The effect of human serum albumin on ZIF-8 used in drug delivery: structural, linear and nonlinear optical properties

Zeolitic Imidazolate Frameworks (ZIF-8) are extremely useful substances that have been utilized in a variety of commercial and medical applications due to their interesting properties. Understanding the properties of ZIF-8 doped human serum albumin with different concentrations can lead to the development of new applications in areas such as sensing, drug delivery, and catalysis. Here, we investigated the extent of interaction between ZIF-8 and HSA by examining the structural, linear, and nonlinear optical properties of ZIF-8@xHSA where x is 2.5, 5, 10 wt%. Scanning electron microscope and Transmission electron microscope images revealed that both ZIF-8 and ZIF-8@10 wt% HSA had regular cubic shapes, with average particle sizes of 38 nm and 49 nm, respectively. The X-ray diffraction shows a crystalline shape for ZIF-8 and ZIF-8@10 wt% HAS. The energy gap of our composite was calculated using the Wemple-Didomenico model, and it exhibited strong concentration-dependent behavior. The Z-scanner was used to investigate the nonlinear properties, which indicated that ZIF-8@10 wt%HSA had a high nonlinear response. As the understanding of this interaction deepens, it is expected that innovative applications in biomedical and pharmaceutical fields will emerge, highlighting the vital connection between HSA and ZIF-8.


Introduction
In the last ten years, there has been a surge in interest in metal-organic frameworks (MOFs), a distinctive type of porous hybrid organic-inorganic materials.Recently, MOFs have been extensively studied in chemical engineering, materials science, and drug delivery [1,2].These structures are gaining attention as potential platforms for biomedical applications due to their unique physical and chemical features [3].They have been subject to thorough investigation because of their structural features, high porosity, adjustable frameworks, a wide variety of pore geometries, and ultrahigh surface area for drug delivery [4].MOFs can be designed to release drugs in a controlled manner, improving their efficacy and reducing side effects.However, there are potential side effects of using MOFs in drug delivery, particularly on proteins.MOFs can interact with proteins in various ways, including binding to active sites or altering protein conformation.This can lead to changes in protein function and potential toxicity.Therefore, it is important to carefully consider the use of MOFs in drug delivery and to thoroughly evaluate their impact on protein function.By understanding the potential side effects of MOFs, researchers can design more effective and safe drug delivery systems that maximize therapeutic benefits while minimizing negative effects on proteins.
Zeolitic Imidazolate Frameworks (ZIF-8) is a type of MOF that has four rings of imidazole links (Zn2 + ions and 2-methylimidazole) [5].ZIF is a suitable platform for controlled drug release because of its high porosity and non-toxicity with high chemical stability [6].ZIF-8 is stable in aqueous sodium hydroxide solutions and water, but it degrades quickly in acidic solutions, indicating its pH sensitivity, which could be useful in creating ZIF-based drug delivery systems [7].The drug's efficacy may improve with more frequent use, but this may result in more adverse effects.Wang, Q, et al. have reported on the uses of Zif-8 and its integrated cycle in anticancer therapeutics, drug delivery, and cancer diagnostics and treatment [8].Recent research has demonstrated that Zif-8 can be used to encapsulate genes and their expression and protect the proteins from solvent effects and degradation [9].The location of the protein within the ZIF-8 framework might depend on the specific experimental conditions, such as the ratio of components, and the synthesis method.In our case, HSA interacts with the external surface of the ZIF-8 particles [10].Surface adsorption might occur if the protein cannot fit or penetrate the pore structure, but can still establish interactions with the outer surface of the MOF > Furthermore, it has been developed using the in vitro hemodialysis release method under aquarium conditions at different pH values [11].The applications of (ZIF-8) in bone tissue engineering have also been studied [12].Human blood contains approximately 7% protein components such as albumin, globulins, fibrinogen, and prothrombin, etc. [13].Human serum albumin is produced by the liver, and the daily rate of albumin synthesis within the liver is about 0.2 g kg body weight [14].The level of albumin in healthy individuals ranges from 33 to 52 g/L.The production of a mesoporous ZIF-8 under physiological conditions has been done by Saha and Mishra [15].Then they studied the antibacterial and anti-inflammatory properties.ZIF-8 was synthesized using common traditional synthesis methods for crystal formation and engineering.ZIF-8 was synthesized via biomimetic mineralization methods [16].An effective protein delivery system based on ZIF-8 has been developed to increase the cutaneous bioavailability of DPSC lysate for anti-photoaging treatment as in [17].Liang et al. study the design of ZIF-based biocomposites for application to areas such as biocatalysis, where control of structural properties such as pore size is highly desired [18].The defects within ZIF-8 can influence the optical properties that cause light to scatter or redirect differently.Furthermore, defects can introduce transition states that can result in modifications of the photonic properties of the material, such as its fluorescence or phosphorescence.So defects can affect the refractive index, absorption, and scattering properties.
Therefore, studying the optical and structural properties of ZIF@HSA with various concentrations can offer valuable insights into the material's properties and performance, leading to the development of new applications and enhanced production processes.The morphological characteristics of ZIF-8@HSA with different concentrations are investigated using SEM and TEM.The UV-spectrophotometer and Z-scanner are used to measure the linear and nonlinear optical properties of ZIF-8@HSA.The structural and optical features of ZIF-8@HSA presented in this work could provide helpful information for synthesizing metal oxide framework-based HSA for specific medical applications.

