Iron-Based Hollow Nanoplatforms for Cancer Imaging and Theranostics.

Over the past decade, iron (Fe)-based hollow nanoplatforms (Fe-HNPs) have attracted increasing attention for cancer theranostics, due to their high safety and superior diagnostic/therapeutic features. Specifically, Fe-involved components can serve as magnetic resonance imaging (MRI) contrast agents (CAs) and Fenton-like/photothermal/magnetic hyperthermia (MTH) therapy agents, while the cavities are able to load various small molecules (e.g., fluorescent dyes, chemotherapeutic drugs, photosensitizers, etc.) to allow multifunctional all-in-one theranostics. In this review, the recent advances of Fe-HNPs for cancer imaging and treatment are summarized. Firstly, the use of Fe-HNPs in single T1-weighted MRI and T2-weighted MRI, T1-/T2-weighted dual-modal MRI as well as other dual-modal imaging modalities are presented. Secondly, diverse Fe-HNPs, including hollow iron oxide (IO) nanoparticles (NPs), hollow matrix-supported IO NPs, hollow Fe-complex NPs and hollow Prussian blue (PB) NPs are described for MRI-guided therapies. Lastly, the potential clinical obstacles and implications for future research of these hollow Fe-based nanotheranostics are discussed.

Single pixel wide gamut dynamic color modulation based on a graphene micromechanical system.

Dynamic color modulation in the composite structure of a graphene microelectromechanical system (MEMS)-photonic crystal microcavity is investigated in this work. The designed photonic crystal microcavity has three resonant standing wave modes corresponding to the three primary colors of red (R), green (G) and blue (B), forming strong localization of light in three modes at different positions of the microcavity. Once graphene is added, it can govern the transmittance of three modes. When graphene is located in the antinode of the standing wave, it has strong light absorption and therefore the structure's transmittance is lower, and when graphene is located in the node of the standing wave, it has weak light absorption and therefore the structure's transmittance is higher. Therefore, the graphene absorption of different colors of light can be regulated dynamically by applying voltages to tune the equilibrium position of the graphene MEMS in the microcavity, consequently realizing the output of vivid monochromatic light or multiple mixed colors of light within a single pixel, thus greatly improving the resolution. Our work provides a route to dynamic color modulation with graphene and provides guidance for the design and manufacture of high resolution, fast modulation and wide color gamut interferometric modulator displays.

Research on the photoluminescence properties of Cu2+-doped perovskite CsPbCl3 quantum dots.

CsPbX3 (X = Cl, Br, and I) quantum dots (QDs) and Cu2+-doped CsPbCl3 QDs with different Cu-to-Pb molar ratios were synthesized via a solvent-based thermal synthesis method. The photoluminescence (PL) properties of these Cu2+-doped CsPbCl3 QDs were also investigated in this study. The results showed that with the increase in the Cl- concentration the surface defects of CsPb(Cl/Br)3 QDs increased, which resulted in an increase in the non-radiative recombination of excitons and weakened the PL intensity. Moreover, Cu2+-doped CsPbCl3 QDs maintained the cubic crystal structure of the initial phases. Owing to the doping of Cu2+ ions, the surface defects of CsPbCl3 QDs were effectively eliminated, which facilitated the excitonic recombination via a radiative pathway. The PL quantum yields (PLQYs) of Cu2+-doped CsPbCl3 QDs were increased to 51%, showing great photostability. From the results, it is believed that Cu:CsPbCl3 QDs can be widely used in optoelectronic devices.

Triple-band black-phosphorus-based absorption using critical coupling.

