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Optical microscope images of salt patterns in dried drops of NaCl water physiological solution. Upper line: magnification x 28; bottom line: magnification x 98
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Complex and elegant patterns of rosette, scallop, Chinese arrow and dendrite shapes on microscopic length scales formed as a result of salt-induced protein self-assembly in sessile drying droplets of protein-salt solutions were described in the literature. The authors are confident in protein nature of these patterns because they used fluorochrom-l...
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Context 1
... drying droplets of complex solutions are natural objects for studying different dynamical processes, which lead to self-assembly of their components[1-9]. These processes are very important for understanding the mecha- nisms of colloidal instability[8,10,11], medical diagnostics [12,13,14], dye coatings quality[15,16], and nano-particle formation[17,18]. Thus, this is a rapidly developing area of basic science, which has a wide number of useful applica- tions. Therefore, correct understanding and interpretation of pattern formation in drying drops is very critical. During the last 10 years we studied the self-organizing processes in sessile drying drops by means of manifold approaches, and we were surprised by the interpretation of the experimental data published in[19]. Recently we observed the same pat- terns in protein-salt solutions at low protein content (not more than 0.5% w), using not only BSA (68 kDa), but also IgG (150 kDa) and carbonic anhydrase (30 kDa)[20,21]. We generally supposed that salt crystals, which demonstrated a broad polymorphysm, fabricated these patterns. However, the authors of[19] enforced us to make some additional ex- periments for verification of our point of view. In the current paper we present our past and recent data concerning this problem. Following the authors of[19], we used 0.2% w bovine serum albumin solution (BSA, 68 kDa, Sigma, USA) in physiological salt solution (0.15 M NaCl, chemically pure, “Reactiv, Inc.”, Russia). Also a pure physiological salt so- lution was used as a subject for investigation. The BSA solution was prepared without buffering, a day prior to ex- perimentation, refrigerated overnight and allowed to come to room temperature before testing. The samples under study were placed, using a micropipette, onto clean glasses in the form of drops 5 ul in volume (6-8 drops for each sample), and let for drying under room conditions. It is not a trivial task to distinguish protein and salt struc- tures under microscope without special analytical techniques. But, it is possible to try to do so resting upon different physical properties of protein and salt. So, the first idea implied the following: if we denaturate albumin and stick it to glass surface, then we can put the glass into water and dissolve salt. So we can display the salt crystals topology. Albumin denaturation was done by intensive warming of glasses with dried drops 10 min above a flame of a spirit-lamp. After warming, the glasses were allowed to come to room temperature, and were rinsed in distilled wa- ter. The second idea was based on different interaction of al- bumin and salt with ethyl alcohol. Ethyl alcohol denaturates proteins, but does not dissolve NaCl crystals. Therefore, the glasses with dried drops of BSA salt solutions were put into 70% alcohol and kept there for 30 min. Then, the glasses were dried at room temperature, and were investigated under microscope. After that, the glasses were rinsed in distilled water and investigated repeatedly. The dried droplets preparation of IgG and carbonic anhydrase salt solutions were described in[21] and[20], respectively. Morphological observations were carried out using MBS-10 and LU- MAM-I3 microscopes, as well as video camera – computer setup and digital camera “Cannon”. Figure 1 shows “protein patterns” as they were described in the paper[19]. The fact is that NaCl itself can form crystals of different morphology in drops during water evaporation (Fig. 2). The complex salt patterns look like the “protein” patterns in[19]. Each of them consists of a large-scale single crystal in the center, and a lot of small crystals in the form of “frills”, which surround it concentrically. The reason for these differences seems to be in different conditions for crystal growth: initial formation of a large crystal leads to depletion a surrounding solution with salt, thus continued water evaporation does not reserve time and substrate for another large crystal growth. In this situation small concen- trical crystal pattern formation is the only feasible way. The main distinction of the