The informative-capacity phenomenon of drying drops

Detection of milk adulteration using coffee ring effect and convolutional neural network

A low-cost and effective method is reported to identify water and synthetic milk adulteration of cow's milk using coffee ring patterns. The cow's milk samples were diluted with tap water (TW), distilled water (DW) and mineral water (MW) and drop cast onto glass slides to observe coffee ring patterns. The area of the ring, total particle area and average particle diameter were extracted from these patterns. For each ring, the ratio of total particle area versus total ring area was calculated. The area ratio, regardless of water adulterants, follows an exponential model with respect to average particle diameter. Unlike TW, the ratio for DW and MW adulterated milk are clustered and classified together with respect to the particle diameter. These results were independent of dilution level and are used for adulterant classification. The ring of milk adulterated using synthetic milk gave multiple concentric rings, flower-like structures, and oil globules throughout the dilution level. An Alexnet model was used to classify water and synthetic milk adulterants in authentic milk. The trained model could achieve 96.7% and 95.8% accuracy for binary and tertiary classification respectively. These results enable us to distinguish synthetic milk from pure milk and segregate DW and MW with respect to TW adulterated milk.

Soluto-thermal Marangoni convection in stationary micro-bioreactors on heated substrates: Tool for in vitro diagnosis of PSA

The investigation of antigen-laden droplet deposition patterns on antibody-immobilized substrates has potential for disease detection. Stationary droplets that contain antigens on surfaces immobilized with antibodies can function as microreactors. Temperature modulation enhances reaction efficiency and reduces detection time in droplet-based systems. Thus, the aim of this study is to explore the impact of substrate heating on the structures of protein deposits and the influence of substrate temperature on thermo-solutal Marangoni convection within the droplets. Previous research has explored deposition patterns as diagnostic tools, but limited investigations have focused on the effects of substrate heating on protein deposit structures and the influence of substrate temperature on thermo-solutal Marangoni convection within droplets, creating a knowledge gap. In this study, we conducted experiments to explore how heating the substrate affects the deposition patterns of droplets containing prostate-specific antigen (PSA) on a substrate immobilized with anti-PSA IgG. Additionally, we investigated the thermo-solutal Marangoni convection within these droplets. Our findings reveal distinct deposition patterns classified into dendritic structures (heterogeneous), transitional patterns, and needle-like (homogeneous) structures. The presence of prominent coffee rings and the variation in crystal size across different groups highlight the interplay between thermal and solutal Marangoni advection. Entropy analysis provides insights into structural differences within and between patterns. This work optimizes substrate temperatures for reduced evaporation and detection times while preserving protein integrity, advancing diagnostic tool development, and improving understanding of droplet-based systems.

Artificial intelligence assisted patient blood and urine droplet pattern analysis for non-invasive and accurate diagnosis of bladder cancer

Bladder cancer is one of the most common cancer types in the urinary system. Yet, current bladder cancer diagnosis and follow-up techniques are time-consuming, expensive, and invasive. In the clinical practice, the gold standard for diagnosis remains invasive biopsy followed by histopathological analysis. In recent years, costly diagnostic tests involving the use of bladder cancer biomarkers have been developed, however these tests have high false-positive and false-negative rates limiting their reliability. Hence, there is an urgent need for the development of cost-effective, and non-invasive novel diagnosis methods. To address this gap, here we propose a quick, cheap, and reliable diagnostic method. Our approach relies on an artificial intelligence (AI) model to analyze droplet patterns of blood and urine samples obtained from patients and comparing them to cancer-free control subjects. The AI-assisted model in this study uses a deep neural network, a ResNet network, pre-trained on ImageNet datasets. Recognition and classification of complex patterns formed by dried urine or blood droplets under different conditions resulted in cancer diagnosis with a high specificity and sensitivity. Our approach can be systematically applied across droplets, enabling comparisons to reveal shared spatial behaviors and underlying morphological patterns. Our results support the fact that AI-based models have a great potential for non-invasive and accurate diagnosis of malignancies, including bladder cancer.

Healthy and Pathological Porcine Blood Drop Evaporation: Effect of the Temperature

This study aims to understand and compare the evaporation dynamics of drops of healthy and pathological porcine blood (glomerulonephritis disease) evaporated on hydrophilic glass substrates at different surface temperatures (T_s): 23, 37, 60, and 90 °C. Subsequently, the different induced phenomena are characterized and described. Additionally, drops of water were evaporated at these four surface temperatures to better understand the difference between healthy and pathological porcine blood. Statistical studies were performed to analyze the evaporation rate, the maximum and average values of Marangoni numbers (Ma), and the evaporated specific time. The statistical tests showed significant differences in these parameters between healthy and pathological blood for each surface temperature. The mean and the maximum of the Ma increase with the increase in T_s caused by the increase in the temperature differences between the edge and the center of the drop. When comparing healthy and diseased blood, the Ma maximum and mean of healthy blood were higher than those of diseased blood for all T_s. Besides, this study emphasizes the influence of temperature on blood evaporation and the pattern caused by the Marangoni effect. These results demonstrate that differences between the two blood types are related to the disease and pave the way to developing a new methodology for medical decision-making.

