Development of a 3D Hydrogel SERS Chip for Noninvasive, Real-Time pH and Glucose Monitoring in Sweat

Traditional diagnostic methods, such as blood tests, are invasive and time-consuming, while sweat biomarkers offer a rapid physiological assessment. Surface-enhanced Raman spectroscopy (SERS) has garnered significant attention in sweat analysis because of its high sensitivity, label-free nature, and nondestructive properties. However, challenges related to substrate reproducibility and interference from the biological matrix persist with SERS. This study developed a novel ratio-based 3D hydrogel SERS chip, providing a noninvasive solution for real-time monitoring of pH and glucose levels in sweat. Encapsulating the probe molecule (4-MBN) in nanoscale gaps to form gold nanoflower-like nanotags with internal standards and integrating them into an agarose hydrogel to create a 3D flexible SERS substrate significantly enhances the reproducibility and stability of sweat analysis. Gap-Au nanopetals modified with probe molecules are uniformly dispersed throughout the porous hydrogel structure, facilitating the effective detection of the pH and glucose in sweat. The 3D hydrogel SERS chip demonstrates a strong linear relationship in pH and glucose detection, with a pH response range of 5.5-8.0 and a glucose detection range of 0.01-5 mM, with R2 values of 0.9973 and 0.9923, respectively. In actual sweat samples, the maximum error in pH detection accuracy is only 1.13%, with a lower glucose detection limit of 0.25 mM. This study suggests that the ratio-based 3D hydrogel SERS chip provides convenient, reliable, and rapid detection capabilities with substantial application potential for analyzing body fluid pH and glucose.

Nonenzymatic Glucose Sensor Using Bimetallic Catalysts

Bimetallic glucose oxidation electrocatalysts were synthesized by two electrochemical reduction reactions carried out in series onto a titanium electrode. Nickel was deposited in the first synthesis stage followed by either silver or copper in the second stage to form Ag@Ni and Cu@Ni bimetallic structures. The chemical composition, crystal structure, and morphology of the resulting metal coating of the titanium electrode were investigated by X-ray diffraction, energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, and electron microscopy. The electrocatalytic performance of the coated titanium electrodes toward glucose oxidation was probed using cyclic voltammetry and amperometry. It was found that the unique high surface area bimetallic structures have superior electrocatalytic activity compared to nickel alone. The resulting catalyst-coated titanium electrode served as a nonenzymatic glucose sensor with high sensitivity and low limit of detection for glucose. The Cu@Ni catalyst enables accurate measurement of glucose over the concentration range of 0.2-12 mM, which includes the full normal human blood glucose range, with the maximum level extending high enough to encompass warning levels for prediabetic and diabetic conditions. The sensors were also found to perform well in the presence of several chemical compounds found in human blood known to interfere with nonenzymatic sensors.

Current scenario on biogenic synthesis of metal oxide nanocomposites using plant specimens and their application towards treatment of wastewater

Various industries such as textile, leather, and paper mills discharge huge amount of industrial effluents to the environment containing unconsumed dyes and toxic heavy metal ions which are very harmful and carcinogenic in nature. The increase in water pollution is adversely impacting the ecosystems and human health. Now, it has become a great challenge to treat the contaminated water/wastewater. Photocatalysis and adsorption are the two techniques gaining significant attention for the removal of toxic pollutants from wastewater effectively. In this regard, metal oxide-based nanomaterials and their composites have gained profound attention in photocatalytic degradation as well as adsorptive removal of toxic pollutants from water due to their chemical reactivity, higher surface area, regeneration efficiency, ample adsorption sites, intriguing photocatalytic activity, and cost-effectiveness. However, the conventional methods, employed to synthesize these metal oxide nanocomposites, involve the use of toxic chemicals which again produce secondary pollutants. Among all biological materials, the use of plant biomolecules is found to be the most effective way to synthesize stable nanomaterials, as the phytoconstituents of plants act as reducing, capping, and stabilizing agent. It is experimentally proved that bio-based nanocomposites have tremendous potential towards the degradation of environmental pollutants. Thus, there is a great need to work on the synthesis of some novel plant-based metal oxide nanocomposites and their applications in the field of water treatment. This review mainly discusses the metal oxide nanocomposites synthesized using plant specimens and their various applications towards treatment of water/wastewater.

