Recognition In Biological Systems Research Articles

An Overview of Microfluidic‐assisted Strategies for Synthesis and Applications of Molecularly Imprinted Polymers

This review gives an overview of using microfluidics in conjunction with molecularly imprinted polymers (MIP), which covers two aspects: on the one hand, on‐chip synthesis of polymer and MIP particles on the nano and the micro scale. This comprises both approaches using two different immiscible solvents and homogeneous matrices to obtain the desired particle morphologies. On the other hand, especially paper‐based microfluidic systems have attracted increasing interest as low‐cost analytical tools that are inherently useful for applying at the point of care. By now, there have been several successful attempts to combine them with MIP (instead of biological recognition systems) and to successfully apply them in environmental samples, food matrices, and for diagnostic applications.

Luminescent Terbium Probe for Time‐Resolved FRET and NSET Binding Assays with Quantum Dots and Gold Nanoparticles

Time‐gated or time‐resolved FRET (TR‐FRET) assays are important tools in biosensing, bioimaging, drug screening, and molecular diagnostics. Efficient TR‐FRET assays require stable lanthanide complexes with high absorption cross sections, high quantum yields, and long photoluminescence lifetimes. Owing to their challenging synthesis, such complexes are relatively rare and new components are of potential interest when developing TR‐FRET probes. Here, we evaluate the recently developed Tb complex CoraFluor‐1 concerning its analytical performance in terbium‐to‐quantum dot FRET and terbium‐to‐gold nanoparticle NSET assays using the prototypical biological recognition system of biotin and streptavidin. Biological binding was quantifiable at sub‐picomolar concentrations in small sample volumes, with broad applicability demonstrated across three commercial fluorescence plate readers used for time‐resolved, spectrally‐resolved, and clinical bioanalysis. Overall, CoraFluor‐1 provided excellent analytical performance as both FRET and NSET donor, validating its potential for developing new TR‐FRET probes for biosensing and bioimaging.

AN EVALUATION OF A GOLD SURFACE FUNCTIONALIZATION PROCEDURE FOR ANTIBODY BINDING AND PROTEIN DETECTION USING 11-MERCAPTOUNDECANOIC ACID (11-MUA)

Immunosensors play an essential role in biological element recognition systems. Among the numerous types of electrodes utilized for immunosensor, gold electrodes with surface modification have attracted considerable attention and have experienced various improvements and developments due to their advantages, compromising high conductivity and chemical stability. Self-assembled monolayer (SAM) has been used as an effective approach for biomarker immobilization onto electrodes. In this study, two types of gold electrodes, namely, sputtered gold on a glass slide and screen-printed gold electrodes, were utilized to assess the performance of the proposed procedure utilizing 11-Mercaptoundecanoic acid (11-MUA). Bovine serum albumin–fluorescein isothiocyanate conjugate (BSA-FITC) and anti-albumin antibody (anti-BSA) were employed as the antigen–antibody pair. Microscope-based fluorescent, Raman spectroscopy and electrical measurements, including cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS), were conducted to validate the success of each step in the surface functionalization process. The results showed that BSA proteins were immobilized on the modified electrode, as indicated by the fluorescent green color observed under the microscope and the changes in surface impedance recorded in Raman spectroscopy, CV and EIS signal graphs. Additionally, the influence of the 11-MUA incubation time and the protein concentration on the performance of the gold electrode surface functionalization process were investigated. The results indicate that an incubation time exceeding 24 h and a protein concentration of 5 [Formula: see text]M was found to be the most optimal conditions. The screen-printed gold electrode exhibited a slightly superior performance in comparison to the sputtered gold electrode. This work has verified the proposed gold surface functionalization process and can serve as a solid foundation for future immunosensor research studies.

Nanomaterial-Based Artificial Vision Systems: From Bioinspired Electronic Eyes to In-Sensor Processing Devices.