patterns in dried drops of salt solution before and after BSA adding (Fig.3) is their topol- ogy: due to the “coffee ring” phenomenon[1,2] in a pure physiological solution the patterns form mainly over a three-boundary line, whereas in BSA salt solutions these patterns lye in the drop centre. It is because protein adsorp- tion to the glass surface takes place in protein salt solutions along with centrifugal stream[20]. Thus, when salt crystal- lization begins at the end of the drop drying process, protein bottom deposits can serve as seeds for crystal growth. The glass warming procedure did not have significant in- fluence on the pattern structure (Fig.4). Following water rinsing these structures vanished from the drop centre, and diminished essentially in height over the drop edge (Fig. 5). Immersion of the glasses into ethyl alcohol led to albumin denaturation, so albumin formed microscopy-scale globules, which disappeared from the glasses partly. But, this proce- dure allowed observing true topology of salt patterns (Fig. 6). These patterns, in turn, vanished fully after the water washing procedure (Fig. 7). The same concentric patterns we observed also in IgG, and in carbonic anhydrase salt solutions (Fig. 8,9). As to the protein mass content in these solutions, it is several fold less than the NaCl content, and up to 70% of protein mass moves to the drop periphery during drying[10], thus also confirming the assumption about the salt nature of these patterns. And what about “specific fluorescence” of “protein pat- terns”? Undoubtedly, it is due to nonspecific light dispersion on the crystal surfaces. It is confirmed also by bright lumi- nescence of large salt crystals in the centre of the “protein patterns”[Fig. 1]. The same “fluorescence”, for example, can be achieved by lateral illumination of crystals by usual light, as is shown in Fig. 2 of this paper. Really, the same effect can be observed using visible light of any wavelength under appropriate light angulation. Thus, we suppose that all the discussions in[19] about the influence of rapid and slow evaporation, as well as protein and salt concentration, should be attributed to salt crystal growth. We are sorry about this delusion. Complex pattern formation in diluted protein salt solu- tions was discussed. Using some simple methods, it was shown that these complex patterns were fabricated by salt. This conclusion contradicts the opinion of some authors. Further investigations by means of special modern analytical techniques should be ...
Context 2
... drying droplets of complex solutions are natural objects for studying different dynamical processes, which lead to self-assembly of their components[1-9]. These processes are very important for understanding the mecha- nisms of colloidal instability[8,10,11], medical diagnostics [12,13,14], dye coatings quality[15,16], and nano-particle formation[17,18]. Thus, this is a rapidly developing area of basic science, which has a wide number of useful applica- tions. Therefore, correct understanding and interpretation of pattern formation in drying drops is very critical. During the last 10 years we studied the self-organizing processes in sessile drying drops by means of manifold approaches, and we were surprised by the interpretation of the experimental data published in[19]. Recently we observed the same pat- terns in protein-salt solutions at low protein content (not more than 0.5% w), using not only BSA (68 kDa), but also IgG (150 kDa) and carbonic anhydrase (30 kDa)[20,21]. We generally supposed that salt crystals, which demonstrated a broad polymorphysm, fabricated these patterns. However, the authors of[19] enforced us to make some additional ex- periments for verification of our point of view. In the current paper we present our past and recent data concerning this problem. Following the authors of[19], we used 0.2% w bovine serum albumin solution (BSA, 68 kDa, Sigma, USA) in physiological salt solution (0.15 M NaCl, chemically pure, “Reactiv, Inc.”, Russia). Also a pure physiological salt so- lution was used as a subject for investigation. The BSA solution was prepared without buffering, a day prior to ex- perimentation, refrigerated overnight and allowed to come to room temperature before testing. The samples under study were placed, using a micropipette, onto clean glasses in the form of drops 5 ul in volume (6-8 drops for each sample), and let for drying under room conditions. It is not a trivial task to distinguish protein and salt struc- tures under microscope without special analytical techniques. But, it is possible to try to do so resting upon different physical properties of protein and salt. So, the first idea implied the following: if we denaturate albumin and stick it to glass surface, then