Atomic Force Microscopy Observations Research Articles

Assembly of a patchy protein into variable 2D lattices via tunable multiscale interactions

Self-assembly of molecular building blocks into higher-order structures is exploited in living systems to create functional complexity and represents a powerful strategy for constructing new materials. As nanoscale building blocks, proteins offer unique advantages, including monodispersity and atomically tunable interactions. Yet, control of protein self-assembly has been limited compared to inorganic or polymeric nanoparticles, which lack such attributes. Here, we report modular self-assembly of an engineered protein into four physicochemically distinct, precisely patterned 2D crystals via control of four classes of interactions spanning Ångström to several-nanometer length scales. We relate the resulting structures to the underlying free-energy landscape by combining in-situ atomic force microscopy observations of assembly with thermodynamic analyses of protein-protein and -surface interactions. Our results demonstrate rich phase behavior obtainable from a single, highly patchy protein when interactions acting over multiple length scales are exploited and predict unusual bulk-scale properties for protein-based materials that ensue from such control.

Effect of atmospheric pressure plasma treatment on surface physicochemical properties of carbon fiber reinforced polymer and its interfacial bonding strength with adhesive

To study the effect of surface physicochemical properties of carbon fiber reinforced polymer (CFRP) on its interfacial bonding strength with adhesive, atmospheric pressure plasma treatment (APPT) using three gases (i.e., argon (Ar), nitrogen (N2) and air (Air)) was conducted on surfaces of CFRP substrates. Atomic force microscope (AFM) observation indicates that APPT only changes the surface morphology of CFRP in a depth of tens of nanometers, and this minor change contributes little to the interfacial bonding strength of CFRP joints. X-ray photo electron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR) analyses reveal that the release agent (mainly the -Si-CH3 group) and other contaminations on CFRP substrate surfaces were effectively removed by APPT, which improves the shear strength of CFRP joints from 8.6 MPa to 23.1 MPa. In addition, polar chemical functional groups (i.e., –NH2, –OH, –COOH) were generated on the CFRP substrate surfaces after APPT when nitrogen and air were used as plasma gases, which not only enhances the surface free energy of CFRP substrate but also combines with adhesive molecules through the form of hydrogen bonds and covalent bonds. With this mechanism, the shear strength of CFRP joints increased further to 28.7 MPa and 31.5 MPa when nitrogen and air were used as the plasma gases, respectively. After a quantitative study, the interfacial bonding strength between CFRP substrate and adhesive is expressed as a function of the concentration of -Si-CH3, –NH2 and –OH groups.

Evaluating the Effect of Azole Antifungal Agents on the Stress Response and Nanomechanical Surface Properties of Ochrobactrum anthropi Aspcl2.2.

Azole antifungal molecules are broadly used as active ingredients in various products, such as pharmaceuticals and pesticides. This promotes their release into the natural environment. The detailed mechanism of their influence on the biotic components of natural ecosystems remains unexplored. Our research aimed to examine the response of Ochrobactrum anthropi AspCl2.2 to the presence of four azole antifungal agents (clotrimazole, fluconazole, climbazole, epoxiconazole). The experiments performed include analysis of the cell metabolic activity, cell membrane permeability, total glutathione level and activity of glutathione S-transferases. These studies allowed for the evaluation of the cells’ oxidative stress response to the presence of azole antifungals. Moreover, changes in the nanomechanical surface properties, including adhesive and elastic features of the cells, were investigated using atomic force microscopy (AFM) and spectrophotometric methods. The results indicate that the azoles promote bacterial oxidative stress. The strongest differences were noted for the cells cultivated with fluconazole. The least toxic effect has been attributed to climbazole. AFM observations unraveled molecular details of bacterial cell texture, structure and surface nanomechanical properties. Antifungals promote the nanoscale modification of the bacterial cell wall. The results presented provided a significant insight into the strategies used by environmental bacterial cells to survive exposures to toxic azole antifungal agents.

