Smartphone-Based Microalgae Monitoring Platform Using Machine Learning

There is a growing demand for microalgae monitoring techniques since microalgae are one of the most influential underwater organisms in aquatic environments. Specifically, such a technique should be hand-held, rapid, and easily accessible in the field since current methods (benchtop microscopy, flow cytometry, or satellite imaging) require high equipment costs and well-trained personnel. This study’s main objective was to develop a field-deployable microalgae monitoring platform using only a single smartphone and inexpensive acrylic color films. It aimed to evaluate the morphological states of microalgae including stress, cell concentration, and dominant species. Using a smartphone’s white LED flash and camera, the platform detected fluorescence and reflectance intensities from microalgal samples in various excitation and emission color combinations. Multidimensional intensity data were evaluated from the smartphone images and used to train a support vector machine (SVM) based machine learning model to classify various morphological states. The SVM classification accuracies were 0.84–0.96 in classifying four- to five-tier stress types, cell concentration, and dominant species and 0.99–1.00 in classifying two-tier stress types and cell concentrations. Additional field samples were collected from the local pond and independently tested using the laboratory-collected training set, showing two-tier classification accuracies of 0.90–1.00. This platform enables accessible and on-site microalgae monitoring for nonexperts and can be potentially applied to monitoring harmful algal blooms (HABs)

Role of Dopamine Chemistry in the Formation of Mechanically Strong Mandibles of Grasshoppers

Role of Dopamine Chemistry in the Formation of Mechanically Strong Mandibles of Grasshopper

Switch of Surface Adhesion to Cohesion by Dopa-Fe³⁺ Complexation, in Response to Microenvironment at the Mussel Plaque/Substrate Interface

Although Dopa-Fe³⁺ complexation is known to play an important role in mussel adhesion for providing mechanical properties, its function at the plaque/substrate interface, where actual surface adhesion occurs, remains unknown, with regard to interfacial mussel adhesive proteins (MAPs) type 3 fast variant (fp-3F) and type 5 (fp-5). Here, we confirmed Dopa-Fe³⁺ complexation of interfacial MAPs and investigated the effects of Dopa-Fe³⁺ complexation regarding both surface adhesion and cohesion. The force measurements using surface forces apparatus (SFA) analysis showed that intrinsic strong surface adhesion at low pH, which is similar to the local acidified environment present during the secretion of adhesive proteins, vanishes by Dopa-Fe³⁺ complexation and alternatively, strong cohesion is generated in higher pH conditions similar to seawater. A high Dopa content increased the capacity for both surface adhesion and cohesion, but not at the same time. In contrast, a lack of Dopa resulted in both weak surface adhesion and cohesion without significant effects of Fe³⁺ complexation. Our findings shed light on how mussels regulate Dopa functionality at the plaque/substrate interface, in response to the microenvironment, and might provide new insight for the design of mussel-inspired biomaterials

Bicontinuous Fluid Structure with Low Cohesive Energy: Molecular Basis for Exceptionally Low Interfacial Tension of Complex Coacervate Fluids

An exceptionally low interfacial tension of a dense fluid of concentrated polyelectrolyte complexes, phase-separated from a biphasic fluid known as complex coacervates, represents a unique and highly sought-after materials property that inspires novel applications from superior coating to wet adhesion. Despite extensive studies and broad interest, the molecular and structural bases for the unique properties of complex coacervates are unclear. Here, a microphase-separated complex coacervate fluid generated by mixing a recombinant mussel foot protein-1 (mfp-1) as the polycation and hyaluronic acid (HA) as the polyanion at stoichiometric ratios was macroscopically phase-separated into a dense complex coacervate and a dilute supernatant phase to enable separate characterization of the two fluid phases. Surprisingly, despite up to 4 orders of magnitude differing density of the polyelectrolytes, the diffusivity of water in these two phases was found to be indistinguishable. The presence of unbound, bulk-like, water in the dense fluid can be reconciled with a water population that is only weakly perturbed by the polyelectrolyte interface and network. This hypothesis was experimentally validated by cryo-TEM of the macroscopically phase-separated dense complex coacervate phase that was found to be a bicontinuous and biphasic nanostructured network, in which one of the phases was confirmed by staining techniques to be water and the other polyelectrolyte complexes. We conclude that a weak cohesive energy between water–water and water–polyelectrolytes manifests itself in a bicontinuous network, and is responsible for the exceptionally low interfacial energy of this complex fluid phase with respect to virtually any surface within an aqueous medium

Asymmetric Collapse in Biomimetic Complex Coacervates Revealed by Local Polymer and Water Dynamics

