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Article

Facile Synthesis of Black Phosphorus Nanosheet@NaReF4 Nanocomposites for Potential Bioimaging

by
Dongya Wang
1,
Jingcan Qin
1,
Chuan Zhang
2,* and
Yuehua Li
1,*
1
Department of Radiology, Shanghai Jiao Tong University Affiliated Sixth People’s Hospital, Shanghai Jiao Tong University School of Medicine, 600 Yi Shan Road, Shanghai 200233, China
2
School of Chemistry and Chemical Engineering, Frontiers Science Center for Transformative Molecules, State Key Laboratory of Metal Matrix Composites, Shanghai Jiao Tong University, 800 Dongchuan Road, Shanghai 200240, China
*
Authors to whom correspondence should be addressed.
Nanomaterials 2022, 12(19), 3383; https://doi.org/10.3390/nano12193383
Submission received: 24 July 2022 / Revised: 21 September 2022 / Accepted: 26 September 2022 / Published: 27 September 2022
(This article belongs to the Section Nanocomposite Materials)
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Abstract

:
Black phosphorus nanomaterials (BPN) have been well developed in tumor therapy. However, lack of diagnostic function limits the development of BPN in biomedicine. Lanthanide-doped nanoparticles are considered as versatile materials for fluorescence or magnetic resonance imaging. Integration of BPN with lanthanide-doped nanoparticles was rarely reported owing to the complex synthesis processes and poor modification effect. Herein, we report a simple and general method for synthesizing BPN@NaReF4 (Re: Gd or Y, Yb, Er) nanocomposite. TEM and XRD characterization confirm efficient combination of BPN and NaGdF4 or NaYF4:Yb,Er (18.2 mol %) after one-step mixing. The FTIR and XPS spectra were used to prove the generation of PO43−-Gd and P-Gd coordination bonds and clarify ligand exchange mechanism. The anchored nanoparticles on BPN were stable and become hydrophilic. The prepared BPN@NaGdF4 exhibit the signals of photoacoustic and magnetic resonance imaging. The obtained BPN@NaYF4:Yb,Er (18.2 mol %) have the potential in fluorescence bioimaging. We believe that this work will expand the applications of BPN in diagnosis and therapy together.

1. Introduction

Black phosphorus, a two-dimensional semiconductor, has attracted much attention from researchers in recent years due to its unique layer-dependent properties [1]. The black phosphorus nanosheet (BPN), exfoliated from its bulk counterpart, exhibits outstanding optical, electronic, thermal, and catalytic performances, and, thus, may be widely applied in optoelectronics [2], energy conversion [3], and biomedicine [4]. Nevertheless, to meet the diversified demand in varied fields, the functionality of black phosphorus nanomaterials should be further improved, especially when used in biomedicine.
With the advantages of high specific area, good biocompatibility, and photothermal/photodynamic properties, BPN was well studied for tumor treatment and showed great therapy performance [5,6]; however, lack of diagnostic function limits the development of BPN in clinical use. To improve it, imaging medium, such as Cy7 dyes [7] or iron oxide [8], was loaded with BPN, realizing bioimaging and therapy together. Sadly, the binding force between BPN and contrast medium is an electrostatic interaction which will cause uncontrollable aggregation of nanomaterial and medium leakage [9,10]. Thus, continual effort in developing effective strategies should be made to endow BPN with bioimaging functions, such as fluorescence imaging or magnetic resonance imaging, which is very common and powerful in clinics [11].
Lanthanide-doped nanoparticles, also called rare-earth nanoparticles (NaReF4), have been developed as an important class of functional nanomaterials for many years. Benefiting from the inner-layer electron transition, lanthanide-doped nanoparticles commonly exhibit light emission with large anti-stokes shift, long luminescence lifetimes, and excellent photostability [12,13]. Moreover, Gd3+ based complex and nanoparticle yield magnetic resonance signals [14]. Thus, lanthanide-doped nanoparticles were widely used for disease diagnosis, including fluorescence imaging and magnetic resonance imaging [15,16,17]. In this regard, integration of lanthanide-doped nanoparticles with BPN to form 0D-2D heterostructure will be an upward trend, realizing integrated diagnostic and therapy. Unfortunately, to the best of our knowledge, the rare-earth nanoparticles were married with BPN just via electrostatic attraction which often suffers inefficient modification and intricate procedures including charged polymer coating or surface modification [18,19]. A simple method of combining rare-earth nanoparticles with BPN is desirable and worthwhile for nanotechnology development.
In this work, we synthesized BPN@NaReF4 (Re: Gd or Y, Yb, Er) heterostructure by a simple process. As the schematics illustration show in Figure 1, the oleic acid-capped NaReF4 in cyclohexane was directly mixed with BPN in water. After vortexing overnight, the NaReF4 in the oil phase was transferred to the aqueous phase and integrated with BPN, forming NaReF4 coordinated BPN nanocomposites. The prepared BPN@NaGdF4 nanocomposites exhibit photoacoustic and magnetic resonance signals and the BPN@NaYF4:Yb,Er (18.2 mol %) demonstrate fluorescence emission, showing the potential application in bioimaging.