Multi-dimensional plasmonic coupling system for efficient enrichment and ultrasensitive label-free SERS detection of bilirubin based on graphene oxide-Au nanostars and Au@Ag nanoparticles

Rapid and sensitive detection of free bilirubin (BR) is essential for early diagnosis of jaundice and other hepatobiliary diseases. Inspired by sandwich immunoassay strategy, a multi-dimensional plasmonic coupling SERS platform composed of graphene oxide-Au nanostars nanocomposites (GANS NCs) and Au@Ag nanoparticles (NPs) was designed for label-free detection of BR. Specifically, GANS NCs were first prepared, and their excellent SERS activity was ascribed to synergistic enhancement effect of electromagnetic enhancement and chemical enhancement. Furthermore, SERS spectroscopy was used to monitor the adsorption process of BR. Subsequently, secondary reinforcing Au@Ag NPs were directly added, ultimately resulting in a multi-dimensional plasmonic coupling effect. The SERS enhancing mechanism of coupled system was discussed through electromagnetic field simulations. Interestingly, the high-density hotspots generated by strong plasmonic coupling in GANS-Au@Ag substrate could lead to more extraordinary SERS enhancing behavior compared to GANS NCs. Sensing efficiency of the SERS platform was examined by BR with a detection limit down to 10^-11 M. Besides, GANS-Au@Ag NCs performed high uniformity and reproducibility. This work not only opens up a new avenue for construction of multi-dimensional plasmonic coupling system, but also offers a new biosensing technology for label-free diagnosis of BR-related diseases, thereby expecting to be applied in clinical diagnosis.

A Combinatorial Study Investigating the Growth of Ultrasmall Embedded Silver Nanoparticles upon Thermal Annealing

Ultrasmall nanoparticles (NPs) with a high active surface area are essential for optoelectronic and photovoltaic applications. However, the structural stability and sustainability of these ultrasmall NPs at higher temperatures remain a critical problem. Here, we have synthesized the nanocomposites (NCs) of Ag NPs inside the silica matrix using the atom beam co-sputtering technique. The post-deposition growth of the embedded Ag NPs is systematically investigated at a wide range of annealing temperatures (ATs). A novel, fast, and effective procedure, correlating the experimental (UV-vis absorption results) and theoretical (quantum mechanical modeling, QMM) results, is used to estimate the size of NPs. The QMM-based simulation, employed for this work, is found to be more accurate in reproducing the absorption spectra over the classical/modified Drude model, which fails to predict the expected shift in the LSPR for ultrasmall NPs. Unlike the classical Drude model, the QMM incorporates the intraband transition of the conduction band electrons to calculate the effective dielectric function of metallic NCs, which is the major contribution of LSPR shifts for ultrasmall NPs. In this framework, a direct comparison is made between experimentally and theoretically observed LSPR peak positions, and it is observed that the size of NPs grows from 3 to 18 nm as AT increases from room temperature to 900 °C. Further, in situ grazing-incidence small- & wide-angle X-ray scattering and transmission electron microscopy measurements are employed to comprehend the growth of Ag NPs and validate the UV + QMM results. We demonstrate that, unlike chemically grown NPs, the embedded Ag NPs ensure greater stability in size and remain in an ultrasmall regime up to 800 °C, and beyond this temperature, the size of NPs increases exponentially due to dominant Ostwald ripening. Finally, a three-stage mechanism is discussed to understand the process of nucleation and growth of the silica-embedded Ag NPs.

Silver Nanoparticle Decorated on Reduced Graphene Oxide-Wrapped Manganese Oxide Nanorods as Electrode Materials for High-Performance Electrochemical Devices

