Assay of Biothiols by Regulating the Growth of Silver Nanoparticles with C-Dots as Reducing Agent

Carbon dots-adorned silver nanoparticles as a straightforward sustainable colorimetric sensor for the rapid detection of ketotifen in eye drops and aqueous humor

The rapid and accurate detection of drug molecules in pharmaceutical formulations and biological samples is of paramount importance. In this research article, we present a novel colorimetric sensor based on carbon dots decorated silver nanoparticles (CDs/AgNPs) for the rapid detection of ketotifen (KTF), a widely used antihistamine drug. The CDs were synthesized via a facile one-step microwave-assisted method and subsequently conjugated onto AgNPs through a simple adsorption process, forming a stable CDs/AgNPs composite. The resulting composite exhibited unique optical properties, including a strong absorption peak at 410 nm with remarkable intensity reduction and color changes upon the addition of KTF. The developed colorimetric sensor exhibited a wide linear range of 3.0-40.0 µg mL-1 (R2 = 0.9996), with a %RSD of 2.41, and a low limit of detection (LOD) of 0.981 µg mL-1. Furthermore, the sensor's practical applicability was evaluated by successfully detecting KTF in eye drops and artificial aqueous humor, demonstrating a remarkable percentage recovery exceeding 96.0 %. Finally, a comprehensive evaluation of the greenness and blueness of the method was performed using analytical eco-scale, GAPI, AGREEprep, and BAGI tools. The results of these assessments indicate its exceptional sustainability. Overall, the proposed method holds significant potential for applications in pharmaceutical quality control and therapeutic monitoring, contributing to improved patient care and drug safety in the field of ophthalmology.

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.

Carbon dots@noble metal nanoparticle composites: research progress report

Carbon dots@noble metal nanoparticle composites are formed by combining carbon dots and metal nanoparticles using various strategies. Carbon dots exhibit a reducing ability and function as stabilisers; consequently, metal-ion solutions can be directly reduced by them to synthesise gold, silver, and gold-silver alloy particles. Carbon dots@gold/silver/gold-silver particle composites have demonstrated the potential for several practical applications owing to their superior properties and simple preparation process. Until now, several review articles have been published to summarise fluorescent carbon dots or noble metal nanomaterials. Compared with metal-free carbon dots, carbon dots@noble metal nanoparticles have a unique morphology and structure, resulting in new physicochemical properties, which allow for sensing, bioimaging, and bacteriostasis applications. Therefore, to promote the effective development of carbon dots@noble metal nanoparticle composites, this paper primarily reviews carbon dots@gold/silver/gold-silver alloy nanoparticle composites for the first time in terms of the following aspects. (1) The synthesis strategies of carbon dots@noble metal nanoparticle composites are outlined. The principle and function of carbon dots in the synthesis strategies are examined. The advantages and disadvantages of these methods and composites are analysed. (2) The characteristics and properties of such composites are described. (3) The applications of these composite materials are summarised. Finally, the potentials and limitations of carbon dots@noble metal nanoparticle composites are discussed, thus laying the foundation for their further development.

Review on Carbon Dot-Based Fluorescent Detection of Biothiols

Biothiols, such as cysteine (Cys), homocysteine (Hcy), and glutathione (GSH), play a vital role in gene expression, maintaining redox homeostasis, reducing damages caused by free radicals/toxins, etc. Likewise, abnormal levels of biothiols can lead to severe diseases, such as Alzheimer's disease (AD), neurotoxicity, hair depigmentation, liver/skin damage, etc. To quantify the biothiols in a biological system, numerous low-toxic probes, such as fluorescent quantum dots, emissive organic probes, composited nanomaterials, etc., have been reported with real-time applications. Among these fluorescent probes, carbon-dots (CDs) have become attractive for biothiols quantification because of advantages of easy synthesis, nano-size, crystalline properties, low-toxicity, and real-time applicability. A CDs-based biothiols assay can be achieved by fluorescent "Turn-On" and "Turn-Off" responses via direct binding, metal complex-mediated detection, composite enhanced interaction, reaction-based reports, and so forth. To date, the availability of a review focused on fluorescent CDs-based biothiols detection with information on recent trends, mechanistic aspects, linear ranges, LODs, and real applications is lacking, which allows us to deliver this comprehensive review. This review delivers valuable information on reported carbon-dots-based biothiols assays, the underlying mechanism, their applications, probe/CDs selection, sensory requirement, merits, limitations, and future scopes.