2. Materials and Methods

2.1. Materials

Bulk black phosphorus crystals were synthesized via a chemical vapor transport method according to our previously reported procedures [20]. N-Methyl-2-pyrrolidone (NMP, 98%), cyclohexane (99.5%), methanol (99.8%), and ethanol (AR) were obtained from Aladdin Biochemical Technology Co., Ltd. (Shanghai, China). Hydrochloric acid (~36%) and sodium hydroxide (>98%) were purchased from Sinopharm Chemical Reagent Co., Ltd. Yttrium(III) acetate hydrate (99.9%), ytterbium(III) acetate hydrate (99.9%), erbium(III) acetate hydrate (99.9%), gadolinium(III) acetate hydrate (99.9%), and oleic acid (OA, 90%) were purchased from Alfa Aesar (Haverhill, MA, USA). Ammonium fluoride (>98%) and 1-Octadecene (90%) was purchased from Sigma-Aldrich (St. Louis, MO, USA). All chemicals were used as received without further purification.

2.2. Characterization

Low-resolution TEM images were taken from a Talos L120C G2 (USA) instrument operated at 120 kV. Powder X-ray diffraction (XRD) patterns were recorded using a Rigaku Mini Flex 600 with Cu Kα radiation (λ = 1.5406 Å). UV-Vis spectra were recorded using a UV-1800 instrument (Shimadzu, Kyoto, Japan). Fluorescence spectra were obtained on an FLS1000 fluorescence spectrometer (Edinburgh Instruments, Livingston, UK). Scanning electronmicroscopy (SEM) images were carried out in a JSM-7800F (JEOL) scanning electron microscope. Raman spectra were obtained using a Renishaw inVia Qontor confocal microscope with a 532 nm laser. FTIR spectra were obtained on a Nicolet iN10 MX instrument (Thermo Scientific, Waltham, MA, USA). X-ray photoelectron spectroscopy (XPS) was performed on an AXIS Ultra DLD (Shimadzu, Kyoto, Japan). Inductively coupled plasma mass spectrometry (ICP-MS, iCAP Q, Thermal Fisher, Waltham, MA, USA) was used to determine the concentration of black phosphorus and gadolinium. Photoacoustic signal was obtained on a VEVO LAZR-X (Fujifilm VisualSonics, Toronto, Canada). The magnetic resonance images and T1 relaxation rate were acquired on the 0.5 T MesoMR23-060H-I (Niumai Electronic Technology, Suzhou, China).

2.3. Synthesis of Black Phosphorus Nanosheets

Bulk BP (200 mg) was ground with NMP and then dispersed in NMP (100 mL). The mixture was first tip-sonicated (working 2 s, interval 2 s, power 650 W) for 3 h in an ice bath, followed by ice bath sonication for 12 h at 300 W. The resulting suspension was centrifuged at 7000 rpm for 20 min, and the collected supernatant was then centrifuged at 14,000 rpm for 20 min. The precipitate was washed with DI water three times and dispersed in the aqueous solution for further use. The concentration of BPN dispersion was determined by ICP-MS.

2.4. Synthesis of NaGdF4 Nanoparticles

Oleic acid capped NaGdF4 (NaGdF4-OA) nanoparticles were prepared using the thermal coprecipitation method according to the literatures [21]. Briefly, oleic acid (4 mL), 1-octadecene (6 mL), and an aqueous solution (2 mL) containing Gd(CH3COO)3 (0.4 mmol) were added to a 50 mL two-neck round-bottom flask. The mixture was stirred at 150 °C for 1 h to remove the water. After the mixture was cooled to room temperature, a methanol solution (5 mL) containing NaOH (1 mmol) and NH4F (1.2 mmol) was added to the flask. The mixture was then stirred at 50 °C for 2 h, followed by maintaining the temperature at 100 °C for another 30 min. Subsequently, the mixture was heated to 280 °C and kept for 2 h under nitrogen atmosphere. After cooling down to room temperature, the oleic acid capped NaGdF4 nanoparticles were collected by centrifugation and washed three times with ethanol. The nanoparticles were dispersed in cyclohexane for further use.

