Schematic representation of the steps for the preparation of nanostructured electrodes. The nanostructures of three types, i.e., pyramids, spherical, and rod-like, were electrodeposited in step 1 and then functionalized with cysteamine self assembled monolayers in step 2. The electrodes were then immersed in antibody solution in the presence of EDC and NHS in step 3, and finally the attachment of antigen in step 4.
(a)–(c) SEM images with the scale of 100 nm, (d)–(f) AFM images of the pyramid, spherical, and rod-like nanostructured electrodes, respectively. The side bar represents the height scale of the nanostructures.
(a) Impedance response and equivalent circuit for the electrochemical cell. It consists of a charge transfer resistance Rct connected parallel to double layer capacitance Cdl, and both are in series to the solution resistance Rs. (b) CV response of (black) bare Au, (red) pyramid, (blue) spherical, (green) rod-like nanostructures using 10 mM Fe (CN)−3 in 1 M KCl. The measurements were performed at a scan rate of 50 mV s−1.
Effect on response of peak current as a function of solution pH for spherical nanostructured immunosensor.
Effect of incubation time on the detection of antigen for the three nanostructured electrodes; circle (red), square (black), and triangle (blue) represent spherical, pyramid, and rod-like nanostructured electrodes, respectively.
CV response of electrochemical immunosensor. (i) Bare Au surface, (ii) nanostructured electrode, (iii) development of cysteamine self assembled monolayer, (iv) immobilization of CEA antibody on (a) pyramid, (b) spherical, (c) rod-like nanostructured electrodes. (d) Variation of the normalized current response with normalized surface area for the (i) spherical, (ii) pyramid, and (iii) rod-like nanostructured electrodes.
The variation in the peak current for (a) bare Au, (b) pyramid, (c)spherical, and (d) rod-like nanostructured electrodes as a function of log of concentration. The concentration of PSA varied from 1 pg ml−1 to 1000 ng ml−1.
Plot of sensitivity and surface coverage as a function of the normalized surface area.
Impedance response of the immunosensor with the concentration of antigen. The inset shows the plot of normalized resistance as a function of the log of concentration.
Selectivity of immunosensor with (i) CEA antibody, (ii) CEA antibody with CEA antigen, (iii) CEA antibody with HBsAg antigen, (iv) CEA antibody with AFP antigens, (v) CEA antibody with PSA antigens.
Cyclic voltammetric responses of the spherical nanostructured immunosensor as a function of the storage days.
Summary of calculated parameters, i.e., surface area, exchange current density (io ), standard rate constant (ko ), electrochemical active surface area (A), and surface coverage for pyramid, spherical, and rod-like nanostructure. The surface area and surface coverage were evaluated from AFM images of nanostructures.
Comparison of sensitivity and association constant for bare Au, pyramid, spherical, and rod-like nanostructures.
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