we can put the glass into water and dissolve salt. So we can display the salt crystals topology. Albumin denaturation was done by intensive warming of glasses with dried drops 10 min above a flame of a spirit-lamp. After warming, the glasses were allowed to come to room temperature, and were rinsed in distilled wa- ter. The second idea was based on different interaction of al- bumin and salt with ethyl alcohol. Ethyl alcohol denaturates proteins, but does not dissolve NaCl crystals. Therefore, the glasses with dried drops of BSA salt solutions were put into 70% alcohol and kept there for 30 min. Then, the glasses were dried at room temperature, and were investigated under microscope. After that, the glasses were rinsed in distilled water and investigated repeatedly. The dried droplets preparation of IgG and carbonic anhydrase salt solutions were described in[21] and[20], respectively. Morphological observations were carried out using MBS-10 and LU- MAM-I3 microscopes, as well as video camera – computer setup and digital camera “Cannon”. Figure 1 shows “protein patterns” as they were described in the paper[19]. The fact is that NaCl itself can form crystals of different morphology in drops during water evaporation (Fig. 2). The complex salt patterns look like the “protein” patterns in[19]. Each of them consists of a large-scale single crystal in the center, and a lot of small crystals in the form of “frills”, which surround it concentrically. The reason for these differences seems to be in different conditions for crystal growth: initial formation of a large crystal leads to depletion a surrounding solution with salt, thus continued water evaporation does not reserve time and substrate for another large crystal growth. In this situation small concen- trical crystal pattern formation is the only feasible way. The main distinction of the patterns in dried drops of salt solution before and after BSA adding (Fig.3) is their topol- ogy: due to the “coffee ring” phenomenon[1,2] in a pure physiological solution the patterns form mainly over a three-boundary line, whereas in BSA salt solutions these patterns lye in the drop centre. It is because protein adsorp- tion to the glass surface takes place in protein salt solutions along with centrifugal stream[20]. Thus, when salt crystal- lization begins at the end of the drop drying process, protein bottom deposits can serve as seeds for crystal growth. The glass warming procedure did not have significant in- fluence on the pattern structure (Fig.4). Following water rinsing these structures vanished from the drop centre, and diminished essentially in height over the drop edge (Fig. 5). Immersion of the glasses into ethyl alcohol led to albumin denaturation, so albumin formed microscopy-scale globules, which disappeared from the glasses partly. But, this proce- dure allowed observing true topology of salt patterns (Fig. 6). These patterns, in turn, vanished fully after the water washing procedure (Fig. 7). The same concentric patterns we observed also in IgG, and in carbonic anhydrase salt solutions (Fig. 8,9). As to the protein mass content in these solutions, it is several fold less than the NaCl content, and up to 70% of protein mass moves to the drop periphery during drying[10], thus also confirming the assumption about the salt nature of these patterns. And what about “specific fluorescence” of “protein pat- terns”? Undoubtedly, it is due to nonspecific light dispersion on the crystal surfaces. It is confirmed also by bright lumi- nescence of large salt crystals in the centre of the “protein patterns”[Fig. 1]. The same “fluorescence”, for example, can be achieved by lateral illumination of crystals by usual light, as is shown in Fig. 2 of this paper. Really, the same effect can be observed using visible light of any wavelength under appropriate light angulation. Thus, we suppose that all the discussions in[19] about the influence of rapid and slow evaporation, as well as protein and salt concentration, should be attributed to salt crystal growth. We are sorry about this delusion. Complex pattern formation in diluted protein salt solu- tions was discussed. Using some simple methods, it was shown that these complex patterns were fabricated by salt. This conclusion contradicts the opinion of some authors. Further investigations by means of special modern analytical techniques should be ...
Citations
... The addition of salts in drops containing proteins leads to the growth of complex aggregates such as Chinese arrows, rosettes, scallops, dendrite shapes, and zigzag patterns [40,[43][44][45][46][47]. Consequently, the increment in salt concentration affects the distribution of the aggregates, on the formation of patterns, by the ion absorption on macromolecules [48,49]. ...