Drying of bio-colloidal sessile droplets: Advances, applications, and perspectives

Drying of biologically-relevant sessile droplets, including passive systems such as DNA, proteins, plasma, and blood, as well as active microbial systems comprising bacterial and algal dispersions, has garnered considerable attention over the last decades. Distinct morphological patterns emerge when bio-colloids undergo evaporative drying, with significant potential in a wide range of biomedical applications, spanning bio-sensing, medical diagnostics, drug delivery, and antimicrobial resistance. Consequently, the prospects of novel and thrifty bio-medical toolkits based on drying bio-colloids have driven tremendous progress in the science of morphological patterns and advanced quantitative image-based analysis. This review presents a comprehensive overview of bio-colloidal droplets drying on solid substrates, focusing on the experimental progress during the last ten years. We provide a summary of the physical and material properties of relevant bio-colloids and link their native composition (constituent particles, solvent, and concentrations) to the patterns emerging due to drying. We specifically examined the drying patterns generated by passive bio-colloids (e.g., DNA, globular, fibrous, composite proteins, plasma, serum, blood, urine, tears, and saliva). This article highlights how the emerging morphological patterns are influenced by the nature of the biological entities and the solvent, micro- and global environmental conditions (temperature and relative humidity), and substrate attributes like wettability. Crucially, correlations between emergent patterns and the initial droplet compositions enable the detection of potential clinical abnormalities when compared with the patterns of drying droplets of healthy control samples, offering a blueprint for the diagnosis of the type and stage of a specific disease (or disorder). Recent experimental investigations of pattern formation in the bio-mimetic and salivary drying droplets in the context of COVID-19 are also presented. We further summarized the role of biologically active agents in the drying process, including bacteria, algae, spermatozoa, and nematodes, and discussed the coupling between self-propulsion and hydrodynamics during the drying process. We wrap up the review by highlighting the role of cross-scale in situ experimental techniques for quantifying sub-micron to micro-scale features and the critical role of cross-disciplinary approaches (e.g., experimental and image processing techniques with machine learning algorithms) to quantify and predict the drying-induced features. We conclude the review with a perspective on the next generation of research and applications based on drying droplets, ultimately enabling innovative solutions and quantitative tools to investigate this exciting interface of physics, biology, data sciences, and machine learning.

Effect of temperature on evaporation dynamics of sheep's blood droplets and topographic analysis of induced patterns

To characterize various induced phenomena and the blood of healthy sheep using several parameters, the evaporation dynamics of 72 drops of sheep blood evaporated at several temperatures: 23, 37, 60, and 90 °C on glass hydrophilic substrates were studied. This allows the prediction of the sheep blood pattern, knowing the surface temperature and vice versa. To determine the variation in the Marangoni number between the center and the triple line, an infrared thermography method was used to measure the temperature variation along the surface of the drop. Simultaneously, a high-performance camera was used to measure the variation in the height of the drop during the evaporation using a superior algorithm software for image analysis, drop shape analyzer, under controlled conditions (Humidity = 40%, T_atm = 23 °C). The study of the evaporation dynamics and pattern formation shows the effect of temperature on the flow circulation inside the drop, resulting in the final deposit. The results showed two categories corresponding to two different evaporation phenomena induced by the thermal Marangoni effect. Furthermore, to transform the induced pattern of sheep blood evaporation into a 3D image, a topographic study was performed using a highly accurate, fast, and flexible optical 3D measurement system. The topographic parameters were subsequently extracted from these 3D images. The statistical study showed a good correlation between the topographic parameters and the surface temperature, and a significant difference between each temperature group for each parameter.

Transition from Dendritic to Cell-like Crystalline Structures in Drying Droplets of Fetal Bovine Serum under the Influence of Temperature

The desiccation of biofluid droplets leads to the formation of complex deposits which are morphologically affected by the environmental conditions, such as temperature. In this work, we examine the effect of substrate temperatures between 20 and 40 °C on the desiccation deposits of fetal bovine serum (FBS) droplets. The final dried deposits consist of different zones: a peripheral protein ring, a zone of protein structures, a protein gel, and a central crystalline zone. We focus on the crystalline zone showing that its morphological and topographical characteristics vary with substrate temperature. The area of the crystalline zone is found to shrink with increasing substrate temperature. Additionally, the morphology of the crystalline structures changes from dendritic at 20 °C to cell-like for substrate temperatures between 25 and 40 °C. Calculation of the thermal and solutal Bénard-Marangoni numbers shows that while thermal effects are negligible when drying takes place at 20 °C, for higher substrate temperatures (25-40 °C), both thermal and solutal convective effects manifest within the drying drops. Thermal effects dominate earlier in the evaporation process leading, we believe, to the development of instabilities and, in turn, to the formation of convective cells in the drying drops. Solutal effects, on the other hand, are dominant toward the end of drying, maintaining circulation within the cells and leading to crystallization of salts in the formed cells. The cell-like structures are considered to form because of the interplay between thermal and solutal convection during drying. Dendritic growth is associated with a thicker fluid layer in the crystalline zone compared to cell-like growth with thinner layers. For cell-like structures, we show that the number of cells increases and the area occupied by each cell decreases with temperature. The average distance between cells decreases linearly with substrate temperature.