Cell-free synthesis of silver nanoparticles in spent media of different Aspergillus species

The recovery and valorization of metals and rare earth metals from wastewater are of great importance to prevent environmental pollution and recover valuable resources. Certain bacterial and fungal species are capable of removing metal ions from the environment by facilitating their reduction and precipitation. Even though the phenomenon is well documented, little is known about the mechanism. Therefore, we systematically investigated the influence of nitrogen sources, cultivation time, biomass, and protein concentration on silver reduction capacities of cell-free cultivation media (spent media) of Aspergillus niger, A. terreus, and A. oryzae. The spent medium of A. niger showed the highest silver reduction capacities with up to 15 μmol per milliliter spent medium when ammonium was used as the sole N-source. Silver ion reduction in the spent medium was not driven by enzymes and did not correlate with biomass concentration. Nearly full reduction capacity was reached after 2 days of incubation, long before the cessation of growth and onset of the stationary phase. The size of silver nanoparticles formed in the spent medium of A. niger was influenced by the nitrogen source, with silver nanoparticles formed in nitrate or ammonium-containing medium having an average diameter of 32 and 6 nm, respectively.

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.

Analyte-mediated formation and growth of nanoparticles for the development of chemical sensors and biosensors

The cornerstone of nanomaterial-based sensing systems is the synthesis of nanoparticles with appropriate surface functionalization that ensures their stability and determines their reactivity with organic or inorganic analytes. To accomplish these requirements, various compounds are used as additives or growth factors to regulate the properties of the synthesized nanoparticles and their reactivity with the target analytes. A different rationale is to use the target analytes as additives or growth agents to control the formation and properties of nanoparticles. The main difference is that the analyte recognition event occurs before or during the formation of nanoparticles and it is based on the reactivity of the analytes with the precursor materials of the nanoparticles (e.g., metal ions, reducing agents, and coatings). The transition from the ionic (or molecular) state of the precursor materials to ordered nanostructured assemblies is used for sensing and signal transduction for the qualitative detection and the quantitative determination of the target analytes, respectively. This review focuses on assays that are based on analyte-mediated regulation of nanoparticles' formation and differentiate them from standard nanoparticle-based assays which rely on pre-synthesized nanoparticles. Firstly, the principles of analyte-mediated nanomaterial sensors are described and then they are discussed with emphasis on the sensing strategies, the signal transduction mechanisms, and their applications. Finally, the main advantages, as well as the limitations of this approach, are discussed and compared with assays that rely on pre-synthesized nanoparticles in order to highlight the major advances accomplished with this type of nano-sensors and elucidate challenges and opportunities for further evolving new nano-sensing strategies.

Glutathione modulated fluorescence quenching of sulfur quantum dots by Cu2O nanoparticles for sensitive assay

Sulfur quantum dots (S-dots) show great potential for applications in various field, due to their favorable biocompatibility, high stability, and antibacterial properties. However, the use of S-dots in chemical sensing is limited by the lack of functional groups on the surface. In this work, a fluorescence glutathione (GSH) assay is developed based on the GSH modulated quenching effect of Cu₂O nanoparticles (NP) on S-dots. The fluorescence of S-dots is effectively quenched after forming complex with Cu₂O NP through a static quenching effect (SQE). Introducing of GSH can trigger the decomposition of Cu₂O NP into GSH-Cu(I) complex, which leads to the weaken of SQE and the partial recover of the fluorescence. The intensity of recovered fluorescence shows a positive correlation with the concentration of GSH in the concentration range of 20 to 500 μM. The fluorescence GSH assay shows excellent selectivity and robustness towards various interferences and high concentration salt, which endow the successful detection of GSH in human blood sample. The presented results provide a new door for the design of fluorescence assays, which also provides a platform for the applications in nanomedicine and environmental science.

Carbon dot composites for bioapplications: a review

Recent advancements in the synthesis of carbon dot composites and their applications in biomedical fields (bioimaging, drug delivery and biosensing) have been carefully summarized. The current challenges and future trends of CD composites in this field have also been discussed.

MnO2 Nanospheres Assisted by Cysteine Combined with MnO2 Nanosheets as a Fluorescence Resonance Energy Transfer System for "Switch-on" Detection of Glutathione

Manganese dioxide nanosheets combined with cysteine-assisted emitting manganese dioxide nanospheres (Cys-MnO₂ nanospheres) is fabricated for the first time as an "off-on" fluorescence detection platform for glutathione (GSH). In this sensing system, Cys-MnO₂ nanospheres served as energy donors, while MnO₂ nanosheets were used as both energy acceptors and recognition units. MnO₂ nanosheets can effectively quench the fluorescence of Cys-MnO₂ nanospheres through the fluorescence resonance energy transfer (FRET). The addition of GSH could reduce MnO₂ nanosheets into Mn²⁺, disrupting the FRET process and restoring the fluorescence of Cys-MnO₂ nanospheres. Under the optimum conditions, the "switch-on" platform we established has a wide response to GSH with a range of 5-50 μM and 150-800 μM, as well as a superior specificity. Importantly, all components of the sensor are nontoxic, biocompatible, easily prepared, and have a high utilization of raw materials. Moreover, the sensing system achieved satisfactory results in human serum, showing a tremendous potential in the field of biomedicine.

