Piia Mäkinen’s research while affiliated with Åbo Akademi University and other places

A homogeneous immunoassay of T4 was developed using a semiautomatic electrochemiluminometer modified from a commercially available fluorometer. In addition, from the same analyte panel an immunometric immunoassay of TSH at similar disposable oxide-covered aluminum rake electrodes was studied using this instrument both on homogeneous and heterogeneous basis. Detection was based on hot electron-induced cathodic electrochemiluminescence utilizing a commercially available Tb(III) chelate label. The assays were reasonably sensitive and comparison was made with other older methods. Thus, it is possible to develop both non-competitive and competitive immunoassays based on detection of hot electron-induced ECL of the labels.

Electrochemiluminescence (ECL) of aromatic Tb(III) chelates at thin insulating film-coated electrodes provides a means for extremely sensitive detection of Tb(III) chelates and also of biologically interesting compounds if these chelates are used as labels in bioaffinity assays. The suitability of silicon electrodes coated with thermally grown silicon dioxide film as disposable working electrodes in sensitive time-resolved ECL measurements is demonstrated, and a rapid electrochemiluminoimmunoassay (ECLIA) of human C-reactive protein (hCRP) is described. Tb(III) chelate labels can be detected almost down to picomolar level, and the calibration curve of these labels covers more than 6 orders of magnitude of chelate concentration. The calibration curve of the present immunometric hCRP assay was found to be linear over a wide range, approximately 4 orders of magnitude of hCRP concentration, the detection limit of the protein being 0.3 ng mL(-1) (mean background + 2SD) on CV values of about 10-30%, depending on the immunoassay incubation time. In the ECLIA measurements, different incubation times were tested from 15 min (giving above-mentioned performance) to as short as only 2 min, which still gave successful results with approximately 20,000 times better detection limit levels than traditional commercial assay methods. During the ECLIA process, also the Si electrode surface morphology was also investigated by atomic force microscope monitoring.