In this work, silver nanoparticles decorated on reduced graphene oxide (rGO) wrapped manganese oxide nanorods (Ag-rGO@MnO2) were synthesized for an active electrode material. MnO2 nanorods were synthesized via a hydrothermal route, and their coating with GO and subsequent reduction at a higher temperature resulted in rGO@MnO2. A further addition of Ag on rGO@MnO2 was performed by dispersing rGO@MnO2 in AgNO3 solution and its subsequent reduction by NaBH4. X-ray diffraction (XRD) analysis showed peaks corresponding to MnO2 and Ag, and the absence of a peak at 2θ = 26° confirmed a few layered coatings of rGO and the absence of any graphitic impurities. Morphological analysis showed Ag nanoparticles anchored on rGO coated MnO2 nanorods. Apart from this, all other characterization techniques also confirmed the successful fabrication of Ag-rGO@MnO2. The electrochemical performance examined by cyclic voltammetry and the galvanic charge–discharge technique showed that Ag-rGO@MnO2 has a superior capacitive value (675 Fg−1) as compared to the specific capacitance value of rGO@MnO2 (306.25 Fg−1) and MnO2 (293.75 Fg−1). Furthermore, the electrode based on Ag-rGO@MnO2 nanocomposite showed an excellent capacity retention of 95% after 3000 cycles. The above results showed that Ag-rGO@MnO2 nanocomposites can be considered an active electrode material for future applications in electrochemical devices.

The Effects of Nature-Inspired Synthesis on Silver Nanoparticle Generation

A wide range of methods can be used for nature-inspired metallic nanoparticle (NP) synthesis. These syntheses, however, are ongoing in the presence of diverse mixtures of different chemical compounds, and all or only a few of these contribute to resultant particle properties. Herein, the linden (Tilia sp.) inflorescence leachate and pure citric and protocatechuic acids were chosen for Ag-AgCl nanoparticle (NP) synthesis, and the resultant particles were then compared. We focused on the following four issues: (1) preparation of Ag-AgCl NPs using the Tilia sp.-based phytosynthetic protocol, (2) analytical determination of the common phenolic, nonphenolic, and inorganic profiles of three Tilia sp. types from different harvesting locations, (3) preparation of Ag-AgCl NPs using a mixture of citric and protocatechuic acids based on chromatographic evaluation, and (4) comparison of Tilia-based and organic acid-based syntheses. Our research confirms that the Tilia organic and inorganic profiles in biomasses are influenced by the harvesting location, and the three sites influenced both the morphology and final NP size. Our processing method was uniform, and this enabled great Ag-AgCl NP reproducibility for each specific biomass. We were then able to prove that the simplified organic acid-based synthesis produced even smaller NPs than Tilia-based synthesis. These findings provide better understanding of the significant influence on NP final properties resulting from other organic acids contained in the linden.

Synthesis approach-dependent antiviral properties of silver nanoparticles and nanocomposites

Numerous viral infections are common among humans, and some can lead to death. Even though conventional antiviral agents are beneficial in eliminating viral infections, they may lead to side effects or physiological toxicity. Silver nanoparticles and nanocomposites have been demonstrated to possess inhibitory properties against several pathogenic microbes, including archaea, bacteria, fungi, algae, and viruses. Its pronounced antimicrobial activity against various microbe-mediated diseases potentiates its use in combating viral infections. Notably, the appropriated selection of the synthesis method to fabricate silver nanoparticles is a major factor for consideration as it directly impacts antiviral efficacy, level of toxicity, scalability, and environmental sustainability. Thus, this article presents and discusses various synthesis approaches to produce silver nanoparticles and nanocomposites, providing technological insights into selecting approaches to generate antiviral silver-based nanoparticles. The antiviral mechanism of various formulations of silver nanoparticles and the evaluation of its propensity to combat specific viral infections as a potential antiviral agent are also discussed.

Efficient and Recyclable Heterogeneous Catalyst Based on PdNPs Stabilized on a Green-Synthesized Graphene-like Nanomaterial: Effect of Surface Functionalization

