Electrochemical detection of superoxide anions in HeLa cells by using two enzyme-free sensors prepared from ZIF-8-derived carbon nanomaterials

Two kinds of carbon-based nanozymes were constructed from the same precursor of zeolitic imidazolate framework-8 (ZIF-8) for O 2 •− determination. Hollow carbon cubic nanomaterial (labelled as HCC) was obtained by chemically etching ZIF-8 with tannic acid and a subsequent calcination. A porous carbon cubic nanomaterial (labelled as PCC) was prepared by directly pyrolysis. Then HCC and PCC were immobilized on the surface of screen printed carbon electrodes (SPCE), fabricating HCC and PCC modified electrodes (denoted as HCC/SPCE and PCC/SPCE). HCC/SPCE, best operated at −0.5 V (vs. Ag/AgCl), has a sensitivity of 6.55 × 10 2  nA μM −1  cm −2 with a detection limit of 207 nM (at S/ N  = 3) for O 2 •− sensing. And PCC/SPCE, best operated at −0.4 V (vs. Ag/AgCl), exhibited a superior performance for O 2 •− detection with a sensitivity of 1.14 × 10 3  nA μM −1  cm −2 and a low detection limit of 140 nM (at S/ N  = 3). The two sensors possess excellent reproducibility and stability. They were used to sense O 2 •− released from HeLa cells. Illustration of the synthesis of the hollow carbon cubic nanomaterial (HCC) and of the porous carbon cubic nanomaterial (PCC), and the scheme for detection of superoxide anions in HeLa cell.