An ultrasensitive colorimetric and fluorescence dual-readout assay for glutathione with a carbon dot-MnO2 nanosheet platform based on the inner filter effect

An ultrasensitive colorimetric and fluorescence dual-readout assay based on the inner filter effect (IFE) was developed for glutathione (GSH) determination, in which carbon dots (C-dots) were used as a fluorophore and MnO₂ nanosheets as an absorber. Due to the excellent optical absorption properties of MnO₂ nanosheets and the good spectral overlap between the fluorophore and absorber, MnO₂ nanosheets could effectively quench the fluorescence of C-dots via the IFE. As the target, GSH could reduce MnO₂ nanosheets to Mn²⁺ ions, which inhibited the IFE and resulted in the fading of solution color and the recovery of the fluorescence signal. And these two kinds of signals were respectively used for qualitative and quantitative detection of GSH. The results showed that this proposed assay could distinguish 10 μM GSH with the naked eye and quantitatively detect GSH within the concentration range of 0.1–400 μM. The limit of detection was 6.6 nM. Moreover, this assay showed sensitive responses in human serum and urine samples, which indicated that this IFE-based assay has great potential in GSH-related clinical and bioanalytical applications.

An ultrasensitive colorimetric and fluorescence dual-readout assay based on carbon dot–MnO₂ nanosheets platform was developed for GSH detection in human body fluid samples.

Gold-Modified Micellar Composites as Colorimetric Probes for the Determination of Low Molecular Weight Thiols in Biological Fluids Using Consumer Electronic Devices

This work describes a new, low-cost and simple-to-use method for the determination of free biothiols in biological fluids. The developed method utilizes the interaction of biothiols with gold ions, previously anchored on micellar assemblies through electrostatic interactions with the hydrophilic headgroup of cationic surfactant micelles. Specifically, the reaction of AuCl4− with the cationic surfactant cetyltrimethyl ammonium bromide (CTAB) produces an intense orange coloration, due to the ligand substitution reaction of the Br− for Cl− anions, followed by the coordination of the AuBr4− anions on the micelle surface through electrostatic interactions. When biothiols are added to the solution, they complex with the gold ions and disrupt the AuBr4−–CTAB complex, quenching the initial coloration and inducing a decrease in the light absorbance of the solution. Biothiols are assessed by monitoring their color quenching in an RGB color model, using a flatbed scanner operating in transmittance mode as an inexpensive microtiter plate photometer. The method was applied to determine the biothiol content in urine and blood plasma samples, with satisfactory recoveries (i.e., >67.3–123% using external calibration and 103.8–115% using standard addition calibration) and good reproducibility (RSD < 8.4%, n = 3).

Biothiol modulated growth and aggregation of gold nanoparticles and their determination in biological fluids using digital photometry

This work describes a novel and easy to use method for the determination of biologically important thiols that relies on their ability to inhibit the catalytic enlargement of AuNP seeds in the presence of ACl₄^- ions and trigger their aggregation. UV-vis spectroscopic monitoring of the plasmon resonance bands of the formed AuNPs showed that the spectral and color transitions depend both on the concentration and the structure of biothiols. The colorimetric changes induced by biothiols were quantified in the concentration range from 5 to 300 μM in the RGB color system with digital photometry using a commercially available flatbed scanner as detector. On the basis of these results, the applicability of the method was tested to the determination of glutathione in red blood cells and cysteine in blood plasma with satisfactory recoveries (88.7-96.5%), low detection limits (1.0 μM), good selectivity against major biomolecules under physiologically relevant conditions and satisfactory reproducibility (<8%). The method requires minimum technical expertise, is easy to use and is performed without scientific equipment, holding promise as a simple assay of biothiol testing even by non-experts.

Recent advances in the construction and analytical applications of carbon dots-based optical nanoassembly

Recently, more and more attention has been focused on the construction and analytical applications of optical nanoassembly through combining carbon dots (CDs) with various other functional nanomaterials. The rational design and manufacture of CDs-based optical nanoassembly will be critical to meeting the needs of analytical science. The last decade has witnessed the immense potential of CDs-based optical nanoassembly in multiple sensing applications owing to their controlled optical properties, adjustable surface chemistry and microscopic morphology. This feature article collects the recent advances in the research and development of CDs-based optical nanoassembly and their applications in analytical sensors, aiming to provide vital insights and suggestions to inspire their broad sensing applications.