Black phosphorus (BP) is an important two-dimensional material that plays a key role in new photoelectric devices. In this work, a triple-band BP-based absorber was proposed, in which a monolayer BP is coupled with the missing angle rectangular structure. Due to the critical coupling of the guided resonance, the BP absorber achieves a triple-band absorption. The results showed that the absorption spectra at 2901.76 nm, 3810.71 nm, and 4676.97 nm under TM polarization achieve a high absorption of 95.45%, 98.68%, and 98.06%, respectively. In addition, the absorption peak and resonance wavelength can be flexibly adjusted by the electron doping of BP, the geometrical parameters of the structure, and the refractive index of the dielectric substrate. Because of the anisotropy properties of BP, the structure exhibits polarization-dependent absorption characteristics. Thus, the missing angle rectangular structure will provide a potential to design mid-infrared absorbers and shows a significant practical application in many photoelectric devices such as photodetectors, modulators, and optical switches.

Fast Polymerization of Polydopamine Based on Titanium Dioxide for High-Performance Flexible Electrodes.

Dopamine (DA) and its derivatives are promising for the fabrication of functional films and devices with excellent conductivity and long-term stability; nevertheless its polymerization process is typically prolonged. We have proposed the accelerated deposition process using ultraviolet (UV) irradiation with the existence of nanotitanium dioxide (nano-TiO2) in order to realize the rapid and stable synthesis of polydopamine (PDA) films. The in situ deposition process of nanostructured coatings such as platinum nanowire (PtNW) was also proposed by reducing the time of polymerization process to less than 1 h. It also increased the platinum (Pt) chelating rate with PDA, which was about 12 times faster than the traditional photo-oxidation method. Compared with the electrodes of the same size based on Ti/Pt sputtering, the impedance of the proposed PDA/TiO2/PtNW coated electrode was as low as 0.0968 ± 0.0054 kΩ at 1 kHz (reduction of 99.74%). An extremely high cathodic charge storage capacity (CSCc) up to 234.4 ± 3.16 mC cm-2 was also observed, which was about 106.5 and 1.6 times higher than that of Ti/Pt and PDA/PtNW electrodes, respectively. In addition to that, significant photocurrent polarization responses were presented for PDA/TiO2/PtNW electrodes with a stable current of -136.1 µA, exhibiting excellent charge transfer and UV absorption capacities. This co-deposition method has demonstrated great potential to speed up the polymerization process and enhance the electrical performance for flexible electrodes.

Outstanding comprehensive performance versus facile synthesis: Constructing core and shell-interchangeable nanocomposites as microwave absorber.

It is still a great challenge to develop high-performance microwave absorption materials (MAMs). Herein, we first proved the excellent synergistic effect of Fe3O4/MoS2 heterostructure based on the theoretical calculations. To effectively utilize the synergistic effect and morphology, core and shell-interchangeable Fe3O4@MoS2 and MoS2@Fe3O4 nanocomposites (NCs) were elaborately constructed. By controlling the hydrothermal temperature, different MoS2 morphologies and contents of Fe3O4@MoS2 NCs were produced, which simultaneously displayed the optimal reflection loss (RL) values (~-50 dB), broad absorption bandwidth (⩾5.0GHz) and high chemical stabilities. With the synthesis temperature increasing from 170 °C to 200 °C, their outstanding microwave absorption (MA) capabilities moved towards the high frequency region and thin matching thickness. Impressively, the Fe3O4@MoS2 obtained at 200 °C presented a minimum RL value of -50.75 dB with the thickness of 2.90 mm and an absorption bandwidth of 5.0 GHz with the thickness of 1.71 mm, and the excellent MA capabilities (RL values <-30 dB) with the low matching thicknesses (<2 mm) could be observed in the frequency range of X and Ku bands. Moreover, compared to the reverse structure MoS2@Fe3O4, the core@shell structure Fe3O4@MoS2 exhibited evidently superior MA comprehensive properties in terms of low optimal RL value, broad absorption bandwidth and high chemical stability, which could be ascribed to the improved impedance matching and microwave attenuation characteristics. Generally, the proposed flower-like core@shell structure Fe3O4@MoS2 NCs presented very extraordinary MA comprehensive properties, which were very attractive candidates for high-performance MAMs.

