Disposable electropolymerized molecularly imprinted electrochemical sensor for determination of breast cancer biomarker CA 15-3 in human serum samples.

Initially, a printed electrode was fabricated in a paper substrate using carbon nanotube ink, graphite pencil and silver nanoparticle ink. For that the electrode was modified with gold nanoparticles and a molecularly imprintedpolymer (MIP) using CA 15-3 as target molecule. The Atomic Force Microscopy (AFM) images exhibited the change in the morphology after each electrode modification. The roughness increasedafter the electropolymerization, and decreased after the extraction procedure. Next, slightly increased again associated to the interaction of CA 15-3 and the imprinted sites. Finally, the Fourier Transform Infrared Spectroscopy (FTIR) results suggested the extraction/rebinding of CA 15-3 in the MIP sensor and also indicated that the NIP sample do not have specific cavities for the CA 15-3. In short, under optimized conditions, the CNE/AuNP is incubated with CA 15-3 (40 U mL-1) for 2 h at 4 °C. Then the electropolymerization was carried out in the potential range of -0.2 to 1.0 V during 20 cycles at scan rate of 50 mV s-1 using a solution containing 15 mM of oPD. After electropolymerization, the sensor was washed with oxalic acid solution for 2 h, leading to the formation of imprinted cavities. The rebinding process was subsequently constructed for 1 h at 4 °C using CA 15-3 solution. The reproducibility and interference studies showed that the sensor can be reproducible and specific for CA 15-3. Then the sensor was applied in determination of CA 15-3 in samples of serum and saliva. The use in serum presented good recovery, but the application in saliva was not satisfactory. Therefore, the sensor CNE/AuNP/MIP could be used in the determination of CA 15-3 in serum samples.

Electrochemical behavior of riboflavin immobilized on different matrices.

The electrochemical behavior of riboflavin (RF) adsorbed on different surfaces of inorganic matrices was investigated using modified carbon paste electrodes. Silica gel and sol-gel silica modified with niobium oxide were denominated as (SN) and (SN(sol-gel)), respectively. These materials were treated with a H3PO4 solution to graft phosphate groups and were denominated as (SNP) and (SNP(sol-gel)). The immobilization of RF on these materials indicated a high electrode stability, avoiding leaching out of the electroactive species (RF) from the electrode surface. The values of formal potential (E0') of the adsorbed RF on the different matrices changed from -283 (SNRF) up to -165 mV (SNPRF(sol-gel)) vs SCE in 0.1 moll(-1) NaNO3 solution at pH 7.0. Compared to the E0' for soluble RF, the values are shifted 183 up to 305 mV toward more positive potentials. The stability of the electrodes and the formal potential of the adsorbed RF on different matrices remained constant upon changing the solution pH from 3 to 8. Some kinetic parameters were estimated; indicating that all systems studied presented a good electron transfer rate.

Electrochemical behavior and electrocatalytic study of the methylene green coated on modified silica gel.

The electrochemical behavior of methylene green (MG) adsorbed on a silica surface modified with niobium oxide (SN) was investigated, using modified carbon paste electrodes. It was also used in an electrocatalytic study of NADH oxidation. The electrode showed a high stability attributed to the presence of SN, which avoids the leaching of the mediator from the electrode surface. The formal potential (E(0')) of the adsorbed MG was -35 mV vs SCE, showing a shift of 30 mV toward more positive potential values, compared to the MG dissolved in aqueous solution. This shift was assigned to the interaction between the basic nitrogen of MG and the acid sites of SN. The variation of the solution pH between 4 and 8 did not affect the stability nor the formal potential. However, for solution pH lower than 4 the formal potential was affected by the acidity of the medium. The electrocatalytic oxidation of NADH at the electrode was investigated. In the solution pH between 5 and 8 the electrocatalytic activity remained almost constant, giving a response signal of 13.3 nA L micromol(-1) cm(-2) and a K(Mapp) of 1.4 x 10(-5) mol L(-1). The electrode gave a linear response range between 5.0 x 10(-4) and 4.0 x 10(-3) mol L(-1) NADH concentration at pH 7.0 at an applied potential of 50 mV vs SCE. Applying a flow injection analysis system, the electrode showed a better analytical performance for NADH detection, presenting a linear response range between 6.0 x 10(-5) and 1.0 x 10(-3) mol L(-1), with an analytical frequency of 30 determinations/h, a detection limit of 8.2 x 10(-6) mol L(-1), and a precision for 25 replicates of 1% expressed as a relative standard deviation.