Analysis of soft and hard nanoparticle alternating multilayers for the development of theory for long-period stacking order structure prepared by Langmuir-Blodgett method

Two types of hard and soft nanoparticles with a size of 5 nm were alternately layered to adjust the multi-particle structure with high regularity, and structural analysis was performed. Specifically, we alternately transferred two kinds of single-particle layers composed of surfactant-modified organo-magnetite and a hydrophobic polymer to a solid substrate using the Langmuir-Blodget (LB) method. The morphology of two-dimensional particle integration in each single particle layer was confirmed by atomic force microscopy observations. The obtained LB multilayers exhibited almost the same periodicity, crystallite size, and lattice distortion, based on X-ray diffraction (XRD) analysis. The alternating multilayers composed of hard and soft particle monolayers were not inferior to single component multilayers in terms of periodicity and regularity. The utilization of this preparation method facilitates effective control of the period of hard and soft layers. It is asserted that the high degree of regularity was attained due to the affinity and miscibility between the organic polymer particle layer and the modified organic chains on the inorganic nanoparticle surface. The most notable result is that in the XRD data, the spacing between inorganic nanoparticles was not enhanced, and the period of the hard-soft particle correlation was confirmed. Therefore, it seems that both layers have the same high degree of regularity.

Hydrogen gas sensor based on nanofibers TiO2-PVP thin film at room temperature prepared by electrospinning

TiO2/PVP nanofibers (NFs) have been deposited onto glass substrate by electrospinning method. X-ray diffraction analysis confirms the formation of anatse phase with high crystallinity and Field emission scanning electron microscopy and atomic force microscopy observations reveal the formation of fibrous nanostructure with a mean diameter in the range 41–281 nm and high porosity. A sensor was fabricated based on TiO2/PVP nanofibers (NFs) by sputtering Pt electrodes onto glass substrate and hydrogen (H2)-sensing performance was examined at room temperature over broad range of concentrations (167–1000 ppm). The results show that the sensor has good response towards H2 with a good sensitivity reaching 63% upon exposure to 1000 ppm of H2 gas at a low power consumption of 60 mW. The improved sensing performance is associated with surface morphology, high porosity and high surface-to-volume ratio of one-dimensional NFs.

Studied on the interaction between Ag-DNA nanocomposites and lipids monolayers

The adsorption behavior of AgNPs-DNA nanocomposites on 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) and 1,2-dimyristoyl-sn-glycero-3-phosphoserine (DMPS) lipid monolayers has been investigated by analyzing adsorption dynamic process, surface pressure-area isotherms (π-A), excess mean area ( $${\Delta \mathrm{A}}_{\mathrm{e}\mathrm{x}\mathrm{c}}$$ ), excess Gibbs free energy ( $$\Delta {\mathrm{G}}_{\mathrm{e}\mathrm{x}}$$ ) and the atomic force microscopy (AFM). The nanocomposites were prepared by sliver nanoparticles (AgNPs) and deoxyribonucleic acid (DNA) via electrostatic attraction. The result of ∆π/π and π-A isotherms indicated that the binding of AgNPs-DNA tends to adsorb on DMPC while the concentration of DNA exceeds 0.4 μg/mL. Excess mean area and thermodynamic analysis of excess Gibbs energy demonstrated that AgNPs-DNA enlarged the interval between DMPC and DMPS molecules, whose phenomena might be the electrostatic repulsion of each AgNPs-DNA molecule. AFM observation showed that the adsorption behavior of AgNPs-DNA on DMPS monolayers had a saturation point, while DMPC was not. Taken together, this work might provide a novel idea and useful basis for the development of metal nanoparticles-based biological materials.

Electrochemical adsorption and passivation on gold surface in alkaline thiourea solutions

An electrochemical method was used to examine Au surface absorption and passivation under the most commonly employed pH conditions in an alkaline Au leaching system. The polarization at different pH values was obtained through the current step curve. At pH 10, no absorption layer was formed. When the pH was increased to 11, an absorption layer was formed through the Au electrode reaction. At pH 12, the entire system could not be stabilized, even after long durations because of the thiourea oxidation and decomposition. The samples were analyzed by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and atomic force microscopy (AFM). AFM observations of the Au plating surface and SEM–EDS analyses for the Au-coated graphite surface indicated that a passivation membrane was formed on the Au surface after its use in the alkaline thiourea Au leaching system. Two-step leaching was used to confirm the conclusions drawn from the experimental results. The two-stage experimental results further confirmed the existence of a passivation membrane.