2.5. Synthesis of NaYF4:Yb,Er (18.2 mol %) Nanoparticles

Oleic acid capped NaYF4:Yb,Er (18.2 mol %) nanoparticles were also prepared by the thermal coprecipitation method according to our previous work [22]. The Y(CH3COO)3 (0.32 mmol), Yb(CH3COO)3 (0.072 mmol) and Er(CH3COO)3 (0.008 mmol) aqueous solution was mixed with oleic acid (3 mL) and 1-Octadecene (7 mL). After stirring at 150 °C for 1 h, the mixture was cooled to room temperature, and then NaOH (1 mmol) and NH4F (1.2 mmol) dissolved in methanol was added followed by stirring at 50 °C for 2 h. Next, the mixture was heated to 100 °C and kept for another 30 min. After purging with nitrogen, the reaction mixture was heated to 290 °C and kept for 1.5 h before cooling down to room temperature. The resulting nanoparticles were collected by centrifugation washed with ethanol. The oleic acid capped NaYF4:Yb,Er (18.2 mol %) nanoparticles were finally obtained and dispersed in cyclohexane.

2.6. Synthesis of Ligand-Free Nanoparticles

Ligand-free rare-earth nanoparticles were prepared according to a procedure in the literature, with slight modification [23]. The oleic acid capped nanoparticles were dispersed in ethanol (1 mL), and after adding hydrochloric acid (1 mL, 1 M), the mixture was ultrasonicated for 1 min. The ligand-free nanoparticles were collected by centrifugation at 14,000 rpm for 20 min and washed with ethanol three times. The ligand-free rare-earth nanoparticles were redispersed in water for the MRI test.

2.7. Synthesis of BPN@NaReF4 Nanocomposites

The oleic acid capped NaGdF4 or NaYF4:Yb,Er (18.2 mol %) in cyclohexane (2 mL, 50~500 μg mL−1) was directly mixed with BPN aqueous solution (2 mL, 100 μg mL−1). After vortex overnight, the nanoparticles in cyclohexane were transferred to water and integrated with BPN in the meantime. The BPN@NaGdF4 or BPN@NaYF4:Yb,Er (18.2 mol %) nanocomposites were collected from the aqueous phase by centrifugation.

3. Results

3.1. Characterization of BPN@NaGdF4 Nanocomposites

NaGdF4 nanocrystals were used as the representative lanthanide-doped nanoparticles to examine the integration between BPN and NaReF4. First, the BPN and NaGdF4 were synthesized separately and characterized with TEM, XRD, absorption spectra, and Raman spectra.
As the XRD pattern shows in Figure S1, the exfoliated black phosphorus nanosheets still have the crystal structure. The lateral size of obtained BPN was 100–200 nm (Figure 2A). The optical bandgap derived from the BPN absorption spectrum was ∼2.18 eV (Figure 3A,B), indicating the ultrathin thickness of the obtained BPN [24]. The Raman spectrum (Figure 3C) shows three characteristic peaks at 361, 438, and 466 cm−1, assigned to the modes of Ag1, B2g, and Ag2, respectively, demonstrating the puckered orthorhombic lattice structure of the exfoliated BPN [25].
The synthesized NaGdF4 nanoparticles, capped by oleic acid, have high uniformity in size (average size of ∼8.3 nm) as shown in Figure 2B and Figure S2. The XRD pattern proves that the obtained NaGdF4 nanoparticles are composed of pure hexagonal NaGdF4 crystals (Figure S1).
After the integration of NaGdF4 and BPN, the product was collected from the aqueous phase. As Figure S3 shows, the amount of NaGdF4 nanoparticles was decreased which indicates the possible combination of BPN and NaGdF4. From the TEM image in Figure 2C, we can see that the nanoparticles were distributed on the surface of BPN and no free nanoparticles were found. XRD pattern in Figure 2D shows combined diffraction peaks of BPN and NaGdF4 nanocrystal. After NaGdF4 coating, the Raman peaks of BPN experience a slight red shift, indicating that the NaGdF4 nanoparticles were successfully loaded on the BPN [26]. To investigate the loading capacity of BPN for NaGdF4 nanoparticles, different amounts of NaGdF4 nanoparticles were added in the oil phase. After the reaction, the collected products were characterized with TEM (Figure S4). It is obvious that the numbers of loaded NaGdF4 nanoparticles are increased with the elevated feeding ratios of NaGdF4 to BPN and keep constant when the ratio is higher than 2. Above all, these results confirm the efficient integration of NaGdF4 with BPN via this simple experimental method.
It should be noted that the optical bandgap of BPN@NaGdF4 calculated from the absorption spectrum is generally consistent with BPN (Figure 3A,B). Due to the layer-dependent bandgap, the optical bandgap can reflect the thickness and aggregation degree [27]. Thus, it is concluded that the rigid NaGdF4 nanoparticles can prevent aggregation of BPN after loading them.