Ratiometric fluorescent sensors for sequential on-off-on determination of riboflavin, Ag+ and l-cysteine based on NPCl-doped carbon quantum dots

The fluorescent sensor, especially ratiometric fluorescent sensor, is one of the most important applications for CQDs, which is becoming a research hotspot. Herein, carbon quantum dots co-doped with nitrogen, phosphorus and chlorine (NPCl-CQDs) were synthesized by acid-base neutralization reaction exothermic carbonization method. The as-fabricated NPCl-CQDs could emit blue fluorescence and possess excellent fluorescence properties. Based on the FRET, multifunctional and ratiometric fluorescent sensors for "on-off-on" sequential determination of riboflavin, Ag⁺, and Cys with good selectivity and high sensitivity were established. The linear range of riboflavin, Ag⁺, and Cys are 0.50-10.18 μM and 15.89-27.76 μM, 0.66-1.46 mM and 1.50-4.20 mM, and 0.01-0.15 μM and 0.15-0.36 μM with the limit of detection of 3.50 nM, 26.38 μM, and 0.96 nM, respectively. Furthermore, the sensors were successfully used to determine riboflavin, Ag⁺, and Cys in tablets, river water, and human urine with the recoveries of 95.2-104.0%, 95.6-102.0%, and 94.8-106.4%, respectively. More importantly, the as-constructed "on-off-on" NPCl-CQDs-based ratiometric fluorescent sensors were applied for detecting riboflavin, Ag⁺, and Cys in HeLa cells with satisfying results. The finding of this study shows the feasibility and effectiveness of the NPCl-CQDs as the available ratiometric fluorescent sensors for the determination of riboflavin, Ag⁺, and Cys in real samples and living cells.

Microwave-assisted preparation of a silver nanoparticles/N-doped carbon dots nanocomposite and its application for catalytic reduction of rhodamine B, methyl red and 4-nitrophenol dyes

In the current work, a silver nanoparticles/nitrogen-doped carbon dots (AgNPs/NCDs) nanocomposite was prepared by a microwave-assisted method that does not require additional reducing or stabilizing agents. Multiple analytical techniques were used to characterize the prepared nanocomposite. The nanocomposite exhibited a surface plasmon resonance (SPR) absorption peak at 420 nm, indicating the development of AgNPs with NCDs. Further, HRTEM results confirmed the formation of the nanocomposite with the appearance of lattice fringes of both materials. Additionally, the nanocomposite did not show any precipitation even after two months of storage. The nanocomposite exhibited high catalytic activity towards the reduction of rhodamine B (RhB, 98.83%), methyl red (MR, 97.14%) and 4-nitrophenol (4-NP, 99.95%) at ambient temperature. Besides, the kinetic analysis revealed that the reduction reaction followed pseudo-first-order kinetics and the calculated rate constants (k) for rhodamine B (RhB), methyl red (MR) and 4-nitrophenol (4-NP) were found to be 0.0296 s-1, 0.0233 s-1 and 0.029 s-1, respectively. Moreover, it is a reusable and stable catalyst for reduction reactions up to five cycles without significant loss in catalytic activity. Finally, a plausible mechanism for the reduction of pollutants is also discussed in detail. As a whole, the prepared nanocomposite might display stunning behaviour for wastewater treatment applications.

A review on recent advances in amino acid and peptide-based fluorescence and its potential applications

Fluorescence is widely used to detect functional groups and ions, and peptides are used in various fields due to their excellent biological activity.

Facile synthesis of AgNPs@SNCDs nanocomposites as a fluorescent 'turn on' sensor for detection of glutathione

The present study illustrates the facile synthesis of silver nanoparticles capped with sulfur and nitrogen co-doped carbon dots (AgNPs@SNCDs) nanocomposites and their application towards the sensitive and selective detection of glutathione (GSH) using a spectrofluorimetry method. SNCDs were synthesized using solvothermal treatment of cysteamine hydrochloride and p-phenylenediamine. The as-fabricated SNCDs were then utilized as capping and stabilizing agents for the preparation of AgNPs@SNCDs nanocomposites using wet chemistry. The size of AgNPs@SNCDs nanocomposites was characterized to be ~37.58 nm or even larger aggregates. Particularly, the quenched fluorescence of AgNPs@SNCDs nanocomposites could be significantly restored upon addition of GSH, and the colour of its solution changed to some extent. The fluorescence intensity ratio of AgNPs@SNCDs nanocomposites at ~450 nm and 550 nm was directly proportional to the GSH concentration within the ranges 8.35-66.83 μM and 66.83-200.5 μM, and the detection limit was 0.52 μM. Furthermore various common organic molecules had no obvious interference in the detection mode. The proposed nanosensor was successfully applied for GSH assay in actual water samples.

