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Melanin-intercalated layered double hydroxide LDH/MNP as a stable photothermal agent

BMC Chemistry volume 18, Article number: 198 (2024) Cite this article

Abstract

Melanin nanoparticles (MNPs) are a type of electronegative compound that can be used as photothermal agent for cancer treatment. Nevertheless, the agglomeration of MNP, which is one of the limitations in practice, contributes to the instability of MNP. Pristine layered double hydroxide (LDH), as a kind of positive inorganic material when there exist no other cargo between its layers, can accommodate electronegative molecules between its layers to endow them with stable properties. Hence, in this study, electronegative MNP was intercalated into LDH lamellas via ion-exchange method to obtain the stable original photothermal agent LDH/MNP, solving the tough problem of MNP’s agglomeration. The surface morphology, X-ray diffraction and fourier transform infrared spectra affirmed the successful intercalation of MNP between LDH lamellas. The Z-average particle sizes of LDH/MNP on day 0, 7 and 14 were measured as 221.8 nm, 227.6 nm and 230.5 nm without obvious fluctuation, while the particle sizes of MNP went through dramatic enlargement from 105.8 nm (day 0) to 856.1 nm (day 7), indicating the better stability of LDH/MNP than MNP. The typical polymer dispersity index (PDI) values on day 0, 7 and 14 verified the better stability of LDH/MNP, too. Photothermal properties of LDH/MNP were assessed and the results ensured the representative photothermal properties of LDH/MNP. The fine cytocompatibility of LDH/MNP was verified via cytotoxicity test. Results confirmed that the agglomeration of MNP disappeared after its intercalation into LDH and LDH/MNP possessed fine stability as well as typical photothermal property. The intercalation of MNP into LDH gave the photothermal agent MNP a promising way for its better stability and long-term availability in photothermal treatment.

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Introduction

Cancer therapy still remains a medical challenge worthy of in-depth research at present. The current treatments for cancer consist of surgical resection, chemotherapy [1, 2], immunotherapy [3,4,5] and photothermal therapy [6,7,8]. Especially, photothermal agents were routinely utilized in photothermal therapy (PTT) with excellent photothermal conversion properties to convert light energy into heat energy under the irradiation of external light source efficiently in order to achieve cancer cell ablation. For example, the inorganic metal nano-material Au–Ag alloy exhibited a significant integrated high-quality photothermal feature with high photothermal conversion efficiency (80.4%) in the near-infrared region [9], the carbon-based nanoparticle such as graphene [10], graphite [11] and carbon nanotubes (CNTs) [12] were also widely used because of their low cost and abundance. Furthermore, the organic compound indocyanine green (ICG) [13] with a large π-conjugated system for absorbing NIR light could efficiently converting the light into thermal energy, too. With the advantages of low-grade invasion, easy to implement and selective local treatments, PTT tend to be an effective method for cancer treatments [14,15,16].

Melanin nanoparticles (MNP, C18H10N2O4) are a kind of endogenous pigment that can be widely found in organisms and possess fine biocompatibility. Besides, MNP can efficiently convert light energy into heat energy under near-infrared light source to achieve photothermal therapy [17,18,19,20]. Therefore, MNP, as a common photothermal agent, is widely used in the study of tumor photothermal treatments. However, the agglomeration of MNP is of common occurrence duing to the hydrophobicity caused by its special molecular structure [21]. The instability of MNP gives the limitation to the application of MNP in photothermal therapy which may reduce the photothermal treatment efficiency and decrease the retention time in vivo, etc. Herein, suitable modification for MNP aiming to decrease its agglomeration and improve the stability of MNP is urgently needed.