High-performance robotic vision empowers mobile and humanoid robots to detect and identify their surrounding objects efficiently, which enables them to cooperate with humans and assist human activities. For error-free execution of these robots' tasks, efficient imaging and data processing capabilities are essential, even under diverse and complex environments. However, conventional technologies fall short of meeting the high-standard requirements of robotic vision under such circumstances. Here, we discuss recent progress in artificial vision systems with high-performance imaging and data processing capabilities enabled by distinctive electrical, optical, and mechanical characteristics of nanomaterials surpassing the limitations of traditional silicon technologies. In particular, we focus on nanomaterial-based electronic eyes and in-sensor processing devices inspired by biological eyes and animal visual recognition systems, respectively. We provide perspectives on key nanomaterials, device components, and their functionalities, as well as explain the remaining challenges and future prospects of the artificial vision systems.

A mini review on biosensor advancements-emphasis on quantum dots

The biosensor is an analytical device that targets the macromolecules and small molecules using a biological recognition system and later converts it into a measurable signal using a transducer. These biosensors are broadly used in various domains, enhancing the existing form and making it more specific for several applications. Presently, it is used for quantifying and detecting the biological-based components in the fields of forensics, medicine, food quality, pharmaceutical and environmental tracking, etc. These biosensors are cost-effective and produce safe and assured treatment for patients by examining the contagious disease biomarkers in the early stage without any side effects. This review has discussed the five essential components of biosensors and the upgraded form of these biosensors. Depending on the detection method, biosensors were classified into different types. Amongst various types, electrochemical and optical biosensors have more sensitivity and are widely used, and are briefly discussed here. Nanomaterials play a significant role in modern medical devices due to their excellent selectivity, high surface-to-volume ratio, strong chemical activity, increased specificity, and sensitivity that pave the way for more discoveries. Several nanomaterial-based biosensors are already on the market. This review mainly focuses on the fabrication methods of metal and metal oxide nanoparticles for sensing applications.

Investigation of differences in the protein transport capability of homochiral nanochannels

Chiral recognition plays a crucial role in the normal functioning of biological systems. The recognition of proteins in chiral environments underpins many fundamental life processes. Taking advantage of the distinct interactions between different proteins and chiral environments, this study presents the design of homochiral metal–organic framework (MOF)/nanochannels based membrane separator, enabling highly selective and high-throughput protein separation. The chiral separation membrane was fabricated by employing TiO2 nanochannel membrane (TM) as the supporting membrane and Ti ion source. Using terephthalic acid (BDC) and d/l-phenylalanine (DP/LP) as ligands, a layered TiMOF (MIL-125(Ti) used in this study) incorporating chiral selector molecules (named as DP/M and LP/M) were synthesized in situ within the TiO2 nanochannels. The bovine serum albumin (BSA) adsorption capacity of DP/M decorated TM was demonstrated to be 2.8 times higher than that of LP/M decorated TM, and was found to be related to the content of the chiral selector DP in the separation membrane. Furthermore, different recognition abilities by the chiral channels were observed for proteins with different isoelectric points. Based on a comprehensive exploration of the variations in the interaction forces between protein and chiral selector molecules, a nanoscale chromatography column-like separation model was proposed. The chiral separation membranes designed in this study provide a new platform for understanding the interactions between chiral compounds and proteins, and open up new avenues for fabricating chiral bio-interface materials, elucidating the role of chiral recognition in biological systems, and developing novel biomaterials and devices.

Controlling Superselectivity of Multivalent Interactions with Cofactors and Competitors.

Moieties that compete with multivalent interactions or act as cofactors are common in living systems, but their effect on multivalent binding remains poorly understood. We derive a theoretical model that shows how the superselectivity of multivalent interactions is modulated by the presence of cofactors or competitors. We find that the role of these participating moieties can be fully captured by a simple rescaling of the affinity constant of the individual ligand–receptor bonds. Theoretical predictions are supported by experimental data of the membrane repair protein annexin A5 binding to anionic lipid membranes in the presence of Ca2+ cofactors and of the extracellular matrix polysaccharide hyaluronan (HA) binding to CD44 cell surface receptors in the presence of HA oligosaccharide competitors. The obtained findings should facilitate understanding of multivalent recognition in biological systems and open new routes for fine-tuning the selectivity of multivalent nanoprobes in medicinal chemistry.

