Highly Selective Colorimetric Sensor of Mercury(II) Ions by Andrographolide-Stabilized Silver Nanoparticles in Water and Antibacterial Evaluation.

Silver nanoparticles (AgNPs) are well known for their exceptional properties and versatility in various applications. This study used andrographolide as a biochemical stabilizer to synthesize AgNPs (andro-AgNPs). The andro-AgNPs were characterized by using UV-vis spectroscopy, revealing a surface plasmon resonance peak at 440 nm. Fourier transform infrared spectroscopy was also used to confirm the presence of AgNPs. Transmission electron microscopy was used to investigate the morphology of andro-AgNPs, which showed a spherical shape with an average diameter of 18.30 ± 5.57 nm (n = 205). Andro-AgNPs were utilized as a colorimetric sensor to detect mercury ions (Hg2+) in water, and the optimized detection conditions were evaluated using UV-vis spectroscopy with a linear range of 15-120 µM. The limit of detection and the limit of quantification for Hg2+ detection were found to be 11.15 and 37.15 µM, respectively. Furthermore, andro-AgNPs exhibited antibacterial properties against both Gram-positive (Staphylococcus aureus) and Gram-negative (Escherichia coli) bacteria. The results imply that andro-AgNPs hold promising potential for future biomedical applications.

A Shear-Thinning, Self-Healing, Dual-Cross Linked Hydrogel Based on Gelatin/Vanillin/Fe3+ /AGP-AgNPs: Synthesis, Antibacterial, and Wound-Healing Assessment.

A shear-thinning and self-healing hydrogel based on a gelatin biopolymer is synthesized using vanillin and Fe3+ as dual crosslinking agents. Rheological studies indicate the formation of a strong gel found to be injectable and exhibit rapid self-healing (within 10 min). The hydrogels also exhibited a high degree of swelling, suggesting potential as wound dressings since the absorption of large amounts of wound exudate, and optimum moisture levels, lead to accelerated wound healing. Andrographolide, an anti-inflammatory natural product is used to fabricate silver nanoparticles, which are characterized and composited with the fabricated hydrogels to imbue them with anti-microbial activity. The nanoparticle/hydrogel composites exhibit activity against Escherichia coli, Staphylococcus aureus, and Burkholderia pseudomallei, the pathogen that causes melioidosis, a serious but neglected disease affecting southeast Asia and northern Australia. Finally, the nanoparticle/hydrogel composites are shown to enhance wound closure in animal models compared to the hydrogel alone, confirming that these hydrogel composites hold great potential in the biomedical field.

Gingerol extract-stabilized silver nanoparticles and their applications: colorimetric and machine learning-based sensing of Hg(ii) and antibacterial properties.

This study focused on synthesizing ginger-stabilized silver nanoparticles (Gin-AgNPs) using a more eco-friendly method that utilized AgNO3 and natural ginger solution. These nanoparticles underwent a color change from yellow to colorless when exposed to Hg2+, enabling the detection of Hg2+ in tap water. The colorimetric sensor had good sensitivity, with a limit of detection (LOD) of 1.46 µM and a limit of quantitation (LOQ) of 3.04 µM. Importantly, the sensor operated accurately without being affected by various other metal ions. To enhance its performance, a machine learning approach was employed and achieved accuracy ranging from 0% to 14.66% when trained with images of Gin-AgNP solutions containing different Hg2+ concentrations. Furthermore, the Gin-AgNPs and Gin-AgNPs hydrogels exhibited antibacterial effects against both Gram-negative and Gram-positive bacteria, indicating potential future applications in the detection of Hg2+ and in wound healing.

Electrochemical biosensor based on cellulose nanofibers/graphene oxide and acetylcholinesterase for the detection of chlorpyrifos pesticide in water and fruit juice.

