Lysine-functionalized silver nanoparticles for visual detection and separation of histidine and histidine-tagged proteins

A review on the chemical and biological sensing applications of silver/carbon dots nanocomposites with their interaction mechanisms

The development of new nanocomposites has a significant impact on modern instrumentation and analytical methods for chemical analysis. Due to their unique properties, carbon dots (CDs) and silver nanoparticles (AgNPs), distinguished by their unique physical, electrochemical, and optical properties, have captivated significant attention. Thus, combining AgNPs and CDs may produce Ag/CDs nanocomposites with improved performances than the individual material. This comprehensive review offers an in-depth exploration of the synthesis, formation mechanism, properties, and the recent surge in chemical and biological sensing applications of Ag/CDs with their sensing mechanisms. Detailed insights into synthesis methods to produce Ag/CDs are unveiled, followed by information on their physicochemical and optical properties. The crux of this review lies in its spotlight on the diverse landscape of chemical and biological sensing applications of Ag/CDs, with a particular focus on fluorescence, electrochemical, colorimetric, surface-enhanced Raman spectroscopy, and surface plasmon resonance sensing techniques. The elucidation of sensing mechanisms of the nanocomposites with various target analytes adds depth to the discussion. Finally, this review culminates with a concise summary and a glimpse into future perspectives of Ag/CDs aiming to achieve highly efficient and enduring Ag/CDs for various applications.

Gold nanoparticles capped with L-glycine, L-cystine, and L-tyrosine: toxicity profiling and antioxidant potential

Biomolecules-based surface modifications of nanomaterials may yield effective and biocompatible nanoconjugates. This study was designed to evaluate gold nanoconjugates (AuNCs) for their altered antioxidant potential. Gold nanoparticles (AuNPs) and their conjugates gave SPR peaks in the ranges of 512-525 nm, with red or blueshift for different conjugates. Cys-AuNCs demonstrated enhanced (p < 0.05) and Gly-AuNCs (p > 0.05) displayed reduced DPPH activity. Gly-AuNCs and Tyr-AuNCs displayed enhanced ferric-reducing power and hydrogen peroxide scavenging activity, respectively. Cadmium-intoxicated mice were exposed to gold nanomaterials, and the level of various endogenous parameters, i.e., CAT, GST, SOD, GSH, and MTs, was evaluated. GSH and MTs in liver tissues of the cadmium-exposed group (G2) were elevated (p < 0.05), while other groups showed nonsignificance deviations than the control group. It is concluded that these nanoconjugates might provide effective nanomaterials for biomedical applications. However, more detailed studies for their safety profiling are needed before their practical applications.

Magnetic solid phase extraction of silver-based nanoparticles in aqueous samples: Influence of particle composition and matrix effects on its application to environmental samples and species-selective elution and determination of silver sulphide nanoparticles with sp-ICP-MS

Silver-based nanoparticles (Ag-b-NPs) are currently a cause for concern because they are being produced in increasing quantities for use in industrial goods and consumer products. This goes hand in hand with their release to the environment and the resultant risks for the entire ecosystem. Therefore, it is essential that these materials are monitored. A promising technique that overcomes a number of shortcomings in handling environmental samples is magnetic solid phase extraction (MSPE) of Ag-b-NPs, which is applied in this study. It has been possible to extract different kinds of Ag-b-NPs at environmentally relevant concentrations in the low ng L^-1 range using iron oxide magnetic particles (IOMPs) of different size and shape with efficiencies in the range from 80 to 100%. Furthermore, environmentally relevant inorganic ions and TiO₂ particles exhibited no major effect on the extraction efficiency. However, natural organic matter (NOM) exhibited a significant influence from 1 mg L^-1 resulting in a 50% drop in extraction efficiency. This effect could be overcome by adding 10 mM Ca²⁺ or increasing the iron oxide magnetic particle (IOMP) concentration to 500 mg L^-1. Applying the presented procedure, Ag-b-NPs added to a river water sample at β_Ag = 50 ng L^-1 were successfully extracted. We also investigated the coextraction of Ag⁺, demonstrating that NOM could eliminate coextraction. The subsequent species-selective elution of Ag₂S-NPs after MSPE, was carried out based on ethylene diamine tetraacetate (EDTA) as eluent in different matrices. A desorption efficiency of 76 ± 6% could be achieved while preserving the Ag₂S-NPs' size. By contrast, core Ag-NPs and AgCl-NPs are dissolved if the presented method is followed.