Nitrogenated Holey Graphene (C2N-h2D): An excellent sensor for neurotransmitter amino acids

Interactions of amino acids with organic surfaces are highly relevant to the development of modern synthetic biomaterials with biocompatibility and low biotoxicity. Biomolecule-surface interactions vary differently according to the molecule orientation, charge state, and distance from the surface. Furthermore, the electron transfer through molecule/surface could also play a key role in biological recognition and signaling systems. Here, using density functional theory (DFT), we investigated the interactions of three neurotransmitter amino acids (NAAs), namely, glycine (Gly), γ-aminobutyric acid (Gaba), and glutamate (Glu), onto a nanosheet of holey nitrogenated graphene (C2N-h2D). In general, the interactions between amino acids and carbon-based surfaces are mediated through weak van der Waals interactions. However, based on interaction energy and charge density difference calculations, there is a strong physisorption process between NAAs and the C2N structure. In particular, Gaba and Glu can act as exclusive electron donor and acceptor, respectively. Our calculations also reveal that, by changing the orientations from neutral to zwitterionic, the Gly molecule changes from a donor to a strong acceptor of electrons. In the case of electron donation, the resistivity on the C2N surface should be reduced. These findings indicate that the C2N surface is an excellent candidate for high-performance biosensor applications. From the band structure point of view, the NAAs molecules introduce occupied flat bands within the bandgap of the C2N single layer, while the surface energy levels keep the bulk characteristics of the semiconductor system. Finally, the optical absorption spectrum of NAAs-C2N systems reveals that these NAAs seem to improve the photoactivity performance of the C2N structure, with the appearance of intraband transitions.

Shape-Dependent Complementary Ditopic Terpyridine Pair with Two Levels of Self-Recognition for Coordination-Driven Self-Assembly.

Molecular recognition in biological systems plays a vital role in the precise construction of biomacromolecules and the corresponding biological activities. Such recognition mainly relies on the highly specific binding of complementary molecular pairs with complementary sizes, shapes, and intermolecular forces. It still remains challenging to develop artificial complementary motif pairs for coordination-driven self-assembly. Herein, a series of shape-dependent complementary motif pairs, based on ditopic 2,2':6',2″-terpyridine (TPY) backbone, are designed and synthesized. The fidelity degrees of self-assemblies from these motifs are carefully evaluated by multi-dimensional mass spectrometry, nuclear magnetic resonance spectroscopy, and molecular modeling. In addition, two levels of self-recognition in both homoleptic and heteroleptic assembly are discovered in the assembled system. Through finely tuning the shape and size of the ligands, a complementary pair is developed with error-free narcissistically self-sorting at two levels of self-recognition, and the intrinsic principle is carefully investigated.

Electrochemical Detection of Plant Pathogens Using Boron-Doped Carbon Nanowalls Immunosensor

This study reports the electrochemical immunosensor development for the detection of bacteria from the <i>Pseudomonas</i> genus &#x2013; the causative of many plant infections, inclusive of canker. This firstly reported assay on carbon-based material included: boron-doped carbon nanowalls (B:CNW) electrodes fabrication, sensor manufacturing, antigen detection, and specificity tests. B:CNW was fabricated by microwave plasma-assisted chemical vapor deposition (CVD) method. Cyclic voltammetry (CV) was applied during the modification step &#x2013; the electrochemical reduction of the diazonium salt. Electrochemical impedance spectroscopy (EIS) measurements confirmed the accurate sensor preparation and were used for the quantitative detection of antigen. The antibodies were utilized as the biological recognition system and immobilized on the sensor surface by covalent linkage. The optimized assay showed high sensitivity towards seven strains of <i>Pseudomonas syringae</i> pv. <i>lachrymans</i> (Psl) in the concentration range of <inline-formula> <tex-math notation="LaTeX">$3.25\times 10^{-3}$ </tex-math></inline-formula>&#x2013; <inline-formula> <tex-math notation="LaTeX">$3.25\times 10^{5}$ </tex-math></inline-formula> CFU/<inline-formula> <tex-math notation="LaTeX">$\mu \text{l}$ </tex-math></inline-formula> (limit of detection, LOD of 0.119 CFU/<inline-formula> <tex-math notation="LaTeX">$\mu \text{l}$ </tex-math></inline-formula>). The specificity of the assay was confirmed on four non-target bacteria: <i>Streptococcus pneumoniae</i>, <i>Streptococcus pyogenes</i>, <i>Bordetella parapertussis</i>, and <i>Haemophilus influenzae</i>. These results indicate the importance of the sensing material choice and its modification procedure as they affect successive analytical performance.

