A ratiometric fluorescent probe based on a novel fluorophore with high selectivity for imaging cysteine in living cells

As a biothiol, cysteine (Cys) is essential to both physiological and pathological processes and has been associated with many diseases, including neurological disorders, rheumatoid arthritis, and renal dysfunction. Therefore, the development of a high-performance probe for detecting Cys levels can help prevent and diagnose disease. In this study, a ratiometric fluorescent probe based on a novel fluorophore was developed for detecting Cys, and it showed high specificity and a rapid response time toward Cys. This probe demonstrates excellent biocompatibility and has been utilized effectively for the imaging of Cys in living cells.

Electrochemical Biosensors for Whole Blood Analysis: Recent Progress, Challenges, and Future Perspectives

Whole blood, as one of the most significant biological fluids, provides critical information for health management and disease monitoring. Over the past 10 years, advances in nanotechnology, microfluidics, and biomarker research have spurred the development of powerful miniaturized diagnostic systems for whole blood testing toward the goal of disease monitoring and treatment. Among the techniques employed for whole-blood diagnostics, electrochemical biosensors, as known to be rapid, sensitive, capable of miniaturization, reagentless and washing free, become a class of emerging technology to achieve the target detection specifically and directly in complex media, e.g., whole blood or even in the living body. Here we are aiming to provide a comprehensive review to summarize advances over the past decade in the development of electrochemical sensors for whole blood analysis. Further, we address the remaining challenges and opportunities to integrate electrochemical sensing platforms.

Use of metal nanoparticles for preconcentration and analysis of biological thiols

Metal nanoparticles (NPs) exhibit several unique physicochemical properties, including redox activity, surface plasmon resonance, ability to quench fluorescence, biocompatibility, or a high surface-to-volume ratio. They are being increasingly used in analysis and preconcentration of thiol containing compounds, because they are able to spontaneously form a stable Au/Ag/Cu-S dative bond. They thus find wide application in environmental and particularly in medical science, especially in the analysis of biological thiols, the endogenous compounds that play a significant role in many biological systems. In this review article, we provide an overview of various types of NPs that have been applied in analysis and preconcentration of biological thiols, mainly in human biological fluids. We first discuss shortly the types of NPs and their synthesis, properties, and their ability to interact with thiol compounds. Then we outline the sample preconcentration and analysis methods that were used for this purpose with special emphasis on optical, electrochemical, and separation techniques.

A homogeneous dopamine-silver nanocomposite coating: striking a balance between the antibacterial ability and cytocompatibility of dental implants

Silver has been widely used for surface modification to prevent implant-associated infections. However, the inherent cytotoxicity of silver greatly limited the scope of its clinical applications. The construction of surfaces with both good antibacterial properties and favorable cytocompatibility still remains a challenge. In this study, a structurally homogeneous dopamine-silver (DA/Ag) nanocomposite was fabricated on the implant surface to balance the antibacterial activity and cytocompatibility of the implant. The results show that the DA/Ag nanocomposites prepared under the acidic conditions (pH = 4) on the titanium surface are homogeneous with higher Ag⁺ content, while an obvious core (AgNPs)-shell (PDA) structure is formed under neutral (pH = 7) and alkaline conditions (pH = 10), and the subsequent heat treatment enhanced the stability of PDA-AgNPs nanocomposite coatings on porous titanium. The antibacterial test, cytotoxicity test, hypodermic implantation and osteogenesis test revealed that the homogeneous PDA-AgNPs nanocomposite coating achieved the balance between the antibacterial ability and cytocompatibility, and had the best outcomes for soft tissue healing and bone formation around the implants. This study provides a facile strategy for preparing silver-loaded surfaces with both good antibacterial effect and favorable cytocompatibility, which is expected to further improve the therapeutic efficacy of silver composite-coated dental implants.