Molecular Functionalization of NiO Nanocatalyst for Enhanced Water Oxidation by Electronic Structure Engineering

Tuning the local environment of nanomaterial-based catalysts has emerged as an effective approach to optimize their oxygen evolution reaction (OER) performance, yet the controlled electronic modulation around surface active sites remains a great challenge. Herein, directed electronic modulation of NiO nanoparticles was achieved by simple surface molecular modification with small organic molecules. By adjusting the electronic properties of modifying molecules, the local electronic structure was rationally tailored and a close electronic structure-activity relationship was discovered: the increasing electron-withdrawing modification readily decreased the electron density around surface Ni sites, accelerating the reaction kinetics and improving OER activity, and vice versa. Detailed investigation by operando Raman spectroelectrochemistry revealed that the electron-withdrawing modification facilitates the charge-transfer kinetics, stimulates the catalyst reconstruction, and promotes abundant high-valent γ-NiOOH reactive species generation. The NiO-C6 F5 catalyst, with the optimized electronic environment, exhibited superior performance towards water oxidation. This work provides a well-designed and effective approach for heterogeneous catalyst fabrication under the molecular level.

Bright Yellow Fluorescent Carbon Dots as a Multifunctional Sensing Platform for the Label-Free Detection of Fluoroquinolones and Histidine

Owing to their diverse properties, fluorescent carbon dots (CDs) have attracted more attention and present enormous potential in development of sensors, bioimaging, drug delivery, microfluidics, photodynamic therapy, light emitting diode, and so forth. Herein, a multifunctional sensing platform based on bright yellow fluorescent CDs (Y-CDs) was designed for the label-free detection of fluoroquinolones (FQs) and histidine (His). The Y-CDs with superior optical and biological merits including high chemical stability, good biocompatibility, and low cytotoxicity were simply synthesized via one-step hydrothermal treatment of o-phenylenediamine ( o-PD) and 4-aminobutyric acid (GABA). The Y-CDs can be utilized to directly monitor the amount of FQs based on fluorescence static quenching owing to the specific interaction between FQs and Y-CDs. Then, the fluorescence of this system can be effectively recovered upon addition of His. The multifunctional sensing platform exhibited high sensitivity and selectivity toward three kinds of FQs and His with low detection limits of 17-67 and 35 nM, respectively. Benefiting from these outstanding characters, the Y-CDs were successfully employed for trace detection of FQs in real samples such as antibiotic tablets and milk products. Furthermore, the probe was also extended to cellular imaging. All of the above prove that this multifunctional sensing platform presents great prospect in multiple applications such as biosensing, biomedicine, disease diagnosis, and environmental monitoring.

Functionalized Silver Nano-Sensor for Colorimetric Detection of Hg2+ Ions: Facile Synthesis and Docking Studies

In the present study, we describe the facile synthesis of silver nanoparticles (AgNPs) and their nanostructures functionalized with 2-aminopyrimidine-4,6-diol (APD-AgNPs) for Hg²⁺ ion detection. The promising colorimetric response of APD-AgNPs to detect Hg²⁺ ions was visible with naked eyes and spectroscopic changes were examined by using a UV-Visible spectrophotometer. The aggregation of APD-AgNPs upon addition of Hg²⁺ ions was due to the chelation effect of the functionalized nanostructures and results in a color change from pale brown to deep yellow color. The probing sensitivity was observed within five minutes with a detection limit of about 0.35 µM/L. The TEM images of APD-AgNPs showed polydispersed morphologies with hexagonal, heptagonal and spherical nanostructures with an average size between 10 to 40 nm. Furthermore, the sensing behavior of APD-AgNPs towards Hg²⁺ ions detection was investigated using docking and interaction studies.