Chemical Imprinting Technology Applied to Analytical Chemistry: Current Status and Future Outlook in Brazil

Chemical imprinting technologies based on molecularly imprinted polymers (MIPs) and ion imprinted polymers (IIPs) have been widely applied in different fields of analytical chemistry since their discoveries in 19721 and 19762, respectively. MIPs and IIPs are considered biomimetic materials with tailor-made synthetic receptors and are, essentially, obtained by co-polymerization of functional and cross-linking monomers in the presence of a target analyte (a molecule for MIPs and an ion for IIPs). The great advantages of these materials over biological recognition systems include their relatively low cost, quick preparation, and, most importantly, their stability in different media. To date, these biomimetic materials have experienced a rapid development with wide applications in electrochemical sensors, luminescence sensors, separation science, sample preparation, and more specific sensor applications such as surface plasmon resonance (SPR) and quartz crystal microbalance (QCM) sensors. In addition, they have been applied for analysis of samples of environmental, food, and forensic interests, as well as for disease diagnostics.3-8 Figure 1 depicts the increasing number of published papers per year over the past 20 years on the topic of MIPs and IIPs; as expected, most of these papers are devoted to the chemical imprinting of molecules.

Recent Advances of Self-Healing Polymer Materials via Supramolecular Forces for Biomedical Applications.

Noncovalent interactions can maintain the three-dimensional structures of biomacromolecules (e.g., polysaccharides and proteins) and control specific recognition in biological systems. Supramolecular chemistry was gradually developed as a result, and this led to design and application of self-healing materials. Self-healing materials have attracted attention in many fields, such as coatings, bionic materials, elastomers, and flexible electronic devices. Nevertheless, self-healing materials for biomedical applications have not been comprehensively summarized, even though many reports have been focused on specific areas. In this Review, we first introduce the different categories of supramolecular forces used in preparing self-healing materials and then describe biological applications developed in the last 5 years, including antibiofouling, smart drug/protein delivery, wound healing, electronic skin, cartilage lubrication protection, and tissue engineering scaffolds. Finally, the limitations of current biomedical applications are indicated, key design points are offered for new biological self-healing materials, and potential directions for biological applications are highlighted.

Boost of the Bio-memristor Performance for Artificial Electronic Synapses by Surface Reconstruction.

Biomaterial-based memristors (bio-memristors) are often adopted to emulate biological synapse functions and applied to construct neural computing networks in brain-inspired chip systems. However, the randomness of conductive filament formation in bio-memristors inhibits their switching performance by causing the dispersion of the device-switching parameters. In this case, a facile porous silk fibroin (p-SF) memristor was obtained through a protein surface reconstruction strategy, in which the size of the hole can be adjusted by the density of hybrid nanoseeds. The porous SF memristors exhibit greatly enhanced electrical characteristics, including uniform I-V cycles, centralized distribution of the switching voltages, and both high and low resistances, compared to devices without pores. The results of three-dimensional (3D) simulations based on classical density functional theory (cDFT) suggest that the reconstructed pores in the SF layers guide the formation and fracture of Ag filaments under an electric field and enhance the overall conductivity by separating Ag+ ion and electron diffusion pathways. Ag+ ions are predicted to preferentially diffuse through pores, whereas electrons diffuse through the SF network. Interestingly, the device conductance can be bidirectionally modulated gradually by positive and negative voltages, can faithfully simulate short-term and long-term plasticity, and can even realize the triplet-spike-timing-dependent plasticity (triplet-STDP) rule, which can be used for pattern recognition in biological systems. The simulation results reveal that a memristor network of this type has an accuracy of ∼95.78% in memory learning and the capability of pattern learning. This work provides a facile technology route to improve the performance of bionic-material memristors.

