Electrochemical Immunosensor Based On Ionic Liquid Modified Carbon Paste Electrode

excellent physical and chemical properties, which widely applied in various fields andhave attracted much attention in the field of analytical chemistry in recent years. Thecarbon paste electrodes (CPE) from the field of analytical chemistry mass productionhave been used as the working electrode in our work because of its simple preparation,low cost, rapid detection and high sensitivity. Room temperature ionic liquids and goldnanoparticles were used to modify the tradition carbon paste electrode, and then thebiomolecules was immobilized to construct novel biosensors. The paper can besummarized as follows:1. Room temperature ionic liquids (RTILs) modified CPE were constructed basedon the substitute of paraffin with N-butylpyridinium hexafluorophosphate (BPPF6) tomix with graphite power. The optical conditions for preparation were selected and thesurface morphologies of the carbon ionic liquid electrode (CILE) were scanned by ascanning electron microscopy. The electrochemical behaviors of the ClLE wereinvestigated using Fe(CN)63-/Fe(CN)64- as probe and compared with that of traditionalcarbon paste electrode. The result showed that the electrochemical response wasgreatly improved by the high conductivity of RTILs and the modified CILE showedgood mechanic property and stability.2. The indirect electrochemistry of HRP is carefully studied on the CILE. HRPwas immobilized on the surface of CILE with sodium alginate (SA) film by step-bystepmethod. The character of HRP in the modified SA film was investigated byelectrochemical, electrochemical impedance spectroscopy and scan electronmicroscopic methods. The results showed that HRP in the SA film retained theessential features of its native structure. So it exhibited excellent electrocatalyticbehaviors to the reduction of H2O2. A pair of well-defined and quasi-reversible cyclic voltammetric peaks was observed. A good linear relationship was found for the peakcurrent and scan rate in the scan rate range from 0.10 to 0.50 V/s. The reduction andoxidation peak currents rise linearly with the linear regression equations as ipc (μA) =31.705ν1/2 (V/s)1/2 - 0.041 (n = 9,γ= 0.9992), ipa (μA) = -30.7ν1/2 (V/s)1/2 + 3.8702 (n =9,γ= 0.9993), respectively, suggesting that the reaction is a quasi-reversible diffusioncontrolledprocess. With the increasing H2O2 concentration the catalytic reduction peakcurrent of SA/HRP/CILE increased linearly. The linear response range of the biosensorto H2O2 concentration was from 1.0μmol/L to 6.0μmol/L and linear regressionequation wasΔi(10-6 A) = 0.592 C (10-6 mol/L) - 0.2153 (n = 7,γ= 0.9847), with adetection limit of 0.5μmol/L at a signal/noise ratio of 3. The results indicated thatHRP in the SA film had a higher sensitivity to H2O2.3. Immunoassay with electrochemical detection is an attractive method due to itshigh sensitivity and low detection limit. It can also compensate its deficiency indifferentiation with immunity. So it is of interest because of wide detection range andlow detection limit. It is suitable for the analysis of small amounts, the instruments aresimple, and the operation is convenient. It was observed that the peak current of nano-Au/CILE increased greatly after the modification of nano-Au. Obviously, theconductivity and stability of nano-Au film increased. Moreover, three-dimensionallyordered nano-Au film electrode had a much larger effective surface area than thegeometrical surface area, as a result of the efficient alignment of the McAb molecules.So the linear sweep voltammetric was used to study the O-Aminophenol–H2O2–horseradish peroxidase (HRP) voltammetric enzyme-linked immunoassay new system. Thismethod had been successfully applied to the detection of alpha-fetoprotein (AFP).Under the optimum conditions, the human serum samples were detected. The resultsshowed good corresponding relationship with those in spectrophotometric ELISAmethod. A good linear relationship was found for the peak current and scan rate in thescan rate range from 0.03 to 0.45 V/s. The reduction and oxidation peak currents riselinearly with the linear regression equations as ipc (10-4 A) = 7.4276ν1/2 (V/s)1/2–0.2494 (n = 10,γ= 0.9987), ipa (10-4 A) = -10.077ν1/2 (V/s)1/2– 0.6483 (n = 10,γ=0.9994), respectively, suggesting that the reaction is a quasi-reversible diffusioncontrolledprocess. Under the optimized experimental conditions, the amperometricresponse increased with the increase of AFP concentration from 0.5 to 80 ng/mL witha correlation coefficient of 0.9948. The regression equation wasΔi (10-4 A) = 0.1655 C(ng/mL) + 2.1453 (n = 10,γ= 0.9948). The detection limit is estimated to be 0.25 ng / mL .