Biothiols induced colour change of silver nanoparticles: A colorimetric sensing strategy

Lysozyme functionalized silver nanoclusters as a dual channel optical sensor for the effective determination of glutathione

This article describes the development of a facile and efficient fluorescence sensor for the determination of glutathione (GSH). Presence of the antioxidant glutathione in blood serum is considered as a biomarker for catastrophe like colorectal cancer. Silver nanoclusters with strong fluorescence and good water solubility synthesized from relatively cheaper precursors are one of the species very much explored in fluorescence sensors and bioimaging. Here, Chicken egg derived-lysozyme functionalized silver nanoclusters (Lyz AgNCs) with red fluorescence emission has been synthesized and developed to a turn-off fluorescence sensor for GSH through which colorimetric determination is also possible. Due to the ground state 'Ag-S' interaction between Lyz AgNCs and GSH, the determination of the analyte is possible from 1.00 × 10-5 M to 1.00 × 10-6 M via fluorimetric and from 9.00 × 10-6 to 8.00 × 10-7 M via spectrophotometric techniques with a limit of detection 2.86 × 10-7 M and 4.76 × 10-7 M, respectively. Selectivity of the sensor has been studied and applicability of the sensor in artificial blood serum samples has been demonstrated.

Signaling strategies of silver nanoparticles in optical and electrochemical biosensors: considering their potential for the point-of-care

Silver nanoparticles (AgNPs) have long been overshadowed by gold NPs' success in sensor and point-of-care (POC) applications. However, their unique physical, (electro)chemical, and optical properties make them excellently suited for such use, as long as their inherent higher instability toward oxidation is controlled. Recent advances in this field provide novel strategies that demonstrate that the AgNPs' inherent capabilities improve sensor performance and enable the specific detection of analytes at low concentrations. We provide an overview of these advances by focusing on the nanosized Ag (in the range of 1-100 nm) properties with emphasis on optical and electrochemical biosensors. Furthermore, we critically assess their potential for point-of-care sensors discussing advantages as well as limitations for each detection technique. We can conclude that, indeed, strategies using AgNP are ready for sensitive POC applications; however, research focusing on the simplification of assay procedures is direly needed for AgNPs to make the successful jump into actual applications.

Size Control and Improved Aqueous Colloidal Stability of Surface-Functionalized ZnGa2O4:Cr3+ Bright Persistent Luminescent Nanoparticles

Near-infrared (NIR)-emitting ZnGa₂O₄:Cr³⁺ (ZGO) persistent luminescent nanoparticles (PLNPs) have recently attracted considerable attention for diverse optical applications. The widespread use and promising potential of ZGO material in different applications arise from its prolonged post-excitation emission (several minutes to hours) that eliminates the need for continuous in situ excitation and the possibility of its excitation in different spectral regions (X-rays and UV-vis). However, the lack of precise control over particle size/distribution and its poor water dispersibility and/or limited colloidal stability required for certain biological applications are the major bottlenecks that limit its practical applications. To address these fundamental limitations, herein, we have prepared oleic acid (OA)-stabilized ZGO PLNPs with controlled size (7-12 nm, depending on the type of alcohol used in synthesis) and monodispersity. A further increase in size (8-21 nm), with a concomitant increase in persistent luminescence, could be achieved using a seed-mediated approach, employing the as-prepared ZGO PLNPs from the first synthesis as the seed and growing layers of the same material by adding fresh precursors. To remove their surface oleate groups and make the nanoparticles hydrophilic, two surface modification strategies were evaluated: modification with only poly(acrylic acid) (PAA) as the hydrophilic capping agent and modification with either PAA or cysteamine (Cys) as the hydrophilic capping agent in conjunction with BF₄^- as the intermediate surface modifier. The latter surface modifications involving BF₄^- conferred long-term (60 days and longer) colloidal stability to the nanoparticles in aqueous media, which is related to their favorable ζ potential values. The proposed generalized strategy could be used to prepare different kinds of surface-functionalized PLNPs with control of size, hydrophilicity, and colloidal stability and enhanced/prolonged persistent luminescence for diverse potential applications.