Enhanced and broadened fluorescence of ZnSe quantum dots enabled by the fluorescence energy transfer system of ZnSe quantum dots and gold nanoparticles.

The enhanced and broadened fluorescence of ZnSe quantum dots (QDs) were studied by using a fluorescence energy transfer system (FETS) of ZnSe QDs and gold nanoparticles (NPs). The FETS were prepared via uniformly dispersing the gold nanoparticles into ZnSe QD solution in the condition of magnetic stirring. Enhanced and broadened fluorescence was observed on the film of the FETS due to the transfer of photo-generated carriers between the ZnSe QDs and the gold NPs, instead of the surface plasma resonance effect. The excitonic and enhanced fluorescence on the FETS film depended on the competition of electron-hole recombination and electron transfer from the ZnSe QDs to the gold NPs. In addition, because of the excitonic fluorescence of the ZnSe QDs absorbed by the gold NPs, the electrons of the s-p band of the gold NPs were further increased to facilitate its energy level shift toward the conduction band of the ZnSe QDs in order to create a blueshift in the enhanced fluorescence. This enhanced and broadened fluorescence method can be applied for controlling fluorescence in photoelectric detection, photodiodes, lightshows, and sensor devices.

Preparation of porous Fe2O3 nanorods-reduced graphene oxide nanohybrids and their excellent microwave absorption properties.

In this paper, α-Fe2O3 nanoparticles (NPs)-reduced graphene oxide (RGO), α-FeOOH nanorods (NRs)-RGO and porous α-Fe2O3 NRs-RGO could be selectively synthesized by hydrothermal method. The investigations indicated that the obtained α-Fe2O3 NPs, α-FeOOH NRs and porous α-Fe2O3 NRs were either attached on the surface of RGO sheets or coated uniformly by the RGO sheets. And the as-prepared nanohybrids exhibited excellent microwave absorption performance, which was proved to be ascribed to the quarter-wavelength matching model. The optimum reflection loss (RL) values for α-Fe2O3 NPs-RGO, α-FeOOH NRs-RGO and porous α-Fe2O3 NRs-RGO were ca. -32.3, -37.4 and -71.4 dB, respectively. Moreover, compared to the obtained α-Fe2O3 NPs-RGO and α-FeOOH NRs-RGO, the as-prepared porous α-Fe2O3 NRs-RGO nanohybrids exhibited enhanced microwave absorption properties because of their special structure and synergetic effect. The possible enhanced microwave absorption mechanisms were discussed in details. Our results confirmed that the geometrical morphology had a great influence on their microwave absorption properties, which provided a promising approach to exploit high performance microwave absorbing materials.

Enhancement effect of defect fluorescence of ZnSe quantum dots on a heterojuction of ZnSe quantum dots and gold nanoparticles.

We studied an enhancement effect of defect fluorescence of ZnSe quantum dots (QDs) on a heterojunction of ZnSe QDs and gold nanoparticles. The photoluminescence (PL) of Au/ZnSe heterojunction is excited by using a 150 nm diameter ultraviolet laser spot of a scanning near-field optical microscope. Owing to the charge transfer of photon-generated carriers from ZnSe QDs, the enhanced PL effect is observed, which results from the increase of the built-in electric field to hinder the electron transfer to gold nanoparticles and is trapped by the defect states of ZnSe QDs. The broadening of defect fluorescence spectra and the reduction of excitonic fluorescence in multi-heterojunction of ZnSe QDs and gold nanoparticles are also observed which is attributed to an increase of their contact areas. We believe that enhanced defect fluorescence method described in this paper have potential applications in forming uniform optoelectronic heterojunction in controlling and boosting fluorescent efficiency of weak PL devices.

Water-assisted and controllable synthesis of core/shell/shell structured carbon-based nanohybrids, and their magnetic and microwave absorption properties.