Moreover, inorganic compounds are also the focus on research [22, 23]. Layered double hydroxides (LDHs) are inorganic materials composed of stacked positively charged layers with intercalated anions, ensuring electrical neutrality. The structural formula of LDH can be expressed as [MIIn MIII(OH)2+2n]+(Am−)1/m×H2O (n = 2–4) [24]. LDH possesses a regular hexagonal structure with numerous hydrophilic -OH groups on its host layers. The interlayer of LDH can accommodate electronegative guests, making it applicable in various fields such as biological materials [25,26,27], wastewater purification [28,29,30,31,32], and electrochemistry [33,34,35,36]. In this research, via hydrothermal method, Mg-Al LDH was synthesized in which the center of the structure was Mg2+, the six vertices were OH−, and the unit layer was formed by the shared edge of the adjacent MgO6 octahedron. Mg2+ located on the layer was replaced by Al3+ isomorphism in a certain range, which made the host layer with permanent positive charge. Then, the electronegative MNP was intercalated between the positive-charged lamellas of LDH by ion exchange method (Scheme 1). Herein, LDH was employed as the carrier of MNP, which was the solution for the agglomeration of MNP. It was the first time that LDH/MNP been investigated and there was no other photothermal agents ever been intercalated between LDH layers for the purpose of photothermal therapy. The intercalation of MNP was confirmed by morphology, X-ray diffraction and fourier transform infrared spectrum testing. The particle size distribution and PDI values of MNP and LDH/MNP at different times of day 0, day7 and day 14 were evaluated. The zeta potentials of LDH, MNP and LDH/MNP were tested, too. Typical photothermal properties of LDH/MNP were studied via certain photothermal experiments and the biocompatibility of LDH/MNP was assessed by cytotoxicity assay.

Scheme 1
figure 1

The synthesis route of LDH/MNP

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Experimental

Materials

MgCl2·6H2O, AlCl3·6H2O and NaOH were purchased from Aladdin Corporation, China. Melanin was obtained from Sigma-Aldrich, St. Louis, MO, USA.

Preparation of Mg-Al LDH

The synthesis of Mg-Al LDH was conducted by hydrothermal method reported before [32]. Briefly, 10 mL MgCl2·6H2O (3.0 mmol) and 10 mL AlCl3·6H2O (1.0 mmol) solutions were mixed uniformly. Afterwards, 40 mL NaOH (0.15 mol/L) was added dropwise under nitrogen atmosphere. The mixture was kept stirring for 20 min. Next, the above mixture was centrifuged and washed using deionized water for three times. Finally, the precipitate was removed into the hydrothermal reactor for reaction at 100 ℃ for 16 h. The Mg-Al LDH suspension was obtained and lyophilized for 48 h.

Preparation of melanin nanoparticle (MNP)

MNP was prepared according to the previous reported method [37]. Generally, 0.1 mol/L NaOH was added into a brown bottle containing 20 mg of melanin and ultrasonic shock was conducted for 30 min until the mixture was completely dissolved. Then, the mixture was placed under the environment of 0 ℃ and 0.1 mol/L HCl was added dropwise until the mixture pH reached 7. Ultra-filtration centrifuge tube was used to centrifuge the mixture to about 1 mL. Subsequently, melanin nanoparticles were obtained by freeze-drying for 48 h.

Preparation of LDH/MNP

The intercalation of MNP between LDH layers was realized by ion exchange method. In short, 20 mg of melanin was uniformly dispersed in 20 mL of deionized water, and the above dispersions was added dropwise into 20 mL of 1 mg/mL LDH solution at 60 ºC under nitrogen atmosphere. The mixture was kept stirring for 24 h. Afterwards, the product was freeze-dried for 48 h.

Characterization studies

Surface morphology analysis

The surface morphologies of LDH and LDH/MNP were observed by transmission electron microscopy JEM100C XII (Electronic Corporation, Japan). Briefly, the dispersions of LDH and LDH/MNP (1 mg/mL) were dropwise added to the copper mesh, after drying at 25 ºC for 48 h, the copper mesh was removed under transmission electron microscopy to observe the surface morphology.

X-ray diffraction (XRD) analysis

The crystal characteristics of LDH and LDH/MNP were observed by DX-27mini X-ray diffract meter (Dandong Haoyuan Instrument, China) with Cu target (wavelength 0.154 nm). The powder sample of LDH and LDH/MNP was evenly spread on the sample plate and the scanning was set at pace of 4 º/min, the scanning range was 5 º to 80 º (2θ) and the ambient temperature was 25 ºC.