Electron/energy co-transfer behavior and reducibility of Cu-chlorophyllin-bonded carbon-dots

Cu-chlorophyllin-bonded carbon dots (CCPh-CDs) have been synthesized at room temperature, and the energy/electron co-transfer behavior between Cu-chlorophyllin molecules (CCPh) and carbon dots (CDs) is investigated via various techniques. The mean diameters of CDs and CCPh-CDs are 2.8 nm and 3.1 nm, respectively, measured by HRTEM. The absorption spectra of CCPh-CDs show two parts: the absorptions of CDs and CCPh are in the wavelength range of 300–500 nm. The PL spectra of CCPh-CDs exhibit very weak intensities, and with the decreasing of CCPh content on CDs, the corresponding intensity increases. Luminescent decay spectra show that the PL decay times of CCPh and CCPh-CDs with the highest CCPh content are single-exponentially fitted to be 3.20 ns and 12.64 ns, respectively. Furthermore, based on the electron transfer and reducibility of CCPh-CDs, Ag/Ag₂O nanoparticles with a mean diameter of 10 nm can be easily prepared at room temperature under ultraviolet irradiation. The PL measurement result reveals that both electron transfer and FRET behavior take place from CCPh-CDs to Ag.

Cu-chlorophyllin-bonded carbon dots (CCPh-CDs) with/without Ag/Ag₂O (CCPh-CD-Ag) were obtained and investigated by optical measurements and luminescence decay spectroscopy.

Acetaldehyde-modified-cystine functionalized Zr-MOFs for pH/GSH dual-responsive drug delivery and selective visualization of GSH in living cells

In recent years, the construction of drug carriers that integrate diagnosis and treatment has become a new trend. In this article, a metal–organic framework (Zr-MOF) was synthesized and functionalized using acetaldehyde-modified-cystine (AMC) to form the functional drug carrier Zr-MOF/AMC which could be used to determine the concentration of glutathione (GSH) for cancer diagnosis, and to achieve pH/GSH dual-responsive release of methotrexate (MTX) for cancer therapy. The cleavage of the AMC disulfide bond by GSH generates two fluorescent molecules that produce strongly enhanced fluorescence, and the intensity is proportional to the GSH concentration. The green fluorescence of Zr-MOF/AMC in cancer cells proves that it can be applied in cell imaging to detect abnormal GSH concentrations for early diagnosis. In addition, MTX loaded on the Zr-MOF/AMC is released by the cleavage of the –S–S– and –C Created by potrace 1.16, written by Peter Selinger 2001-2019 ]]> N– bonds at the high GSH concentration and low pH in cancer cells. This dual-responsive drug release helps to deliver drugs to cancer cells more precisely. All the experiments suggest that this novel type of pH/GSH dual-responsive Zr-MOF/AMC nanoparticle may serve as a new drug delivery system for cancer diagnosis and treatment.

In recent years, the construction of drug carriers that integrate diagnosis and treatment has become a new trend.

Amperometric sensing of catechol by using a nanocomposite prepared from Ag/Ag2O nanoparticles and N,S-doped carbon quantum dots

This work describes the synthesis of a nanocomposite consisting of Ag₂O, silver nanoparticles and N,S-doped carbon quantum dots (Ag₂O/Ag@NS-CQD). The NS-CQD were prepared by hydrothermal treatment of p-aminobenzenesulfonic acid. They act as both the reducing and stabilizing agent for synthesis of Ag₂O/Ag@NS-CQD. The composite was characterized by UV-vis spectroscopy, transmission electron microscopy, X-ray diffraction and X-ray photoelectron spectroscopy. The glassy carbon electrode (GCE) was modified by coating it with Ag₂O/Ag@NS-CQD. It exhibits excellent amperometric response to catechol, typically at a low working potential of around 0.25 V. Under the best experimental conditions, the sensor has a wide linear response (0.2 to 180 μM) and a low detection limit (13 nM; at S/N = 3). The method was applied to analysis of spiked water samples and gave satisfactory results. Graphical abstract Schematic representation of the preparation of the Ag/Ag2O@N,S-doped carbon quantum dots composite using p-aminobenzenesulfonic acid and silver nitrate as the starting materials. The corresponding modified glassy carbon electrode exhibits the excellent amperometric sensing performance toward catechol at pH 7.0 with low detection limit and good selectivity.