Cationic surfactant-directed structural control of NaCl crystals from evaporating sessile droplets

We report morphological regulation of NaCl (sodium chloride) crystals through the evaporative crystallisation process of microdroplets containing a cationic surfactant CTAB (cetyltrimethylammonium bromide). Various fascinating evaporative salt morphologies are observed using different combinations of salt (C_NaCl) and surfactant (C_CTAB) concentrations. Each observed morphology is carefully explained by the interplaying physical phenomena, such as crystallisation, micellisation, evaporative dewetting, and surface adsorption of anionic couneterions. Salt morphologies are investigated for low (C_NaCl = 0.1 (M)), intermediate (C_NaCl = 0.5 (M)) and high (C_NaCl = 2 (M)) concentrations, whereas surfactant concentrations are varied four orders of magnitudes (from 0.0001 (M) to 0.1 (M)). Interestingly, we observe a threshold in C_CTAB at 0.001 (M), beyond which the peripheral rings of dried deposits are found to be composed of CTAB for C_NaCl = 0.1 (M), while the same is seen to be made up of NaCl for C_NaCl = 2 (M). We have explained the morphological evolution by the process of competitive surface adsorption phenomenon between Cl^- and Br^- counter ions. Such a detailed study of saline droplet crystallisation in the presence of a cationic surfactant underpins the fundamental understanding of the crystallisation process. In addition, it may further impact application sectors where crystallisation of saline solution plays an important role, especially in the presence of additives.

Patterns from dried drops as a characterisation and healthcare diagnosis technique, potential and challenges: A review

When particulate-laden droplets evaporate, they leave behind complex patterns on the substrate depending on their composition and the dynamics of their evaporation. Over the past two decades, there has been an increased interest in interpreting these patterns due to their numerous applications in biomedicine, forensics, food quality analysis and inkjet printing. The objective of this review is to investigate the use of patterns from dried drops as a characterisation and diagnosis technique. The patterns left behind by dried drops of various complex fluids are categorised. The potential applications of these patterns are presented, focussing primarily on healthcare, where the future impact could be greatest. A discussion on the limitations which must be overcome and prospective works that may be carried out to allow for widespread implementation of this technique is presented in conclusion.

The Effect of Substrate Temperature on the Evaporative Behaviour and Desiccation Patterns of Foetal Bovine Serum Drops

The drying of bio-fluid drops results in the formation of complex patterns, which are morphologically and topographically affected by environmental conditions including temperature. We examine the effect of substrate temperatures between 20 °C and 40 °C, on the evaporative dynamics and dried deposits of foetal bovine serum (FBS) drops. The deposits consist of four zones: a peripheral protein ring, a zone of protein structures, a protein gel, and a central crystalline zone. We investigate the link between the evaporative behaviour, final deposit volume, and cracking. Drops dried at higher substrate temperatures in the range of 20 °C to 35 °C produce deposits of lower final volume. We attribute this to a lower water content and a more brittle gel in the deposits formed at higher temperatures. However, the average deposit volume is higher for drops dried at 40 °C compared to drops dried at 35 °C, indicating protein denaturation. Focusing on the protein ring, we show that the ring volume decreases with increasing temperature from 20 °C to 35 °C, whereas the number of cracks increases due to faster water evaporation. Interestingly, for deposits of drops dried at 40 °C, the ring volume increases, but the number of cracks also increases, suggesting an interplay between water evaporation and increasing strain in the deposits due to protein denaturation.

The contact angle of an evaporating droplet of a binary solution on a super wetting surface

We study the dynamics of the contact angle of a droplet of a binary solution evaporating on a super wetting surface. Recent experiments have shown that although the equilibrium contact angle of such a droplet is zero, the contact angle can show complex time dependence before reaching the equilibrium value. We analyse such phenomena by extending our previous theory for the dynamics of an evaporating single component droplet to a double component droplet. We show that the time dependence of the contact angle can be quite complex. Typically, it first decreases slightly, and then increases and finally decreases again. Under certain conditions, we find that the contact angle remains constant over a certain period of time during evaporation. We study how the plateau or peak contact angle depends on the initial composition and the humidity. This theory explains the experimental results reported previously.

Diagnostic tests based on pattern formation in drying body fluids - A mapping review

There are numerous diagnostic tests based on pattern formation in desiccating body fluids, where the pattern or some of its characteristics constitute the diagnostic test outcome. However, partially due to the development in different time periods, and partially due to publications in languages different from English, most of these diagnostic tests exist as separate approaches and have never been grouped, systematized, nor compared with each other. In the present mapping review, we performed a wide literature search with the aim to collect all diagnostic tests based on pattern formation in desiccating body fluids. Furthermore, we grouped the identified diagnostic tests according to their experimental protocols, type of body fluids investigated, and target conditions, and propose so for the first time a classification of different diagnostic tests based on pattern formation in desiccating body fluids. The literature search revealed 1603 publications, out of which 141 were included into the review. Following three main classification criteria (way of deposition of the fluid for desiccation, addition of reagents, and spatial restrictions during evaporation), we identified six different methods; following a further classification concerning the analyzed body fluid we identified 30 different diagnostic tests based on pattern formation in evaporating body fluids. Amongst these tests are well-known procedures such as ferning tests (tear ferning for the assessment of tear film quality, saliva and cervical mucus ferning for the detection of the fertile period, and amniotic fluid ferning for the diagnosis of fetal membrane rupture), whereas other tests are less well-established. In the latter group, the most frequently investigated body fluids were serum, saliva, and blood; the most frequently addressed target conditions were cancer, inflammation, and benign tumors. We recommend conducting further systematic reviews and meta-analyses concerning groups of methods addressing the same target condition.

