A label-free immunosensor for diagnosis of dengue infection with simple electrical measurements

The interdigitated electrodes and electrical measurements for the diagnosis of dengue infection using antigen–antibody conjugation method are reported. As a proof of concept, pre-inactivated dengue virus was firstly immobilized indirectly onto the immunosensor surface, pre-coated with sol–gel derived barium strontium titanate (BST) thin film and modified with organic self-assembled monolayer (SAM) formed by 3-aminopropyltriethoxysilane (APTS) and a cross-linker glutaraldehyde over the interdigitated electrodes. The modified sensor surface served as selective sensing probe to capture/conjugate the dengue antibody molecules present in patient's serum. Our immunosensor is based on non-faradaic process, using only de-ionized water as electrolyte during the simple electrical measurements. Both ac impedance spectroscopy and dc I–V measurements between the electrodes gave a clearly discernable and repeatable signal to positively identify the presence of dengue antibody in the serum. Direct correlation was obtained between the signal outputs with respect to antibody concentrations. The measured signal changes in impedance/current without/with the presence of dengue antibody were attributed to the surface conductivity change upon biomolecules immobilization and the dipole-induced interfacial polarization potential at the SAM film/biomolecules interface. By monitoring the impedance or current change, the antibody molecules in the patient's serum could be positively detected.