyl methane-4,4]-di-isocyanate as functional monomers, phloroglucinol as the cross-linker, and diphenylmethane as the porogen. The non-imprinted polymer (NIP) was synthesized using same condition but without the pesticides template. The obtained MIP and NIP were coated onto both side of electrode surface by spin coating. The frequency shifts of MIP exhibit higher than frequency shift of NIP about ten times and seven times for the CBF and the PFF, respectively. The linearity ranges were 0.5-1000 µM for CBF-MIP and 10-1,000 µM for PFF-MIP.