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 Label-Free Fluorometric Glutathione Assay Based on a Conformational Switch of G-quadruplex

In this paper, a label-free fluorescent method for glutathione (GSH) detection based on a thioflavin T/G-quadruplex conformational switch is developed. The sensing assay is fabricated depending on the virtue of mercury ions to form a thymine–thymine mismatch, which collapses the distance between two ssDNA and directs the guanine-rich part to form an intra-strand asymmetric split G-quadruplex. The newly formed G-quadruplex efficiently reacts with thioflavin T and enhances the fluorescent intensity. In the presence of GSH, Hg²⁺ is absorbed, destroying the G-quadruplex formation with a significant decrease in fluorescence emission. The proposed fluorescent assay exhibits a linear range between 0.03–5 μM of GSH with a detection limit of 9.8 nM. Furthermore, the efficacy of this method is examined using human serum samples to detect GSH. Besides GSH, other amino acids are also investigated in standard samples, which display satisfactory sensitivity and selectivity. Above all, we develop a method with features including potentiality, facility, sensitivity, and selectivity for analyzing GSH for clinical diagnostics.

Covalent Decoration of MoS2 Platforms by Silver Nanoparticles through the Reversible Addition-Fragmentation Chain Transfer Reaction

Two-dimensional nanomaterials decorated by metal nanoparticles have gained great interest, due to their potential applications in different areas ranging from electrochemical sensing to photothermal therapy. However, metal nanoparticles that are noncovalently immobilized on the surface of two-dimensional nanomaterials can be dissociated from their surface in the complex mediums. This challenge can be overcome by covalent attachment of nanoparticles to the surface of these platforms. In this work, MoS₂ sheets are decorated by silver nanoparticles (AgNPs) through a reversible addition-fragmentation chain transfer (RAFT) reaction. Reactive centers were created on the surface of freshly exfoliated MoS₂ and a two-dimensional platform with the ability of initiating the RAFT reaction was obtained. Afterwards, silver nanoparticles with acrylamide functionality were synthesized and attached on the surface of MoS₂ sheets by the RAFT reaction. MoS₂-AgNPs hybrids were characterized by different spectroscopy and microscopy methods as well as thermal and elemental analyses, and then they were used for the electrochemical determination of dipyridamole in aqueous solution. Taking advantage of the straightforward synthesis and the possible MoS₂-AgNPs distance adjustment, a variety of hybrid systems with unique physicochemical and optoelectronic properties can be constructed by using this method.

Enhanced LSPR performance of graphene nanoribbons-silver nanoparticles hybrid as a colorimetric sensor for sequential detection of dopamine and glutathione

In the present study, a novel plasmonic sensing platform was proposed for sequential colorimetric detection of dopamine (DA) and glutathione (GSH) in human serum sample by taking advantage of plasmon hybridization in graphene nanoribbons/sliver nanoparticles (GNR/Ag NPs) hybrid. DA was detected based on etching strategy and morphology transition of label-free Ag NPs hybridized with GNR. As a result of the etching process, hexagonal Ag NPs were changed to smaller corner-truncated nanoparticles and a blue shift was observed in its plasmonic band, accompanied by the color change from green to red. Sequentially, GSH induced aggregation of Ag NPs which resulted in a decrease in absorption intensity of Ag NPs plasmonic band and a color change from red to gray. By employing GNR/Ag NPs hybrid as a sensitive colorimetric sensor, DA and GSH were successfully detected in low concentrations of 0.04 μM and 0.23 μM, respectively. The same experiment was carried out in the absence of GNR and the detection limits were obtained 0.46 and 1.2 μM for DA and GSH, respectively. These results confirmed the effective role of GNR on the sensitivity improvement of GNR/Ag NPs hybrid. The proposed simple and sensitive sensing approach offered a beneficial and promising platform for sequential detection of DA and GSH in the biological samples.