Toxicity of nanomaterials found in human environment

The US National Nanotechnology Initiative (NNI) defines nanotechnology as “the understanding and control of matter at dimensions between approximately 1 and 100 nm, where unique phenomena enable novel applications.” Recent scientific reports available in the literature clearly demonstrate the potential benefits of nanotechnology in consumer and industrial products. More and more nanomaterials are expected to be used in consumer products. This is expected to lead to increased human exposure to nanomaterials in their daily lives. Therefore, the effect of nanomaterials present in human environment is an area of increasing scientific interest. The information presented in this review is obtained from the current literature. It indicates that nanomaterials found in human environment may have potential for toxicological effects. However, the current literature on toxicological effects of nanomaterials is diverse. The current data are presented from studies without harmonization. These studies have used different in vitro and in vivo test models, different sources of test nanomaterials, different methods for nanomaterial characterization, and different experimental conditions. Therefore, these data are hard to interpret. More research on nanomaterial characterization, biological interaction, toxicity, and health effects is needed. The test methods need to be validated. Positive and negative controls for nanotoxicity need to be identified. Toxicity data harmonization needs to be done. Therefore, general information is not currently available for risk evaluation of certain nanomaterials that might be present in consumer products or that may enter into the market in future. Standardized and validated methods are necessary for toxicity assessment of nanomaterials. Therefore, in the absence of standardized validated methods any specific regulatory testing requirements for nanomaterials are currently premature. We conclude that the benefits of nanomaterials found currently in human environment are many, but their overall adverse effects on human health are limited.

Nitrogen-doped carbon nanoparticle modulated turn-on fluorescent probes for histidine detection and its imaging in living cells

In this work, nitrogen-doped carbon nanoparticle (N-CNP) modulated turn-on fluorescent probes were developed for rapid and selective detection of histidine. The as synthesized N-CNPs exhibited high fluorescence quantum yield and excellent biocompatibility. The fluorescence of N-CNPs can be quenched selectively by Cu(II) ions with high efficiency, and restored by the addition of histidine owing to the competitive binding of Cu(II) ions and histidine that removes Cu(II) ions from the surface of the N-CNPs. Under the optimal conditions, a linear relationship between the increased fluorescence intensity of N-CNP/Cu(II) ion conjugates and the concentration of histidine was established in the range from 0.5 to 60 μM. The detection limit was as low as 150 nM (signal-to-noise ratio of 3). In addition, the as-prepared N-CNP/Cu(II) ion nanoprobes showed excellent biocompatibility and were applied for a histidine imaging assay in living cells, which presented great potential in the bio-labeling assay and clinical diagnostic applications.

Analyte-induced photoreduction method for visual and colorimetric detection of tyrosine

A new method based on photochemical formation of silver nanoparticles (AgNPs) was developed for detection of tyrosine (Tyr). To selectively detect Tyr and to simplify the detection procedure, the photoactivity of Tyr was utilized to trigger the photochemical reduction in production of AgNPs. The drastic change of solution color caused by the surface plasmon resonance (SPR) absorption band of the formed AgNPs was used to extract the quantitative information of Tyr. This developed method is simple in detection, while both the sensitivity and selectivity are significant improved. Meanwhile, the solution color was changed from colorless to dark yellow after the formation of AgNPs, which allows a much higher sensitivity in visual identification when compared with the SPR band shifting technique commonly, used in conventional colorimetric methods. To optimize the detection system and to understand the mechanism in this proposed method, parameters such as irradiation time, intensity of light source, and the concentration of Tyr were systematically examined. Results indicated that these factors mainly affected the reaction rate of photoreduction. The morphologies of the formed AgNPs were similar, but with small differences in particle sizes. In the examination of selectivity, sixteen other amino acids were examined. Results indicated that only amino acids of tryptophan, cysteine and histidine are photoactive and possess potential interferences in analysis of Tyr. Quantitative studies indicated that a linear response up to 10 μM with a detection limit of 100 nM could be obtained. For visually detection, color change could be observed with a concentration as low as 500 nM of Tyr.