This work reports for the first time a straightforward and efficient approach to covalent surface functionalization of a sustainable graphene-like nanomaterial with abundant carboxylic acid groups. This approach results in an efficient and robust chelatant platform for anchoring highly dispersed ultrasmall palladium particles with excellent catalytic activity in the reduction of both cationic (methylene blue, MB) and anionic (eosin-Y, Eo-Y) toxic organic dyes. The large-specific-surface-area (S_BET = 266.94 m²/g) graphene-like nanomaterial (GHN) was prepared through a green and cost-effective pyrolysis process from saccharose using layered bentonite clay as a template. To introduce a high density of carboxylic acid functions, GHN was first doubly functionalized by successive grafting reaction using two different strategies: (i) in the first case, GHN was first grafted by (3-glycidyloxypropyl) trimethoxysilane (GPTMS) and then bifunctionalized by chemical grafting of tris(4-hydroxyphenyl)methane triglycidyl ether (TGE). In the second case, the grafting order of the two molecules has been reversed. GHN-GPTMS-TGE provided the highest number of grafted reactive epoxy groups, and it was selected for further functionalization with carboxylic acid functions via a ring-opening reaction through a two-step hydrolysis (H₂SO₄)/oxidation (KMnO₄) approach. The GHN nanomaterial bearing carboxylic acid groups was then treated with sodium hydroxide to produce a deprotonated carboxylic acid-rich platform. Finally, due to a high density of accessible chelatant carboxylic acid groups, GHN-COO^- binds strongly a great amount of Pd²⁺ ions to form stable complexes which after reduction by NaBH₄ leads to highly dispersed, densely anchored, and uniformly distributed nanoscale Pd particles (d ∼ 4.5 nm) on the surface of the functionalized GHN. The GHN-COO^-@PdNPs nanohybrid proved to be highly efficient for dye reduction by NaBH₄ in aqueous solution at room temperature. Moreover, because of the high stability of the as-prepared graphene-like supported PdNPs, it exhibited very good reusability and could be recycled up to eight times without any significant loss in activity.

Three-dimensional SERS sensor based on the sandwiched G@AgNPs@G/PDMS film

Three-dimensional (3D) SERS substrate with the denser "hotspots" is synthesized by the constriction of PDMS film decorated with sandwiched graphene@AgNPs@graphene (G@AgNPs@G) nanostructure. Graphene layers above and below the AgNPs are used to absorb molecules onto the "hotspots", and prevent the oxidation of AgNPs in our design. PDMS films can be easily shrunk for 3D structures, causing advantages in enhancement ability and light-matter interaction. Benefiting from the above advantages, a detection limit of 10^-14 M (CV) and enhancement factor (EF) of 3.9 × 10⁹ were obtained in our experiment. Theoretical analyses (FDTD) were also used to study the enhancement mechanism. For practical purposes, in-situ detection of MG molecules on the fish surface and the label-free detection of DNA base of adenine (A) and cytosine (C) were also studied. The high enhancement factor, great sensitivity, reliability, and stability of substrate reasonably proved that it can be used as an excellent SERS substrate for biomolecular detection.

Role of Graphene in Constructing Multilayer Plasmonic SERS Substrate with Graphene/AgNPs as Chemical Mechanism-Electromagnetic Mechanism Unit

Graphene–metal substrates have received widespread attention due to their superior surface-enhanced Raman scattering (SERS) performance. The strong coupling between graphene and metal particles can greatly improve the SERS performance and thus broaden the application fields. The way in which to make full use of the synergistic effect of the hybrid is still a key issue to improve SERS activity and stability. Here, we used graphene as a chemical mechanism (CM) layer and Ag nanoparticles (AgNPs) as an electromagnetic mechanism (EM) layer, forming a CM–EM unit and constructing a multi-layer hybrid structure as a SERS substrate. The improved SERS performance of the multilayer nanostructure was investigated experimentally and in theory. We demonstrated that the Raman enhancement effect increased as the number of CM–EM units increased, remaining nearly unchanged when the CM–EM unit was more than four. The limit of detection was down to 10⁻¹⁴ M for rhodamine 6G (R6G) and 10⁻¹² M for crystal violet (CV), which confirmed the ultrahigh sensitivity of the multilayer SERS substrate. Furthermore, we investigated the reproducibility and thermal stability of the proposed multilayer SERS substrate. On the basis of these promising results, the development of new materials and novel methods for high performance sensing and biosensing applications will be promoted.

