A.K.M. Kafi

DNA as a support for glucose oxidase immobilization at prussian blue-modified glassy carbon electrode in biosensor preparation

An amperometric glucose biosensor has been developed using DNA as a matrix of Glucose oxidase (GOx) at Prussian-blue (PB)-modified glassy carbon (GC) electrode. GC electrode was chemically modified by the PB. GOx was immobilized together with DNA at the working area of the PB-modified electrode by placing a drop of the mixture of DNA and GOx. The response of the biosensor for glucose was evaluated amperometrically. Upon immobilization of glucose oxidase with DNA, the biosensor showed rapid response toward the glucose. On the other hand, no significant response was obtained in the absence of DNA. Experimental conditions influencing the biosensor performance were optimized and assessed. This biosensor offered an excellent electrochemical response for glucose concentration in micro mol level with high sensitivity and selectivity and short response time. The levels of the relative standard deviation (RSDs), (<4%) for the entire analyses reflected a highly reproducible sensor performance. Through the use of optimized conditions, a linear relationship between current and glucose concentration was obtained up to 4 x 10(-4) M. In addition, this biosensor showed high reproducibility and stability.

Influence of anions on electrochemical redox reactions and electrical properties using a viologen derivative

Self-assembled monolayers of alkane derivatives with sulfur-containing head groups on gold substrates have been widely examined recently, since the binding between S atoms and the Au surface is strong. Viologen derivatives have been extensively investigated because of their well-known electrochemical behavior, including behavior as the electron acceptors for the electric charge delivery mediation of devices. Self-assembled viologen monolayers were prepared on the gold surface of a quartz crystal microbalance (QCM) that has been used as a nanogram order mass detector. The self-assembly of viologen derivatives has been determined by the resonant frequency shift of a QCM using a quartz crystal analyzer (QCA). Well-defined peaks were observed at nearly equal charges during the redox reaction in cyclic voltammetry (CV). The electrochemical behavior of self-assembled viologen monolayers has been measured by the electrochemical QCM (EQCM) method. We also used scanning tunneling microscopy (STM) to manipulate the surface on a nanometer scale to form nano-structures and measured current–voltage (I–V) characteristics using scanning tunneling spectroscopy (STS).

Brewster angle microscopic study of mixed lipid-protein monolayer at the air-water interface and its application in biosensing.

This study investigated lipid-protein LB film formation with Brewster angle microscopy. Our experimental results show that hemoglobin (Hb) molecules can enter the lipid layer and remain for an extended time. We investigated the KCl effect on the LB monolayer of lipid-protein. The lipid-Hb monolayer was transferred from the air-water interface to a QCM gold electrode. UV-vis spectra showed that Hb retained its natural structure in the lipid layer. Cyclic voltammetric (CV) and amperometric systems were applied in this study in order to confirm the remaining bioactivity and sensitivity of Hb to hydrogen peroxide (H(2)O(2)). Lipid-Hb-modified electrodes showed well-defined redox peaks, indicating that the direct electron transfer between Hb and the electrode was enhanced by Hb incorporated in lipid layer. Based on this phenomenon, a novel biosensor for H(2)O(2) was designed. Experimental conditions influencing the biosensor performance such as pH, and potential were optimized and assessed. The levels of the R.S.D.s (<5%) for the entire analyses reflected the highly reproducible sensor performance. Using optimized conditions the linear range for the detection of H(2)O(2) was observed from 1 x 10(-6) to 1.00 x 10(-4) molL(-1) with a detection limit of 4.00 x 10(-7) molL(-1) (based on the S/N=3).

Electrochemical properties of heme-protein in lauric acid films and its application as a biosensor

In this research, the enhancement of electron-transfer activity of hemoglobin (Hb) in lauric acid film was investigated for the first time. This type of composite film was made on a glassy carbon electrode by a casting method. Cyclic voltammetric result of the modified electrode displays a well-defined redox peak, which was attributed to the direct electrochemical response of Hb. Our results illustrate that Hb exchange electrons directly with electrode and exhibits the characteristics of peroxidase. When we use this modified electrode as a biosensor, it gives excellent performance in the electrocatalytic reduction of hydrogen peroxide (H2O2). The parameters such as pH and applied potential of the biosensor influencing in H2O2 detection were optimized carefully. Through the optimal conditions, the proposed biosensor shows the linear range for H2O2 determination was from 1×10−5 to 1.25×10−4 mol L−1 with a detection limit of 1×10−7 mol L−1. The biosensor retained more than 90% of the initial response after 14 d.

Brewster angle microscopic study of mixed lipid-protein monolayer at air-water interface and its electrochemical properties

This study investigated the lipid-protein LB Fdm formation with Brewster angle microscope. Our experimental results show that Hb molecule can enter the lipid layer and stands for long time. This kind of lipid-Hb film is very useful for designing sensitive biosensors.