Synthesis Monitoring, Characterization and Cleanup of Ag-Polydopamine Nanoparticles Used as Antibacterial Agents with Field-Flow Fractionation

Advances in nanotechnology have opened up new horizons in nanomedicine through the synthesis of new composite nanomaterials able to tackle the growing drug resistance in bacterial strains. Among these, nanosilver antimicrobials sow promise for use in the treatment of bacterial infections. The use of polydopamine (PDA) as a biocompatible carrier for nanosilver is appealing; however, the synthesis and functionalization steps used to obtain Ag-PDA nanoparticles (NPs) are complex and require time-consuming cleanup processes. Post-synthesis treatment can also hinder the stability and applicability of the material, and dry, offline characterization is time-consuming and unrepresentative of real conditions. The optimization of Ag-PDA preparation and purification together with well-defined characterization are fundamental goals for the safe development of these new nanomaterials. In this paper, we show the use of field-flow fractionation with multi-angle light scattering and spectrophotometric detection to improve the synthesis and quality control of the production of Ag-PDA NPs. An ad hoc method was able to monitor particle growth in a TLC-like fashion; characterize the species obtained; and provide purified, isolated Ag-PDA nanoparticles, which proved to be biologically active as antibacterial agents, while achieving a short analysis time and being based on the use of green, cost-effective carriers such as water.

A novel l-cysteine sensor using in-situ electropolymerization of l-cysteine: Potential to simple and selective detection

This work presents an all-in-one origami paper-based electrochemical platform for simple and inexpensive l-cysteine (Cys) detection using Cys as a monomer for modifying electrode surfaces. The proposed method combines the steps of electropolymerization and detection into a single device to offer a highly convenient method for the end-user. In comparison, the sensitivity toward Cys detection is a significantly increased using this modified electrode. The developed device provided a linear concentration range of 10-800 μM with a limit of detection of 5.5 μM. For application, the device was successfully applied to detect Cys in different food products such as wheat flour, bread, and cake with satisfactory results, yielding excellent intra-day and inter-day relative standard deviations (1.5-4.9%) and recoveries (84.2-110.8%). This discovery is important from the viewpoint of the development of Cys detection in other applications in the future.

Electrochemical Amino Acid Sensing: A Review on Challenges and Achievements

The rapid growth of research in electrochemistry in the last decade has resulted in a significant advancement in exploiting electrochemical strategies for assessing biological substances. Among these, amino acids are of utmost interest due to their key role in human health. Indeed, an unbalanced amino acid level is the origin of several metabolic and genetic diseases, which has led to a great need for effective and reliable evaluation methods. This review is an effort to summarize and present both challenges and achievements in electrochemical amino acid sensing from the last decade (from 2010 onwards) to show where limitations and advantages stem from. In this review, we place special emphasis on five well-known electroactive amino acids, namely cysteine, tyrosine, tryptophan, methionine and histidine. The recent research and achievements in this area and significant performance metrics of the proposed electrochemical sensors, including the limit of detection, sensitivity, stability, linear dynamic range(s) and applicability in real sample analysis, are summarized and presented in separate sections. More than 400 recent scientific studies were included in this review to portray a rich set of ideas and exemplify the capabilities of the electrochemical strategies to detect these essential biomolecules at trace and even ultra-trace levels. Finally, we discuss, in the last section, the remaining issues and the opportunities to push the boundaries of our knowledge in amino acid electrochemistry even further.

Superhydrophobic functionalized cellulosic paper by copper hydroxide nanorods for oils purification

Oily water contamination has been sighted as one of the most global environmental pollution. Herein, copper hydroxide nanorods layer was constructed onto cellulosic filter paper surface cured with polydopamine, Ag nanoparticles, and Cu NPs through immersion method. This work has been aimed to produce a superhydrophobic and superoleophilic cellulosic filter paper. The structure, crystalline, and morphological properties of these modified cellulosic filter paper were investigated. Scanning electron microscope images confirmed that the modified surface was rougher compared with the pristine surface. The contact angle measurement confirmed the hydrophobic nature of these modified surfaces with a water contact angle of 169.7°. The absorption capacity was 8.2 g/g for diesel oil and the separation efficiency was higher than 99%. It was noted that the flux in the case of low viscosity solvent as n-hexane was 9663.5 Lm-2 h-1, while for the viscous oil as diesel was 1452.7 Lm-2 h-1.

NIR-/pH-Responsive Nanocarriers Based on Mesoporous Hollow Polydopamine for Codelivery of Hydrophilic/Hydrophobic Drugs and Photothermal Synergetic Therapy

Combined therapy system has become an efficient strategy to overcome drug resistance and strengthen therapeutic effects. Herein, an efficient NIR-/pH-triggered dual-drug-loaded nanoplatform was designed for combined chemo-photothermal therapy. The hydrophobic anticancer drug bortezomib (BTZ) was first loaded in mesoporous polydopamine nanospheres (MPDAs) through the acid-sensitive borate ester bond. Afterward, pH-responsive carboxymethyl chitosan (CMCS) conjugated on the surface of MPDA could capture another anticancer drug doxorubicin (DOX) and exhibited controlled release behavior in an acidic tumor microenvironment. Meanwhile, under NIR laser irradiation, hyperthermia produced by the photothermal conversion agent MPDA could efficiently ablate cancer cells and further promote drug release. In vitro and in vivo experiments emphasized that the synthesized MPDA-BTZ@CMCS-DOX nanostructure exhibited efficient accumulation in the tumor site, resulting in sustained release of BTZ and DOX and realizing NIR-/pH-triggered chemotherapy and photothermal synergistic ablation of cancer.