Electrochemical Sodium Ion Sensor Based on Silver Nanoparticles/Graphene Oxide Nanocomposite for Food Application

High sodium ion (Na+) consumption leads to high blood pressure which causes many health issues. Real-time determination of Na+ content in food is still important to limit Na+ intake and control the taste of food. In this work, we have developed an electrochemical sensor based on agglomeration of silver nanoparticles (AgNPs) and graphene oxide (GO) modified on a screen-printed silver electrode (SPE) for Na+ detection at room temperature by using cyclic voltammetry (CV). The AgNPs were synthesized through a simple green route using Pistia stratiotes extract as a reducing agent under blue light illumination and mixed with the GO to be a Na+ selective sensing nanocomposite. The AgNPs/GO/SPE sensor showed high sensitivity (0.269 mA/mM/cm2), high selectivity, linear relationship (0–100 mM), good stability, and excellent reproducibility to Na+ detection as well as low limit of detection (9.344 mM) for food application. The interfering species such as K+, Zn2+, Na+, Mg2+, glucose, and ascorbic acid did not have any influence on the Na+ determination. The AgNPs/GO/SPE sensor was successfully applied to determine Na+ in real samples such as fish sauce and seasoning powder of instant noodle.

Electrochemical non-enzymatic glucose sensors: recent progress and perspectives

This review summarizes recent advances in the development of electrocatalysts for non-enzymatic glucose detection. The sensing mechanism and influencing factors are discussed, and the perspectives and challenges are also addressed.

Photo-organometallic, Nanoparticle Nucleation on Graphene for Cascaded Doping

Controlling the doping levels in graphene by modifying the electric potential of interfaced nanostructures is important to understand "cascaded-doping"-based applications of graphene. However, graphene does not have active sites for nanoparticle attachment, and covalently adding functional groups on graphene disrupts its planar sp²-hybridization, affecting its cascaded doping. Here we show a hexahepto (η⁶) photo-organometallic chemistry to interface nanoparticles on graphene while retaining the sp²-hybridized state of carbon atoms. For testing cascaded doping with ethanol interaction, transition metal oxide nanoparticles (TMONs) (Cr₂O₃/CrO₃, MoO₃, and WO₃) are attached on graphene. Here, the transition metal forms six σ-bonds and π-back-bonds with the benzenoid rings of graphene, while its opposite face binds to three carbonyl groups, which enable nucleation and growth of TMONs. With a radius size ranging from 50 to 100 nm, the TMONs downshift the Fermi level of graphene (-250 mV; p-doping) via interfacial charge transfer. This is consistent with the blue shift of graphene's G and 2D Raman modes with a hole density of 3.78 × 10¹² cm^-2. With susceptibility to ethanol, Cr_xO₃ nanoparticles on graphene enable cascaded doping from ethanol that adsorbs on Cr_xO₃, leading to doping of graphene to increase the electrical resistance of the TMONs-graphene hybrid. This nanoparticle-on-graphene construct can have several applications in gas/vapor sensing, electrochemical catalysis, and high-energy-density supercapacitors.

Ag and Au nanoparticles/reduced graphene oxide composite materials: Synthesis and application in diagnostics and therapeutics

The exceptional electrical, thermal, optical and mechanical properties have made two dimensional sp² hybridized graphene a material of choice in both academic as well as industrial research. In the last few years, researchers have devoted their efforts towards the development of graphene/polymer, graphene/metal nanoparticle and graphene/ceramic nanocomposites. These materials display excellent mechanical, electrical, thermal, catalytic, magnetic and optical properties which cannot be obtained separately from the individual components. Fascinating physical and chemical properties are displayed by noble metal nanomaterials and thus they represent model building blocks for modifying nanoscale structures for diverse applications extending from catalysis, optics to nanomedicine. Insertion of noble metal (Au, Ag) nanoparticles (NPs) into chemically derived graphene is thus of primary importance to open new avenues for both materials in various fields where the specific properties of each material act synergistically to provide hybrid materials with exceptional performances. This review attempts to summarize the different synthetic procedures for the preparation of Ag and Au NPs/reduced graphene oxide (rGO) composites. The synthesis processes of metal NPs/rGO composites are categorised into in-situ and ex-situ techniques. The in-situ approach consists of simultaneous reduction of metal salts and GO to obtain metal NPs/rGO nanocomposite materials, while in the ex-situ process, the metal NPs of desired size and shape are first synthesized and then transferred onto the GO or rGO matrix. The application of the Ag NPs and Au NPs/rGO composite materials in the area of biomedical (drug delivery and photothermal therapy) and biosensing are the focus of this review article.

