Actinomycin D br The sensitivity of Ru S
The sensitivity of [email protected]–C/GCE, S–C/GCE, and GCE for ORS was evaluated by using 300 μM H2O2 in N2 saturated of 0.1 M PBS (pH 7) at a scan rate of 100 mV s−1. Fig. 3C illustrates the electrocatalytic re-duction performance of H2O2 at diﬀerent electrodes. No peak diﬀerence was observed after adding 300 μM of H2O2 to S–C/GCE and GCE, whereas the peak of [email protected]–C/GCE significantly decreased owing to the electrochemical reduction of H2O2 at a low applied potential (–0.35 V). The excellent signal and low applied potential observed for [email protected] S–C/ GCE were attributed to the presence of Ru at the electrode surface and high-charge transfer [12,13,46]. The signaling validity of [email protected]–C/GCE for H2O2 sensing was studied using CV for various addition con-centrations of H2O2 at optimal conditions. Fig. 3D illustrates that the reduction peak current was significantly decreased when H2O2 con-centration increased, indicating the validity of the proposed electrode for the sensitive signaling of H2O2.
Basing on the previous reports regarding the mechanism of reduc-tion of H2O2 based on metal nanoparticles [4,47,48], we summarized the corresponding mechanism on [email protected]–C as follows: M.Y. Emran et al. Sensors & Actuators: B. Chemical 284 (2019) 456–467
Scheme 2. The electrochemical sensing of H2O2 released from cancer cells (Hela cells) after cells stimulation by ascorbic Actinomycin D (AA). The H2O2- molecules diﬀused at the surface of [email protected] under applied potential of -0.35 V. The reduction process proceeded in 0.1 M PBS (pH = 7) with the electrochemical transfer of 2e−/2H+.
of H2O2 in the solution regenerated the Ru° and formed H2O and O2. The conducted mechanism is aﬀected by the diﬀusion and reduction of
H2O2 and electron transfer at the electrode surface. The spherical mi-
(1) croporous S-doped carbon facilitated the electron transfer, provided a
diﬀusion pathway for the targeted molecules, and induced the signaling
(2) transduction process at the electrode surface. Thus, these microspheres can be used for the production of highly sensitive and selective elec-
As presented in Eqs. (1)–(3) and Scheme 2; the H2O2 molecules are diﬀused at the surface of Ru and reduced to form H2O molecules with
accepting 2e- and formation of Ru(II) oxide. Consequently, the presence
The pH-dependent eﬀect was studied in a pH range of 5–8 in N2 saturated with 0.1 M PBS. CV-measurements were performed at a scan rate of 100 mV−1 for 300 μM H2O2 on [email protected]–C/GCE. Figure S4 A shows the CV results for [email protected]–C/GCE at varying pH values before and after the addition of 100 μM H2O. When pH was plotted against Ia - Ib (Ia the current after adding H2O2 and Ib the current before adding H2O2), a significant signal enhancement at pH = 7 became evident (Fig. S4B). These results indicated that pH 7 is optimal for H2O2 biosensing. This value is near physiological pH [11–13,46].
The electrochemical kinetics of H2O2 at [email protected]–C/GCE was in-vestigated under varying scan rates. Figure S4C shows the CVs of 300 μM H2O2 on [email protected]–C/GCE at scan rates ranging from 10 mV s-1 to 500 mV s−1. The redox current of H2O2 increased when the scan rate with positive applied potential shift increased. This increase was due to the high electron transfer at increased scan rate. A linear relationship between cathodic and anodic peak current and the square root of scan
0.991) (Fig. S4D). These findings indicated that the catalytic reduction mechanism of H2O2 at the electrode surface was a diﬀusion-controlled process [8,49,50].
3.5. Sensitive monitoring and selective signalling of H2O2 on [email protected]–C
Highly sensitive and selective nonenzymatic H2O2 sensors with ex-hibiting fast response time, reliable stability, and reproducibility has attracted great attention in electrochemistry because of their practical clinical applications. The sensitivity of the designed modified electrodes was investigated by chronoamperometric measurements. Fig. 4A shows the amperometric response of [email protected]–C/GCE for various injection of H2O2 in N2 saturated with 0.1 M PBS (pH 7) at applied potential 0.35 V (vs Ag/AgCl) under stirring conditions. The results indicate that within the addition of H2O2, the amperometric response showed a high-current response and 98% of the steady-state current in every 5 s. Therefore, the H2O2 concentration level can be rapidly monitored in the living cells, despite the fast- and self-degradation in normal physiological