Fourier transform infrared spectroscopy (FT-IR) analysis

The FT-IR test was performed with the TENSOR II infrared spectrometer (Bruker Corporation, German). Briefly, the KBr was mixed with the powder sample of LDH and LDH/MNP (mass ratio 100:1) and pressed after grinding respectively. The test range was set from 500 cm− 1 to 4000 cm− 1. The analysis was performed at room temperature of 25 ºC.

Particle size and zeta potential measurement

The particle size and zeta potential of MNP and LDH/MNP were measured using Zetasizer Nano-ZS90 (Malvern Instrument, Inc., UK). The wavelength was 677 nm and the constant Angle was 90º. The measurements were repeated three times at room temperature and the average values were adopted. The concentration of MNP and LDH/MNP suspensions were 1 mg/mL. The zeta potentials of LDH, MNP and LDH/MNP were tested under the same experiment condition too.

Photothermal characterization of LDH/MNP in vitro

The photothermal conversion properties and photothermal stability of LDH/MNP was evaluated as follows. The LDH/MNP dispersions with different concentrations of 300/150/100/50/25/0 µg/mL and LDH dispersions of 100 µg/mL were put into containers and irradiated by laser (wavelength 808 nm, power density 1 W·cm− 2) for 5 min, respectively. The real-time temperatures of the solutions were recorded every 15 s using an infrared thermal imager. After then, the LDH/MNP dispersions of 100 µg/mL were irradiated with different laser power densities (0.5/0.75/1.0/1.25 W·cm− 2), and the real-time temperatures of the solution were recorded at an interval of 15 s using an infrared thermal imager, too. The LDH/MNP dispersions with a concentration of 100 µg/mL were irradiated with laser (wavelength 808 nm, power density 1 W·cm− 2) for 5 min, and cooled naturally for 5 min then. The above 10 min was set as one cycle and the LDH/MNP dispersions were irradiated continuously for 6 cycles. The real-time temperature of the solution was recorded at an interval of 15 s to obtain the photothermal stability of LDH/MNP.

Cytotoxicity of LDH and LDH/MNP

The in vitro cytocompatibility of LDH and LDH/MNP was determined by Cell Counting Kit-8 (CCK-8) (GlpBio Corporation, USA). Normal cells H9C2 were inoculated into a 96-well plate and cultured in a cell incubator with 5% CO2 at 37 ºC for 24 h. Afterwards, 10 µL of LDH and LDH/MNP dispersions with different concentrations of 1000 µg/mL, 500 µg/mL, 250 µg/mL and 100 ug/mL were added respectively and incubated for 24 h, afterwards 10 µL CCK-8 solutions were added to the 96-well plate. After incubation for 4 h, cell absorption was detected at 450 nm by microplate reader.

Results and discussion

Surface morphology of LDH and LDH/MNP

The transmission electron microscopy micrographs of LDH and LDH/MNP were showed in Fig. 1. It could be observed via Fig. 1(a) that LDH presented regular hexagon structure with fine dispersion and the average particle size of LDH was around 100 nm. In Fig. 1(b), LDH/MNP nanoparticles also appeared a relatively fine particle distribution with the average particle size of 200 nm. In addition, it could be obviously observed that the color of most LDH/MNP was darker than that of LDH which was caused by the intercalation of the black-colored MNP. Besides, it could be seen from Fig. 1(b) that the edges of LDH/MNP nanoparticles became slightly smooth compared with LDH.

Fig. 1
figure 1

TEM micrographs of LDH (a) and LDH/MNP (b)

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X-ray diffraction (XRD) analysis of LDH and LDH/MNP

The X-ray diffraction patterns of LDH (a) and LDH/MNP (b) in Fig. 2 were presented to clarify the crystallization and the intercalation of MNP. The diffraction peaks of LDH at 11.48° (003), 23.18° (006) and 35.18° (012) were the typical characteristic peaks of LDH [38, 39]. After the intercalation of MNP between LDH layers, the typical peak of (003), (006) and (012) shifted left to the angle of 10.04°, 20.06° and 34.10°. The peak at low angle regions of (003) reflection related to the basal spacing between the layers and the interlayer spacing d003 of LDH and LDH/MNP could be calculated from the Bragg’s Law (\(\:2\text{d}\text{sin}{\uptheta\:}=\text{n}{\uplambda\:};\:\text{n}=1,\:{\uplambda\:}=0.154\:\text{n}\text{m}\)) as 0.7699 nm and 0.8799 nm respectively. The results ensured the increasing of the interlayer spacing after the intercalation of MNP into the pristine LDH and this was because the melanin possessed the bigger molecule size than the Cl− and CO32− in the pristine LDH. The increasing spacing of LDH/MNP showed the successful intercalation of MNP between LDH interlamination.