In this work, cellulose nanofibers and graphene oxide are used to fabricate a simple and reliable electrochemical biosensor, based on acetylcholinesterase (AChE) for the detection of highly dangerous organophosphates (OPs), utilizing chlorpyrifos as a representative sample. AChE is an enzyme that is essential for neurotransmission and catalyzes the conversion of acetylcholine (ATCh) into thiocholine and acetic acid. The pesticide used in this work, chlorpyrifos, inhibits the catalytic activity of AChE on ATCh, and this inhibition can be measured using square wave voltammetry (SWV). Utilizing a process of surface modification, layers of cellulose nanofibers, graphene oxide, a chitosan-graphene oxide composite, and acetylcholinesterase (AChE/CS-GO/GO/CNFs) were immobilized on a screen-printed carbon electrode (SPCE). The modified SPCE working electrode was characterized using scanning electron microscopy and graphene oxide trapped in the cellulose nanofibers was found to increase the sensitivity of the biosensor. The modified biosensor demonstrated good performance for detection of chlorpyrifos over a linear range of 25-1000 nM under optimum conditions, and the limits of detection and quantification were 2.2 nM and 73 nM, respectively. Our sophisticated technique might offer a more precise, straightforward, quick, and environmentally friendly way to assess chlorpyrifos contamination in water and juice samples.

Aptamer-based colorimetric detection of the DNA damage marker 8-oxo-dG using cysteamine-stabilised gold nanoparticles.

8-Oxo-7,8-dihydro-2'-deoxyguanosine (8-oxo-dG) is a crucial biomarker for oxidative DNA damage and carcinogenesis. Current strategies for 8-oxo-dG detection often require sophisticated instruments and qualified personnel. In this study, cysteamine-stabilised gold nanoparticles (cyst-AuNPs) were synthesised and used for colorimetric detection of 8-oxo-dG in urine. Sensing of 8-oxo-dG is based on the anti-aggregation of cyst-AuNPs, mediated by the specific recognition of 8-oxo-dG and its aptamer. In the absence of 8-oxo-dG, the aptamer was adsorbed onto the surface of cyst-AuNPs, resulting in aggregation and the development of a purple colour solution. Upon addition of the target molecule 8-oxo-dG, the aptamer specifically bound to it and could not induce the aggregation of cyst-AuNPs, leading to the dispersion of cyst-AuNPs in the solution. Simple visual examination could be used to monitor the purple-to-red colour change that started at 12 nM, a threshold concentration for visual analysis. The absorbance at 525 nm increased in direct relation to the number of the target molecule 8-oxo-dG. This aptamer/cyst-AuNPs system showed excellent sensing ability for the 8-oxo-dG concentration in the range of 15-100 nM, with a detection limit as low as 10.3 nM and a detection time of 30 min. Interference experiments showed that the developed colorimetric strategy had a good sensitivity. This simple and rapid colorimetric method has successfully been applied to inspect 8-oxo-dG concentration in real urine samples and provided recoveries between 93.6 and 94.1%, with a limit of quantification (LOQ) of 34.3 nM, which was comparable with an enzyme-linked immunosorbent-based detection of 8-oxo-dG. This new, easy-to-use, and rapid method could be used as an alternative and initiative strategy for the development of an on-site analysis of 8-oxo-dG in urine.

Andrographolide stabilized-silver nanoparticles overcome ceftazidime-resistant Burkholderia pseudomallei: study of antimicrobial activity and mode of action.

Burkholderia pseudomallei (B. pseudomallei) is a Gram-negative pathogen that causes melioidosis, a deadly but neglected tropical disease. B. pseudomallei is intrinsically resistant to a growing list of antibiotics, and alternative antimicrobial agents are being sought with urgency. In this study, we synthesize andrographolide-stabilized silver nanoparticles (andro-AgNPs, spherically shaped with 16 nm average diameter) that show excellent antimicrobial activity against B. pseudomallei, including ceftazidime-resistant strains, being 1-3 orders of magnitude more effective than ceftazidime and 1-2 orders of magnitude more effective than other green-synthesized AgNPs. The andro-AgNPs are meanwhile non-toxic to mammalian cell lines. The mode of action of Andro-AgNPs toward B. pseudomallei is unraveled by killing kinetics, membrane neutralization, silver ions (Ag+) release, reactive oxygen species (ROS) induction, membrane integrity, and cell morphology change studies. The antimicrobial activity and mode of action of andro-AgNPs against B. pseudomallei reported here may pave the way to alternative treatments for melioidosis.

