Labeless AC impedimetric antibody-based sensors with pgml(-1) sensitivities for point-of-care biomedical applications.

This paper describes the development and characterisation of labeless immunosensors for (a) the cardiac drug digoxin and (b) bovine serum albumin (BSA). Commercial screen-printed carbon electrodes were used as the basis for the sensors. Two methods were used to immobilise antibodies at the electrode surface. Aniline was electropolymerised onto these electrodes to form a thin planar film of conductive polyaniline; the polyaniline film was then utilised as a substrate to immobilise biotinylated anti-digoxin using a classical avidin-biotin affinity approach. As an alternative approach, poly(1,2-diaminobenzene) was electrodeposited onto the carbon electrodes and this modified surface was then sonochemically ablated to form an array of micropores. A second electropolymerisation step was then used to co-deposit conductive polyaniline along with antibodies for BSA within these pores to produce a microarray of polyaniline protrusions with diameters of several mum, containing entrapped anti-BSA. The resulting antibody grafted electrodes were interrogated using an AC impedance protocol before and following exposure to digoxin or BSA solutions, along with control samples containing a non-specific IgG antibody. The impedance characteristics of both types of electrode were changed by increasing concentrations of antigen up to a saturation level. Calibration curves were obtained by subtraction of the non-specific response from the specific response, thereby eliminating the effects of non-specific adsorption of antigen. Both the use of microelectrode arrays and affinity binding protocols showed large enhancements in sensitivity over planar electrodes containing entrapped antibodies and gave similar sensitivities to our other published work using affinity-based planar electrodes. Detection limits were in the order of 0.1ngml(-1) for digoxin and 1.5ngml(-1) for BSA.

Label-less immunosensor assay for myelin basic protein based upon an ac impedance protocol.

This paper describes the development and characterization of a label-less immunosensor for myelin basic protein (MBP) and its interrogation using an ac impedance protocol. Commercial screen-printed carbon electrodes were used as the basis for the sensor. Polyaniline was electrodeposited onto the sensors, and this modified surface then utilized to immobilize a biotinylated antibody for MBP using a classical avidin-biotin approach. Electrodes containing the antibodies were exposed to solutions of MBP and interrogated using an ac impedance protocol. The real component of the impedance of the electrodes was found to increase with increasing concentration of antigen. Control samples containing a nonspecific IgG antibody were also studied, and calibration curves were obtained by subtraction of the responses for specific and nonspecific antibody-based sensors, thereby accounting for and eliminating the effects of nonspecific adsorption of MBP. A logarithmic relationship between the concentration of MBP in buffer solutions and the impedimetric response was observed.

Detection of fluoroquinolone antibiotics in milk via a labeless immunoassay based upon an alternating current impedance protocol.

This paper describes the construction of a labeless immunosensor for the antibiotic ciprofloxacin in milk and its interrogation using an ac impedance protocol. Commercial screen-printed carbon electrodes were used as the basis for the sensor. Polyaniline was electrodeposited onto the sensors and then utilized to immobilize a biotinylated antibody for ciprofloxacin using classical avidin-biotin interactions. Antibody loaded electrodes were exposed to solutions of antigen in milk and interrogated using an ac impedance protocol. The faradaic component of the impedance of the electrodes was found to increase with increasing concentration of antigen. Control samples containing a nonspecific IgG antibody were also studied but were found to display large nonspecific responses, probably due to the antibody binding some of the large number of components found in milk. Control sensors could, however, be fabricated using antibodies specific for species not found in milk. Calibration curves could be obtained by subtraction of the responses for specific and control antibody-based sensors, thereby eliminating the effects of nonspecific adsorption of antigen. Sensors exposed to ciprofloxacin in milk gave increases in impedance whereas ciprofloxacin in phosphate buffer led to decreases, indicating the possibility of developing sensors which can both detect and differentiate between free and chelated antigen.