... Although in the scientific literature, several works report the pattern formation of dried droplets of proteins [24,40,[43][44][45][46][47][48][49][52][53][54][55], the effectiveness of this method to reveal the coexistence of macromolecules of the same species, with different conformational states, is still unknown. Advances in strategies to detect conformational changes in proteins through the analysis of deposits could lead to the development of rapid methodologies capable of diagnosing pathologies. ...
... Partially unfolded proteins, salts, relative humidity, type of substrate, and initial droplet volume drive the aggregation and mass transport mechanism that give rise to the final morphology of patterns in dried droplets [40,43,44,[47][48][49]52,54]. Therefore, exploring how these control parameters modify the efficiency of the detection of proteins in different conformational states is an investigation that we would like to do in the future. ...
The morphological analysis of patterns in dried droplets has allowed the generation of efficient techniques for the detection of molecules of medical interest. However, the effectiveness of this method to reveal the coexistence of macromolecules of the same species, but different conformational states, is still unknown. To address this problem, we present an experimental study on pattern formation in dried droplets of bovine serum albumin (BSA), in folded and unfolded conformational states, in saline solution (NaCl). Folded proteins produce a well-defined coffee ring and crystal patterns all over the dry droplet. Depending on the NaCl concentration, the crystals can be small, large, elongated, entangled, or dense. Optical microscopy reveals that the relative concentration of unfolded proteins determines the morphological characteristics of deposits. At a low relative concentration of unfolded proteins (above 2%), small amorphous aggregates emerge in the deposits, while at high concentrations (above 16%), the “eye-like pattern”, a large aggregate surrounded by a uniform coating, is produced. The radial intensity profile, the mean pixel intensity, and the entropy make it possible to characterize the patterns in dried droplets. We prove that it is possible to achieve 100% accuracy in identifying 4% of unfolded BSA contained in a protein solution.
... Evaporation of bio-fluid droplets has been applied as a medical diagnosis tool in earlier works [47,48,49]. Devineau et al. [50] analyzed the pattern formation of evaporating protein droplets containing suspended polystyrene particles. ...
Hypothesis
The droplets ejected from an infected host during expiratory events can get deposited as fomites on everyday use surfaces. Recognizing that these fomites can be a secondary route for disease transmission, exploring the deposition pattern of such sessile respiratory droplets on daily-use substrates thus becomes crucial.
Experiments
The used surrogate respiratory fluid is composed of a water-based salt-protein solution, and its precipitation dynamics is studied on four different substrates (glass, ceramic, steel, and PET). For tracking the final deposition of viruses in these droplets, 100 nm virus emulating particles (VEP) are used and their distribution in dried-out patterns is identified using fluorescence and SEM imaging techniques.
Findings
The final precipitation pattern and VEP deposition strongly depend on the interfacial transport processes, edge evaporation, and crystallization dynamics. A constant contact radius mode of evaporation with a mixture of capillary and Marangoni flows results in spatio-temporally varying edge deposits. Dendritic and cruciform-shaped crystals are majorly seen in all substrates except on steel, where regular cubical crystals are formed. The VEP deposition is higher near the three-phase contact line and crystal surfaces. The results showed the role of interfacial processes in determining the initiation of fomite-type infection pathways in the context of COVID-19.
... The complexity of crack patterns increase notoriously when droplets contain a mixture of protein and liquid crystals [20,21]. Moreover, the addition of salts induces the formation of a diversity of complex structures such as amorphous peripheral ring, dendritic shapes, rosettes, scallops, Chinese arrows, and zigzag patterns [22][23][24][25][26][27]. ...