Enhanced wound healing properties of guar gum/curcumin-stabilized silver nanoparticle hydrogels.

Biocompatible materials that act as scaffolds for regenerative medicine are of enormous interest. Hydrogel-nanoparticle composites have great potential in this regard, however evaluations of their wound healing and safety in vivo in animal studies are scarce. Here we demonstrate that a guar gum/curcumin-stabilized silver nanoparticle hydrogel composite is an injectable material with exceptional wound healing and antibacterial properties. We show that the curcumin-bound silver nanoparticles themselves exhibit low cytotoxicity and enhance proliferation, migration, and collagen production in in vitro studies of human dermal fibroblasts. We then show that the hydrogel-nanoparticle composite promotes wound healing in in vivo studies on rats, accelerating wound closure by > 40% and reducing bacterial counts by 60% compared to commercial antibacterial gels. Histopathology indicates that the hydrogel composite enhances transition from the inflammation to proliferation stage of healing, promoting the formation of fibroblasts and new blood vessels, while target gene expression studies confirm that the accelerated tissue remodeling occurs along the normal pathways. As such these hydrogel composites show great promise as wound dressing materials with high antibacterial capacity.

A Disposable Electrochemical Biosensor Based on Screen-Printed Carbon Electrodes Modified with Silver Nanowires/HPMC/Chitosan/Urease for the Detection of Mercury (II) in Water.

This work describes the facile preparation of a disposable electrochemical biosensor for the detection of Hg(II) in water by modifying the surface of a screen-printed carbon electrode (SPCE). The surface modification consists of the immobilization of a composite layer of silver nanowires, hydroxymethyl propyl cellulose, chitosan, and urease (AgNWs/HPMC/CS/Urease). The presence of the composite was confirmed by scanning electron microscopy (SEM) and its excellent conductivity, due chiefly to the electrical properties of silver nanowires, enhanced the sensitivity of the biosensor. Under optimum conditions, the modified SPCE biosensor showed excellent performance for the detection of Hg(II) ions, with an incubation time of 10 min and a linear sensitivity range of 5-25 µM. The limit of detection (LOD) and limit of quantitation (LOQ) were observed to be 3.94 µM and 6.50 µM, respectively. In addition, the disposable and portable biosensor exhibited excellent recoveries for the detection of Hg(II) ions in commercial drinking water samples (101.62-105.26%). The results are correlated with those obtained from inductively coupled plasma optical emission spectrometry (ICP-OES), indicating that our developed sensor is a reliable method for detection of Hg(II) in real water samples. The developed sensor device is a simple, effective, portable, low cost, and user-friendly platform for real-time detection of heavy metal ions in field measurements with potential for other biomedical applications in the future.

Tannic Acid-Stabilized Silver Nanoparticles Used in Biomedical Application as an Effective Antimelioidosis and Prolonged Efflux Pump Inhibitor against Melioidosis Causative Pathogen.

Burkholderia pseudomallei is the causative pathogen of melioidosis and this bacterium is resistant to several antibiotics. Silver nanoparticles (AgNPs) are an interesting agent to develop to solve this bacterial resistance. Here, we characterize and assess the antimelioidosis activity of AgNPs against these pathogenic bacteria. AgNPs were characterized and displayed a maximum absorption band at 420 nm with a spherical shape, being well-monodispersed and having high stability in solution. The average size of AgNPs is 7.99 ± 1.46 nm. The antibacterial efficacy of AgNPs was evaluated by broth microdilution. The bactericidal effect of AgNPs was further assessed by time-kill kinetics assay. Moreover, the effect of AgNPs on the inhibition of the established biofilm was investigated by the crystal violet method. In parallel, a study of the resistance induction development of B. pseudomallei towards AgNPs with efflux pump inhibiting effect was performed. We first found that AgNPs had strong antibacterial activity against both susceptible and ceftazidime-resistant (CAZ-resistant) strains, as well as being efficiently active against B. pseudomallei CAZ-resistant strains with a fast-killing mode via a bactericidal effect within 30 min. These AgNPs did not only kill planktonic bacteria in broth conditions, but also in established biofilm. Our findings first documented that the resistance development was not induced in B. pseudomallei toward AgNPs in the 30th passage. We found that AgNPs still showed an effective efflux pump inhibiting effect against these bacteria after prolonged exposure to AgNPs at sublethal concentrations. Thus, AgNPs have valuable properties for being a potent antimicrobial agent to solve the antibiotic resistance problem in pathogens.