Pattern formation in drying blood drops

Patterns in dried droplets are commonly observed as rings left after spills of dirty water or coffee have evaporated. Patterns are also seen in dried blood droplets and the patterns have been shown to differ from patients afflicted with different medical conditions. This has been proposed as the basis for a new generation of low-cost blood diagnostics. Before these diagnostics can be widely used, the underlying mechanisms leading to pattern formation in these systems must be understood. We analyse the height profile and appearance of dispersions prepared with red blood cells (RBCs) from healthy donors. The red cell concentrations and diluent were varied and compared with simple polystyrene particle systems to identify the dominant mechanistic variables. Typically, a high concentration of non-volatile components suppresses ring formation. However, RBC suspensions display a greater volume of edge deposition when the red cell concentration is higher. This discrepancy is caused by the consolidation front halting during drying for most blood suspensions. This prevents the standard horizontal drying mechanism and leads to two clearly defined regions in final crack patterns and height profile. This article is part of a discussion meeting issue 'A cracking approach to inventing new tough materials: fracture stranger than friction'.

Pattern Formation upon Evaporation of Sessile Droplets of Polyelectrolyte/Surfactant Mixtures on Silicon Wafers

The formation of coffee-ring deposits upon evaporation of sessile droplets containing mixtures of poly(diallyldimethylammonium chloride) (PDADMAC) and two different anionic surfactants were studied. This process is driven by the Marangoni stresses resulting from the formation of surface-active polyelectrolyte–surfactant complexes in solution and the salt arising from the release of counterions. The morphologies of the deposits appear to be dependent on the surfactant concentration, independent of their chemical nature, and consist of a peripheral coffee ring composed of PDADMAC and PDADMAC–surfactant complexes, and a secondary region of dendrite-like structures of pure NaCl at the interior of the residue formed at the end of the evaporation. This is compatible with a hydrodynamic flow associated with the Marangoni stress from the apex of the drop to the three-phase contact line for those cases in which the concentration of the complexes dominates the surface tension, whereas it is reversed when most of the PDADMAC and the complexes have been deposited at the rim and the bulk contains mainly salt.

Data-driven time-dependent state estimation for interfacial fluid mechanics in evaporating droplets

Droplet evaporation plays crucial roles in biodiagnostics, microfabrication, and inkjet printing. Experimentally studying the evolution of a sessile droplet consisting of two or more components needs sophisticated equipment to control the vast parameter space affecting the physical process. On the other hand, the non-axisymmetric nature of the problem, attributed to compositional perturbations, introduces challenges to numerical methods. In this work, droplet evaporation problem is studied from a new perspective. We analyze a sessile methanol droplet evolution through data-driven classification and regression techniques. The models are trained using experimental data of methanol droplet evolution under various environmental humidity levels and substrate temperatures. At higher humidity levels, the interfacial tension and subsequently contact angle increase due to higher water uptake into droplet. Therefore, different regimes of evolution are observed due to adsorption-absorption and possible condensation of water which turns the droplet from a single component into a binary system. In this work, machine learning and data-driven techniques are utilized to estimate the regime of droplet evaporation, the time evolution of droplet base diameter and contact angle, and level of surrounding humidity. Droplet regime is estimated by classification algorithms through point-by-point analysis of droplet profile. Decision tree demonstrates a better performance compared to Naïve Bayes (NB) classifier. Additionally, the level of surrounding humidity, as well as the time evolution of droplet base diameter and contact angle, are estimated by regression algorithms. The estimation results show promising performance for four cases of methanol droplet evolution under conditions unseen by the model, demonstrating the model's capability to capture the complex physics underlying binary droplet evolution.

Texture Analysis of Dried Droplets for the Quality Control of Medicines

The quality control of medicines guarantees the effectiveness of treatments for diseases. We explore the use of texture analysis of patterns in dried droplets as a tool to readily detect both impurities and changes in drug concentration. Four types of medicines associated with different routes of administration were analyzed: Methotrexate, Ciprofloxacin, Clonazepam, and Budesonide. We use NaCl and a hot substrate at 63 ∘C to promote aggregate formation and to reduce droplet drying time. Depending on the medicine, optical microscopy reveals different complex aggregates such as circular to oval splatters, fern-like islands, crown shapes, crown needle-like and bump-like patterns as well as dendritic branched and star-like crystals. We use some physical features of the stains (as the stain diameter and superficial area) and gray level co-occurrence matrix (GLCM) to characterize patterns of dried droplets. Finally, we show that structural analysis of stains can achieve 95% accuracy in identifying medicines with 30% water dilution, while it achieves 99% accuracy in detecting drugs with 10% other substances.