A carbon dot-based fluorescent nanoprobe for the associated detection of iron ions and the determination of the fluctuation of ascorbic acid induced by hypoxia in cells and in vivo

Maintaining the redox balance of biological systems is a key point to maintain a healthy physiological environment. Excessive iron ions (Fe³⁺) can cause apoptosis, tissue damage and death. Fortunately, ascorbic acid (AA) as a reducing agent has been evaluated for the reduction of Fe³⁺. Moreover, AA plays an important role in relieving hypoxia-induced oxidative stress. Therefore, the real-time imaging of the Fe³⁺ and AA fluctuations is important for understanding their biofunctions in cells and in vivo. In this work, we developed a fluorescent nanoprobe carbon dot-desferrioxamine B (CD-DB) by the conjugate connection of CDs and desferrioxamine B (a complexing agent for Fe³⁺) for the associated detection of Fe³⁺ and AA. CD-DB exhibited excellent sensitivity and selectivity for the detection of Fe³⁺ and AA. The nanoprobe CDs-DB@Fe obtained by the reaction of CD-DB and Fe³⁺ was suitable for tracing the dynamic changes of AA in cells and in vivo. Therefore, CDs-DB@Fe was used for monitoring the fluctuation of AA in hypoxic cell models, hypoxic zebrafish models and liver ischemia mice models. These results exhibited the decrease in AA under hypoxic conditions because AA was consumed to neutralize free radicals and relieve hypoxia-induced oxidative stress damage. The ideal biocompatibility and low toxicity make our nanoprobe a potential candidate for the research of the physiological effects of AA in vivo.

Metal organic framework MIL-53(Fe) as an efficient artificial oxidase for colorimetric detection of cellular biothiols

Biothiols play critical roles in many biological processes and their aberrant is related to a variety of syndromes. A simple and reliable colorimetric method is developed in this work for biothiols detection based on an oxidase mimic, a metal organic framework (MOF) MIL-53(Fe), and a peroxidase substrate 3,3',5,5'-tetramethylbenzidine (TMB). In this design, MIL-53(Fe) is utilized to catalyze the conversion of TMB to a blue colored 3,3',5,5'-tetramethylbenzidine diimine, which can be read on a spectrophotometer at 652 nm. The oxidation-induced blue color generation can be efficiently inhibited by biothiols, thus a colorimetric analytical method is proposed for biothiols detection based on the above system. Under optimal conditions, a linear relationship in a range from 1 to 100 μM and a limit of detection (LOD) at 120 nM are achieved with Cys as a model target. The developed platform is further applied to evaluate cellular biothiols in normal (RWPE-1) and cancer (LNCap) cell lines, revealing that the overall biothiols level in LNCap is much higher than that in RWPE-1. This work renders a powerful tool for identifying cancer cells in a simple manner for biomedical diagnosis associated with biothiols.

Glutathione Regulated Inner Filter Effect of MnO2 Nanosheets on Boron Nitride Quantum Dots for Sensitive Assay

Glutathione (GSH) can help the body maintain the function of the normal immune system and its level change is associated with a variety of diseases. To achieve the ultrasensitive assay of GSH, a "switch on" nanosensor is designed on the basis of GSH regulating the inner filter effect (IFE) of MnO₂ nanosheets (MnO₂ NS) on boron nitride quantum dots (BNQDs). Here, the fluorescence of BNQDs is quenched efficiently in the presence of redoxable MnO₂ NS because of the superior light absorption capability; however, the introduction of GSH can trigger the decomposition of MnO₂ to Mn²⁺ and weaken the IFE, causing the partial fluorescence recovery. The recovered fluorescence is dependent on the concentration of GSH. Under the optimal conditions, this sensing platform shows the response to GSH in the range of 0.5-250 μM with the detection limit of 160 nM. On the basis of the GSH activated reduction of MnO₂ NS, the MnO₂ NS/BNQDs nanoprobes exhibit good selectivity to GSH. The practical application of the proposed system is demonstrated by detecting the GSH in human plasma samples with satisfying results.

One-pot synthesis of dual carbon dots using only an N and S co-existed dopant for fluorescence detection of Ag. SPECTROCHIMICA ACTA. PART A, MOLECULAR AND BIOMOLECULAR SPECTROSCOPY 2019;208:162-171. [PMID: 30312843 DOI: 10.1016/j.saa.2018.10.004]

Luminescent carbon-based nanoparticles, named often as carbon dots (CDs), were synthesized from citric acid (CA) and guanidine thiocyanate (GITC) via an N and S co-doped hydrothermal procedure. In the present structure characterization, N and S elements could be sufficiently doped by means of the heteroatom or the functional groups bonded on the surface of CDs. The as-prepared CDs solution showed blue color fluorescence under ultraviolet excitation, yet the PL spectra exhibited a repetitive emission process from excitation-independent to excitation-dependent. In view of the triexponential feature of fluorescence lifetimes of CDs, one possibility was proposed to be co-existence of two types of CDs with different surface states. Additionally, the as-prepared CDs were used as a sensing probe for the detection of Ag⁺ taking into consideration of the possible interactions between Ag⁺ and various fluorophores attached to the CD surface. As expected, the changes of fluorescence intensities were linearly proportional to the different concentration ranges of Ag⁺, which suggests the complex nature of the quenching mechanism. And for the first time, the SCN group was found to accelerate the quenching of CDs towards Ag⁺, promising a new approach for efficient detection of Ag⁺ for the application in industrial pollutants.