The Decoration of ZnO Nanoparticles by Gamma Aminobutyric Acid, Curcumin Derivative and Silver Nanoparticles: Synthesis, Characterization and Antibacterial Evaluation.

Zinc oxide nanoparticles (ZnO NPs) are applied in various applications in catalysis, biosensing, imaging, and as antibacterial agents. Here we to prepare ZnO nanomaterials decorated by γ-amino butyric acid (GABA), curcumin derivatives (CurBF2) and silver nanoparticles (CurBF2-AgNPs). The structures of all ZnO nanostructures were characterized using Fourier transform infrared (FT-IR) spectroscopy, X-ray diffraction (XRD), UV-VIS spectrophotometry, fluorescence spectrophotometry, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and high-resolution transmission electron microscopy (HR-TEM). Further, their antibacterial activities against Gram-negative (Escherichia coli) and Gram-positive (Staphylococcus aureus) bacteria were investigated through analysis of minimum inhibitory concentration (MIC) method. Among the prepared nanostructures, the ZnO NPs-GABA/CurBF2-AgNPs showed excellent antibacterial activity against both Gram-positive and -negative bacteria. ZnO NPs fabricated here may have potential use in future anti-bacterial compositions and coatings technologies.

Colorimetric detection of Hg(II) by γ-aminobutyric acid-silver nanoparticles in water and the assessment of antibacterial activities.

In this work, we report the synthesis of silver nanoparticles (AgNPs) via a wet-chemical reduction procedure using citrate (Cit) and γ-aminobutyric acid (GABA) as stabilizers. The formation of GABA-Cit@AgNPs was confirmed by UV-vis spectroscopy with a surface plasmon resonance band at 393 nm clearly confirming the formation of silver nanoparticles. AgNPs were characterized using UV-vis spectroscopy, attenuated total reflectance-fourier transform infrared spectroscopy (ATR-FTIR), transmission electron microscope (TEM), energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), dynamic light scattering (DLS), and zeta potential. The as-prepared AgNPs can be used for the detection of hazardous mercury ions (Hg2+) in water by colorimetric method with a limit of detection (LOD) and limit of quantitation (LOQ) of 2.37 µM and 3.99 µM, respectively. The linear working range for Hg2+ detection is 5-35 µM and the sensor probe was applied to investigate Hg2+ in real drinking water samples with satisfied results. Rapid response to Hg2+ is also observed when the nanoparticles are composited within hydrogels. Moreover, GABA-Cit@AgNPs shows antibacterial activity against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus). The fast and sensitive response of the proposed Hg2+ sensor, together with its antibacterial activities, makes GABA-Cit@AgNPs potentially applicable for the development of cheap, portable, colorimetric sensors in fieldwork.

Development of Low-Cost AuNP-Based Aptasensors with Truncated Aptamer for Highly Sensitive Detection of 8-Oxo-dG in Urine.

8-Oxo-7,8-dihydro-2'-deoxyguanosine (8-oxo-dG), an oxidized form of guanosine residues, is a critical biomarker for various cancers. Herein, a sensitive citrate-capped gold nanoparticle-based aptasensor device has been developed for the detection of 8-oxo-dG in urine. We previously designed a 38-nt anti-8-oxo-dG-aptamer by a computer simulation and the experimental validation has been performed in the present work. The analytical performance of the 38-nt aptamer from the in silico design was compared with the parent 66-nt aptamer. This assay is based on the principle of salt-induced aggregation of citrate-capped gold nanoparticles. Based on this sensing mechanism, the difference between the absorbance in the presence and absence of 8-oxo-dG at λ = 525 nm (ΔA525) increased linearly as a function of 8-oxo-dG concentrations in the ranges of 10-100 and 15-100 nM for 38-nt and 66-nt aptasensors, respectively. This method can provide detection limits of 6.4 nM for 8-oxo-dG in the 38-nt aptasensor and 13.2 nM in the 66-nt aptasensor. Similar to the 66-nt aptamer, the shortened aptamer, 38-nt long, can provide high sensitivity and selectivity with rapid detection time. In addition, using the 38-nt aptamer as a recognition component in the developed portable low-cost device showed high sensitivity in the detection range of 15-100 nM with a detection limit of 12.9 nM, which is much lower than the threshold value (280 nM) for normal human urine. This easy-to-use device could effectively and economically be utilized for monitoring 8-oxo-dG in real urine samples and potentially serve as a prototype for a commercial device.