Immobilization and 3D Hot-Junction Formation of Gold Nanoparticles on Two-Dimensional Silicate Nanoplatelets as Substrates for High-Efficiency Surface-Enhanced Raman Scattering Detection

We synthesize a high-efficiency substrate for surface-enhanced Raman scattering (SERS) measurements, which is composed of gold nanoparticles (AuNPs) on two-dimensional silicate nanoplatelets acting as an inorganic stabilizer, via the in-situ reduction of hydrogen tetrachloroaurate (III) by sodium citrate in an aqueous solution. Silicate platelets of ~1-nm thickness and various sizes, viz. laponite (50 nm), sodium montmorillonite (Na⁺⁻MMT, 100 nm), and mica (500 nm), are used to stabilize the AuNPs (Au@silicate), which are formed with uniform diameters ranging between 25 and 30 nm as confirmed by transmission electron microscopy (TEM). In particular, the laponite SERS substrate can be used in biological, environmental, and food safety applications to measure small molecules such as DNA (adenine molecule), dye (Direct Blue), and herbicide (paraquat) as it shows high detection sensitivity with a detection limit of 10-9 M for adenine detection. These highly sensitive SERS substrates, with their three-dimensional hot-junctions formed with AuNPs and two-dimensional silicate nanoplatelets, allow the highly efficient detection of organic molecules. Therefore, these Au@silicate nanohybrid substrates have great potential in biosensor technology because of their environmentally-friendly and simple fabrication process, high efficiency, and the possibility of rapid detection.

Interaction of 5-S-cysteinyl-dopamine with graphene oxide: an experimental and theoretical study for the detection of a Parkinson's disease biomarker

Spectroscopic and theoretical analysis in the adsorption of 5-S-Cys-DA over GO for the development of platform biosensors with Raman spectroscopy.

Graphene-based nanoplatforms for surface-enhanced Raman scattering sensing

Surface-enhanced Raman scattering (SERS) is one of the important techniques for sensing applications in biological analysis, disease diagnosis, environmental science, and food safety. Graphene provides an excellent nanoplatform for SERS sensing due to its two-dimensional flat structure, uniform electronic and photonic properties, excellent mechanical stability, atomic uniformity, and high biocompatibility. In this review, we summarize recent advances in the fabrication of various graphene-based nanoplatforms for SERS sensing. We present the strategies, such as self-assembly, in situ synthesis, one-pot synthesis, liquid phase reduction, and biomimetic synthesis, for the fabrication of graphene-based hybrid metallic and alloy nanoplatforms, and then demonstrate the potential applications of graphene-based nanoplatforms for the SERS sensing of ions, organic dyes, pesticides, bacteria, DNA, proteins, cells, and other chemicals in great detail. In addition, we also discuss the future development of this interesting research field and provide several perspectives. This work will be helpful for readers to understand the fabrication and sensing mechanisms of graphene-based SERS sensing nanoplatforms; meanwhile, it will promote the development of new materials and novel methods for high performance sensing and biosensing applications.

Electrical and Mechanical Properties of Ink Printed Composite Electrodes on Plastic Substrates

Printed flexible electrodes with conductive inks have attracted much attention in wearable electronics, flexible displays, radio-frequency identification, etc. Conventional conductive inks contain large amount of polymer which would increase the electrical resistivity of as-printed electrodes and require high sintering temperature. Here, composite electrodes without cracks were printed on polyimide substrate using binder-free silver nanoparticle based inks with zero-dimensional (activated carbon), one-dimensional (silver nanowire and carbon nanotube) or two-dimensional (graphene) fillers. The effect of fillers on resistivity and flexibility of printed composite electrodes were evaluated. The graphene filler could reduce the resistivity of electrodes, reaching 1.7 × 10−7 Ω·m after low power laser sintering, while the silver nanowire filler improved their flexibility largely during bending tests. The microstructural changes were examined to understand the nanojoining process and their properties.