Rapid diagnosis provides better clinical management of patients, helps control possible outbreaks, and increases survival. The study of deposits produced by the evaporation of droplets is a useful tool in the diagnosis of some health problems. With the aim to improve diagnostic time in clinical practice where we use the evaporation of droplets, we explored the effects of substrate temperature on pattern formation of dried droplets in globular protein solutions. Three deposit groups were observed: “functional” patterns (from 25 to 37 ∘C), “transition” patterns (from 44 to 50 ∘C), and “eye” patterns (from 58 to 63 ∘C). The dried droplets of the first two groups show a ring structure (“coffee-ring”) that confines a great diversity of aggregates such as needle-like structures, tiny blade-shape crystals, highly symmetrical crystallization patterns, and amorphous salt aggregates. In contrast, the “eye” patterns are deposits with a large inner aggregate surrounded by a coffee ring, and they can appear from the evaporation of droplets in protein binary mixtures and blood serum. Interestingly, the unfolding proteins correlates with the formation of “eye” patterns. We measured stain diameter, “coffee-ring” thickness, radial density profile, and entropy computed by GLCM-statistics to quantify the structural differences among deposit groups. We found that “functional” patterns are structurally indistinguishable among them, but they are clearly different from elements of the other deposit groups. An exponential decay function describes pattern formation time as a function of substrate temperature, which is independent from protein concentration. Patterns formation at 32 ∘C takes place up to 63% less time and preserves the structural characteristics of dried droplets in proteins formed at room temperature. Therefore, we argue that droplet evaporation at this substrate temperature could be an excellent candidate to make a more efficient diagnosis based on droplet evaporation of biofluids.
... The evaporation of droplets with dissolved salt has been investigated [6][7][8][9][10][11][12][13][14]. It was reported that a concentric pattern may be formed by repeated pinning and slipping during the evaporation of droplets containing L-ascorbic acid [8] and bovine serum albumin [9]. ...
... The evaporation of droplets with dissolved salt has been investigated [6][7][8][9][10][11][12][13][14]. It was reported that a concentric pattern may be formed by repeated pinning and slipping during the evaporation of droplets containing L-ascorbic acid [8] and bovine serum albumin [9]. Shahidzadeh et al. investigated recrystallization dynamics for different substrates [11]. ...
... Such modification of crystal morphologies may have an effect on the macroscopic physical properties, e.g., refractive index, electric conductivity, and mechanical properties [3,4,7,[15][16][17][18][19][20]]. Yet, we note that elucidating the specific mechanisms behind such a rich phenomenology is a formidable challenge; recrystallization in a salt solution due to evaporation is a complex phenomenon, with coupling between ma- terial transport, hydrophobicity, thermal behavior, shrinking, and local concentration [6,[8][9][10][11][12][13][14]. ...
Crystal patterns formed by evaporation play important roles in industrial technologies. Recently, it was found that a concentric pattern and an orchid pattern may be seen when a pinned sessile droplet dries. Due to complex coupling between evaporation and crystallization, the mechanism behind this unique recrystallization phenomenon is yet to be determined. Here, we investigate the formation of these macroscopic patterns using microscopy. Then we show that diffusion-limited aggregation, absorption, and dewetting from the substrate all play a role in its development. In addition, it is found that anisotropy of the core is a key parameter for the pattern formation on a long length scale.
... 4 Solely hydrodynamics can explain canonical cases like the classical coffee-stain case as long as particles behave as hard spheres and Marangoni flows are negligible, i.e. all streamlines end at the contact line. More generaly, nonetheless, the morphology of the final deposit depends on complex physico-chemical processes mainly involving particle-wall, particleinterface and particle-particle interactions that can lead to a large variety of complex aggregates such as amorphous peripheral ring, dendritic shapes, rosettes, scallops, Chinese arrows, zigzag patterns, undulated branches, and interlocked chains [29][30][31][32][33][34]. Moreover, the complex structural characteristics of the deposit patterns have been exploited to the diagnostic health problems [35], to explore cell motility [36,37], calorimetric properties in membranes [38], authenticate consumable beverages [39], among many others uses. ...
