Label-free bioelectronic immunoassay for the detection of human telomerase reverse transcriptase in urine

The aim of our study was to prospectively evaluate the potential diagnostic value and clinical applicability of label-free electrochemical detection of human telomerase reverse transcriptase (hTERT). The expression of human telomerase reverse transcriptase (hTERT) was analyzed by adsorptive transfer differential pulse stripping voltammetry (DPSV) from the cell lysates prepared from the urine samples of consenting adults. The principle of the electrochemical determination relies on the intrinsic electro-activity of the proteins. Tyrosine (Tyr), Tryptophan (Trp) and Cysteine (Cys) residues in proteins are oxidizable at carbon electrodes. We employ the direct oxidation of these electro-active amino acids in a label-free voltammetric immunoassay. Monitoring the changes in the electrochemical signals of antibodies (Abs), before and after the binding of the antigens (Ags), provides the basis for our label-free immunoassay. We have also performed reverse-transcription-polymerase chain reaction (RT-PCR) as the conventional method for the confirmation of the electrochemical data. Positive control tests were performed with DPSV and RT-PCR using the exfoliated T24 cell lines. The electrochemical oxidation peak current of the hTERT-mAb was detected at ∼0.60 V (vs. Ag/AgCl). The binding of hTERT expressed by T24 cells caused a decrease in the peak signal of hTERT-mAb. There was a linear relationship between the number of cells in the lysates, and the drop in the current peak. The label-free electrochemical method offers a rapid, simple and reproducible non-invasive assay for hTERT expression in the cell lysates. This assay has a promising potential to provide a useful and new tool for future investigations, facilitating the analysis of hTERT expression in the cell lysates of urine samples for cancer diagnosis and follow-up.