Experimental techniques
Zeolitic Imidazolate Frameworks (ZIF-8) and human serum albumin (HSA) powders were procured from Sigma Aldrich.HSA with different concentrations (2.5, 5, 10 wt%) has been prepared by using distilled water.The solution was sonicated followed by stirring for 6 h to obtain a clear solution.Three different concentrations of HSA (2.5, 5, and 10 wt%) have been mixed individually with ZIF-8 by using the shaker for 15 min until the solution is completely clear.UV-Vis spectrophotometer is used to measure the optical absorption of HSA with different concentrations and ZIF-8@HSA in the wavelength range (200-1200 nm).Finally, the nonlinear optical properties of HSA with different concentrations and ZIF-8@HSA have been analyzed using the Z-scanner setup (Scheme 1).

SEM
Scanning Electron Microscopy (SEM) is an important tool for studying the surface of MOFs (Metal-Organic Frameworks) because it allows researchers to observe the morphology and microstructure of the MOF surface at a high resolution.Figure 1a, b shows the SEM images of ZIF-8 and ZIF-8@10 wt% HSA.The SEM micrograph of ZIF-8 reveals the characteristic cubic structure for ZIF-8 with an average particle size of about 38 nm.The cubic grains can reveal the presence of defects such as voids, cracks, and dislocations.These defects can act to change the mechanical, optical, and electrical properties of the material.The average size of ZIF-8@(10 wt% HSA has increased to 46 nm after the formation of the composite structure.This can be interpreted by the presence of HSA can promote the aggregation of the ZIF-8 particles by adsorption, reducing their electrostatic repulsion and stabilizing the interactions between particles.This could lead to the formation of larger agglomerates and contribute to the increase in average particle sizeThe increase in grain size could lead to an increase in light absorption.This is because larger grains have a larger surface area and can absorb more light.The SEM micrograph of ZIF-8@HSA indicated that the HSA is homogeneously distributed in the ZIF-8 matrix.

TEM
Transmission electron microscopy (TEM) is an important analytical tool to investigate the surface morphological features of a material in depth.TEM images offer important information related to particle size and particle distribution on the surface of the material [31].The TEM images of ZIF-8 and ZIF-8@(10 wt%) HSA at a scale of 100 nm were depicted in Fig. 2. The TEM images demonstrate the uniform distribution of spherical particles with an average size of 40-60 nm.The TEM image of ZIF-8@(10 wt%) HSA shows uniform distribution of HSA in the ZIF-8 matrix, which is in agreement with the morphological features obtained in SEM images.The TEM images also reveal the high crystallinity uniform shape and high porous nanostructure for ZIF-8@HSA.The TEM images reveal the high crystallinty in which the grains show a uniform shape suggesting consistency in the particle size and morphology.Furthermore, the gaps between the grains indicate the high porous nanostructure for ZIF-8@HAS.The highly porous nature of the nanostructure is also visible, which is important for applications like gas separation, drug delivery, and catalysis.These images can help researchers study the properties and potential applications of such hybrid materials.

XRD
The XRD is potentially used to study the crystalline shape of fabricated material.Figure 3 shows the XRD of HSA, ZIF-8, and ZIF-8@HSA.As we can see from Fig. HSA shows an amorphous behavior because most of the flexible proteins have unstable and disordered crystals suitable for XRD analysis [19].The XRD of ZIF-8 and ZIf-8@10 wt% HSA shows similar high peak intensity at 7.4°, 10.4 0 , 12.7°, 18.12 o , and 26.72° that are related to (110), (002), (022), (113), and (224).The crystalline shape of ZIF-8@10 wt% HAS will act to increase its light absorption."