By controlling the pyrolysis temperature, core/shell/shell structured Fe/Fe5C2/carbon nanotube bundles (Fe/Fe5C2/CNTBs), Fe/Fe3C/helical carbon nanotubes (Fe/Fe3C/HCNTs) and Fe/Fe3C/chain-like carbon nanospheres (Fe/Fe3C/CCNSs) with high encapsulation efficiency could be selectively synthesized in large-scale by water-assisted chemical vapor deposition method. Water vapor was proved to play an important role in the growth process. Because of α-Fe nanoparticles tightly wrapped by two layers, the obtained core/shell/shell structured nanohybrids showed high stabilities and good magnetic properties. The minimum reflection loss values of the as-prepared nanohybrids reached approximately -15.0, -46.3 and -37.1 dB, respectively. The excellent microwave absorption properties of the as-prepared core/shell/shell structured nanohybrids were considered to the quarter-wavelength matching model. Moreover, the possible enhanced microwave absorption mechanism of the as-prepared Fe/Fe3C/HCNTs and Fe/Fe3C/CCNSs were discussed in details. Therefore, we proposed a simple, inexpensive and environment-benign strategy for the synthesis of core/shell/shell structured carbon-based nanohybrids, exhibiting a promising prospect as high performance microwave absorbing materials.

Enhanced photoluminescence of corrugated Al2O3 film assisted by colloidal CdSe quantum dots.

We present the enhanced photoluminescence (PL) of a corrugated Al2O3 film enabled by colloidal CdSe quantum dots. The colloidal CdSe quantum dots are fabricated directly on a corrugated Al2O3 substrate using an electrochemical deposition (ECD) method in a microfluidic system. The photoluminescence is excited by using a 150 nm diameter ultraviolet laser spot of a scanning near-field optical microscope. Owing to the electron transfer from the conduction band of the CdSe quantum dots to that of Al2O3, the enhanced photoluminescence effect is observed, which results from the increase in the recombination rate of electrons and holes on the Al2O3 surface and the reduction in the fluorescence of the CdSe quantum dots. A periodically-fluctuating fluorescent spectrum was exhibited because of the periodical wire-like corrugated Al2O3 surface serving as an optical grating. The spectral topographic map around the fluorescence peak from the Al2O3 areas covered with CdSe quantum dots was unique and attributed to the uniform deposition of CdSe QDs on the corrugated Al2O3 surface. We believe that the microfluidic ECD system and the surface enhanced fluorescence method described in this paper have potential applications in forming uniform optoelectronic films of colloidal quantum dots with controllable QD spacing and in boosting the fluorescent efficiency of weak PL devices.

Structures, stabilities and spectral properties of borospherene B44- and metalloborospherenes MB440/- (M = Li, Na, and K).

Density functional theory (DFT) and time-dependent density functional theory (TD-DFT) calculations are carried out to study the stabilities, photoelectron, infrared, Raman and electronic absorption spectra of borospherene B44- and metalloborospherenes MB440/- (M = Li, Na, and K). It is found that all atoms can form stable exohedral metalloborospherenes M&B440/-, whereas only Na and K atoms can be stably encapsulated inside B440/- cage. In addition, relative energies of these metalloborospherenes suggest that Na and K atoms favor exohedral configuration. Importantly, doping of metal atom can modify the stabilities of B44 with different structures, which provides a possible route to produce stable boron clusters or metalloborospherenes. The calculated results suggest that B44 tends to get electrons from the doped metal. Metalloborospherenes MB44- are characterized as charge-transfer complexes (M2+B442-), where B44 tends to get two electrons from the extra electron and the doped metal, resulting in similar features with anionic B442-. In addition, doping of metal atom can change the spectral features, such as blueshift or redshift and weakening or strengthening of characteristic peaks, since the extra metal atom can modify the electronic structure. The calculated spectra are readily compared with future spectroscopy measurements and can be used as fingerprints to identify B44- and metalloborospherenes.

