vitro release profiles of DOX from AM-PEG/DOX NSs under different treatments. (g) The SPR angle change versus miRNA concentration of ssDNA-AuNRs and ssDNA. (h) Comparison of the LOD of antimonenebased SPR sensor with other reported miRNA sensors."/>
Figure 2.11 (a) Time-dependent photothermal heating curves of PEG-modified AMQDs with different concentrations under irradiation of NIR laser (808 nm, 2 Wcm−2). (b) Relative tumor volumes after treatment with saline (G1), NIR (G2), PEG-modified AMQDs (G3), PEG-coated AMQDs +NIR (G4). (c) Intracellular PA signal versus time. (d) Photoacoustic tomography (PAT) images of tumor at various time points after injection of BSA-AMNFs. (e) DOX concentration-dependent loading capacities on AM-PEG NSs. (f) In vitro release profiles of DOX from AM-PEG/DOX NSs under different treatments (pH and pH+NIR). (g) The SPR angle change versus miRNA concentration of ssDNA-AuNRs and ssDNA. (h) Comparison of the LOD of antimonene-based SPR sensor with other reported miRNA sensors. (a, b) Reproduced with permission [61]. Copyright 2017, Wiley-VCH. (c, d) Reproduced with permission [63]. Copyright 2019, Wiley-VCH. (e, f) Reproduced with permission [64]. Copyright 2018, Wiley-VCH. (g, h) Reproduced with permission [65]. Copyright 2019, Nature Publishing Group.
Furthermore, LPE-produced antimonene nanoflakes (AMNFs) were used as ideal contrast agents for PAI, due to the excellent photoacoustic (PA) performance [63]. AMNFs showed high molar extinction coefficient of 2.24 × 109 in the NIR window (800 nm), high photothermal conversion capability with temperature increment up to 207.9°C after 30 min NIR irradiation, and high PTCE of 42.36%, indicating superior performance of AMNFs to other widely used PAI contrast agents, such as organic small molecule dyes, gold nanomaterials. AMNFs also exhibited a dose-dependent and wavelength-independent PA signal with the lowest detection limit of 0.6986 μg mL−1. Besides, the low thermal conductivity (15.1 Wm−1K−1) and high interfacial thermal conductivity of AMNFs resulted in a stronger PA signal. The photon emission was absent in AMNFs, ensuring the maximum photothermal conversion. To increase the biocompatibility, bovine serum albumin (BSA) was coated on the surface of AMNFs. The above excellent PA performance of BSA-AMNFs allowed sensitively monitoring the cellular uptake process in vitro and clearly imaging the small volume tumor in vivo (Figures 2.11c, d).
Tao et al. adopted PEG-modified antimonene (AM-PEG) nanosheets (NSs) as a robust photonic drug-delivery platform for multimodal-imaging-guided cancer theranostics [64]. AM-PEG NSs first showed considerable PTCE of 41.8% and high loading capacity of doxorubicin (DOX) molecules with the largest value of 150% (Figure 2.11e). Then, the release of DOX molecules presented both pH-sensitive and NIR-sensitive characteristics, which enabled the platform to be designed simpler (Figure 2.11f). In vitro, AM-PEG/DOX NSs exhibited photo-induced deep penetrating ability into tumor spheroids and enhanced intracellular uptake. Therefore, combined with NIR irradiation, AM-PEG/DOX NSs killed almost all the tumor cells, indicating an efficient therapeutic effect. In vivo, AM-PEG/DOX NSs continued to accumulate and retain in the tumor sites, then completely eliminated the tumors and inhibited their growth, attributing to a synergistic effect of PTT and chemotherapy. With good biocompatibility and potential degradability, AM-PEG NSs were very promising drug-delivery platform for cancer theranostics.