Infrared Spectroscopy of Blood

The magnitude of infectious diseases in the twenty-first century created an urgent need for point-of-care diagnostics. Critical shortages in reagents and testing kits have had a large impact on the ability to test patients with a suspected parasitic, bacteria, fungal, and viral infections. New point-of-care tests need to be highly sensitive, specific, and easy to use and provide results in rapid time. Infrared spectroscopy, coupled to multivariate and machine learning algorithms, has the potential to meet this unmet demand requiring minimal sample preparation to detect both pathogenic infectious agents and chronic disease markers in blood. This focal point article will highlight the application of Fourier transform infrared spectroscopy to detect disease markers in blood focusing principally on parasites, bacteria, viruses, cancer markers, and important analytes indicative of disease. Methodologies and state-of-the-art approaches will be reported and potential confounding variables in blood analysis identified. The article provides an up to date review of the literature on blood diagnosis using infrared spectroscopy highlighting the recent advances in this burgeoning field.

Effects of substrate temperature on patterns produced by dried droplets of proteins

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.

Effect of Particle Concentration on Surfactant-Induced Alteration of the Contact Line Deposition in Evaporating Sessile Droplets

Controlling and suppressing the so-called "coffee-ring effect" (CRE) is an issue of cardinal importance and intense interest in many industries and scientific fields. Here, the combined effect of the particle and surfactant concentration on the CRE is investigated by gradually adding Triton X-100 surfactant to colloidal suspensions of SiO₂ nanoparticles in ethanol for various particle concentrations. First, the effect of particle concentration on the contact line dynamics during the evaporation of a sessile droplet is investigated. It is shown that increasing the particle concentration leads to an increase in pinning time and ring width, whereas the droplet's initial and dynamic contact angle remains unchanged. Afterward, the effect of different concentrations of surfactant is studied for different particle concentrations. It is concluded that the surfactant concentration at which the CRE is suppressed is dependent on the initial particle concentration of the colloid, and it increases as the particle concentration increases. Furthermore, as adding surfactant with a concentration lower than this critical concentration results in an unsuppressed CRE, it is shown that surpassing this concentration will result in a depletion of particles in the contact line. Moreover, it is demonstrated that this critical surfactant concentration has no significant effect on the droplet's geometry and the total evaporation time.

Concentration-driven phase transition and self-assembly in drying droplets of diluting whole blood

Multi-colloidal systems exhibit a variety of structural and functional complexity owing to their ability to interact amongst different components into self-assembled structures. This paper presents experimental confirmations that reveal an interesting sharp phase transition during the drying state and in the dried film as a function of diluting concentrations ranging from 100% (undiluted whole blood) to 12.5% (diluted concentrations). An additional complementary contact angle measurement exhibits a monotonic decrease with a peak as a function of drying. This peak is related to a change in visco-elasticity that decreases with dilution, and disappears at the dilution concentration for the observed phase transition equivalent to 62% (v/v). This unique behavior is clearly commensurate with the optical image statistics and morphological analysis; and it is driven by the decrease in the interactions between various components within this bio-colloid. The implications of these phenomenal systems may address many open-ended questions of complex hierarchical structures.

Drop Drying on the Sensor: One More Way for Comparative Analysis of Liquid Media

It is known that the processes of self-organization of the components of drying a liquid drop on a solid substrate are well reproduced under the same external conditions and are determined only by the composition and dispersion of the liquid. If the drop dries on the surface of the sensor device, these processes can be recorded and used as a passport characteristic of the liquid. The first half of the article is devoted to the description of the principles of the method and the proof of the validity of our assumptions. The second half of the article is devoted to the development of a user-friendly version of the device, where the change in the real and imaginary parts of the electrical impedance of the resonator was used as an informative parameter. The measure of the closeness of the relative positions of the hodographs of the compared samples on the complex plane is used as a criterion for the similarity-/-difference of various liquids. The design of a new sensor device and the results of its tests for distinguishing between different brands of alcoholic beverages and reconstituted milk of different concentrations are presented.

Interfacial energy driven distinctive pattern formation during the drying of blood droplets

HYPOTHESIS

Dried blood droplet morphology may potentially serve as an alternative biomarker for several patho-physiological conditions. The deviant properties of the red blood cells and the abnormal composition of diseased samples are hypothesized to manifest through unique cell-cell and cell-substrate interactions leading to different morphological patterns. Identifying distinctive morphological trait from a large sample size and proposing confirmatory explanations are necessary to establish the signatory pattern as a potential biomarker to differentiate healthy and diseased samples.

EXPERIMENTS

Comprehensive experimental investigation was undertaken to identify the signatory dried blood droplet patterns. The corresponding image based analysis was in turn used to differentiate the blood samples with a specific haematological disorder "Thalassaemia" from healthy ones. Relevant theoretical analysis explored the role of cell-surface and cell-cell interactions pertinent to the formation of the distinct dried patterns.

FINDINGS

The differences observed in the dried blood patterns, specifically the radial crack lengths, were found to eventuate from the differences in the overall interaction energies of the system. A first-generation theoretical analysis, with the mean field approximation, also confirmed similar outcome and justified the role of the different physico-chemical properties of red blood cells in diseased samples resulting in shorter radial cracks.