A sensitive plasmonic probe based on in situ growth of a Ag shell on a Au@N-CD nanocomposite for detection of isoniazid in environmental and biological samples

In this study, a new plasmonic probe based on the wavelength shift of the surface plasmon resonance band of a Au@N-CD nanocomposite was introduced for the determination of isoniazid.

Paper-based devices for biothiols sensing using the photochemical reduction of silver halides

This study describes the development of paper-based devices for the determination of biothiols. The devices are inexpensive (composed of paper and silver halide particles), and the analytical protocol is easily executable with minimum technical expertise and without the need of specialized equipment; the user has to add a test sample, illuminate the device with a UV lamp, and read the color change of the sensing area using a simple imaging device (i.e., cell-phone camera) or a bare eye. The detection mechanism of the assay is based on the biothiols-mediated photoreduction of nanometer-sized silver chloride particles deposited on the surface of paper; photoreduced silver chloride particles have a grayish coloration that depends on the concentration of biothiols in the tested solution. This is the first time that the UV-mediated photoreduction of solid silver halides particles is used for analytical purposes. The performance of the devices has been tested on the detection of total biothiols content of artificial body fluids and protein-free human blood plasma samples, and the results were satisfactory in terms of sensitivity, selectivity, recoveries and reproducibility.

Glutathione: Antioxidant Properties Dedicated to Nanotechnologies

Which scientist has never heard of glutathione (GSH)? This well-known low-molecular-weight tripeptide is perhaps the most famous natural antioxidant. However, the interest in GSH should not be restricted to its redox properties. This multidisciplinary review aims to bring out some lesser-known aspects of GSH, for example, as an emerging tool in nanotechnologies to achieve targeted drug delivery. After recalling the biochemistry of GSH, including its metabolism pathways and redox properties, its involvement in cellular redox homeostasis and signaling is described. Analytical methods for the dosage and localization of GSH or glutathiolated proteins are also covered. Finally, the various therapeutic strategies to replenish GSH stocks are discussed, in parallel with its use as an addressing molecule in drug delivery.

Nucleotide-Based Assemblies for Green Synthesis of Silver Nanoparticles with Controlled Localized Surface Plasmon Resonances and Their Applications

The sizes, shapes, and surface characteristics of nanomaterials determine their unique physical, chemical, and biological properties. Localized surface plasmon resonance (LSPR) is one of the unique optical properties of noble-metal nanoparticles. The synthesis of nanomaterials using biomolecules as templates offers an excellent strategy to control and regulate their features. Herein, for the first time, we demonstrate a green synthesis approach of silver nanoparticles (AgNPs) using nucleotide-based assemblies as templates. Moreover, we investigate the influence of different nucleotide-based assemblies and metal ions on the preparation of AgNPs, implying that AgNPs with different LSPR absorptions originating from their surrounding and size could be synthesized. The synthetic route is green, energy-effective, and feasible. On the basis of the unique LSPR-controlled property, the AgNP composites were applied for cryptography, biothiol detection, and designing logic gates. This work offers a promising method for the synthesis of nanomaterials with multiapplications.

A label-free fluorimetric detection of biothiols based on the oxidase-like activity of Ag+ ions

In this work, a label-free and sensitive fluorimetric method has been developed for the detections of biothiols including cysteine (Cys), homocysteine (Hcy), and glutathione (GSH), based on the specific biothiol-induced inhibition of the oxidase-like activity of silver ions (Ag⁺). It is well established that o-phenylenediamine (OPD) can be oxidized by Ag⁺ ions to generate fluorescent 2,3-diaminophenazine (OPDox). The introduction of biothiols would inhibit the oxidation of OPD by Ag⁺ due to the strong coordination between biothiols and Ag⁺. The changes of fluorescence intensities obtained in the Ag⁺-OPD system exhibited good linear correlations in the ranges of 0.50-30.0μM for Cys, 1.0-45.0μM for Hcy and 0.50-40.0μM for GSH. The detection limits (S/N=3) of Cys, Hcy and GSH were 110nM, 200nM and 150nM, respectively. Subsequently, the developed fluorimetric method was successfully applied for the detection of biothiols in human serum.