Besides, the relative intensity of characteristic diffraction peaks in Fig. 2a performed stronger than that in Fig. 2b. Specifically, the stronger XRD intensity of pristine LDH was due to its regular hexagonal structure without any impurities. However, when MNP intercalated, the space between the LDH layers became wider and MNP could be seen as the impurity for pristine LDH, leading to the weaker relative intensity of LDH/MNP. The relative intensities of LDH and LDH/MNP were consistent with the TEM micrographs in Fig. 1 and the weakened crystalline form of LDH/MNP corresponded to the roundish shape of LDH/MNP.

Fig. 2
figure 2

XRD patterns of LDH and LDH/MNP. Scan angle from 5° to 80° (2θ), leg speed 4°/min

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Fourier transform infrared spectroscopy (FT-IR) analysis of LDH, MNP and LDH/MNP

Fourier Transform Infrared (FT-IR) spectra of LDH, MNP and LDH/MNP were shown in Fig. 3 to further confirm the existence of MNP in LDH/MNP. With regard to LDH in Fig. 3(a), the strong broad absorption band at 3400 cm− 1 to 3600 cm− 1 belonged to the stretching vibration of the -OH groups on LDH laminates [40, 41]. The narrow and strong absorption peaks at 1380 cm− 1 could be ascribed to the asymmetric stretch vibration caused by CO32− groups existed between LDH layers [42, 43]. The wide absorption band at 620 cm− 1 to 890 cm− 1 referred to the metal-oxygen-metal and oxygen-metal-oxygen stretching from LDH laminates [44, 45]. For the FT-IR spectra of MNP in Fig. 3(b), there was a broad absorption band at 3400 cm− 1 to 3600 cm− 1, generated by the stretching vibration of O-H and the stretching vibration of N-H from the indole structure of melanin [45]. The absorption peak observed at 1630 cm− 1 was derived from the characteristic absorption peak of aromatic groups C = O and C = C from MNP [45], which was a characteristic absorption peak of melanin. The band around 900 cm− 1 was attributed to the C-H bending vibration among the ring structure of the benzene in MNP. In the FT-IR spectra of LDH/MNP, the characteristic peak belonged to MNP at 1630 cm− 1 was observed, indicating the existence of MNP. The characteristic absorption peaks of LDH at 3400 cm− 1 to 3600 cm− 1 and 620 cm− 1 to 890 cm− 1 were observed, too, indicating the existence of LDH. In addition, the wider and stronger absorption band in the FTIR spectra of LDH/MNP in the range of 3400–3600 cm− 1 may caused by the accumulation of both stretching vibration of O-H and stretching vibration of N-H wthin LDH and MNP. No absorption peak at 1380 cm− 1 was observed which illustrated that the CO32− groups between the pristine LDH layers were replaced by MNP via ion exchange [47, 48]. Moreover, the band around 900 cm− 1 in Fig. 3(b) had almost disappeared in Fig. 3(c). This was because that the bending vibration of C-H was extremely susceptible to external influences and when the MNP intercalated between the LDH layers, the bending vibration of C-H was weakend by the interaction between MNP and the laminates of LDH. As a consequence, the disappearing of the band at 900 cm− 1 could laterally prove the intercalation of the MNP between LDH layers. The FT-IR results confirmed the existence of MNP and LDH in the system of LDH/MNP. Combined with the XRD results in Fig. 2, the intercalation of MNP between LDH layers could be verified in LDH/MNP.