Complex coacervation is a phenomenon characterized by the association of oppositely charged polyelectrolytes into micrometer-scale liquid condensates. This process is the purported first step in the formation of underwater adhesives by sessile marine organisms, as well as the process harnessed for the formation of new synthetic and protein-based contemporary materials. Efforts to understand the physical nature of complex coacervates are important for developing robust adhesives, injectable materials, or novel drug delivery vehicles for biomedical applications; however, their internal fluidity necessitates the use of in situ characterization strategies of their local dynamic properties, capabilities not offered by conventional techniques such as X-ray scattering, microscopy, or bulk rheological measurements. Herein, we employ the novel magnetic resonance technique Overhauser dynamic nuclear polarization enhanced nuclear magnetic resonance (DNP), together with electron paramagnetic resonance (EPR) line shape analysis, to concurrently quantify local molecular and hydration dynamics, with species- and site-specificity. We observe striking differences in the structure and dynamics of the protein-based biomimetic complex coacervates from their synthetic analogues, which is an asymmetric collapse of the polyelectrolyte constituents. From this study we suggest charge heterogeneity within a given polyelectrolyte chain to be an important parameter by which the internal structure of complex coacervates may be tuned. Acquiring molecular-level insight to the internal structure and dynamics of dynamic polymer complexes in water through the in situ characterization of site- and species-specific local polymer and hydration dynamics should be a promising general approach that has not been widely employed for materials characterization

Mussel-Mimetic Protein-Based Adhesive Hydrogel

Hydrogel systems based on cross-linked polymeric materials which could provide both adhesion and cohesion in wet environment have been considered as a promising formulation of tissue adhesives. Inspired by marine mussel adhesion, many researchers have tried to exploit the 3,4-dihydroxyphenylalanine (DOPA) molecule as a cross-linking mediator of synthetic polymer-based hydrogels which is known to be able to achieve cohesive hardening as well as adhesive bonding with diverse surfaces. Beside DOPA residue, composition of other amino acid residues and structure of mussel adhesive proteins (MAPs) have also been considered important elements for mussel adhesion. Herein, we represent a novel protein-based hydrogel system using DOPA-containing recombinant MAP. Gelation can be achieved using both oxdiation-induced DOPA quinone-mediated covalent and Fe³⁺-mediated coordinative noncovalent cross-linking. Fe³⁺-mediated hydrogels show deformable and self-healing viscoelastic behavior in rheological analysis, which is also well-reflected in bulk adhesion strength measurement. Quinone-mediated hydrogel has higher cohesive strength and can provide sufficient gelation time for easier handling. Collectively, our newly developed MAP hydrogel can potentially be used as tissue adhesive and sealant for future applications

Tuning and Characterizing Nanocellulose Interface for Enhanced Removal of Dual-Sorbate (As^V and Cr^VI) from Water Matrices

Cellulose nanofiber (CNF) is one of the emerging green candidates for the various domains due to its sustainability, abundance availability, and high surface area. However, its effectiveness in the environmental aspect of toxic heavy metal removal required improvement by tuning the interface between CNF and heavy metals, and by understanding removal mechanisms. Herein, we synthesized four types of surface-functionalized CNF from waste coffee-filters for enhanced uptake of As^V and Cr^VI in the different water matrices. Among them, Fe³⁺-cross-linked CNF-Fe₂O₃ <b>(</b>FF) and mussel-inspired dopamine conjugated CNF (DP) demonstrated significant performance in water treatment for As^V and Cr^VI, respectively, than commercial activated carbon based adsorbents. Combined X-ray absorption near-edge spectroscopy (XANES), extended X-ray absorption fine structure (EXAFS) spectroscopy, and data fitting elucidated the complexation mode of As^V and Cr^VI to each CNF derivative which suggested that As^V binds through a bidentate-binuclear complex and that Cr^VI binds to catecholic OH as a trinuclear complex. Simultaneously, the transformation of harmful Cr^VI into nontoxic Cr^III was observed in DP which supports their potential practical applications. Taken together, our comprehensive data not only provide the material fabrication, interface behavior, and impact of water quality parameters in simulated and real contaminated waters but also explore the holistic understanding of the heavy metal removal mechanism and adsorbate–adsorbent interfacial interaction of these novel CNF derivatives

Improved Performance of Protected Catecholic Polysiloxanes for Bioinspired Wet Adhesion to Surface Oxides

A facile synthetic strategy for introducing catecholic moieties into polymeric materials based on a readily available precursor (eugenol) and efficient chemistries [tris­(pentafluorophenyl)­borane-catalyzed silation and thiol–ene coupling] is reported. Silyl protection is shown to be critical for the oxidative stability of catecholic moieties during synthesis and processing, which allows functionalized polysiloxane derivatives to be fabricated into 3D microstructures as well as 2D patterned surfaces. Deprotection gives stable catechol surfaces whose adhesion to a variety of oxide surfaces can be precisely tuned by the level of catechol incorporation. The advantage of silyl protection for catechol-functionalized polysiloxanes is demonstrated and represents a promising and versatile new platform for underwater surface treatments