3.2. Mechanism of BPN@NaGdF4 Preparation

To investigate the reason why NaGdF4 can be bound with BPN, the FTIR and XPS spectra were acquired. For the FTIR spectrum of BPN@NaGdF4 nanocomposites (Figure 4A), the peaks at 2920, 2854, 1554, and 1454 cm−1 disappeared, unlike with OA capped NaGdF4, which confirms removal of the OA [22]. According to the literature, the BPN is easily oxidized and PO43− can be generated on the surface of BPN [28,29]. From the FTIR spectrum of BPN, we can recognize the peaks located in the 1115–975 cm−1 range which are from PO43− [30,31]. The XPS spectra (Figure 4B) also show the binding energy of POx especially for the BPN@NaGdF4 sample. Thus, the PO43− were indeed existed on the as-prepared BPN and BPN@NaGdF4 nanocomposites.
It is well known that the PO43– can easily replace the CO2−, as the PO43− has a stronger coordination ability for rare earth than carboxyl [32,33]. In this case, we believe that the oleic acid with CO2− was displaced by PO43− on the BPN, and PO43–-Gd coordination was formed. Thus, the NaGdF4 nanoparticles can be integrated with BPN.
In addition to the coordination of PO43− for Gd element, the P-Gd coordination [34] has also been studied. As shown in Figure 4B–D, after the combination of BPN and NaGdF4, the XPS peaks of P 2p and Gd 4d are shifted to higher binding energy while the Gd 3d XPS peaks exhibit no change, indicating strong interaction between P and Gd atoms. By XPS-peak-differentiation-imitating analysis for P 2p and Gd 4d XPS spectra [35,36], there are two new emerged peaks that can all be assigned to P-Gd coordination.
Generally, the coordination bond is stable. In this case, we examined whether the anchored NaGdF4 on BPN can be dropped or not. The prepared BPN@NaGdF4 nanocomposites in water were stirred vigorously overnight and TEM was conducted. In Figure S8, almost no free NaGdF4 nanoparticles can be observed. Thus, the anchored NaGdF4 nanoparticles on BPN by this method are stable.
Above all, we concluded that the PO43− groups on BPN replace the CO2− contained oleic acids on the surface of NaGdF4 and PO43−-Gd as well as P-Gd coordination bonds are formed, realizing firm integration of NaGdF4 and BPN.
To prove the generality of such synthesis method, NaYF4:Yb,Er (18.2 mol %) nanoparticles with an average size of 22 nm were prepared to modify BPN (Figure 5A,B). After the modification process, the amount of NaYF4:Yb,Er (18.2 mol %) nanoparticles in upper cyclohexane was reduced (Figure S9) and the TEM image of the product shows that the NaYF4:Yb,Er (18.2 mol %) nanoparticles were effectively anchored on BPN (Figure 5C). Consequently, we believe that the described experimental method in this work can be used to integrate other lanthanide-doped nanoparticles with BPN.