Fig. 3
figure 3

FT-IR spectra of LDH (a), MNP (b), LDH/MNP (c) and the summarized FT-IR spectra of LDH, MNP and LDH/MNP (d). Region from 4000 cm− 1 to 500 cm− 1. The test of the powders was carried out by using KBr disks and test temperature was 25 ºC

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Particle size of MNP and LDH/MNP on day 0, 7 and 14

The stability of MNP and LDH/MNP was evaluated via the particle size distributions and PDI values. The particle sizes of MNP and LDH/MNP dispersed in PBS on day 0, 7 and 14 were showed respectively in Fig. 4(a) and Fig. 4(b). As shown in Fig. 4(a), the particle size distribution of MNP performed huge differentiation on day 0, 7 and 14 while the particle size distribution of LDH/MNP in Fig. 4(b) exhibited unapparent change, illustrating the fine stability of LDH/MNP. In Fig. 4(c), the average particle sizes of MNP were 105.8 nm, 856.1 nm and 2673 nm on day 0, 7 and 14 respectively. The abnormal particle enlargement of MNP was observed on day 7 and the larger particle size was not conducive to realize endocytosis. Therefore, according to the particle size on day 7, which was 856.1 nm, the MNP cannot be employed as a suitable photothermal agent anymore. However, the average particle size of LDH/MNP was 221.8 nm, 227.6 nm and 230.5 nm on day 0, 7 and 14 respectively. The particle size of LDH/MNP was consistent with the TEM micrograph results of LDH/MNP in Fig. 1(b). The stable unchanged particle sizes on different days indicated that the LDH/MNP held fine stability and LDH/MNP was free of agglomeration. Polymer dispersity index (PDI) commonly indicated the molecular weight distribution and it was inversely proportional to molecular weight distribution. In Fig. 4(d), the PDI values of MNP on day 0, 7 and 14 were tested as 0.448, 0.576 and 1 respectively. The results in Fig. 4(d) revealed that the distribution of MNP had become uneven gradually as time passed. However, for LDH/MNP, the PDI values on day 0, 7 and 14 were 0.054, 0.107 and 0.173, performing no major changes basically. The stable PDI values manifested the fine particle distribution of LDH/MNP. The gradually increasing particle size and suboptimal distribution of MNP from day 0 to day 14 were caused by the hydrophobicity of MNP. Concretely, there were conjugated systems in the major molecular structure of MNP which was nonpolar (Scheme 1). This nonpolar structure rendered MNP the hydrophobicity property in aquatic environment. As a result, the separated hydrophobic groups tended to aggregate together, resulting in the poorer particle distribution of MNP over time. However, when the electronegative MNP intercalated between the interlamellar spaces of LDH by swapping out the original less electronegative Cl− and CO32− via ion exchange method, LDH/MNP became stable in aquatic environment because of the huge number of hydroxyl groups on the surface of LDH layers while at the same time the hydrophobic groups of MNP were wrapped in LDH. Hence, after the intercalation of MNP, LDH/MNP possessed better dispersion and stability than MNP and the particle size of LDH/MNP maintained ~ 200 nm within 14 days.

Fig. 4
figure 4

Size distributions of MNP (a) and LDH/MNP (b) dispersed in PBS on day 0, 7 and 14 with the concentration of 1 mg/mL; (c) Z-averange particle sizes of MNP and LDH/MNP dispersed in PBS on day 0, 7 and 14 with the concentration of 1 mg/mL; (d) Polymer dispersity index (PDI) values of MNP and LDH/MNP dispersed in PBS on day 0, 7 and 14 with the concentration of 1 mg/mL

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Zeta potential of LDH, MNP and LDH/MNP

As the testing results in Fig. 5, the average zeta potentials of LDH and MNP were + 35.3 mv and − 30.0 mv respectively, declaring that MNP could intercalate into the LDH layers by ion exchange way. Moreover, after the intercalation of MNP into LDH layers, the average zeta potential of synthesized LDH/MNP had decreased to 0.06 mv, indicating the electro neutralization between MNP and LDH. In detail, the negatively charged MNP replaced the relatively weaker electronegative groups of Cl− and CO32− between LDH layers by means of ion exchange, leading to the zeta potential decrease of MNP/LDH.