Determination of solid electrolyte interphase formation mechanism on negative electrode surface in Li-O2 battery electrolyte by operando electrochemical atomic force microscopy observation

Solid electrolyte interphase (SEI) on the negative electrode surface affect the electrochemical operation and cycle performance of the Li-O2 batteries. Two-type of SEI formation processes involving the O2 molecule on negative electrode surface have been suggested: (i) direct electrochemical reaction and (ii) indirect multi-step chemical reaction. In this research, the operando electrochemical atomic force microscopy observation was conducted to determine the proper model. Well-polished cupper substrate was used as model working electrode and was observed during the cyclic-voltammetry operation in the tetraglyme (G4) based electrolyte with and without dissolved O2. In the pristine electrolyte, in which O2 is not dissolved, no solid formation was observed. In the O2-dissolved electrolyte, the solid formation was suddenly observed from 1.3 V vs. Li counter electrode (LiCE) in the negative scan, which voltage is remarkably lower than the onset voltage of reduction current at 1.8 V vs. LiCE. This significant delay of solid formation against the electron transfer reaction strongly supported the multi-step solid formation model. The direct observation of electrode surface coupled with electrochemical operation determine the SEI formation mechanism in the Li-O2 battery.

Ultrasound driven conformational and physicochemical changes of soy protein hydrolysates

The effect of ultrasound on the conformational and physicochemical properties of soy protein isolate hydrolysates (SPHs) was investigated. SPHs were prepared at hydrolysis times of 20 min, 60 min, and 180 min, then treated with ultrasound for 10 min, 20 min, and 30 min at a frequency of 20 kHz and output powers of 150 W and 450 W. The structural properties and antioxidant capacities of the aqueous layer of SPHs (ASPHs) after sonication were evaluated by Fourier-transform infrared spectroscopy (FTIR), intrinsic fluorescence, DPPH radical scavenging activity assays, and microscopy observations. Results obtained showed that ultrasound treatment significantly disrupted the peptide aggregates formed during protein hydrolysis. The protein solubility was significantly increased after sonication (by up to 18.33%), as did the percentage of proteins with MW < 1 kDa in ASPHs. The antioxidant capacity of ASPHs also increased, as measured by DPPH assay. FTIR analysis of ASPHs indicated that the protein secondary structures were different, with an increase in β-sheet and a decrease in α-helix and β-turn. Furthermore, the changes in fluorescence spectra of ASPHs showed the transition of protein tertiary structure with a greater exposure of Trp residues in the side chains. Scanning electron microscope (SEM) and atomic force microscope (AFM) observations of the morphological structure of ASPHs further confirmed the significant effect of sonication on disrupting peptide aggregates. In conclusion, ultrasound can be used as an efficient treatment to promote the solubility of protein hydrolysates.

Thermal and optical properties of aromatic polyamide–hydrazides modified with multiwalled carbon nanotubes

Three wholly aromatic polyamide–hydrazides I–III containing various amounts of meta-/para-phenylene rings and their multiwalled carbon nanotube (MWCNT) composites have successfully been synthesized. These polymers were synthesized via a low-temperature solution polycondensation reaction of either meta-aminobenzhydrazide or para-aminobenzhydrazide (PABH) with an equimolar amount of isophthaloyl chloride (ICl) producing polymer I (100% meta-phenylene rings) and II (50% para-phenylene rings/50% meta-phenylene rings), respectively. The polymer III (75% para-phenylene rings/25% meta-phenylene rings) was synthesized by reacting PABH with mixture of equimolar ratios of terephthaloyl chloride and ICl. MWCNTs (0.1 wt%) have been incorporated into these three polymer matrices via a solution sonication technique. The structures of the polymers were confirmed by elemental analyses, Fourier-transform infrared, and proton nuclear magnetic resonance spectroscopy. The homogeneous distribution of the MWCNTs within the polymer matrices was proved by field emission scanning electron microscopy, transmission electron microscopy, and atomic force microscopy observations. Thermal and optical properties of the as-prepared polymers were being enhanced to some extent upon inclusion of MWCNTs as illustrated from the results of thermogravimetric analysis and ultraviolet–visible spectroscopy.

Preparation of a Si(111) Atomically Flat Substrate via Wet Etching and Evaluation as an AFM Substrate for Observations of Isolated Chains, Crystals, and Crystallization of Isotactic Poly(methyl methacrylate) at the Molecular Level.