3.3. Bioimaging Properties of BPN@NaReF4 Nanocomposites

The black phosphorus nanomaterials have been reported exhibit photoacoustic property owing to the excellent photothermal conversion and thermal stability [37,38,39]. We then examine the photoacoustic signal of BPN and BPN@NaGdF4 nanocomposites. The photoacoustic signal of BPN was strongest when the excitation wavelength was 710 nm (Figure S10). The photoacoustic intensities all show good linear positive correlations with the concentrations of BPN (Figure 6A,B). The BPN@NaGdF4 nanocomposites with 200 μg mL−1 BPN display obvious photoacoustic imaging effect.
Gd-based chelates (Gd-DTPA, Gd-DOTA, etc.), as a class of T1 contrast agent, have been widely used in routine clinical magnetic resonance imaging (MRI) diagnosis [40,41]. NaGdF4 nanoparticles have also been well studied as contrast agent and show enhanced MRI effect [15,16]. In this case, the relaxation rate of NaGdF4 nanoparticles and BPN@NaGdF4 were evaluated. As shown in Figure 6C,D and Figure S11, the NaGdF4 nanoparticles after BPN loading still exhibit comparable MRI signal compared with ligand-free NaGdF4.
The NaYF4:Yb,Er (18.2 mol %) nanoparticles are considered to be the more efficient NIR-to-visible upconverting nanomaterials, showing much potential in bioimaging application. As Figure 7 shows, when excited by a 980 nm laser, NaYF4:Yb,Er (18.2 mol %) nanoparticles have three emission peaks. After loading with BPN, the emission peaks in 507–575 nm range are quenched more severely owing to stronger absorption of BPN for shorter wavelength light (Figure 2A). The emerged emission peaks at 647 nm and 697 nm may be the results of light scattering or fluorescence emission of BPN. We speculate that there could be energy transfer between BPN and NaYF4:Yb,Er (18.2 mol %) and it will be further investigated in the future. In a word, the BPN@NaYF4:Yb,Er (18.2 mol %) nanocomposites still exhibit satisfied fluorescence emission for bioimaging application.

4. Conclusions

In this work, the BPN@NaReF4 (Re: Gd or Y, Yb, Er) nanocomposites were successfully synthesized via simple mixing. The formation mechanism of BPN@NaGdF4 is that the oleic acid on the surface of NaGdF4 can be substituted with the PO43− on the surface of BPN. Coordination bonds (PO43−-Gd and P-Gd) are generated between Gd and PO43− or P, so that the modified NaGdF4 on BPN are stable. The prepared BPN@NaGdF4 nanocomposites have the properties of photoacoustic and magnetic resonance imaging. The BPN@NaYF4:Yb,Er (18.2 mol %) nanocomposites in aqueous still show satisfied fluorescence emission and can be used for fluorescence bioimaging in future.

Supplementary Materials

The supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/nano12193383/s1. Figure S1: XRD patterns of as-prepared BPN and NaGdF4; Figure S2: size distribution of the oleic acid capped NaGdF4 nanoparticles; Figure S3: pictures of reaction bottle containing NaGdF4 and BPN; Figure S4: TEM images of BPN@NaGdF4; Figure S5: SEM images of the BPN, NaGdF4 and BPN@NaGdF4 nanocomposites; Figure S6: XPS survey spectra; Figure S7: FTIR spectrum of as-synthesized BPN; Figure S8: TEM image of BPN@NaGdF4 nanocomposites after rigorously stirring overnight; Figure S9: pictures of reaction bottle containing NaYF4:Yb,Er (18.2 mol %) and BPN; Figure S10: Photoacoustic signal of BPN at different excitation wavelengths; Figure S11: magnetic resonance imaging of ligand-free NaGdF4 and BPN-NaGdF4 nanocomposites.

Author Contributions

Conceptualization, D.W.; Funding acquisition, C.Z. and Y.L.; Investigation, D.W.; Supervision, C.Z. and Y.L.; Writing—original draft, D.W.; Writing—review and editing, J.Q. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by National Natural Science Foundation of China (No.81871329), New developing and Frontier Technologies of Shanghai Shen Kang Hospital Development Center (No. SHDC12018117), and China Postdoctoral Science Foundation funded project (No.2020M671152).

Data Availability Statement

The data presented in this study are available on request from the first author.

Acknowledgments

We would like to acknowledge Yangyang Huang for their technical support in TEM characterization. We acknowledged the Instrumental Analysis Center of Shanghai Jiao Tong University for providing XPS analysis.

Conflicts of Interest

The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript; or in the decision to publish the results.