Fig. 5
figure 5

Zeta potential of LDH, MNP and LDH/MNP with the concentration of 1 mg/mL

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Photothermal characterization of LDH/MNP in vitro

The photothermal performance analysis of LDH/MNP in vitro were showed in Fig. 6. Figure 6(a) exhibited the temperature-time curve of LDH dispersions with concentration of 100 ug/mL irradiated by laser for 5 min (wavelength 808 nm and laser power density of 1 W·cm− 2), illustrating that the temperature of LDH stayed still as room temperature and did not significantly increased with the increasing of irradiated time. Hence, it is confirmed that LDH held no photothermal property. The temperature-time curves of LDH/MNP dispersions with different concentrations (0/25/50/100/150/300 µg/mL) under 5 min of laser irradiation (wavelength 808 nm and laser power density of 1 W·cm− 2) was shown in Fig. 6(b). The results proved that at the same time point, the temperature became higher as the concentration of the LDH/MNP increased and the photothermal property of LDH/MNP was positively correlated with the concentration of LDH/MNP. Besides, when the concentration of LDH/MNP reached 300 µg/mL, the temperature of the dispersions reached 58.5 ℃ after 5 min of irradiation, which was enough to achieve killing effect on cancer cells [49]. Combining the results in Fig. 1(a), it could be ensured that the photothermal property of LDH/MNP was generated by the interlamellar photothermal agent MNP.

After irradiation for 5 min under different laser power density of 0.5/0.75/1.0/1.25 W·cm− 2 (wavelength 808 nm), the temperature-time curves of LDH/MNP (100 µg/mL) were summarized in Fig. 6(c). The temperature of MNP/LDH raised as the laser power density became higher. The experimental results proved that the photothermal characteristics of LDH/MNP were positively correlated with the laser power density. When the temperature raised enough to kill the cancer cell (usually 42–45 °C [49]), the laser power density could be chosen as the optimal one. In Fig. 6(c), when the laser power density was 0.75 W·cm− 2, the temperature reached 44 °C after 5 min of irritation and the optimal laser power density was 0.75 W·cm− 2.

Fig. 6
figure 6

(a) Temperature variation curve of LDH dispersions (100 µg/mL) (wavelength 808 nm, power density 1 W·cm− 2); (b) Temperature variation curves of LDH/MNP dispersions under different concentrations (300/150/100/50/25/0 µg/mL) (wavelength 808 nm, power density 1 W·cm− 2); (c) Temperature variation curves of LDH/MNP dispersions (100 µg/mL) at 808 nm wavelength and different power densities (0.5/0.75/1.0/1.25 W·cm− 2); (d) Photothermal stability of LDH/MNP dispersions (100 µg/mL) after 6 cycles of laser irradiation (wavelength 808 nm, power density 1 W·cm− 2)

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Figure 6(d) displayed the photothermal stability of LDH/MNP. Generally, the LDH/MNP dispersions of 100 µg/mL were irradiated for 5 min and cooled naturally for 5 min under the conditions of wavelength 808 nm and power density of 1 W·cm− 2. After 6 cycles of uninterrupted operation, it could be summarized that the temperature of LDH/MNP remained the same value in every single cycle, indicating the stable photothermal property of LDH/MNP. According to the series of photothermal property experiments above, LDH/MNP was proved with typical photothermal property and stability, and could be used as a novel photothermal agent in tumor photothermal treatments.

Cytotoxicity of LDH and LDH/MNP

The biocompatibilities of LDH and LDH/MNP were determined via CCK-8 and the results were shown in Fig. 7. With the concentration of LDH increasing from 10 µg/mL to 1000 µg/mL, the average survival rate of LDH against normal H9C2 cells remained above 95%. This was due to the fine biocompatibility of LDH. Besides, as the concentration of LDH/MNP increased from 10 µg/mL to 1000 µg/mL, the average survival rate of LDH/MNP against normal H9C2 cells increased up to more than 100%. This phenomenon could be explained as that MNP was an amino acid derivative and could provide nutrients during cell growth in order to promote cell proliferation. Hence, it could be concluded that both LDH and LDH/MNP possessed fine biocompatibility and free of toxicity.