Watercolor or aquarelle is one of the oldest painting methods in which pigments suspended in an aqueous liquid are deposited over a substrate, typically an absorbing material such as paper. The physical processes which lead to pattern formation have not been studied in any depth, in spite of being closely related to flows in other contexts. Identifying and understanding these processes is of imperative importance to restore and preserve watercolor paintings. Here, we report an experimental study of the effect of the pigment concentration and paper humidity on the pattern formation derived from evaporation of droplets of watercolor paintings. Optical analysis reveals the formation of color gradients, stratifications, flat regions, borders, dendritic shapes, and radial tips. We found that droplet evaporation on dry paper forms ring-shaped stains which resemble to the \emph{coffee-stain effect} regardless of the nature of the pigment. The mean pixel intensity of such deposits follows an exponential function that saturates at high concentration, while the thickness of the coffee ring increase for watercolor inks containing colloidal particles and does not change for non-colloidal . Our experiments reveal that water distribution on the paper surface, and not the volumetric absorption of water on the paper, determine the structural characteristics of watercolor stains. We show evidence that the cornerstone in the creation of complex patterns in watercolor paintings is driven by the coffee ring effect and imbibition processes. Our findings aim to serve as framework for further investigations of the complex processes involved in this ancient art form and could guide restoration processes needed to preserve the heritage value of historical watercolor artworks.
... 20,21 In contrast to this interpretation, Yakhno et al. presented the experimental results showing that these patterns could be salt crystals, while macromolecular proteins only served as crystal seeds. 22,23 The main chemical compositions of crystal-like patterns are, therefore, still not fully understood. Additionally, because of the limitation of current experimental techniques and the complexity of crystallike patterns, most research has been conducted by taking only macroscopic approaches to examine the entire or a certain region of desiccation patterns. ...
The renewed interest in plasma desiccation patterns focuses on the potential of these patterns to be developed to a platform of low-cost and facile diagnostic methods to interpret health conditions of donors. During desiccation, several physical mechanisms are simultaneously acting on the plasma sessile drop; these include material redistribution, build-up/release of local internal stresses, protein aggregation and salt crystallization. After desiccation, cracking patterns and “superimposed” crystal-like patterns are formed. It has been reported that these characteristic patterns were influenced by changes in plasma compositions caused by diseases. Potential applications of these patterns in diagnosis are, however, limited by our understanding of formation mechanisms of cracking patterns and chemical compositions of crystal-like patterns. To address these limitations, this research studied morphologies of desiccated plasma patterns and the influence of sodium chloride to the pattern formation at both macroscopic and microscopic levels. Experimental results show that cracking patterns of plasma from healthy adults form throughout the desiccated deposit; propagation directions of cracks are found to have correlations to local dominant stresses, which are governed by the development of gelation. Crystal-like patterns are located in the drop center, which are caused by the heterogeneous distribution of macromolecular proteins and sodium chloride within the plasma sessile drop during desiccation; these patterns are influenced by the concentration of sodium chloride. With the increase of the concentration of sodium chloride, the distribution area of crystal-like patterns enlarges; whereas, the number of cracks decreases.
... Метод оценки влияния химических и физических факторов... Природа структур, получаемых при высушивании солевых растворов биополимеров (белков, ДНК, полисахаридов), не имеет однозначной интерпретации. Так, в работе [17] предполагается, что эти структуры состоят из комплексов, содержащих соль, воду и биополимер в кристаллическом состоянии; в работе [18] обосновывается индуцированная солью «самосборка» молекул белков в структуры на пленке; в работах [19][20] аргументируется солевая природа кристаллических структур. Согласно теоретическим моделям, характер формируемых текстур, в основном, определяется динамикой течений, диффузией частиц и стабильностью коллоидной системы [21,22]. ...
Subject and purpose. In this paper, we studied the relationship of the structural and aggregation state of biopolymers with the quantitative characteristics of the textures of the films formed during the drying of biopolymer solutions.
Methods and methodology. The structural changes of the biopolymer were determined by IR, UV and fluorescence spectroscopy, the size and surface potential of biopolymer particles were determined by dynamic light scattering, the state of the water environment was determined by microwave dielectrometry. To obtain films, saline solutions of calf thymus Na-DNA, bovine serum albumin (BSA) or human serum albumin (HSA) were dried in a glass cuvette under thermostatically controlled conditions. For the numerical characterization of textures, the relative area, fractal dimension and characteristics of zigzag patterns were used.
