Development of carbon-based DNA-biosensors for the purpose of electrochemical characterization of bisphenol-A : diploma thesis

U ovom radu ispitivano je elektrokemijsko ponašanje elektrode od ugljikove paste te dijamantne elektrode dopirane borom u svrhu elektrokemijskog određivanja bisfenola A. Ove elektrode su zbog svoje pristupačnosti i osjetljivosti vrlo pogodni kandidati za (bio)senzore. Mjerenja su vršena u otopini fosfatnog pufera (0,1 M) pri pH 7. Elektroanalitičko određivanje bisfenola A vršeno je uporabom diferencijalne pulsne voltametrije, DPV (engl. differential pulse voltammetry). Elektroda od ugljikove paste pokazala je bolji odziv. Iako obje elektrode literaturno posjeduju veliki potencijal za uporabu kao DNA-biosenzori, pokazano je da dobiveni rezultati znatno ovise o tretmanu kojem je površina elektrode podlegla prije uporabe. Isto tako, ističe se važnost modifikacije aktivne površine elektrode, odnosno same imobilizacije DNA u kontekstu utjecaja na dobivene rezultate.In the present paper the electrochemical behavior of carbon paste and boron doped diamond electrode was tested for purpose of bisphenol A electrochemical determination. Since electrodes like these are very affordable and since they possess great sensitivity, they are very suitable (bio)sensor candidates. The measurements were carried out in the phosphate buffer solution (0,1M) at pH 7. The electroanalytical determination of bisphenol A was done using differential pulse voltammetry. The carbon paste electrode exhibited better response. Even though both electrodes possess a great potential for being used as DNA-biosensors, it was shown that obtained results depend on the treatment the electrode underwent before the utilization. Also, the importance of the surface area modification, as well as the immobilization of DNA was accentuated in the context of the influence they have on the obtained results

Voltammetric Electrochemical Behavior of Carbon Paste Electrode Containing Intrinsic Silver for Determination of Cysteine

In this paper, the electrochemical behavior of cysteine is described, using carbon paste electrodes (CPEs) modified with ternary silver-copper sulfide containing intrinsic silver at two pH values (pH 3 and 5). Experiments have revealed that presence of cysteine has a large impact on the electrochemical behavior of modified CPEs. Observed phenomena take place in solution, as well as at the surface of the modified CPEs, and can be applied for electroanalytical purposes. Based on the electrochemical behavior observed in the examined system, differential pulse voltammetry (DPV) was selected as an electroanalytical method for determination of cysteine. The effects of the various parameters on the electroanalytical signal, such as the amount of electroactive material, electroanalytical parameters, pH etc., were investigated using differential pulse voltammograms. The results indicated that electrochemical signal characterized with well-defined cathodic peak at 0.055 V vs. Ag/AgCl (3 M) in acetic buffer solution at pH 5 can be used for indirect electrochemical determination of cysteine. The optimization procedure revealed that the most sensitive and stabile electrode was that containing 5% modifier. The DPV response of the electrode, in the presence of cysteine, showed two different linear concentration ranges of 0.1 to 2.5 μM, and 5.6 to 28 μM. The explanation of the origin of two linear ranges is proposed. The lower concentration range was characterized by remarkable sensitivity of the 11.78 μA μM−1, owing to the chosen indirect method of determination. The calculated limit of detection (LOD), as well as limit of quantification (LOQ) were 0.032 and 0.081 μM, respectively. The influence of interfering agents on the electroanalytical response was examined, and low or no interference on the DPVs was observed. The proposed method was validated and applied for the determination of cysteine in pharmaceutical preparations with satisfactory recoveries in the range of 97 to 101.7%

Voltammetric Electrochemical Behavior of Carbon Paste Electrode Containing Intrinsic Silver for Determination of Cysteine

In this paper, the electrochemical behavior of cysteine is described, using carbon paste electrodes (CPEs) modified with ternary silver-copper sulfide containing intrinsic silver at two pH values (pH 3 and 5). Experiments have revealed that presence of cysteine has a large impact on the electrochemical behavior of modified CPEs. Observed phenomena take place in solution, as well as at the surface of the modified CPEs, and can be applied for electroanalytical purposes. Based on the electrochemical behavior observed in the examined system, differential pulse voltammetry (DPV) was selected as an electroanalytical method for determination of cysteine. The effects of the various parameters on the electroanalytical signal, such as the amount of electroactive material, electroanalytical parameters, pH etc., were investigated using differential pulse voltammograms. The results indicated that electrochemical signal characterized with well-defined cathodic peak at 0.055 V vs. Ag/AgCl (3 M) in acetic buffer solution at pH 5 can be used for indirect electrochemical determination of cysteine. The optimization procedure revealed that the most sensitive and stabile electrode was that containing 5% modifier. The DPV response of the electrode, in the presence of cysteine, showed two different linear concentration ranges of 0.1 to 2.5 μM, and 5.6 to 28 μM. The explanation of the origin of two linear ranges is proposed. The lower concentration range was characterized by remarkable sensitivity of the 11.78 μA μM−1, owing to the chosen indirect method of determination. The calculated limit of detection (LOD), as well as limit of quantification (LOQ) were 0.032 and 0.081 μM, respectively. The influence of interfering agents on the electroanalytical response was examined, and low or no interference on the DPVs was observed. The proposed method was validated and applied for the determination of cysteine in pharmaceutical preparations with satisfactory recoveries in the range of 97 to 101.7%