Synthesis and characterization of maltol capped silver nanoparticles and their potential application as an antimicrobial agent and colorimetric sensor for cysteine

Maltol capped silver nanoparticles (McAgNPs) were synthesized using maltol (3-hydroxy-2-methyl-4-pyrone) as reducing and capping agent. McAgNPs were characterized by Visible and FTIR (Fourier transform infrared) spectroscopy, dynamic light scattering (DLS), and atomic force microscopy (AFM). Bright yellow color McAgNPs showed surface plasmon resonance (SPR) band at 436 nm, spherical shape and the average size between 35 to 50 nm. McAgNPs revealed higher stability against varying storage time, temperature, pH and salt concentrations. McAgNPs were successfully utilized for the selective and highly sensitive colorimetric detection of cysteine (Cys). Addition of Cys in a solution of McAgNPs, resulted a rapid change in color from yellow to orange because of the formation of nanoaggregates as confirmed by Visible/FTIR spectroscopy, DLS, and AFM studies. The estimated limit of detection (0.043 μM) was found to be more sensitive than previously reported other optical methods. The practical applicability of probe was also established by spiking the known concentrations of Cys in biological (blood plasma and urine) and environmental (tap and lake water) samples with significant recovery rates (92-104.6%). Despite being nontoxic to various tested cell lines, McAgNPs demonstrated potent antimicrobial, antibiofilm, and biofilm eradicating activities, thus potentially valuable in diagnostics and/or the synthesis of other nanocomposite material for broader applications.

The synthesis of thiol-stabilized silver nanoparticles and their application towards the nanomolar-level colorimetric recognition of glutathione

The synthesis and characterization of 5-methyl-1,3,4-thiadiazole-2-thiol fabricated silver nanoparticles and their application to detect glutathione.

Supramolecular interactions of oxidative stress biomarker glutathione with fluorone black

Oxidative stress biomarkers, including glutathione (GSH) and related compounds, are involved in a variety of interactions enabling redox potential maintenance in living cells and protection against radicals. Since the oxidative stress is promoting and, in many cases, inducing serious illnesses, monitoring of GSH levels can aid in diagnostics and disease prevention. Herein, we report on the discovery of the formation of a supramolecular ensemble of GSH with fluorone black (9-phenyl fluorone, FB) which is optically active and enables sensitive determination of GSH by resonance elastic light scattering (RELS). We have found that supramolecular interactions of GSH with FB can be probed with spectroscopic, RELS, and electrochemical methods. Our investigations show that RELS intensity for FB solutions increases with GSH concentration while fluorescence emission of FB is not affected, as quenching begins only above 0.8mM GSH. The UV-Vis difference spectra show a positive peak at 383nm and a negative peak at 458nm, indicating a higher-energy absorbing complex in comparison to the non-bonded FB host. Supramolecular interactions of FB with GSH have also been corroborated by electrochemical measurements involving two configurations of FB-GSH ensembles on electrodes: (i) an inverted orientation on Au-coated quartz crystal piezoelectrode (Au@SG-FB), with strong thiolate bonding to gold, and (ii) a non-inverted orientation on glassy carbon electrode (GCE@FB-GS), with weak π-π stacking attachment and efficient charge mediation through the ensemble. The formation of a supramolecular ensemble with hydrogen bonding has also been confirmed by quantum mechanical calculations. The discovery of supramolecular FB-GSH ensemble formation enables elucidating the mechanisms of strong RELS responses, changes in UV-Vis absorption spectra, and the electrochemical reactivity. Also, it provides new insights to the understanding of the efficient charge-transfer in redox potential homeostasis which is likely based on an intermediate formation of a similar type of supramolecular ensembles.

Selective recognition of creatinine - Development of a colorimetric sensor

The present report describes a simple and cost effective protocol for colourimetric determination of creatinine (CR), L-cysteine stabilized copper nanoparticles (L-cys-CuNPs) exhibited selective and sensitive interaction with CR. Utilizing this interaction, a colourimetric sensor has been developed based on the reduction in LSPR intensity as monitored by a UV-visible spectrophotometer. The developed sensor exhibited a linear dynamic range of 5.33 × 10^-6 to 3.33 × 10^-7 M. Proposed sensor is simple and cost - effective compared to methods based on noble metal nanoparticles and the sensitivity to determine CR was as low as 4.54 × 10^-10 M. The sensor was successfully applied for quantification of CR in artificial serum and urine samples. Sensor developed in this work has a high potential for rapid and on-site determination of CR in physiological and clinical samples.