A new formaldehyde sensor from silver nanoclusters modified Tollens' reagent.

A selective colorimetric assay for detecting formaldehyde (FA) was proposed based on silver nanoclusters (AgNCs) templated by polymethacrylic acid (PMAA). The chemodosimeter was easily fabricated by the formation of Tollens' reagent in the presence of AgNCs (AgNCs@Tollens). The detection principle was based on the change in the color caused by the change in the particle size from nanoclusters (no LSPR) to nanoparticles (with LSPR) upon the reduction of Tollens' reagent by FA. In the presence of FA, the intensity of a new absorbance band with a maximum at a wavelength of 430 nm corresponding to the LSPR of the AgNPs linearly increased as a function of the FA concentration, exhibiting a color change that could be observed by the naked eye. This method provided a working range of 30-50 µM with lower detection limit (LOD) of 27.99 µM. The proposed method exhibited excellent selectivity towards FA over other aldehyde-containing compounds.

A fluorescent sensor based on thioglycolic acid capped cadmium sulfide quantum dots for the determination of dopamine.

A fluorescent sensor based on thioglycolic acid-capped cadmium sulfide quantum dots (TGA-CdS QDs) has been designed for the sensitive and selective detection of dopamine (DA). In the presence of dopamine (DA), the addition of 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC) and N-hydroxysuccinimide (NHS) activates the reaction between the carboxylic group of the TGA and the amino group of dopamine to form an amide bond, quenching the fluorescence of the QDs. The fluorescence intensity of TGA-CdS QDs can be used to sense the presence of dopamine with a limit of detection of 0.68µM and a working linear range of 1.0-17.5µM. This sensor system shows great potential application for dopamine detection in dopamine drug samples and for future easy-to-make analytical devices.

Gelation-driven selection in dynamic covalent C[double bond, length as m-dash]C/C[double bond, length as m-dash]N exchange.

Knoevenagel barbiturate derivatives bearing long alkyl chains were proven to form organogels in suitable solvents based on supramolecular interactions. Their reaction with imines allows for component exchange through C[double bond, length as m-dash]C/C[double bond, length as m-dash]N recombination. The effect of various parameters (solvents, chain length, and temperature) on the C[double bond, length as m-dash]C/C[double bond, length as m-dash]N exchange reaction has been studied. Mixing Knoevenagel compound K and imine I-16 in a 1 : 1 ratio generated a constitutional dynamic library containing the four constituents K, I-16, K'-16, and I'. The reversible exchange reaction was monitored by 1H-NMR, showing marked changes in the fractions of the four constituents on sol-gel interconversion as a function of temperature. The library composition changed from statistical distribution of the four constituents in the sol state to selective amplification of the gel forming K'-16 constituent together with that of its agonist I'. The process amounts to self-organization driven component selection in a constitutional dynamic organogel system undergoing gelation. This process displays up-regulation of the gel-forming constituent by component redistribution through reversible covalent connections.

Kinetic Selectivity and Thermodynamic Features of Competitive Imine Formation in Dynamic Covalent Chemistry.

