Analytical & Bioanalytical Electrochemistry
Volume:2 Issue: 4, Dec 2010

The goal of this study was to design an aptamer-based sandwich assay with electrochemical detection for activated protein C (APC), a kind of serine protease that plays important roles as anticoagulant, anti-inflammatory and cytoprotective agent. Two sandwich assay formats were tested, one using an anti-APC monoclonal antibody as capturing receptor and a biotinylated aptamer as detection receptor and the other using the same aptamer both for capturing and detection. The assay takes advantage of sandwich binding of two affinity ligands for increased specificity, magnetic beads as carriers of affinity ligands (antibodies or aptamers) for fast magnetic separation, and electrochemical measurement for sensitive detection. Streptavidin-alkaline phosphatase (AP) was fixed to the secondary aptamer through biotin-streptavidin affinity. A magnet placed under the surface of a graphite screenprinted electrode (SPE) captured magnetic beads carrying the affinity complex, and the electrochemical detection was thus achieved through the addition of AP substrate (α-naphthyl phosphate). Differential pulse voltammetry (DPV) was employed to detect the α-naphthol (the enzymatic reaction product) on the surface of the SPE, which was related to the concentration of the target protein. The conditions for the aptamer immobilization and for the protein binding have been optimized.

The Bolousov-Zhabotinskii (BZ) oscillating chemical reaction was applied for determination of L-penicillamine by using a platinum wire as an indicator electrode in the potentiometric method. L-penicillamine can make perturbation in the period of (BZ) oscillating chemical reaction. This perturbation is used as an analytical signal. The effects of different variables of BZ oscillating system were evaluated on the perturbation of period caused by L-penicillamine using statistical experimental design for obtained an optimum condition. A linear response between oscillating period and the logarithm of L-penicillamine concentration was found in the range of 9.0×10-7- 9.0×10-5 M. Under optimum conditions, detection limit (2σ) was obtained 8.7×10-7 M. The relative standard deviation (%RSD) for 4.0×10-6 M L-penicillamine is 4% (n = 5).

A poly glutamic acid film modified electrode exhibited a catalytic response to guanosine oxidation potential and higher peak current value. Linear concentration curve was obtained in the concentration interval of 1.0 a 10.0 mol L-1 in 0.04 mol L-1 B-R buffer pH 2.0 with a detection limit of 0.198 mol L-1. The electrode was used for the determination of guanosine in the potential of +1.1 V (vs. Ag/AgCl) using differential pulse voltammetry (DPV) at urine sample with good recovery.

The article discusses the easy ways of sample monitoring with the help of chemical sensors and biosensors. Now-a-days easy methods to monitor different kind of ions, chemicals etc. has been a challenging area to explore. The incorporation of principles of green chemistry and environmental friendly ways makes the study more interesting as well as applicable to wide range without creating much harm to the society. The core discussion here is on the wide range of applicability of sensors as potentiometric sensors. The simplicity of methods involved and convenient deduction of results makes this study an important area to be worked upon. Modified chemical sensors and biosensors are being generated and synthesized in order to device an easy solution to environmental hazards. Further the scope of this work is not limited to any class of chemicals but it can be applied for the detection of various ions, biologically important species, proteins, carbohydrates, and even for the detection of the hereditary character carrying DNA sequences.

Understanding the physicochemical interaction between the novel drug 8-Azaguanine (8-AG) and its biological receptor DNA is very important. Molecular modeling on the complex formed between 8-AG and DNA presented this complex to be fully capable of participating in the formation of a stable intercalation site. The molecular geometries of 8-AG and DNA bases were optimized with the aid of B3LYP/6-31G* method. Properties of the isolated intercalator and its stacking interactions with adenine···thymine (AT) and guanine···cytosine (GC) nucleic acid base pairs were studied with the DFTB method. Interaction energies of drug···base pair complexes were found to be -6.11 kcal/mol and -6.17 kcal/mol for AT···8-AG and GC···8-AG, respectively.