Having more delocalized 5s/5p orbitals, antimonene can interact strongly with single-stranded DNA (ssDNA), allowing for ultrasensitive detection of cancer-associated MicroRNA (miRNA) molecules. Xue et al. developed an antimonene-based surface plasmon resonance (SPR) sensor and performed trace attomolar-level quantitative detection of miRNA-21 and miRNA-155 [65]. Benefiting from the signal amplification of gold nanorods (AuNRs), this antimonene-based SPR biosensor showed an extremely low limit of detection (LOD) of 10 aM to miRNA-21, which was the highest sensitivity comparing to other reported miRNA sensors (Figures 2.11g, h).
2.4.6 Magneto-Optic Storage
Nonmagnetic doping in antimonene can induce the sp-electron ferromagnetic order with a high Curie temperature (Tc). Tang et al. synthesized fluorinated antimonene (F-antimonene) via an electrochemical exfoliation and synchronous fluorination (EESF) method and explored its magnetic properties [66]. The Tc value of F-antimonene was obtained as high as 717 K, and it was one of the highest Tc value determined experimentally for 2D ferromagnetic materials. Moreover, the saturation magnetization of F-antimonene (~0.1 emu g−1) was obtained at the F/Sb ratio of 0.20. Based on the first-principles calculations considering the spin-orbit coupling (SOC) effect of heavy Sb element, the long-range ferromagnetic order of F-antimonene resulted from the F adatom and its low-carrier-density sp-electron-polarized impurity subbands. Robust high-Tc ferromagnetism in few-layer F-antimonene offers potentials in the magneto-optic storage and magnetic transport applications.
2.5 Conclusion and Outlook
Antimonene, a newly discovered 2D materials, has remarkable optical, electronic, optoelectronic, physical, and chemical properties, including environmental stability, wideband saturable adsorption, tunable band gap, high carrier mobility, generous active sites, superior photothermal performance, and biocompatibility, which enable it to have potential applications in many fields. In traditional 2D materials, changes in the number of layers usually affect only the size of band gap. What makes 2D antimonene unique is its strong spin-orbit coupling and the semi-metallic nature of its bulk form, allowing for adjustable electronic behaviors by varying the layer numbers. These significant features drive researchers to prepare antimonene to better understand its properties and develop its practical applications. Like other 2D materials, mechanical exfoliation was the first method to peel off high-quality mono- or few-layer antimonene at ambient conditions, and then LPE was used to realize the scalable production of antimonene. The epitaxial growth technique was further explored to deposit large-area few- or even single-layer antimonene on different substrates. Other methods were also developed to prepare antimonene with various morphs, such as solution-phase synthesis, plasma-assisted growth, and CVD. Future research can focus on achieving more effective exfoliation, since the successful preparation of antimonene was the premise of verifying the theoretically predictive properties and exploring its practical applications.
Recent works have unveiled some appealing properties of antimonene in experiments and further demonstrated its practical applications. Few-layer antimonene showed broadband nonlinear optical response and high photothermal efficiency (48%), allowing for the applications in lasers, optical switchers, optical modulators, and optical thresholders, which were important in the next-generation optical communication. With a tunable band gap (0–2.28 eV) and high carrier mobility, antimonene was employed as an effective photoactive material in the PVSCs and organic photovoltaics. Generous active sites and large surface area in antimonene made it a suitable catalyst in the catalytic process of CO2RR, HER, and OER. On the basis of high theoretical capacity (660 mAh g−1) along with fast ion diffusion, few-layer antimonene was considered to be an excellent electrode material in SIBs, LIBs, and supercapacitors. As an effective photothermal and contrast agent, antimonene can be used in the PTT, PDT, and PAI for high-performance cancer theranostics. Based on the current status of research on the properties and applications of antimonene, it is expected to enhance the performance by functionalization or modification and then develop its potential applications in more other fields.
To summarize, it is particularly important to predict the properties of antimonene more accurately in theory. Moreover, effective methods are needed to exfoliate or synthesize 2D antimonene, and then, high performance and diverse applications are expected to be realized in future.
References
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