An ultrasensitive colorimetric sensor for efficient detection of Hg2+ at physiological pH

The estimation of Hg²⁺ in a buffer system (Tris buffer; pH 7.4) has been performed using a novel, enzyme-based, indirect detection method with the aid of non-functionalized AgNPs.

A novel magnetic fluorescent chemosensor for Cu2+ based on self-assembled systems of azobenzene and α-cyclodextrin

A novel fluorescent and colorimetric chemosensor for Cu²⁺ has been designed and fabricated.

Nanoparticles in relation to peptide and protein aggregation

Over the past two decades, there has been considerable research interest in the use of nanoparticles in the study of protein and peptide aggregation, and of amyloid-related diseases. The influence of nanoparticles on amyloid formation yields great interest due to its small size and high surface area-to-volume ratio. Targeting nucleation kinetics by nanoparticles is one of the most searched for ways to control or induce this phenomenon. The observed effect of nanoparticles on the nucleation phase is determined by particle composition, as well as the amount and nature of the particle's surface. Various thermodynamic parameters influence the interaction of proteins and nanoparticles in the solution, and regulate the protein assembly into fibrils, as well as the disaggregation of preformed fibrils. Metals, organic particles, inorganic particles, amino acids, peptides, proteins, and so on are more suitable candidates for nanoparticle formulation. In the present review, we attempt to explore the effects of nanoparticles on protein and peptide fibrillation processes from both perspectives (ie, as inducers and inhibitors on nucleation kinetics and in the disaggregation of preformed fibrils). Their formulation and characterization by different techniques have been also addressed, along with their toxicological effects, both in vivo and in vitro.

A portable chemical sensor for histidine based on the strategy of click chemistry

A novel portable chemical sensor is developed in combination of the personal glucose meters (PGM) with click chemistry for sensitive and selective determination of histidine. Invertase-labeled alkynyl-DNA can be modified onto the surfaces of Streptavidin Magnespheres Paramagnetic Particles (PMPs) through copper(I) catalyzed azide-alkyne cycloaddition (CuAAC) reaction and formed invertase-functionalized PMPs, which can be separated easily. The presence of invertase can convert sucrose to glucose and can be monitored by the PGM easily. The presence of histidine can inhibit the CuAAC, so the read-out signal of PGM decreased. The difference in signals from the PGM before and after addition of histidine has a good linear correlation with the logarithm of the histidine concentrations in the range of 0.01~100 μM with a detection limit of 3.4 nM, which is lower than those of many other chemical sensors. Moreover, the assay of histidine in milk samples is demonstrated with satisfactory results.

Fluorescent and colorimetric magnetic microspheres as nanosensors for Hg2+ in aqueous solution prepared by a sol-gel grafting reaction and host-guest interaction

Fluorescent sensing TSRh6G-β-cyclodextrin fluorophore/adamantane-modified inclusion complex magnetic nanoparticles (TFIC MNPs) have been synthesized via the cooperation of a host-guest interaction and sol-gel grafting reaction. Powder X-ray diffraction, transmission electron microscopy, Fourier transform infrared spectroscopy, and UV-visible absorption and emission spectroscopy have been employed to characterize the material. Fluorescence and UV-visible spectra have shown that the resultant multifunctional nanoparticle sensors exhibit selective 'turn-on' type fluorescent enhancements and a clear color change from light brown to pink with Hg(2+). Owing to a larger surface area and high permeability, TFIC MNPs exhibit remarkable selectivity and sensitivity for Hg(2+), and its detection limit measures up to the micromolar level in aqueous solution. Most importantly, magnetic measurements have shown that TFIC magnetic nanoparticles are superparamagnetic and they can be separated and collected easily using a commercial magnet. These results not only solve the limitations in practical sensing applications of nanosensors, but also enable the fabrication of other multifunctional nanostructure-based hybrid nanomaterials.

