Electrospun Polymer Nanofibers Decorated with Noble Metal Nanoparticles for Chemical Sensing

State-of-the-art nanosensors and kits for the detection of antibiotic residues in milk and dairy products

Antibiotic resistance is increasingly seen as a future concern, but antibiotics are still commonly used in animals, leading to their accumulation in humans through the food chain and posing health risks. The development of nanomaterials has opened up possibilities for creating new sensing strategies to detect antibiotic residues, resulting in the emergence of innovative nanobiosensors with different benefits like rapidity, simplicity, accuracy, sensitivity, specificity, and precision. Therefore, this comprehensive review provides pertinent and current insights into nanomaterials-based electrochemical/optical sensors for the detection of antibitic residues (ANBr) across milk and dairy products. Here, we first discuss the commonly used ANBs in real products, the significance of ANBr, and also their binding/biological properties. Then, we provide an overview of the role of using different nanomaterials on the development of advanced nanobiosensors like fluorescence-based, colorimetric, surface-enhanced Raman scattering, surface plasmon resonance, and several important electrochemical nanobiosensors relying on different kinds of electrodes. The enhancement of ANB electrochemical behavior for detection is also outlined, along with a concise overview of the utilization of (bio)recognition units. Ultimately, this paper offers a perspective on the future concepts of this research field and commercialized nanomaterial-based sensors to help upgrade the sensing techniques for ANBr in dairy products.

SERS Assays Based on Electrospun Nanofibers: Preparation and Analytical Applications

Surface-enhanced Raman spectroscopy (SERS) is a powerful tool and an up-to-date method of analytical chemistry due to its high sensitivity and fingerprint recognition capabilities. Nowadays SERS due to its label-free detection capabilities is being actively developed in medical fields, for example in the analysis of biologically important substances in different matrixes, for potential on-site detection of toxic substances, food safety, and so on. To get the SERS signal, it is necessary the presence of plasmonic nanostructures in the SERS substrates. Electrospun nanofibers have been an attractive alternative to SERS-platforms due to the diversity of advantages, including ease of preparation, structure flexibility, and others. In this review, we summarized the methods of plasmonic nanostructures incorporating substrate based on electrospun nanofibers. Also, the analytical application of SERS-active electrospun nanofibers with embedded nanostructures focused on biologically significant molecules is observed in detail. Finally, the future outlook in the application of these substrates in bioanalysis as the most promising area in analytical chemistry is presented.

CuNi Alloy NPs Anchored on Electrospun PVDF-HFP NFs Catalyst for H2 Production from Sodium Borohydride

Non-noble Cu_xNi_1-x (x = 0, 0.1, 0,2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1) alloy nanoparticles supported on poly(vinylidene fluoride-co-hexafluoropropene) (PVDF-HFP) nanofibers (NFs) are successfully fabricated. The fabrication process is executed through an electrospinning technique and in situ reduction in Cu²⁺ and Ni²⁺ salts. The as-synthesized catalysts are characterized using standard physiochemical techniques. They demonstrate the formation of bimetallic NiCu alloy supported on PVDF-HFP. The introduced bimetals show better catalytic activity for sodium borohydride (SBH) hydrolysis to produce H₂, as compared to monometallic counterparts. The Cu_0.7 Ni_0.3/PVDF-HFP catalyst possesses the best catalytic performance in SBH hydrolysis as compared to the others bimetallic formulations. The kinetics studies indicate that the reaction is zero order and first order with respect to SBH concentration and catalyst amount, respectively. Furthermore, low activation energy (Ea = 27.81 kJ/mol) for the hydrolysis process of SBH solution is obtained. The excellent catalytic activity is regarded as the synergistic effects between Ni and Cu resulting from geometric effects over electronic effects and uniform distribution of bimetallic NPs. Furthermore, the catalyst displays a satisfying stability for five cycles for SBH hydrolysis. The activity has retained 93% from the initial activity. The introduced catalyst has broad prospects for commercial applications because of easy fabrication and lability.

Fabrication and evaluation of chitosan modified filter paper for chlorpyrifos detection in wheat by surface-enhanced Raman spectroscopy

BACKGROUND

Chlorpyrifos is a commonly used organophosphorus pesticide in agriculture. However, its neurotoxicity poses a huge threat to human health. In the present study, a chitosan-modified filter paper-based surface enhanced Raman scattering active substrate (Ch/AgNPs/paper) was fabricated and used to detect trace amounts of chlorpyrifos in 120 treated wheat samples.

RESULTS

Results showed that the Ch/AgNPs/paper substrate could be used to enhance the chlorpyrifos spectral fingerprint only up to a concentration of 0.000558 mg L^-1 . Following Raman spectra acquisition, three pre-processing methods, including Savitzky-Golay (Savitsky-Golay filter with a second order polynomial) smoothing with first derivative and second derivative and normalization, were used to reduce baseline variation and increase resolutions of spectral peak features of the original spectra dataset. Then, prediction models based on partial least squares were established for detecting chlorpyrifos pesticide residue in wheat. The partial least squares model with normalization yielded optimal result, with a correlation coefficient of 0.9764, root mean square error of prediction of 1.22 mg L^-1 in the prediction, and relative analysis deviation of 4.12. Five unknown samples were prepared to verify the accuracy of the prediction model. The predicted recoveries were calculated to be between 97.25% and 119.38% with an absolute t value of 0.598. The value of a t-test shows that the prediction model is accurate and reliable.