Naked eye and optical biosensing of cysteine over the other amino acids using β-cyclodextrin decorated silver nanoparticles as a nanoprobe

A simple, highly selective and efficient sensing approach based on a β-CD AgNP colorimetric nanoprobe has been demonstrated, which permits quick and specific determination of Cys over other important amino acids.

Application of response surface methodology and green carbon dots as reducing agents in speciation of iron

Herein, green synthetic approach was used to produce reducing carbon dots (CDs) and for the first time, corresponding reducing strengths were estimated.

Low-cost colorimetric assay of biothiols based on the photochemical reduction of silver halides and consumer electronic imaging devices

This work describes a new approach for the determination of free biothiols in biological fluids that exploits some of the basic principles of early photographic chemistry - that was based on silver-halide recording materials - and uses broadly-available imaging devices (i.e. flatbed scanners) as detectors. Specifically, the proposed approach relies on the ability of biothiols to bind to silver ions and dissociate the silver halide crystals thus changing the photosensitivity of silver halide crystal suspension. The changes induced by biothiols on the light intensity transmitted through the silver halide suspension, after photochemical reduction, were measured with a simplified photometric approach that employs a flatbed scanner operating in transmittance mode. The overall analytical procedure for the determination of biothiols was easily executable, fast and could be applied with inexpensive and commercially available materials and reagents. What is more, physiologically relevant biothiol levels could be inspected even by the unattended eye. The developed assay was successfully applied to the determination of biothiols in urine and blood plasma samples with detection limits as low as 10μM, satisfactory recoveries (92-97%), good reproducibility (6.7-8.8%) and high selectivity against other major components of biological fluids. The utility of the method to the determination of reduced/oxidized thiol ratio's as well as its application under natural light illumination, without external energy sources, was also demonstrated and is discussed with regard to point-of need applications in facility-limited settings.

Determination of gold nanoparticles in environmental water samples by second-order optical scattering using dithiotreitol-functionalized CdS quantum dots after cloud point extraction

This work presents a new method for the sensitive and selective determination of gold nanoparticles in water samples. The method combines a sample preparation and enrichment step based on cloud point extraction with a new detection motif that relies on the optical incoherent light scattering of a nano-hybrid assembly that is formed by hydrogen bond interactions between gold nanoparticles and dithiotreitol-functionalized CdS quantum dots. The experimental parameters affecting the extraction and detection of gold nanoparticles were optimized and evaluated to the analysis of gold nanoparticles of variable size and surface coating. The selectivity of the method against gold ions and other nanoparticle species was also evaluated under different conditions reminiscent to those usually found in natural water samples. The developed method was applied to the analysis of gold nanoparticles in natural waters and wastewater with satisfactory results in terms of sensitivity (detection limit at the low pmolL^-1 levels), recoveries (>80%) and reproducibility (<9%). Compared to other methods employing molecular spectrometry for metal nanoparticle analysis, the developed method offers improved sensitivity and it is easy-to-operate thus providing an additional tool for the monitoring and the assessment of nanoparticles toxicity and hazards in the environment.

Nanoparticle-based paper sensor for thiols evaluation in human skin

A new sensitive non-invasive gold nanoparticle-based sensor that enables to detect thiols in the human skin has been developed. The detection procedure implied the assessment of the color change of a paper sensor resulting from aggregation of gold nanoparticles caused by thiols. The ratio of the intensity of the photo image blue channel vs the red one (in units of RGB coloration) served as analytical response. The main thiol in the skin is glutathione, therefore, it was used as model biothiol and spiking substance. The range of linearity for glutathione was 8-75µM, the detection limit was 6.9µM. RSD≤7% is for inter-day determination of 10μM glutathione and RSD≤12% is the intra-day value. The recovery of 5µM and 10µM of glutathione was evaluated by applying solution, containing thiol-spikes, on skin. The results varied in the range 77-138%. A hundred-fold excess of serine, alanine, histidine, threonine, creatinine, urea, and ammonia; a ten-fold excess of glycine, proline, leucine, isoleucine, phenylalanine, asparagine; and a five-fold excess of valine, tryptophan, tyrosine, and uric acid, which can be extracted from the skin and is contained in the test matrix, have no significant effect on 10µM glutathione signal. Thiols level in the skin of volunteers (21-65 years old, men and women) detected with the use of a proposed non-invasive sensor was 11.6-47.5µM.

Cysteine, homocysteine and glutathione guided hierarchical self-assemblies of spherical silver nanoparticles paving the way for their naked eye discrimination in human serum

Herein, we unravel a new strategy of analyte guided self-assembly of a silver nanoprobe into three hierarchical alignments viz. flowers, thorns and petals which led to chromogenic discrimination of cysteine, homocysteine and glutathione.