Hierarchically Designed Ag@Ce6Mo10O39 Marigold Flower-Like Architectures: An Efficient Electrode Material for Hybrid Supercapacitors

We facilely prepared silver nanoparticle-decorated Ce₆Mo₁₀O₃₉ marigold flower-like structures (Ag NPs@CM MFs) for use as an effective positive material in hybrid supercapacitors (HSCs). With the aid of ethylenediaminetetraacetic acid (EDTA) as a chelating agent, self-assembled CM MFs were synthesized by a single-step hydrothermal method. When the electrochemical properties were tested in an aqueous alkaline electrolyte, the synthesized CM MFs with 0.15 g of EDTA exhibited a relatively high charge storage property (55.3 μA h/cm² at 2 mA/cm²) with a battery-type redox behavior. The high capacity performance is mainly because of the large surface area of the CM MFs, and the hierarchically connected nanoflakes provide wide open wells for rapid accessibility of electrolyte ions and enable fast transportation of electrons. A further improvement in electrochemical performance was achieved (62 μA h/cm² at 2 mA/cm²) by decorating Ag NPs on the surface of the CM MFs (i.e., Ag NPs@CM MFs), which is attributed to the increased electric conductivity. Considering the synergistic effect and the high electrochemical activity, Ag NPs@CM MFs were further employed as an effective positive electrode for the fabrication of pouch-type HSC with porous carbon (negative electrode) in an alkaline electrolyte. The HSC exhibited a high cell potential (1.5 V) with maximum energy and power densities of 0.0183 mW h/cm² and 10.237 mW/cm², respectively. The potency of HSC in practical applications was also demonstrated by energizing red and yellow light-emitting diodes as well as a three-point pattern torch light.

Nanoparticle-plant interaction: Implications in energy, environment, and agriculture

In the recent techno-scientific revolution, nanotechnology has gained popularity at a rapid pace in different sectors and disciplines, specifically environmental, sensing, bioenergy, and agricultural systems. Controlled, easy, economical, and safe synthesis of nanomaterials is desired for the development of new-age nanotechnology. In general, nanomaterial synthesis techniques, such as chemical synthesis, are not completely safe or environmentally friendly due to harmful chemicals used or to toxic by-products produced. Moreover, a few nanomaterials are present as by-product during washing process, which may accumulate in water, air, and soil system to pose serious threats to plants, animals, and microbes. In contrast, using plants for nanomaterial (especially nanoparticle) synthesis has proven to be environmentally safe and economical. The role of plants as a source of nanoparticles is also likely to expand the number of options for sustainable green renewable energy, especially in biorefineries. Despite several advantages of nanotechnology, the nano-revolution has aroused concerns in terms of the fate of nanoparticles in the environment because of the potential health impacts caused by nanotoxicity upon their release. In the present panoramic review, we discuss the possibility that a multitudinous array of nanoparticles may find applications convergent with human welfare based on the synthesis of diverse nanoparticles from plants and their extracts. The significance of plant-nanoparticle interactions has been elucidated further for nanoparticle synthesis, applications of nanoparticles, and the disadvantages of using plants for synthesizing nanoparticles. Finally, we discuss future prospects of plant-nanoparticle interactions in relation to the environment, energy, and agriculture with implications in nanotechnology.

Advancement of Ag-Graphene Based Nanocomposites: An Overview of Synthesis and Its Applications

Graphene has been employed as an excellent support for metal nanomaterials because of its unique structural and physicochemical properties. Silver nanoparticles (AgNPs) with exceptional properties have received considerable attention in various fields; however, particle aggregation limits its application. Therefore, the combination of AgNPs and graphene based nanocomposites (Ag-graphene based nanocomposites) has been widely explored to improve their properties and applications. Excitingly, enhanced antimicrobial, catalytic, and surface enhanced Raman scattering properties are obtained after their combination. In order to have a comprehensive knowledge of these nanocomposites, this Review highlights the chemical and biological synthesis of Ag-graphene nanocomposites. In particular, their applications as antimicrobial agents, catalysts, and sensors in biomedicine, agricultural protection, and environmental remediation and detection are covered. Meanwhile, the factors that influence the synthesis and applications are also briefly discussed. Furthermore, several important issues on the challenges and new directions are also provided for further development of these nanocomposites.