To observe a polymer chain deposited on a substrate by atomic force microscopy (AFM) at the molecular level, the substrate should be atomically flat and stable under laboratory conditions and adsorb polymer chains firmly. Therefore, substrates used under laboratory conditions are practically limited to mica, highly ordered pyrolytic graphite, and atomically stepped sapphire, and polymers observed by AFM at the molecular level are also limited. A silicon wafer is frequently used as a substrate for AFM observation for somewhat macroscopic observations, but the surface of the silicon wafer is too rough to observe polymer chains deposited on it at the molecular level. In this study, we prepared an atomically stepped Si(111) substrate via wet etching in NH4F and evaluated it as an AFM substrate. The Si(111) substrate was stable as an AFM substrate, and isolated poly(methyl methacrylate) (it-PMMA) chains and a crystalline monolayer deposited on the substrate were observed by AFM at the molecular level. An it-PMMA amorphous monolayer deposited on mica crystallized under high humidity, but that on the Si(111) substrate did not because of the difference in the surface nature and the crystal structure of the substrates. The Si(111) substrate was hydrophobic, and the it-PMMA monolayers could be deposited as a multilayer, which could not be formed on hydrophilic mica. The crystallization behavior of an it-PMMA amorphous multilayer and an amorphous/crystalline mixed multilayer on the Si(111) substrate was also evaluated.

Surface Roughness and Microbial Adhesion After Finishing of Alkasite Restorative Material

This study is aimed to evaluate and compare the surface roughness and microbial adhesion to alkasite restorative material (Cention N), resin-modified glass ionomer (RMGI), and composite resin. And to examine the correlation between bacterial adhesion and surface roughness by different finishing systems.&lt;br/&gt;Specimens were fabricated in disk shapes and divided into four groups by finishing methods (control, carbide bur, fine grit diamond bur, and white stone bur). Surface roughness was tested by atomic force microscope and surface observation was performed by scanning electron microscope. Colony forming units were measured after incubating Streptococcus mutans biofilm on specimens using CDC biofilm reactor.&lt;br/&gt;Cention N surface roughness was less than 0.2 μm after finishing procedure. Control specimens of resin and Cention N specimens were significantly (&lt;i&gt;p&lt;/i&gt; = 0.01) rougher. Pearson correlation coefficient (PCC = 0.13) indicated a weak correlation between surface roughness and &lt;i&gt;S. mutans&lt;/i&gt; adhesion to the specimens.&lt;br/&gt;Compared with resin specimens, RMGI and Cention N showed lower microbial adhesion. Surface roughness and bacterial adhesion were not significantly different, regardless of the finishing systems.

Influence of PECVD-TiO2 film morphology and topography on the spectroscopic ellipsometry data fitting process

TiO2 films of different thickness are deposited on silicon substrate at low temperature and pressure by a Helicon-PECVD reactor. The evolution of film morphology and topography is observed by scanning electron microscopy (SEM) and atomic force microscopy (AFM), meanwhile the spectroscopic ellipsometry (SE) measurements are performed to investigate the film growth mechanism and optical constants. The SEM and AFM observations show that all the films exhibit a columnar structure, moreover all the columns are vertical grown and well-organized when the thickness below [Formula: see text][Formula: see text]80 nm. As the thickness is increased to [Formula: see text][Formula: see text]150 nm, 250 nm and 450 nm, the column size is increased in the top layers, the whole film morphology becomes inhomogeneous, which leads to a decreased density and rougher surface. By fitting the SE measurements, a suitable gradient physical model is found to describe the film morphologies, the model consists of a native SiO2 layer on Si substrate, a mediate layer mixed TiO2 with void whose concentration gradient changed from bottom to top, and a top roughness layer. For thick films ([Formula: see text][Formula: see text]450 nm), the absorption and scattering on the rough surface is considered in order to keep the precision of SE fits. It is found that the optical index is decreased with film thickness, which is related to the evolution of structure in the top layers.