The kinetic and thermodynamic selectivities of imine formation have been investigated for several dynamic covalent libraries of aldehydes and amines. Two systems were examined, involving the reaction of different types of primary amino groups (aliphatic amines, alkoxy-amines, hydrazides and hydrazines) with two types of aldehydes, sulfobenzaldehyde and pyridoxal phosphate in aqueous solution at different pD (5.0, 8.5, 11.4) on one hand, 2-pyridinecarboxaldehyde and salicylaldehyde in organic solvents on the other hand. The reactions were performed separately for given amine/aldehyde pairs as well as in competitive conditions between an aldehyde and a mixture of amines. In the latter case, the time evolution of the dynamic covalent libraries generated was followed, taking into consideration the operation of both kinetic and thermodynamic selectivities. The results showed that, in aqueous solution, the imine of the aliphatic amine was not stable, but oxime and hydrazone formed well in a pH dependent way. On the other hand, in organic solvents, the kinetic product was the imine derived from an aliphatic amine and the thermodynamic products were oxime and hydrazone. The insights gained from these experiments provide a basis for the implementation of imine formation in selective derivatization of mono-amines in mixtures as well as of polyfunctional compounds presenting different types of amino groups. They may in principle be extended to other dynamic covalent chemistry systems.

A circular dichroism sensor for selective detection of Cd2+ and S2- based on the in-situ generation of chiral CdS quantum dots.

We demonstrate an advance in the fabrication of circular dichroism (CD) sensors for detection of Cd2+ and S2- based on chiral CdS quantum dots (QDs) generated by a facile in-situ reaction. The chiral quantum dots are generated in solutions composed of Cd2+, S2-, cysteamine (CA) and L-penicillamine (L-PA), with the number of the generated particles limited by either the Cd2+ or S2- concentration. We show that the magnitude of the CD signal produced by the QDs is linearly related to the initial concentration of Cd2+ and S2-, with excellent selectivity over other ions. Our sensor functions over concentration ranges of 65-200µM and 7-125µM with detection limits of 59.7 and 1.6µM for Cd2+ and S2-, respectively. The sensor is applied in real water samples with results comparing favorably with those obtained from ICP-OES (for Cd2+) and HPLC (for S2-).

Dynamic Covalent Chemistry of Nucleophilic Substitution Component Exchange of Quaternary Ammonium Salts.

Dynamic covalent libraries (DCLs) of quaternary ammonium cations were set up by reversible nucleophilic substitution (S(N)2' and S(N)2) exchange reactions of ammonium salts and tertiary amines. The reactions were conducted at 60 °C to generate thermodynamically and kinetically controlled mixtures of quaternary ammonium compounds and tertiary amines, and were accelerated by using iodide as a nucleophilic catalyst. Microwave irradiation was used to assist the exchange reaction between the pyridinium salts and pyridine derivatives. Finally, experiments towards the generation of dynamic ionic liquids were performed. The results of this study pave the way for the extension of dynamic combinatorial chemistry to nucleophilic substitution reactions.

Self-assembled coordination nanoparticles from nucleotides and lanthanide ions with doped-boronic acid-fluorescein for detection of cyanide in the presence of Cu2+ in water.

The sensor molecule, F-oBOH, containing boronic acid-linked hydrazide and fluorescein moieties was synthesized. For anion sensing applications, F-oBOH was studied in aqueous media. Unfortunately, F-oBOH was found to be hydrolyzed in water. Therefore, a new strategy was developed to prevent the hydrolysis of F-oBOH by applying self-assembly coordination nanoparticles network (F-oBOH-AMP/Gd(3+) CNPs). Interestingly, the nanoparticles network displayed the enhancement of fluorescent signal after adding Cu(2+) following by CN(-). The network, therefore, possessed a high selectivity for detection of CN(-) compared to other competitive anions in the presence of Cu(2+). Cyanide ion could promote the Cu(2+) binding to F-oBOH incorporated in AMP/Gd(3+) CNPs to give the opened-ring form of spirolactam resulting in the fourfold of fluorescence enhancement compared to Cu(2+) complexation without CN(-). Additionally, the log K value of F-oBOH-AMP/Gd(3+) CNPs⊂Cu(2+) toward CN(-) was 3.97 and the detection limits obtained from naked-eye and spectrofluorometry detections were 20µM and 4.03µM, respectively. The proposed method was demonstrated to detect CN(-) in drinking water with high accuracy.