Machine Learning Analysis for Quantitative Discrimination of Dried Blood Droplets

One of the most interesting and everyday natural phenomenon is the formation of different patterns after the evaporation of liquid droplets on a solid surface. The analysis of dried patterns from blood droplets has recently gained a lot of attention, experimentally and theoretically, due to its potential application in diagnostic medicine and forensic science. This paper presents evidence that images of dried blood droplets have a signature revealing the exhaustion level of the person, and discloses an entirely novel approach to studying human dried blood droplet patterns. We took blood samples from 30 healthy young male volunteers before and after exhaustive exercise, which is well known to cause large changes to blood chemistry. We objectively and quantitatively analysed 1800 images of dried blood droplets, developing sophisticated image processing analysis routines and optimising a multivariate statistical machine learning algorithm. We looked for statistically relevant correlations between the patterns in the dried blood droplets and exercise-induced changes in blood chemistry. An analysis of the various measured physiological parameters was also investigated. We found that when our machine learning algorithm, which optimises a statistical model combining Principal Component Analysis (PCA) as an unsupervised learning method and Linear Discriminant Analysis (LDA) as a supervised learning method, is applied on the logarithmic power spectrum of the images, it can provide up to 95% prediction accuracy, in discriminating the physiological conditions, i.e., before or after physical exercise. This correlation is strongest when all ten images taken per volunteer per condition are averaged, rather than treated individually. Having demonstrated proof-of-principle, this method can be applied to identify diseases.

Drying Droplets with Soluble Surfactants

We propose a theory for the drying of liquid droplets of surfactant solutions. We show that the added surfactant hinders droplet receding and facilitates droplet spreading, causing a complex behavior of the contact line of an evaporating droplet: the contact line first recedes, then advances, and finally recedes again. We also show that the surfactant can change the deposition pattern from mountain-like to volcano-like and then to coffee-ring-like. Specially, when the contact line motion undergoes a clear receding-advancing transition, a two-ring pattern is formed. The mechanism of the two-ring formation is different from the stick-slip mechanism proposed previously and may be tested experimentally.

Desiccation Patterns of Plasma Sessile Drops

The renewed interest in plasma desiccation patterns focuses on the potential of these patterns to be developed into 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, buildup/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.

Morphology modulation in evaporative drying mediated crystallization of sodium chloride solution droplet with surfactant

We report the evaporative drying of an aqueous droplet containing a dilute solution of sodium chloride (NaCl) on a hydrophobic substrate made of cross-linked poly-dimethyl siloxane (PDMS). The salt concentration Cn was varied between 0.08 molar (M) and 2.0 M. The contact line of the evaporating droplets shows significant initial retraction for all Cn, before they get pinned. While the final morphology comprises a few small NaCl crystals deposited around the pinned contact line, in droplets with a low Cn (<0.5 M), it transforms to a single large salt crystal when Cn > 0.7 M with no peripheral deposition. We further show that the deposition morphology drastically changes when an anionic surfactant, sodium dodecyl sulfate (SDS), is added into the salt-solutions. Even in the surfactant-laden droplets, the final deposition morphology changes significantly as a function of Cn. It transforms from a thick SDS ring surrounding a fractal-like deposit of NaCl crystallites at lower Cn to a peripheral deposit of NaCl crystals at higher Cn due to competition between micelle formation and crystallization. However, the crystallographic orientation of the deposited NaCl crystals remains unaltered irrespective of the presence of surfactant.

Controlling the contact angle of biological sessile drops for study of their desiccated cracking patterns

Current exploration of cracking patterns of desiccated biological sessile drops as a new approach of scientific research is progressing rapidly. It has been proposed that biological fluids are naturally capable of storing information. Cracking patterns of desiccated biological sessile drops have the potential to provide a facile means to study the links between compositions of biofluids, their structures and their functions. This potential is, however, limited by our current inability to control the influences of non-pathological factors on cracking patterns. Among the non-pathological factors, the initial sessile drop contact angle has a strong influence on cracking patterns through affecting the material transport and stress distributions within the drop. In this work, we developed a method to control the initial drop contact angle on a glass surface to enable the investigation of the contact angle-induced pattern changes in a biological sessile drop. Human blood was selected as the biofluid in this study, because of its richness in cracking patterns. It has been found that the increase in the initial contact angle enlarges the orthoradial cracks close to the drop edge and compresses the width of the peripheral region. We have also concluded that the number of cracks in the central region of the desiccated pattern can be correlated with the drop contact angle. This work also provides a novel protocol for fabricating standardized substrates for studies of desiccation patterns of biological and other complex colloidal fluids.

Multi-ring Deposition Pattern of Drying Droplets

We propose a theory for the multi-ring pattern of the deposits that are formed when droplets of the suspension are dried on a substrate. Assuming a standard model for the stick-slip motion of the contact line, we show that as droplets evaporate many concentric rings of deposits are formed but are taken over by a solid-circle pattern in the final stage of drying. An analytical expression is given to indicate when the ring pattern changes to a solid-circle pattern during the evaporation process. The results are in qualitative agreement with existing experiments, and the other predictions on how the evaporation rate, droplet radius, and receding contact angle affect the pattern are all subject to an experimental test.

Texture analysis of protein deposits produced by droplet evaporation

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.

Pattern formation of stains from dried drops to identify spermatozoa motility

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%.