Coating silver metal-organic frameworks onto nitrogen-doped porous carbons for the electrochemical sensing of cysteine

Nitrogen-doped porous carbons (N-PC) were coated for the first time with silver metal-organic frameworks (Ag-MOF) by the hydrothermal route. The resulted N-PC@Ag-MOF composites present high stability because of the strong interaction between N atoms of N-PC and Ag⁺ ions of Ag-MOF. It was discovered that the electrodes modified with N-PC@Ag-MOF composites display much higher conductivity than the one modified with Ag-MOF. Especially, they provide stable and sharp electrochemical signals of solid-state AgBr at a low potential approaching zero (i.e., 0.02 V), which may aid to overcome the drawback of the traditional electroanalysis at high overpotentials with serious interferences from the samples background. More importantly, the yielded AgBr signals selectively decrease induced by cysteine (Cys) through the specific thiol-bromine replacement reactions that transfer AgBr into non-electroactive Ag-Cys. The proposed method facilitates the selective detection of Cys with two linear working ranges of 0.10 to 100 μM and 100 to 1300 μM, respectively. The N-PC@Ag-MOF-based sensors have been used for detection of spiked Cys in milk samples with good recovery efficiencies. The developed electroanalysis strategy for probing Cys through the specific thiol-bromine replacement has potential applications in the food analysis fields. Ag-MOF was coated onto heteroatoms co-doped porous carbons carriers for the selective electroanalysis strategy for cysteine at the potential approaching zero using Br^- ions.

Facile synthesis of core-shell CuS-Cu2S based nanocomposite for the high-performance glucose detection

Glucose detection is of great importance for the medical diagnosis, food biotechnology and pharmaceutical analysis. In this study, we synthesized a core-shell CuS-Cu₂S decorated carbon nanotube-graphene nanocomposite via a facile hydrothermal method. It exhibits great sensing performance towards glucose with wide linear range ranging from 0.001 to 2 mM, ultra-sensitivity of 1923 μA·cm^-2·mM^-1 and 0.33 μM detection limit in alkaline solutions. The excellent electrocatalytic activity originates from the synergistic effect between heterogeneous copper sulfides structures and carbon nanomaterials. Besides, the fabricate sensor also has great durability, selectivity and great potential for practical applications.

Hierarchically Structured Janus Membrane Surfaces for Enhanced Membrane Distillation Performance

Commercial hydrophobic poly(vinylidene fluoride) (PVDF) membranes are vulnerable to membrane fouling and pore wetting, hampering the use of membrane distillation (MD) for the treatment of surfactant- and oil-containing feed streams. To address these challenges, we designed novel Janus membranes with multilevel roughness to mitigate foulant adhesion and prevent pore wetting. Specifically, fouling- and wetting-resistant Janus MD membranes with hierarchically structured surfaces were tailored via a facile technique that involved oxidant-induced dopamine polymerization followed by in situ immobilization of silver nanoparticles (AgNPs) on commercial PVDF hollow fiber substrates. These membranes demonstrated outstanding antifouling properties and salt rejection performances in comparison to membranes with single-level structures. We ascribed the membranes' excellent performances to the coupled effects of improved surface hydrophilicity and self-healing mechanism brought about by AgNPs. Furthermore, the newly engineered membranes exhibited antibacterial properties in Bacillus acidicola solutions as evidenced by clear inhibition zones observed on a confocal laser scanning microscope. The development of hierarchically structured Janus MD membranes with multilevel roughness paves a way to mitigate membrane fouling and pore wetting caused by low-surface-tension feed streams in the MD process.

