DNAzyme-based Y-shaped label-free electrochemiluminescent biosensor for lead using electrically heated indium-tin-oxide electrode for in situ temperature control

The temperature control in the traditional DNAzyme-based electrochemiluminescent (ECL) biosensors for Pb2+ is realized through bulk solution heating, which needs tedious procedures, relative large equipment and this limits their application. Moreover, the ECL indicators had been modified on the DNA through chemical reaction, which has the limitation of low efficiency and high cost. In this study, electrically heated indium-tin-oxide (ITO) electrode is applied to adjust the temperature instead of the whole bulk solution heating. Y-shaped double strand DNA (dsDNA) was formed through the hybridization of DNAzyme, substrate and capture DNA, then Ru (phen)(3)(2+) was embedded into the groove of dsDNA and acted as the ECL indicator, which avoided the costly labeling procedure of ECL indicator on DNA. The results indicated that the two different ways of heating had the same effects on the DNA hybridization and DNAzyme action, but the temperature controlled by the heated electrode is simpler and quicker than that with bulk solution heating. Furthermore, the performance of the biosensor had been further improved at an elevated electrode surface temperature because temperature affected the performance of the ECL of Ru(phen)(3)(2+) greatly. Under the optimized conditions, the ECL signal has a linear relationship with logarithm concentration of Pb2+ in the range of 0.25 (similar to) 500 pM with a detection limit of 0.2 pM at the electrode temperature of 45 degrees C, and this outcome was approximately 5 times lower than that at 25 degrees C of electrode surface temperature. The proposed biosensor has been applied to detect Pb2+ in soil samples with satisfactory results.