Effect of photocatalysis (TiO2/UVA) on the inactivation and inhibition of Pseudomonas aeruginosa virulence factors expression

ABSTRACT Water disinfection using visible light-active photocatalyst has recently attracted more attention due to its potential to inactivate microbes. In this study, we have investigated the efficiency of photocatalysis (TiO2/UVA) on the inactivation of Pseudomonas aeruginosa and the attenuation of its virulence factors. For this aim, the photocatalytic effects of TiO2/UVA on the cultivability and viability of P. aeruginosa were investigated. Furthermore, during the photocatalysis, the morphology of the bacterial cells was examined by atomic force microscopy (AFM) while the virulence factors were assessed by protease and lipase activities in addition to the mobility and communication of cells. The results revealed that during the photocatalysis the bacterial cells lost their cultivability and viability on agar under the action of the reactive oxygen species generated by the photocatalytic reaction. In addition, AFM observations have shown a damage of the bacterial membrane and a total disruption of the bacterial cells. Moreover, the major virulence factors such as biofilm, lipase and protease expression have been markedly inhibited by TiO2/UVA treatment. In addition, the bacteria lost their ability of communication ‘quorum sensing’ and mobility with twitching and swarming types after 60 min of photocatalytic treatment. Accordingly, TiO2/UVA is an effective method to reduce P. aeruginosa virulence and to prevent biofilm formation.

Proteolysis kinetics and structural characterization of ultrasonic pretreated sunflower protein

Proteolysis kinetics and structure attributes of sunflower meal protein (SMP) pretreated using sonication of frequency type single (20, 40 kHz) and dual (20/40 kHz) were examined. A simplified model with impeded enzyme reaction was developed and the proteolysis of SMP in a heterogeneous system was successfully described. Initial observed rate (kin) increased after sonication, demonstrating the impacts of sonication on SMP by enhancing proteolysis (enzymolysis) and altering the structure of SMP, which was validated by circular dichroism (CD) spectroscopy, ultraviolet-visible (UV-Vis) spectroscopy, scanning electron microscopy (SEM), atomic force microscopy (AFM), Fourier transform infrared (FTIR) spectroscopy and sodium dodecyl sulfide polyacrylamide gel electrophoresis (SDS-PAGE) analyses. From SMP characterization, there was a reduction in α-helix, enhancement in absorption intensity and alterations in functional groups of SMP following sonication. SEM and AFM observations indicated that sonicated SMP unfolded and exhibited more heterogenous structures, and irregular small-sized particles than control, especially at 20/40 kHz. SDS-PAGE profile displayed notable changes in molecular weight after sonication, which evidenced limited unfolding in SMP conformation. The kinetic model has possibility of being used to control enzymolysis; and structural attributes could guide in the development of ultrasonic equipment for use of pretreating protein for enzymolysis.

Growth Kinetics and Spoilage Potential of Co-culturing Acinetobacter johnsonii and Pseudomonas fluorescens from Bigeye Tuna (Thunnus obesus) During Refrigerated Storage.

A. johnsonii and P. fluorescens are the well-known specific spoilage organisms in aquatic products and the study of the interactions between A. johnsonii and P. fluorescens are limited. This study aims to evaluate the growth kinetics, spoilage potential and interactions ofA.johnsonii andP. fluorescens isolated from spoiled bigeye tuna (Thunnus obesus) by inoculating into sterile fish slices and stored at 4°C for 6days. The growth kinetics of A. johnsonii and P. fluorescens were fitted with Baranyi and Roberts model. The chemical indexes (total volatile base nitrogen (TVB-N), trimethylamine (TMA), pH, proteolytic activity and protein content) of each inoculated block of bigeye tuna were increased during refrigerated storage. Moreover, the higher contents of chemical indexes were observed in co-culture with A. johnsonii and P. fluorescens compared with single culture of A. johnsonii and P. fluorescens. In addition, atomic force microscopy (AFM) observation of co-culturing A. johnsonii and P. fluorescens inoculation into sterile fish slices revealed damage of myofibrillar protein structures and the protein degradation. Based on these parameters, a rapid method to evaluate spoilage potential of A. johnsonii and P. fluorescens was positively correlated with TVB-N value, TMA value and pH value (P < 0.05) by the correlation coefficient. Consequently, spoilage potential of microorganisms became stronger evaluated in a mixed culture than single culture. This paper provides insight for a detection method of interactions of A. johnsonii and P. fluorescens during refrigerated storage.

