Real-time in vitro detection of cellular H2O2 under camptothecin stress using horseradish peroxidase, ionic liquid, and carbon nanotube-modified carbon fiber ultramicroelectrode

Single-walled carbon nanotubes (SWCNTs), horseradish peroxidase (HRP), and 1-butyl-3-methylimidazolium tetrafluoroborate (BMIM·BF 4 ) were employed to construct a cellular H 2 O 2 sensor based on direct electron transfer. At a working potential of −0.35   V, HRP-BMIM·BF 4 /SWCNTs/CFUME showed a dynamic range of up to 10.2   μM with a low detection limit of 0.13   μM (S/N   =   3) and a high sensitivity of 4.25   A/M   cm 2 . The apparent Michaelis-Menten constant ( K m,app ) was estimated to be as low as 15.4   μM, which suggested that HRP molecules entrapped in the BMIM·BF 4 and SWCNTs immobilized at the carbon fiber ultramicroelectrode maintained a very high affinity. Because of the extremely small dimension and low working potential, HRP-BMIM·BF 4 /SWCNTs/CFUME enabled direct amperometric real-time monitoring of H 2 O 2 in HeLa cells treated with the anticancer drug, camptothecin, without requiring complex data processing and extra surface coatings to prevent interference. HRP-BMIM·BF 4 /SWCNTs/CFUME testing clearly showed that the H 2 O 2 level significantly increased in HeLa cells under camptothecin stress. When HeLa cells were cultured in medium without camptothecin, the H 2 O 2 level remained stable during the whole measurement process. These results indicate that HRP-BMIM·BF 4 /SWCNTs/CFUME could be a powerful tool for real-time investigation of cellular H 2 O 2 level, especially under anticancer drug stress. This method could provide in-depth insights regarding the occurrence, development, and apoptosis of tumors.