Electroanalytical Determination of Cysteine Using the Electrodes Based on Ternary Silver-Copper Sulfides

The amperometric determination of cysteine, using an electrode based on ternary silver-copper sulfide, is presented. Electrochemical characterizations (using cyclic voltammetry) of three electrode materials revealed that the electrode based on the material that consists of jalpaite (Ag3CuS2), doped with a small amount of metallic silver, has the best electrocatalytical performance for cysteine oxidation. For the amperometric determination, 0.142 V at pH 5 and 0.04 V at pH 7 vs. Ag/AgCl, related to the electrocatalytical oxidation of thiol group, were chosen. Electrochemical impedance spectroscopy together with Fourier transform infrared spectroscopy (FTIR) revealed that oxidation takes place on the electrode surface with fouling effect, which does not affect a wide linear working range between 1 μM and 100 μM. Sensitivities, at pH 5 and pH 7, are calculated to be 0.11 μA μM−1 and 0.10 μA μM−1, respectively. The detection limits were determined to be 0.036 μM and 0.024 μM for pH 5 and pH 7, respectively. In the presence of uric acid, folic acid, ascorbic acid, and glucose no interference was noticed. This electrode showed remarkable stability and excellent reproducibility. The electrode was exploited for the determination of cysteine in a dietary supplement with the excellent recoveries

Application of the Stripping Voltammetry Method for the Determination of Copper and Lead Hyperaccumulation Potential in <i>Lunaria annua</i> L.

Various species of the Brassicaceae family are known to hyperaccumulate metals. Lunaria annua L., a plant from the Brassicaceae family, is an oilseed crop known for its pharmaceutical and nutraceutical applications. In this work, Lunaria annua L. was investigated for its accumulation potential in copper and lead-contaminated soil. Concentrations of copper and lead were measured before planting (in seeds and soils) and after the plant was harvested (in soils and plant). Two types of soils were used: a soil sample collected from the Botanical Garden of the Faculty of Science, University of Split (soil 1, S1) and a commercially available organic mineral substrate (soil 2, S2). Measured pH values showed that the S1 (pH = 8.58) was moderately alkaline soil. On the other hand, the purchased organic soil, S2 (pH = 6.35), was poorly acidic to neutral. For the determination of copper (Cu) and lead (Pb), square wave anodic stripping voltammetry (SWASV), using a glassy carbon electrode modified with mercury film, was applied. The concentrations of Pb and Cu were determined and calculated in the sample using the standard addition method. Obtained results have shown that Lunaria annua L. is a lead hyperaccumulator (4116.2 mg/kg in S1 and 3314.7 mg/kg in S2) and a potential copper accumulator (624.2 mg/kg in S1 and 498.9 mg/kg in S2). Likewise, the results have shown that the higher the pH is, the lower the possibility that metal accumulation exists

Application of the Stripping Voltammetry Method for the Determination of Copper and Lead Hyperaccumulation Potential in Lunaria annua L.

Various species of the Brassicaceae family are known to hyperaccumulate metals. Lunaria annua L., a plant from the Brassicaceae family, is an oilseed crop known for its pharmaceutical and nutraceutical applications. In this work, Lunaria annua L. was investigated for its accumulation potential in copper and lead-contaminated soil. Concentrations of copper and lead were measured before planting (in seeds and soils) and after the plant was harvested (in soils and plant). Two types of soils were used: a soil sample collected from the Botanical Garden of the Faculty of Science, University of Split (soil 1, S1) and a commercially available organic mineral substrate (soil 2, S2). Measured pH values showed that the S1 (pH = 8.58) was moderately alkaline soil. On the other hand, the purchased organic soil, S2 (pH = 6.35), was poorly acidic to neutral. For the determination of copper (Cu) and lead (Pb), square wave anodic stripping voltammetry (SWASV), using a glassy carbon electrode modified with mercury film, was applied. The concentrations of Pb and Cu were determined and calculated in the sample using the standard addition method. Obtained results have shown that Lunaria annua L. is a lead hyperaccumulator (4116.2 mg/kg in S1 and 3314.7 mg/kg in S2) and a potential copper accumulator (624.2 mg/kg in S1 and 498.9 mg/kg in S2). Likewise, the results have shown that the higher the pH is, the lower the possibility that metal accumulation exists