Fig. 7
figure 7

Cell viability under different concentrations of LDH, LDH/MNP, incubated with normal cell H9C2

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Conclusion

In this study, LDH was prepared via hydrothermal method, and the photothermal agent MNP was successfully intercalated between LDH layers via ion exchange method to acquire a novel stable photothermal system LDH/MNP. In the system of LDH/MNP, LDH acted as a functional carrier to load the photothermal agent MNP and enhance the stability, while MNP performed as the photothermal factor to endow the system with typical photothermal properties. Morphology characterization of TEM, XRD and FT-IR results confirmed the successful intercalation of MNP between LDH layers. The nanoparticle size distribution and PDI values further verified the stability and better particle distribution of LDH/MNP than MNP. The photothermal performance results showed that LDH/MNP possessed stable and typical photothermal characteristics. Cytotoxicity test proved that LDH/MNP was of fine cytocompatibility and free of toxicity. Therefore, LDH/MNP could be employed as a photothermal agent possessing better stability, favorable dispersions, typical photothermal properties and fine cell compatibility. LDH/MNP could replace MNP in field of photothermal therapy with stable property. The present research had laid a foundation for further studies on the efficient photothermal therapy of LDH/MNP in vivo.

Statistical analysis

All experiments were repeated at least three times for statistical analysis and the data were presented as means ± standard deviation. One-way ANOVA with Bonferroni’s correction was used to compare differences between at least three groups. In all pictures, no significance represented as ns, P* < 0.05 represented one star, P** < 0.01 represented two stars, P*** < 0.001 represented three stars, P**** < 0.0001 represented four stars.

Data availability

No datasets were generated or analysed during the current study.

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Acknowledgements

We gratefully acknowledge the financial support provided by the Basic Research Program of Shanxi Province (NO: 202103021223237). Furthermore, the authors extend appreciation to Zujian Feng, a PhD from institute of Biomedical Engineering, Chinese Academy of Medical Science & Peking Union Medical College, for his valuable and thoughtful suggestions on the measurements and relevant problems of LDH/MNP.

Funding

This work has been financially supported by the Basic Research Program of Shanxi Province (NO: 202103021223237), National Natural Science Foundation of China (No: 82120108016, 82071987), Four Batches of Scientific Research Projects of Shanxi Provincial Health Commission (NO: 2020TD11, NO: 2020SYS15, NO: 2020XM10, NO: 2020XM49), Key Laboratory of Nano-imaging and Drug-loaded Preparation of Shanxi Province (NO: 202104010910010), Applied Basic Research Program of Shanxi Province (20210302124174).

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Authors and Affiliations

  1. Department of Polymer Science and Engineering, Key Laboratory of Systems Bioengineering (Ministry of Education), School of Chemical Engineering and Technology, Tianjin University, Tianjin, 300072, China

    Xue Li & Anjie Dong

  2. Department of Chemistry, School of Basic Medicine, Shanxi Medical University, Shanxi, 030001, China

    Xue Li

  3. The First Clinical Medical College of Shanxi Medical University, Shanxi, 030001, China

    Yixuan Wang, Xinkai Geng & Jinghua Sun

  4. Shanxi Bethune Hospital, Third Hospital of Shanxi Medical University, Shanxi Academy of Medical Sciences, Tongji Shanxi Hospital, Taiyuan, 030032, China

    Yulong Liu

  5. The Radiology Department of Shanxi Provincial People’s Hospital, Fifth Hospital of Shanxi Medical University, Shanxi, 030001, China

    Ruiping Zhang

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  1. Xue Li
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Contributions

X.L.: research idea conceptualization; supervised the study; data analysis; manuscript editing and funding acquisition. Y.W. and X.G.: investigation and validation. J.S. and Y.L.: responsible for formal analysis and supervision. A.D. and R.Z.: contributed to resources, writing-review & editing. All authors read and approved the final manuscript.

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Correspondence to Ruiping Zhang.

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The authors declare no competing interests.

Abbreviations

LDH referred to layered double hydroxide and MNP referred to melanin nanoparticle in this article.

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Li, X., Wang, Y., Geng, X. et al. Melanin-intercalated layered double hydroxide LDH/MNP as a stable photothermal agent. BMC Chemistry 18, 198 (2024). https://doi.org/10.1186/s13065-024-01312-1

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BMC Chemistry

ISSN: 2661-801X

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