Bioinspired gold nanoparticles decorated reduced graphene oxide nanocomposite using Syzygium cumini seed extract: Evaluation of its biological applications

The development of novel functionalized reduced graphene oxide nanocomposite materials keeping in mind environmental and health perspectives via green approaches is currently gaining enormous research interest in the field of nanoscience and nanotechnology. Herein, we report a bio-inspired green synthesis approach for gold nanoparticles decorated reduced graphene oxide nanocomposite in which Syzygium cumini seed extract (SCSE) is applied as natural reducing and stabilizing agent for the simultaneous reduction of chloroauric acid and graphene oxide (GO). The obtained nanocomposite was thoroughly investigated using UV-visible and FT-IR spectroscopy, XRD, SEM-EDX, TEM-SAED, Raman spectroscopy and XPS analysis. These characterization techniques clearly confirmed the successful synthesis of gold nanoparticles decorated reduced graphene oxide nanocomposite. In addition, this study evaluated the systematic and detailed analysis of AuNPs-rGO-NC and its efficacy towards cellular and antibacterial toxicological behavior. A detailed in-vitro cytotoxicity study was performed by analysing the percentage inhibition of cell viability, generation of reactive oxygen species (ROS) in cell lines using 3‑(4,5‑dimethylthiazol‑2‑yl)‑2,5‑diphenyltetrazolium bromide (MTT) assay on human colorectal (HCT116) and lung (A549) cancer cell lines. Further, antibacterial toxicological evaluation was performed by analysing diameter of inhibition Zone (DIZ), activity index (AI), minimum bactericidal concentration (MBC), minimum inhibitory concentration (MIC), growth kinetics (GrK) and death kinetics (DeK) against Gram-negative bacterial strain Escherichia coli and Gram-positive bacterial strains Staphylococcus aureus and Bacillus subtilis. The cytotoxicity and antibacterial toxicological assays revealed that the synthesized nanocomposite showed significant anti-cancer activity towards A549 cell line and Gram-negative bacterial strain Escherichia coli compared to the rest.

Silver nanoparticles deposited on graphene oxide for ultrasensitive surface-enhanced Raman scattering immunoassay of cancer biomarker

Graphene oxide (GO) exhibits distinctive Raman scattering features for its high frequency D (disordered) and tangential modes (G-band), which are characteristically sharp at 1580 cm-1 and 1350 cm-1, respectively, but are too weak for sensitive quantitation purposes. By depositing silver nanoparticles on the surface of GO in this contribution, both D and G bands of GO become enhanced. The enzyme label of this method controls the dissolution of silver nanoparticles on the surface of GO through hydrogen peroxide which is produced by the oxidation of the enzyme substrate. With the dissolution of the silver nanoparticles a greatly decreased SERS signal of GO was obtained. This strategy involves dual signal amplification of the enzyme and nanocomposites to improve the detection sensitivity. As a proof of concept, prostate specific antigen (PSA), a biomarker for prostate cancer, is successfully detected as a target by forming a sandwich structure in immunoassay. The SERS immunoassay possesses excellent analytical performance in the range 0.5 pg mL-1 to 500 pg mL-1 with a limit of detection of 0.23 pg mL-1, making the detection of PSA serum samples from prostate cancer patients satisfactory, demonstrating that the sensitive enzyme-assisted dissolved AgNPs SERS immunoassay of PSA has potential applications in clinical diagnosis.

A Review on Applications of Two-Dimensional Materials in Surface-Enhanced Raman Spectroscopy

Two-dimensional (2D) materials, such as graphene and MoS2, have been attracting wide interest in surface enhancement Raman spectroscopy. This perspective gives an overview of recent developments in 2D materials’ application in surface-enhanced Raman spectroscopy. This review paper focuses on the applications of using bare 2D materials and metal/2D material hybrid substrate for Raman enhancement. The Raman enhancing mechanism of 2D materials will also be discussed. The progress covered herein shows great promise for widespread adoption of 2D materials in SERS application.

Fermi level equilibration of Ag and Au plasmonic metal nanoparticles supported on graphene oxide

For the first time, the process of Fermi level equilibration has been studied and compared for plasmonic metal nanoparticles (PMNPs) supported on conducting substrates i.e. graphene oxide (GO) sheets.

Synthesis and characterization of graphene/carbonized paper/tannic acid for flexible composite electrodes

A simple and low-cost approach toward flexible and free-standing electrodes is developed.