Mechanisms of pattern formation from dried sessile drops

The formation of patterns after the evaporation of colloidal droplets deposited on a solid surface is an everyday natural phenomenon. During the past two decades, this topic has gained broader audience due to its numerous applications in biomedicine, nanotechnology, printing, coating, etc. This paper presents a detailed review of the experimental studies related to the formation of various deposition patterns from dried droplets of complex fluids (i.e., nanofluids, polymers). First, this review presents the fundamentals of sessile droplet evaporation including evaporation modes and internal flow fields. Then, the most observed dried patterns are presented and the mechanisms behind them are discussed. The review ends with the categorisation and exhaustive investigation of a wide range of factors affecting pattern formation.

Biofluid spectroscopic disease diagnostics: A review on the processes and spectral impact of drying

The complex patterns observed from evaporated liquid drops have been examined extensively over the last 20 years. Complete understanding of drop deposition is vital in many medical processes, and one which is essential to the translation of biofluid spectroscopic disease diagnostics. The promising use of spectroscopy in disease diagnosis has been hindered by the complicated patterns left by dried biological fluids which may inhibit the clinical translation of this technology. Coffee-ring formation, cracking and gelation patterns have all been observed in biofluid drops, and with surface homogeneity being a key element to many spectroscopic techniques, experimental issues have been found to arise. A better understanding of the fundamental processes involved in a drying droplet could allow efficient progression in this research field, and ultimately benefit the population with the development of a reliable cancer diagnostic.

Drying drops : Drying drops containing solutes: From hydrodynamical to mechanical instabilities

The drying of complex fluids involves a large number of microscopic phenomena (transport and organization of non-volatile solutes) as well as hydrodynamic and mechanical instabilities. These phenomena can be captured in drying sessile drops where different domains can be identified: strong concentration gradients, formation of a glassy or porous envelope that withstands mechanical stress, and consolidation of a layer strongly adhering to the substrate at the drop edge. In colloidal systems, we quantify the evolution of the particle volume fraction at a nanometric scale and microscopic scale and identify the conditions for the envelope formation at the free surface by balancing the effect of diffusion and evaporation. When a solid envelope is formed at a drop surface, the mechanical instabilities induced by the drying result in different drop shapes. Finally, large drying stresses build up in the solid layer adhering on the substrate, and possibly cause crack formation. In particular, we study how crack patterns are affected by the contact angle of drops and the drying conditions. A particular interest of the review is devoted to drying pattern of solutes.

Patterns produced by dried droplets of protein binary mixtures suspended in water

Patterns formed by the evaporation of a drop containing biological molecules have provided meaningful information about certain pathologies. In this context, several works propose the study of protein solutions as a model to understand the formation of deposits of biological fluids. Generally, dry droplets of proteins in a saline solution create complex aggregates. Here, we present an experimental study on the formation of patterns produced by the evaporation of droplet suspensions containing a protein binary mixture. We explore the structural aspect of such deposits by using optical and atomic force microscopy. We found that salt is unnecessary for the formation of complex structures such as crystal clusters, dendritic and undulated branches, and interlocked chains. Such structural features allow us to differentiate among protein binary mixtures. Finally, we discuss the potential use of this finding to reveal the presence of a protein suspensions, the folded and unfolded state of a protein, as well as their structural changes.

Deposition Patterns of Two Neighboring Droplets: Onsager Variational Principle Studies

When two droplets containing nonvolatile components are sitting close to each other, asymmetrical ring-like deposition patterns are formed on the substrate. We propose a simple theory based on the Onsager variational principle to predict the deposition patterns of two neighboring droplets. The contact line motion and the interference effect of two droplets are considered simultaneously. We demonstrate that the gradients of evaporation rate along two droplets is the main reason for forming asymmetrical deposition patterns. By tracing the relative motion between the contact line and the solute particles, we found that the velocities of solute particles have no cylindrical symmetry anymore because of the asymmetrical evaporation rate, giving the underlying mechanism of forming asymmetrical patterns. Moreover, controlling the evaporation rate combined with varying the contact line friction, fan-like and eclipse-like deposition patterns are obtained. The theoretical results of pinned contact line cases are qualitatively consistent with the pervious experimental results.

Blood drop patterns: Formation and applications

The drying of a drop of blood or plasma on a solid substrate leads to the formation of interesting and complex patterns. Inter- and intra-cellular and macromolecular interactions in the drying plasma or blood drop are responsible for the final morphologies of the dried patterns. Changes in these cellular and macromolecular components in blood caused by diseases have been suspected to cause changes in the dried drop patterns of plasma and whole blood, which could be used as simple diagnostic tools to identify the health of humans and livestock. However, complex physicochemical driving forces involved in the pattern formation are not fully understood. This review focuses on the scientific development in microscopic observations and pattern interpretation of dried plasma and whole blood samples, as well as the diagnostic applications of pattern analysis. Dried drop patterns of plasma consist of intricate visible cracks in the outer region and fine structures in the central region, which are mainly influenced by the presence and concentration of inorganic salts and proteins during drying. The shrinkage of macromolecular gel and its adhesion to the substrate surface have been thought to be responsible for the formation of the cracks. Dried drop patterns of whole blood have three characteristic zones; their formation as functions of drying time has been reported in the literature. Some research works have applied engineering treatment to the evaporation process of whole blood samples. The sensitivities of the resultant patterns to the relative humidity of the environment, the wettability of the substrates, and the size of the drop have been reported. These research works shed light on the mechanisms of spreading, evaporation, gelation, and crack formation of the blood drops on solid substrates, as well as on the potential applications of dried drop patterns of plasma and whole blood in diagnosis.