Water and the Cation-π Interaction.

The cation-π interaction and the hydrophobic effect are important intermolecular forces in chemistry and play major roles in controlling recognition in biological systems. We compared their relative contributions to the binding of molecular "dumbbell" guests in synthetic container hosts in water. The guests offered direct, intramolecular competition between trimethylammonium groups, -N+(CH3)3, and tert-butyl groups, -C(CH3)3, for the internal surfaces (aromatic panels) of the containers. In contrast with previous studies, the container molecules consistently preferred binding to the uncharged tert-butyl groups, regardless of the presence of anionic, cationic, or zwitterionic groups on the container peripheries. This preference is determined by solvation of the polar trimethylammonium group in water, which outcompetes the attraction between the positive charge and the π-surfaces in the container. The synthetic container complexes provide a direct measure of the relative strengths of cation-π interactions and desolvation in water. Interactions with the uncharged tert-butyl group are more than 12 kJ mol-1 more favorable than the cation-π interactions with the trimethylammonium group in these cavitand complexes.

Poly(amino acid)s-based star AIEgens for cell uptake with pH-response and chiral difference

Chiral aggregation-induced emission luminogens (AIEgens) are the new-generation chiral sensors that regulate chiral signals from the molecular level to the macroscopic assembly. Expanding applications of chiral AIEgens and in-depth understanding of their chiral recognition in biological systems are meaningful. Herein, two star chiral AIEgens, consisting of tetraphenylethene (TPE) as core and poly(N-acryloyl-L(D) valine) (PLV or PDV) as arms, were precisely synthesized via atom transfer radical polymerization (ATRP) technique and named TPE-PLV and TPE-PDV. They possessed typical AIE characteristics and exhibited an increase in concentration-dependent fluorescence intensity. The two AIEgens were pH-responsive and had strong AIE-related emission in acidic solution. Importantly, AIEgens can enter the living cells by ATP dependent endocytosis, then light them up. The interactions between the AIEgens and living human hepatocarcinoma (HepG2) cells revealed that the internalization process of TPE-PLV and TPE-PDV was both chiral-dependent and pH-responsive. This novel strategy for synthesizing poly(amino acid)s functionalized AIEgens could inspire the development of promising fluorescent materials with chirality.

A Principal Curves-Based Method for Electronic Tongue Data Analysis

Electronic tongues are a type of sensor inspired in the biological recognition system, where sensorial and instrumental techniques are used to determine flavors or substances present in the samples analyzed. The sensor arrays used in electronic tongues are generally non-specific and are designed to provide global information about the solution’s response. As a consequence, it usually becomes necessary to use data processing techniques that are capable of providing specific information from the samples under investigation. In this context, here we employed a Principal Curves based method to evaluate the experimental data obtained from an impedimetric electronic tongue used to evaluated distinct flavors enhancers of similar compostions. For the classification of concentrations, the best results were in the range of 88.02 to 91.15%, using electrode architectures E1 (Poly allylamine hydrochloride (PAH), reduced graphene oxide (rGO), polyaniline (PANI) and copper tetrasulfonated phthalocyanine (CuTsPc)) and E6 (PAH and CuTsPc). In the classification of substances, again the E1 architecture was highlighted, with 90.15% accuracy. These results shown that principal curves may be a promising technique for electronic tongues data analysis.

Pressure-Based Bioassay Perceived by a Flexible Pressure Sensor with Synergistic Enhancement of the Photothermal Effect.