Results. The paper presents a mini-review of the results during the development of a method for assessing the influence of biologically active substances (inorganic and organic) and physical factors (temperature and gamma irradiation) on biopolymers by the changes in texture parameters. It is shown that the formation of zigzag structures is sensitive to the structural and aggregation effects of biologically active substances and physical factors, and requires the presence of chloride ions.
Conclusion. A method for assessing the influence of the corresponding factors by the changes in texture parameters is proposed. The presented results clarify the role of biopolymer, as well as salt cations and anions, in the formation of textures (in particular, zigzag structures) on the surface of films, and show the relationship of structural changes and aggregation of biopolymer with quantitative characteristics of zigzag patterns.
... 31 The observations of BSA−salt solution complex drying patterns are further improvised using fluorochrom-labeled albumin. 32,33 Drying drops of blood plasma for different lungs diseases are found to form distinguishable patterns. 34 Recently, the pattern formation of mixtures of two proteins (lysozyme and BSA) are studied in detail. ...
Pattern formation during evaporation of biofluids has numerous biomedical applications e.g., in disease identification. The drying of a bi-disperse colloidal droplet involves formation of coffee ring patterns owing to the deposition of constituent particles. In the present study, we examine the distinctly different pattern formations during the drying of a colloidal solution depending on the nature of the constituent proteins. The pattern formations of two oppositely charged proteins, namely HSA and lysozyme, have been studied in presence of fluorescence polystyrene beads of two different sizes (providing better image contrast for further analysis). The variation of pattern formation has been studied by varying the concentrations of the proteins as well as the particles. Furthermore, using image analysis, the patterns are segmented into different regions for quantification. To explain the variations in the patterns, we delve into the interplay of the interactions, especially the capillary and the DLVO forces (between the particles and the substrate). The developed methodology based on the coffee ring effect may be used to identify individual proteins.
... The study of protein solutions is a good starting point for understanding the transport mechanisms and aggregation processes during droplet evaporation of biofluids. The protein-salt interaction allow the formation of a large variety of complex aggregates [26][27][28][29][30] . Deposits composed by lysozyme and NaCl exhibit an amorphous peripheral ring and dendritic shapes 31,32 , while protein deposits of BSA and NaCl show structures such as rosettes, scallops, Chinese arrows and zigzag patterns 28 . ...
The deposit patterns derived from droplet evaporation allow current development of medical tests and new strategies for diagnostic in patients. For such purpose, the development and implementation of algorithms capable of characterizing and differentiating deposits are crucial elements. We report the study of deposit patterns formed by the droplet evaporation of binary mixtures of proteins containing NaCl. Optical microscopy reveals aggregates such as tip arrow-shaped, dendritic and semi-rosette patterns, needle-like and scalloped lines structures, as well as star-like and prism-shaped salt crystals. We use the first-order statistics (FOS) and gray level co-occurrence matrix (GLCM) to characterize the complex texture of deposit patterns. Three significant findings arise from this analysis: first, the FOS and GLCM parameters structurally characterize protein deposits. Secondly, they conform to simple exponential laws that change as a function of the NaCl concentration. Finally, the parameters are capable of revealing the different structural changes that occur during the droplet evaporation
... Ions, on the other hand, induce the formation of crystals around colloids deposited on the substrate. Rosette, scallop, dendrite shapes and amorphous rings appear inside of the deposits promoted by the intricate aggregation caused by ionic interactions [17][18][19]. Other ubiquitous features in the deposits are cracks that appear in the gel phase of a droplet due to large stresses during the deposit shrinkage [14,20]. ...
We study how cell motility affects the stains left by the evaporation of droplets of a biofluid suspension containing mouse spermatozoa. The suspension, which contains also a high concentration of salts usually needed by motile cells, forms, upon drying, a crystallized pattern. We examine the structural characteristics of such patterns by optical microscopy. The analysis reveals that cell motility affects the formation of elongated crystals with lateral tips, as well as the creation of interlocked aggregates. We prove that a lacunarity algorithm based on polar symmetry, distinguishes among deposits generated by motile and non-motile cells with an accuracy greater than 95%.