Highly selective and sensitive recognition of cobalt(II) ions directly in aqueous solution using carboxyl-functionalized CdS quantum dots as a naked eye colorimetric probe: applications to environmental analysis

Quantum dots (QDs) are usually used as fluorescent probe, and they are difficult to use in colorimetric detection. However, in this report carboxyl-functionalized CdS (COF-CdS) QDs were synthesized in aqueous solution for colorimetric detection following a classic method. On the basis of inducing the aggregation of COF-CdS QDs, a simple naked eye colorimetric method with high sensitivity and selectivity was developed for the sensing of Co(2+) ions in aqueous solutions. The Co(2+) ions induced COF-CdS QDs results in a marked enhancement of the UV-vis absorption spectra at 360 nm, and the process was accompanied by a visible color change from colorless to yellowish brown within 5 min, which proves a sensitive detection of Co(2+) ions. The sensing of Co(2+) ions can therefore be easily achieved by a UV-vis spectrophotometer or even by the naked eye. Under the optimized circumstances, this method yields excellent sensitivity (LOD = 0.23 μg mL(-1)) and selectivity toward Co(2+) ions. The calibration plot of (A - A(0)) at 360 nm against concentration of Co(2+) ions was linear over the range from 0.5 to 14 μg mL(-1) with a correlation coefficient of 0.9996. The accuracy and reliability of the method were further ascertained by recovery studies via standard addition method with percent recoveries in the range of 99.63-102.46%. The plausible mechanism for the color change reaction has also been discussed. Our attempt may provide a cost-effective, rapid, and simple solution for the inspection of Co(2+) ions in the presence of a complex matrix from environmental aqueous samples.

An indicator-displacement assay for naked-eye detection and quantification of histidine in human urine

A simple and efficient colorimetric method for the naked-eye detection and quantification of histidine in biological fluids was developed based on an indicator-displacement assay (IDA) and the Ni(2+)-histidine affinity pair. In this IDA approach, a commercially available dye, murexide, was used as the indicator and the selective detection of histidine was achieved based on the competition between indicator and histidine for the binding with Ni(2+). The competition of histidine with murexide for Ni(2+) resulted in an obvious color change of the solution from yellow to purple, and the permitted naked-eye detection of trace histidine. The developed bioassay allows the rapid, sensitive and selective detection of histidine in urine samples, and does not need complicated sample pretreatment. The detection limit was 0.4 μM with a linear range from 2 to 30 μM. The relative standard deviation for 11 replicate detections of 8 μM histidine was 2.0%. The developed sensor was successfully applied to the determination of histidine in human urine samples with recoveries from 97 to 105%.

Development of a histidine-targeted spectrophotometric sensor using Ni(II)NTA-functionalized Au and Ag nanoparticles

An antibody-free diagnostic reagent has been developed based on the aggregation-induced colorimetric change of Ni(II)NTA-functionalized colloidal gold and silver nanoparticles. This diagnostic strategy utilizes the high binding affinity of histidine-rich proteins with Ni(II)NTA to capture and cross-link the histidine-rich protein mimics with the silver and gold nanoparticles. In model studies, the aggregation behavior of the Ni(II)NTA nanoparticles was tested against synthetic targets including charged poly(amino acid)s (histidine, lysine, arginine, and aspartic acid) and mimics of Plasmodium falciparum histidine-rich protein 2 (pfHRP-II). Aggregation of the nanoparticle sensor was induced by all of the basic poly(amino acid)s including poly(l-histidine) within the pH range (5.5-9.0) tested, which is likely caused by the coordination between the multivalent polymer target and Ni(II)NTA groups on multiple particles. The peptide mimics induced aggregation of the nanoparticles only near their pK(a)'s with higher limits of detection. In addition, monomeric amino acids do not show any aggregation behavior, suggesting that multiple target binding sites are necessary for aggregation. Long-term stability studies showed that gold but not silver nanoparticles remained stable and exhibited similar aggregation behavior after 1 month of storage at room temperature and 37 °C. These results suggest that Ni(II)NTA gold nanoparticles could be further investigated for use as a sensor to detect histidine-rich proteins in biological samples.