Effect of selective distribution of MWCNTs on the solid-state rheological and dielectric properties of blends of PMMA and LDPE

The effects of adding multi-walled carbon nanotubes (MWCNTs) on the solid-state rheological and dielectric properties of blends of poly(methyl methacrylate) (PMMA) and low-density polyethylene (LDPE) were studied as a function of varying polymer ratio. Dynamic mechanical thermal analysis (DMTA) was performed in torsion mode, on the blends and their composites with MWCNTs. For a PMMA/LDPE blend with a ratio of 80:20, the evolution of the loss tangent with temperature showed a single thermal event, associated with the glass transition (Tg) of PMMA, confirming that co-continuity has not been achieved. Upon loading with 2 wt.% MWCNTs, a decrease in the magnitude of this peak is observed. Even though the MWCNTs preferentially locate in the polymer phase first to melt, i.e., LDPE, selective solvent extraction on this sample demonstrated that some of the MWCNTs are trapped in the major phase, PMMA. Moreover, DMTA measurements also revealed the formation of a “rheological” percolated network at ~ 3.5 wt.% MWCNTs in PMMA/LDPE blends with polymer ratios of 50:50 and 20:80, but not in 80:20. In contrast, for the same MWCNT concentration, a 80:20 blend displayed a well-developed AC conductivity plateau at low frequencies and highly enhanced dielectric properties, as a consequence of the high concentration of micro-capacitors formed by polymer films sandwiched by nanotubes within the LDPE phase, as proven from atomic force microscopy observations.

Corrosion resistance of sol-gel ZrO2 coatings deposited on stainless steel

Corrosion-resistant ZrO2 coatings were deposited on stainless steel plates using organic (A) and inorganic (B) Zr precursors containing polyethylene glycol as structure directing agent. The dipping-drying cycles were repeated five times; the coatings were then treated at 500 °C. The samples were studied by atomic force microscopy (AFM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and by automated contact-angle goniometry. The corrosion resistance of the ZrO2 coatings were examined in NaCl and artificial sea water. The XRD analyses revealed a crystallized monoclinic ZrO2 phase. The AFM observation proved that after the corrosion attack the surface had no signs of corrosion (scratches or cracks). The A and B coatings had corrosion rates of 4×10−5 and 2×10−4 g/m2 h, respectively. The A coatings possessed a fine grained structure and a lower wettability (contact angle of 107°) and a lower oxygen content than the B coatings, which determined their better corrosion properties in both corrosive media.

Fabrication and characterization of acid soluble collagen stabilized Pickering emulsions

The objective of present study was to assess the feasibility of using acid soluble collagen as stabilizer to fabricate stable oil-in-water (O/W) Pickering emulsions. The effect of acid soluble collagen concentrations, pH values and ionic strengths on the particle size distribution, rheological properties and Turbiscan stability of emulsions was investigated. Atomic force microscopy (AFM) observation showed that the acid soluble collagen exhibited thread-like structure, the length reached 600–900 nm and the diameter was in about 20 nm. The concentration of acid soluble collagen significantly affected the stability of Pickering emulsions. The results indicated that when the concentration was lower than 0.1 wt%, phase separation of Pickering emulsion occurred. With increased concentration of acid soluble collagen varying from 0.01 to 1.5 wt%, the stability of Pickering emulsions was improved, accompanied with a diminution in droplet sizes. Rheological results showed that the obtained Pickering emulsion exhibited gel-like structure, and the increase of acid soluble collagen concentrations contributed to larger elastic modulus (G’) and viscosity modulus (G”) of emulsions, which was beneficial for the stability of emulsions. In addition, ionic strengths and pH values also affected the physical properties of Pickering emulsions. These novel findings in this work could extend the knowledge about acid soluble collagen as potential edible Pickering stabilizer.

Inside black pearls

The quality of natural and cultured pearls depends on the size, shape and properties of the surface. The inner structure of the pearl is not known, and not taken into account. Indeed, it is assumed that the cultured pearl is a nucleus covered by a thin organic layer, a thin prismatic layer and a thick nacreous layer. The examination of spherical and pear shape samples resulting from the grafting of the black lip pearl oyster (Pinctada margaritifera) shows that this assumption is, in most cases, erroneous. Optical, electron and atomic force microscopic observations, infrared and Raman analyses, as well as micro X-ray fluorescence and micro X-ray absorption near-edge spectroscopy data show that the inner structure of a pearl does not depend on its shape. Both circle or pear shape and spherical pearls show a large variability of the inner structures and composition. There are no two identical samples. Moreover, the arrangement is irregular within a single pearl, and some structures (aragonitic pseudo-prisms) do not exist in the shell.