A novel probe for colorimetric and near-infrared fluorescence detection of cysteine in aqueous solution, cells and zebrafish

Cysteine(Cys) is tightly related to physiological and pathological of human, and the imbalance of concentration of cysteine in the intracellular are associated with many diseases. Here, a novel NIR fluorescent probe TCF-Cys was designed and synthesized, and both the optimal excitation and emission wavelength of them were between 650 and 900 nm, that within the "optical window" of biological tissues. In aqueous solution, TCF-Cys, which with an acrylate extremity as a recognizing unit, exhibited excellent "turn-on" fluorescence response for Cys superior to other amino acids and thiols with a limit of detection of 0.1323 μM. Moreover, as an excellent naked-eye colorimetric indicator, TCF-Cys could effectively distinguishing the Cys, Hcy and GSH in aqueous solution through color change. Then, the response mechanism of TCF-Cys for Cys was revealed by TLC, ¹H NMR, HPLC, HRMS and DFT calculation. Finally, TCF-Cys was successfully employed to fluorescence specifically map of exogenous and endogenous Cys in living cells and zebrafish with low toxicity.

Ag-Based nanocomposites: synthesis and applications in catalysis

Ag-Based nanocomposites, including supported Ag nanocomposites and bimetallic Ag nanocomposites, have been intensively investigated as highly efficient catalysts because of their high activity and stability, easy preparation, low cost, and low toxicity. Herein, we systematically summarize and comprehensively evaluate versatile synthetic strategies for the preparation of Ag-based nanocomposites, and outline their recent advances in catalytic oxidation, catalytic reduction, photocatalysis and electrocatalysis. In addition, the challenges and prospects related to Ag-based nanocomposites for various catalytic applications are also discussed. In light of the most recent advances in Ag-based nanocomposites for catalysis applications, this review provides a comprehensive assessment on the material selection, synthesis and catalytic characteristics of these catalysts, which offers a strategic guide to build a close connection between Ag nanocomposites and catalysis applications.

ESIPT-based fluorescent probe for cysteine sensing with large Stokes shift over homocysteine and glutathione and its application in living cells

An HBT-based fluorescent probe for Cys with a large Stokes shift and high selectivity was developed that operates by the ESIPT process.

Enhanced silver loaded antibacterial titanium implant coating with novel hierarchical effect

In this study, we present a novel strategy for hierarchical antibacterial implant coating by controlling structural and componential features as regulators of surface bactericidal property. Anodized titanium dioxide nanotubes and self-polymerized polydopamine were both used as preliminary antibacterial agents with a significant positive effect on surface bioactivity. At the same time, the storage capacity of nanotubes and the in situ reduction activity of polydopamine can introduce large amounts of strong attached silver nanoparticles for enhanced stable antibacterial performance. The surface morphology, chemical composition, and hydrophilicity had been thoroughly characterized. The sustained silver release performances were continuously monitored. The successively in vitro inhibition on Staphylococcus aureus growth of titanium dioxide nanotube, polydopamine layer and silver nanoparticles demonstrated the hierarchical antibacterial property of the final silver nanoparticles-incorporated polydopamine-modified titanium dioxide nanotube coating (silver/polydopamine/nanotube). Moreover, the bioactivity investigation indicated the vital role of polydopamine-modified titanium dioxide nanotube coating on preserving healthy osteoblast activity at the implant interface. The unique hierarchical coating for titanium implant may be a promising method to maximize antibacterial capacity and maintain good cellular activity at the same time.

A near-infrared fluorescent probe based on BODIPY derivative with high quantum yield for selective detection of exogenous and endogenous cysteine in biological samples

Cysteine (Cys) is involved in cellular growth and Cys deficiency is related with many diseases. So far, a number of fluorescent probes have been constructed for the detection of Cys successfully. However, the probes are difficult to discriminate Cys from Hcy and the emission wavelength of the probes is in ultraviolet or visible range. Herein, a NIR fluorescent probe named NIR-BODIPY-Ac is synthesized and used to detect Cys. The emission wavelength of the probe is at 708 nm that belongs to near-infrared (NIR) region by attaching indolium to BODIPY core, which is suitable for bioimaging in vivo. Moreover, the probe exhibits high fluorescence quantum yield (Φ = 0.51) after the addition of Cys and high sensitivity toward Cys with 81-fold fluorescence enhancement. The linear range of the probe for Cys covers from 0.2 to 30 μM with a detection limit of 0.05 μM. Furthermore, the probe shows high selectivity towards Cys owing to the fact that there is more fast reaction rate between the probe and Cys than that of Hcy. In particular, the NIR fluorescent probe is applied for the detection of exogenous and endogenous Cys in biological samples such as cell, tissue and mouse with satisfactory results.