An effective signal amplification strategy based on temperature-amplification synergistic pressure was designed for the sensitive detection of carcinoembryonic antigen (CEA) by using a noncontact point-of-care testing (POCT) aptasensor with a flexible pressure sensor based on a poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS)-modified sponge (PEDOT:PSS-sponge). In the biological recognition system, target analyte triggered the release of platinum nanoparticle-labeled complementary DNA (Pt-cDNA) from CEA aptamer-conjugated magnetic beads. On the basis of the unique characteristics of platinum nanoparticles (e.g., catalytic ability for H2O2 decomposition, peroxidase-like catalytic activity, and photothermal characteristics), the platinum nanoparticles (PtNPs) could not only catalyze hydrogen peroxide (H2O2) to produce a large amount of oxygen (O2) but could also assist the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) to a photothermal agent ox-TMB with the increasing temperature. Under 808 nm near-infrared (NIR) laser irradiation, an increase in the pressure and temperature occurred simultaneously in the closed detection cell. Meanwhile, the increasing temperature could be helpful for further increasing the pressure. The flexible pressure sensor was compressed in a closed system to cause a decrease in contact resistance, thereby establishing a correlation between the concentration and the resistance-readable analysis. Under optimum conditions, the dynamic detection range of this detection strategy for target CEA was between 0.2 and 80 ng mL-1, and the limit of detection (LOD) was 0.15 ng mL-1. Overall, the signal amplification strategy of temperature coordination provides possibilities for the future development of sensitive and portable POCT protocols.

Ionic Current Rectification Triggered Photoelectrochemical Chiral Sensing Platform for Recognition of Amino Acid Enantiomers on Self-Standing Nanochannel Arrays.

Chirality is an intrinsic and essential property of nature, and the enantiomeric discrimination of chiral molecules can provide important information leading to a better understanding of chiral recognition in biological systems and furthering the development of useful molecular devices in biochemical and pharmaceutical studies. Therefore, the exploration of new detection techniques with high accuracy and reliability for high-throughput enantioselective detection is still highly desirable. Herein, a chiral enantiomers selective recognition platform based on self-standing titanium dioxide nanochannel arrays (TiO2 NCAs) is proposed to implement the ionic current rectification triggered photoelectrochemical (PEC) detection, which provides a novel sensing platform to discriminate chiral amino acid through synchronous output dual response signals of ionic current and photocurrent. The utilization of nanochannel arrays guaranteed the high-throughput detection, and the dual signal model avoided a "false positive" detection. In addition, based on the fabricated detection platform, various chiral substances can be facilely detected through integrating different chiral regulation units, which shed light on the construction of reliable chiral sensors for practical applications in a biological environment.

Recognition and Stabilization of Unsaturated Fatty Acids by a Polyaromatic Receptor.

Selective recognition of natural fatty acids is intrinsically difficult owing to the long, flexible, and poorly interactive hydrocarbon chains. Inspired by biological recognition systems, we herein demonstrate the exclusive binding of a monounsaturated fatty acid by an artificial polyaromatic receptor from a mixture of the unsaturated and corresponding saturated substrates (i.e., oleic and stearic acids) in water. The selectivity stems from multiple CH-π/π-π interactions between the host framework and the guest in its roughly coiled conformation. Moreover, competitive binding experiments elucidate higher binding affinities of the receptor for oligo- and polyunsaturated fatty acids (e.g., α-linolenic acid and EPA). Within the receptor, the biosubstrates are remarkably stabilized against air, light, and heat owing to the polyaromatic shielding effect.

Recognition and Stabilization of Unsaturated Fatty Acids by a Polyaromatic Receptor

AbstractSelective recognition of natural fatty acids is intrinsically difficult owing to the long, flexible, and poorly interactive hydrocarbon chains. Inspired by biological recognition systems, we herein demonstrate the exclusive binding of a monounsaturated fatty acid by an artificial polyaromatic receptor from a mixture of the unsaturated and corresponding saturated substrates (i.e., oleic and stearic acids) in water. The selectivity stems from multiple CH–π/π–π interactions between the host framework and the guest in its roughly coiled conformation. Moreover, competitive binding experiments elucidate higher binding affinities of the receptor for oligo‐ and polyunsaturated fatty acids (e.g., α‐linolenic acid and EPA). Within the receptor, the biosubstrates are remarkably stabilized against air, light, and heat owing to the polyaromatic shielding effect.