Heteronanostructured Co@carbon nanotubes-graphene ternary hybrids: synthesis, electromagnetic and excellent microwave absorption properties.

In order to explore high efficiency microwave absorption materials, heteronanostructured Co@carbon nanotubes-graphene (Co@CNTs-G) ternary hybrids were designed and produced through catalytic decomposition of acetylene at the designed temperature (400, 450, 500 and 550 °C) over Co3O4/reduced graphene oxide (Co3O4/RGO). By regulating the reaction temperatures, different CNT contents of Co@CNTs-G ternary hybrids could be synthesized. The investigations indicated that the as-prepared heteronanostructured Co@CNTs-G ternary hybrids exhibited excellent microwave absorption properties, and their electromagnetic and microwave absorption properties could be tuned by the CNT content. The minimum reflection loss (RL) value reached approximately -65.6, -58.1, -41.1 and -47.5 dB for the ternary hybrids synthesized at 400, 450, 500 and 550 °C, respectively. And RL values below -20 dB (99% of electromagnetic wave attenuation) could be obtained over the as-prepared Co@CNTs-G ternary hybrids in the large frequency range. Moreover, based on the obtained results, the possible enhanced microwave absorption mechanisms were discussed in details. Therefore, a simple approach was proposed to explore the high performance microwave absorbing materials as well as to expand the application field of graphene-based materials.

Comparative study on the spectral properties of boron clusters Bn(0/-1)(n = 38-40).

The all-boron fullerenes B40(-1) and B39(-1) discovered in recent experiments are characterized and revealed using photoelectron spectroscopy. Except for the photoelectron spectroscopy, one may identify such boron clusters with other spectroscopic techniques, such as infrared spectra and Raman spectra. Insight into the spectral properties of boron clusters is important to understand the boron clusters and find their potential applications. In this work, density functional theory (DFT) and time-dependent density functional theory (TD-DFT) calculations are carried out to comparatively study the vibrational frequencies, infrared spectra, Raman spectra and electronic absorption spectra of boron clusters Bn(0/-1)(n = 38-40). The numerical simulations show that such boron clusters have different and meaningful spectral features. These spectral features are readily compared with future spectroscopy measurements and can be used as fingerprints to distinguish the boron clusters Bn(0/-1) with different structures (cage structure or quasi-planar structure) and with different sizes (n = 38-40).

Formic acid catalyzed gas-phase reaction of H2O with SO3 and the reverse reaction: a theoretical study.

The formic acid catalyzed gas-phase reaction between H(2)O and SO(3) and its reverse reaction are respectively investigated by means of quantum chemical calculations at the CCSD(T)//B3LYP/cc-pv(T+d)z and CCSD(T)//MP2/aug-cc-pv(T+d)z levels of theory. Remarkably, the activation energy relative to the reactants for the reaction of H(2)O with SO(3) is lowered through formic acid catalysis from 15.97 kcal mol(-1) to -15.12 and -14.83 kcal mol(-1) for the formed H(2)O⋅⋅⋅SO(3) complex plus HCOOH and the formed H(2)O⋅⋅⋅HCOOH complex plus SO(3), respectively, at the CCSD(T)//MP2/aug-cc-pv(T+d)z level. For the reverse reaction, the energy barrier for decomposition of sulfuric acid is reduced to -3.07 kcal mol(-1) from 35.82 kcal mol(-1) with the aid of formic acid. The results show that formic acid plays a strong catalytic role in facilitating the formation and decomposition of sulfuric acid. The rate constant of the SO(3)+H(2)O reaction with formic acid is 10(5) times greater than that of the corresponding reaction with water dimer. The calculated rate constant for the HCOOH+H(2)SO(4) reaction is about 10(-13) cm(3) molecule(-1) s(-1) in the temperature range 200-280 K. The results of the present investigation show that formic acid plays a crucial role in the cycle between SO(3) and H(2)SO(4) in atmospheric chemistry.