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Figure 1. Schematic illustrations of BPN@NaReF4 synthesis and corresponding experimental process.
Figure 1. Schematic illustrations of BPN@NaReF4 synthesis and corresponding experimental process.
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Figure 2. The TEM images of BPN (A), NaGdF4 (B), and BPN@NaGdF4 (C); (D) XRD pattern of the as-synthesized BPN@NaGdF4 nanocomposites.
Figure 2. The TEM images of BPN (A), NaGdF4 (B), and BPN@NaGdF4 (C); (D) XRD pattern of the as-synthesized BPN@NaGdF4 nanocomposites.
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Figure 3. (A) The absorption spectra of BPN and BPN@NaGdF4; (B) direct Tauc plots used to determine the optical bandgap. α is the absorbance and hν is the photon energy of the incident light; and (C) Raman spectra of BPN and BPN@NaGdF4.
Figure 3. (A) The absorption spectra of BPN and BPN@NaGdF4; (B) direct Tauc plots used to determine the optical bandgap. α is the absorbance and hν is the photon energy of the incident light; and (C) Raman spectra of BPN and BPN@NaGdF4.
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Figure 4. (A) FTIR spectra of BPN, NaGdF4, and BPN@NaGdF4 nanocomposites; (B) high-resolution P 2p XPS spectra of BPN and BPN@NaGdF4 nanocomposites; high-resolution Gd 3d (C) and Gd 4d (D) XPS spectra of NaGdF4 and BPN@NaGdF4 nanocomposites.
Figure 4. (A) FTIR spectra of BPN, NaGdF4, and BPN@NaGdF4 nanocomposites; (B) high-resolution P 2p XPS spectra of BPN and BPN@NaGdF4 nanocomposites; high-resolution Gd 3d (C) and Gd 4d (D) XPS spectra of NaGdF4 and BPN@NaGdF4 nanocomposites.
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Figure 5. TEM image of OA capped NaYF4:Yb,Er (18.2 mol %) nanoparticles (A) and the corresponding size distribution (B); (C) TEM image of BPN@NaYF4:Yb,Er (18.2 mol %) nanocomposites.
Figure 5. TEM image of OA capped NaYF4:Yb,Er (18.2 mol %) nanoparticles (A) and the corresponding size distribution (B); (C) TEM image of BPN@NaYF4:Yb,Er (18.2 mol %) nanocomposites.
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Figure 6. Photoacoustic intensity of BPN (A) and BPN@NaGdF4 (B) with different concentrations of BPN and their linear fit. Inset: corresponding photoacoustic imaging; Relaxation rate R1 (1/T1) of ligand-free NaGdF4 (C) and BPN@NaGdF4 (D) versus Gd3+ concentration.
Figure 6. Photoacoustic intensity of BPN (A) and BPN@NaGdF4 (B) with different concentrations of BPN and their linear fit. Inset: corresponding photoacoustic imaging; Relaxation rate R1 (1/T1) of ligand-free NaGdF4 (C) and BPN@NaGdF4 (D) versus Gd3+ concentration.
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Figure 7. Room-temperature upconversion emission spectra of the oleic acid capped NaYF4:Yb,Er (18.2 mol %) nanoparticles dispersed in cyclohexane and BPN@NaYF4:Yb,Er (18.2 mol %) in water.
Figure 7. Room-temperature upconversion emission spectra of the oleic acid capped NaYF4:Yb,Er (18.2 mol %) nanoparticles dispersed in cyclohexane and BPN@NaYF4:Yb,Er (18.2 mol %) in water.
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Wang, D.; Qin, J.; Zhang, C.; Li, Y. Facile Synthesis of Black Phosphorus Nanosheet@NaReF4 Nanocomposites for Potential Bioimaging. Nanomaterials 2022, 12, 3383. https://doi.org/10.3390/nano12193383

AMA Style

Wang D, Qin J, Zhang C, Li Y. Facile Synthesis of Black Phosphorus Nanosheet@NaReF4 Nanocomposites for Potential Bioimaging. Nanomaterials. 2022; 12(19):3383. https://doi.org/10.3390/nano12193383

Chicago/Turabian Style

Wang, Dongya, Jingcan Qin, Chuan Zhang, and Yuehua Li. 2022. "Facile Synthesis of Black Phosphorus Nanosheet@NaReF4 Nanocomposites for Potential Bioimaging" Nanomaterials 12, no. 19: 3383. https://doi.org/10.3390/nano12193383

APA Style

Wang, D., Qin, J., Zhang, C., & Li, Y. (2022). Facile Synthesis of Black Phosphorus Nanosheet@NaReF4 Nanocomposites for Potential Bioimaging. Nanomaterials, 12(19), 3383. https://doi.org/10.3390/nano12193383

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