Most nanozyme research is limited to oxidase and peroxidase. Here, we reported the N, P, or S doped carbon nanotubes (CNTs) for enzyme mimics of nicotinamide adenine dinucleotide (NADH) oxidase and cytochrome c (Cyt c) reductase. Through the doping of N element, the NADH oxidase-like activity of CNTs is highly improved, and the maximum initial velocity for N doped CNT (N-CNT) is increased by 4.28 times compared to that before the modification. Through the analysis of NADH oxidation products, we found that biologically active NAD⁺ was produced, and the oxygen was selectively reduced to water or hydrogen peroxide, which is consistent with natural NADH oxidase. Furthermore, we found for the first time that carbon nanotubes can promote the transfer of electrons from NADH to Cyt c, thereby can mimic the properties of Cyt c reductase.

Recently, a study of mimic enzyme has received more attentions. However, the investigation on the oxidoreductase activity of electron mediators in the biological respiratory chain is still rare. Herein, we found that cadmium sulfide (CdS) nanorods can catalyze the formation of superoxide anions. Due to the role of the photo-generated holes and the nicotinamide adenine dinucleotide (NADH) oxidation promoted by superoxide anion (O₂^•−), the CdS exhibits NADH oxidase-like activity and can be coupled with dehydrogenase to realize the recycling of NADH. It is worth mentioning that the bio-electron acceptor, cytochrome c (Cyt c), as a chromogenic substrate, can accept electrons transferred from O₂^•−, which demonstrates the Cyt c reductase-like activity of CdS under physiological pH conditions. For different substrates, O₂^•− induced from CdS show oxidizing capacity for NADH and reducing capacity for Cyt c, which provides a new perspective for the in-depth study of new nanozyme.

Enhanced cellular uptake efficiency of nanoparticles is important for their biomedical applications, including photothermal therapy (PTT) for cancer. In this study, a one-pot method was used to construct a positively charged and magnet-responsive nanocomposite comprising reduced graphene oxide anchoring iron oxide (RGI) with a polyethylenimine (PEI) modification, to improve the efficiency of cell internalization. The surface charge can be finely tuned using PEIs of different molecular weights. The obtained RGI_1.8k composite (RGI modified by 1.8 kDa PEI) could load indocyanine green (ICG) at a high mass ratio of 10:3 and ablate cancer cells using low-density laser irradiation because of its positively charged surface. In addition, the hybrids of RGI_1.8k and ICG could kill most cancer cells at a laser density of 0.7 W/cm² in vitro and 0.3 W/cm² in vivo. At the same time, cell viability could be controlled by converting the external magnetic-field direction because of the enrichment of the magnet-responsive composite in vitro and in vivo. Furthermore, RGI_1.8k-ICGs could be used as T₂-weighted magnetic resonance and infrared thermal imaging agents. Coupled with the magnetic target effect, the imaging signal could be improved significantly. Therefore, RGI_1.8k-ICGs represent a new highly efficient PTT and imaging agent with great potential for cancer treatment.