Three-dimensional patterns from the thin-film drying of amino acid solutions

Experimental atomic force microscopy (AFM) images show the dried-in patterns from amino acid solutions which can be in the form of dots or networks. The three-dimensional lattice-gas Kinetic Monte Carlo (KMC) model is applied to simulate the formation of dot-like and network-like particle structures from the evaporating thin films of solutions. A sigmoidal jump in the chemical potential value is implemented to obtain dual-scale structures with the grain size distribution peaking at two distinctive values. The simulated and experimental results are qualitatively comparable.

Patterns from drying drops

The objective of this review is to investigate different deposition patterns from dried droplets of a range of fluids: paints, polymers and biological fluids. This includes looking at mechanisms controlling the patterns and how they can be manipulated for use in certain applications such as medical diagnostics and nanotechnology. This review introduces the fundamental properties of droplets during evaporation. These include profile evolution (constant contact angle regime (CCAR) and constant radius regime (CRR)) and the internal flow (Marangoni and Capillary flow (Deegan et al. [22])). The understanding of these processes and the basic physics behind the phenomenon are crucial to the understanding of the factors influencing the deposition patterns. It concludes with the applications that each of these fluids can be used in and how the manipulation of the deposition pattern is useful. The most commonly seen pattern is the coffee-ring deposit which can be seen frequently in real life from tea/coffee stains and in water colour painting. This is caused by an outward flow known as capillary flow which carries suspended particles out to the edge of the wetted area. Other patterns that were found were uniform, central deposits and concentric rings which are caused by inward Marangoni flow. Complex biological fluids displayed an array of different patterns which can be used to diagnose patients.

Salt-induced pattern formation in evaporating droplets of lysozyme solutions

Solute self-organization during evaporation of colloidal sessile droplets has attracted the attention of researchers over the past few decades due to a variety of technological applications. Recently, pattern formation during evaporation of various biofluids has been studied due to potential applications in screening and diagnosis. The complex morphological patterns in the deposit are unique to various disorders and are influenced by various physical mechanisms occurring during evaporation. These complex patterns can be better understood by studying evaporation of model solutions of biological relevance. Here, we examine the general features of pattern formation during sessile droplet evaporation of aqueous lysozyme solutions with varying concentrations of NaCl. Lysozyme is a globular protein found in biological fluids such as tears and saliva. The morphological evolution of the droplet is studied by time-lapse video during evaporation via reflection optical microscopy. The final deposits exhibit an amorphous peripheral ring and interior regions containing crystallites and dendritic forms, dependent on NaCl concentration. Scanning electron microscopy (SEM) images demonstrate the multi-scale hierarchical nature of these structures.

Characteristic size for onset of coffee-ring effect in evaporating lysozyme-water solution droplets

Liquid droplets containing suspended particles deposited on a solid surface often form a ring-like structure due to the redistribution of solute during evaporation, a phenomenon known as the "coffee ring effect". The complex patterns left on the substrate after evaporation are characteristic of the nature of the solute and the particle transport mechanisms. In this study, the morphological evolution and conditions for coffee ring formation for simplified model biological solutions of DI water and lysozyme are examined by AFM and optical microscopy. Lysozyme is a globular protein found in high concentration, for example, in human tears and saliva. The drop diameters studied are very small, ranging from 1 to 50 μm. In this size range, protein motion and the resulting dried residue morphology are highly influenced by the decreased evaporation time of the drop. In this work, we consider the effect of droplet size and concentration on the morphology of the deposited drop as well as the minimal conditions for coffee ring formation in this system. Two distinct deposit types are observed: a simple cap-shaped deposit for drops with small diameters and a ring-like deposit at larger diameters. Ring formation occurs at a critical diameter, which depends systematically on initial lysozyme concentration.

Raman spectroscopy of synovial fluid as a tool for diagnosing osteoarthritis

For many years, viscosity has been the primary method used by researchers in rheumatology to assess the physiochemical properties of synovial fluid in both normal and osteoarthritic patients. However, progress has been limited by the lack of methods that provide multiple layers of information, use small sample volumes, and are rapid. Raman spectroscopy was used to assess the biochemical composition of synovial fluid collected from 40 patients with clinical evidence of knee osteoarthritis (OA) at the time of elective surgical treatment. Severity of knee osteoarthritis was assessed by a radiologist using Kellgren/Lawrence (K/L) scores from knee joint x rays, while light microscopy and Raman spectroscopy were used to examine synovial fluid (SF) aspirates (2 to 10 microL), deposited on fused silica slides. We show that Raman bands used to describe protein secondary structure and content can be used to detect changes in synovial fluid from osteoarthritic patients. Several Raman band intensity ratios increased significantly in spectra collected from synovial fluid in patients with radiological evidence of moderate-to-severe osteoarthritis damage. These ratios can be used to provide a "yes/no" damage assessment. These studies provide evidence that Raman spectroscopy would be a suitable candidate in the evaluation of joint damage in knee osteoarthritis patients.