Linear optical properties
UV-visible spectroscopy is used to analyze the optical properties of the materials.It can be used to determine concentrations, identify unknown compounds, and provide information about the physical and electronic structures of organic and inorganic compounds.Figure 4 shows the variation of optical absorption as a function of wavelength for three different concentrations of HSB in distilled water.The intensity of absorption spectra shows dependence on the concentration of HSA and delivers a maximum at 310 nm for HSA with 7.5 wt%.It is interesting to notice that the absorption intensity shows a red shift with increasing concentrations of HSA.HSA.We can conclude from the UV-Vis spectra Fig. 2 TEM images of a ZIF-8 b ZIF-8@(wt%) HSA Nano powders Fig. 3 The XRD of HAS, ZIF-8, and ZIF-8@10 wt% HAS that the absorption of light within HSA increased by about 58% as the HSA concentration increased to 10 wt%.Tan increase in HSA concentration can lead to an increase in light absorption due to chromospheres within the protein.These chromospheres, such as tryptophan and tyrosine residues, can absorb light at specific wavelengths and contribute to the overall absorption spectrum of the HSA.
Figure 5 shows the relationship between optical absorption and concentration of HSA at 310 nm wavelength.From the graph, we notice that the optical absorption of ZIF-8 decreased at the wavelength 270 nm. Figure 6 depicts the relationship between the optical absorption of ZIF-8@HSA and wavelength.We note from the graph that the optical absorption of the mixed material increased with the increase of the HSA concentration.The increase in our composite porosity can lead to an increase in the surface area available for light absorption.This increased surface area can allow for more efficient absorption of light by the MOF material.
The electron transition and optical energy band gap values for ZIF-8@HSA were determined by using Bardeen's equation [20,21]: where B, E g , and r being constants related to energy level split, energy gap, and a number that represents the transition process.The type of band-to-band electrical transitions and the electron density profile of the valence and conduction bands is determined where r is a constant.The experimental data have been fitted using Eq. 1 for different values of r.The indirectly allowed transitions were determined to provide the best fit at r = 1/2.Figure 7 depicts the relationship between (hv) 0.5 and h.In Eq. 2, a slope-partitioned straight line represents the value of C. The values of Eg, at the straight-line intersection with the x-axis, were determined.The energy gap of ZIF-8@HSA and HSA, have been illustrated in Fig. 8.As we can see from Fig. that as HSA concentration increases the energy gap also increase.This may be related to the change in HUMO (highest occupied molecular orbital) and LUMO (lowest occupied molecular orbital) energy levels of the ZIF-8@HSA which leads to an increase in the energy gap.This decrease happens within the HUMO and LUMO because of the strong interaction of the two materials [6,22].Table 1 shows a comparison between the energy gap of our investigated composite with previously published E g values.
(1) ( h ) r = B(h − E g ) Fig. 4 The optical absorption variation with wavelength for different concentrations (2.5, 5, and 10) wt% for HSA Fig. 5 Maximum optical absorption of HSA with different concentrations at 310 nm Fig. 6 The optical absorption of ZIF-8 and ZIF-8@HSA with different concentrations

Nonlinear optical properties
The interaction of atomic oscillators in materials with highintensity light results in nonlinear optical phenomena.Communications, bioimaging, data storage, and other industries use organic compounds with high nonlinear characteristics.Figure 9 shows the variation of the normalized transmission of ZIF-8@HSA and the z-position of the z-scanner.The nonlinear refractive index could be calculated as follows [26,27]: where where ΔT is the broadening of the normalized transmission on the first peak, S is the laser beam aperture used in the Z-scanner [28,29].L o is the effective absorption length.While is called the nonlinear absorption and it is calculated using: (2) 7 (αhγ) 1/2 with a photon energy of ZIF-8@HSA with different concentrations Fig. 8 The energy gap of ZIF-8@HSA with different conc Fig. 9 The normalized transmission variation with the z-position for ZIF-8@HSA by using Z-scanner The results of the normalized transmission have been used utilized to calculate the nonlinear properties of the different concentrations of ZIF-8@HSA.All the nonlinear properties have been listed in Table 2.

Conclusion
The interaction of the metal-organic framework ZIF-8 as a promising MOF with different concentrations of HSA up to 10 wt% has been investigated.We utilized SEM and TEM to study the morphological features of ZIF-8@ HSA with different concentrations.The ZIF-8@HSA had a cubic shape that was regulated with an average size of about 40 nm.TEM images indicated that ZIF-8@(10 wt%) HAS exhibited high porosity.The researchers used a UVspectrophotometer and Z-scanner to measure the linear and nonlinear optical properties of ZIF@HSA.They found that ZIF-8@HSA had maximum absorption at a wavelength of about 310 nm and that the energy gap of the ZIF-8@HSA was 2.93 eV at a concentration of 10 wt%.The z-scanner results indicated that the ZIF-8@HSA displayed high values for optical nonlinearity.Due to these superior morphological and optical features, the researchers suggest that these ZIF-8@HSA composites could potentially be utilized in biomedical applications.

Scheme 1 .Fig. 1
Scheme 1.The experimental setup for the z-scanner for measuring the nonlinear optical properties of our investigated composites

Table 1
The energy gap previously published paper for different doped ZIF-8