CONCLUSION

The present study demonstrates that the proposed method can achieve rapid detection of chlorpyrifos in wheat. © 2022 Society of Chemical Industry.

Optical sensors based on electrospun membranes – principles, applications, and prospects for chemistry and biology

Electrospun membranes are promising substrates for receptor layer immobilization in optical sensors. Either colorimetric, luminescence, or Raman scattering signal can be used to detect the analyte.

Gold-Polymer Nanocomposites for Future Therapeutic and Tissue Engineering Applications

Gold nanoparticles (AuNPs) have been extensively investigated for their use in various biomedical applications. Owing to their biocompatibility, simple surface modifications, and electrical and unique optical properties, AuNPs are considered promising nanomaterials for use in in vitro disease diagnosis, in vivo imaging, drug delivery, and tissue engineering applications. The functionality of AuNPs may be further expanded by producing hybrid nanocomposites with polymers that provide additional functions, responsiveness, and improved biocompatibility. Polymers may deliver large quantities of drugs or genes in therapeutic applications. A polymer alters the surface charges of AuNPs to improve or modulate cellular uptake efficiency and their biodistribution in the body. Furthermore, designing the functionality of nanocomposites to respond to an endo- or exogenous stimulus, such as pH, enzymes, or light, may facilitate the development of novel therapeutic applications. In this review, we focus on the recent progress in the use of AuNPs and Au-polymer nanocomposites in therapeutic applications such as drug or gene delivery, photothermal therapy, and tissue engineering.

Electrospun polymeric nanofiber decorated with sea urchin-like gold nanoparticles as an efficient and stable SERS platform

Surface enhanced Raman scattering (SERS)-based nanoprobes have been used as well-established analytical tools enabling single-molecule detection. In this work, we report a facile method to decorate sea urchin-like gold nanoparticles (SUGNPs) on the surface of PMMA/P4VP nanofibers. Firstly, PMMA/P4VP nanofibers within the submicrometer size range were prepared by applying the electrospinning technique. Then, the incorporation of SUGNPs on the surface of PMMA/P4VP nanofiber was achieved by immersing PMMA/P4VP nanofiber into freshly prepared SUGNP aqueous solution through the specific Au-N interactions. The as-fabricated SUGNP-coated PMMA/P4VP nanofibers exhibited good sensitivity and reproducibility in SERS measurements with the relative standard deviation down to 6.6%, by employing 4-mercaptobenzoic acid as a probe molecule with 30 min of soaking time. Hence, we envisage that the SUGNP-coated PMMA/P4VP nanofibers can act as efficient and stable SERS substrates for potential applications in molecular detection as well as chemical and biological analysis.

SERS-active substrate assembled by Ag NW-embedded porous polystyrene fibers

Here we demonstrate a novel SERS-active substrate assembled by silver nanowire (Ag NW)-embedded porous polystyrene (PS) fibers. Ag NWs are synthesized through a glycerol-mediated solvothermal method firstly, then electrospun into PS porous fibers. The as-synthesized Ag NWs are embedded in PS fiber and aligned orderly along the axial direction. Porous structure appears in PS fiber due to the phase separation induced by rapid evaporation of solvents. Large amounts of holes not only greatly improve the sample collection efficiency of the SERS-active substrate, but also significantly facilitate the adsorption of target molecules on the surface of Ag NWs, thus increasing the probability of enhancement of target molecules. In addition, compared with polyvinyl alcohol (PVA) and polyvinyl pyrrolidone (PVP), PS has better solvent resistance. The detection limit of 4-aminothiophenol (4-ATP) on our fabricated electrospun fiber mats is 10⁻⁷ M, and the electrospun fiber mats showed good reproducibility of SERS signal detection. This study proposes a feasible strategy for the large-scale preparation of flexible SERS-active substrate assembled by Ag NW-embedded porous PS fibers. The produced flexible SERS substrates may have potential application in wearable sensors for the trace detection of chemical and biological molecules.

SERS-active substrate assembled by Ag NW-embedded porous PS fibers has high sample collection efficiency for the target molecule.

Synthesis of novel catalytic composite nanofibers containing ruthenium nanoparticles stabilized by a citric acid-β-cyclodextrin polymer

The elaboration of catalytic composite nanofibers (NFs) by electrospinning through a one-pot strategy is described. First, aqueous colloidal suspensions of ruthenium nanoparticles (Ru NPs) formed by reduction of a Ru(iii) salt with NaBH4 and stabilized by poly(cyclodextrin citrate) (PCD) were prepared. Then, poly(vinyl alcohol) (PVA) of different molecular weights was dissolved in the colloidal suspensions that were electrospun. SEM analyses of the resulting nanowebs displayed uniform NFs, whose diameters ranged between 300 and 700 nm and enlarged upon increasing (i) PVA molecular weight, (ii) nanosuspension viscosity, (iii) the amount of NaBH4 and (iv) the PCD/Ru NP concentration. TEM analysis confirmed that Ru NPs with a mean diameter of around 2 nm were observed at the surface of NFs, embedded in the PVA matrix of NFs. HAADF-STEM and EDS mapping clearly showed that Ru NPs were homogeneously distributed onto and into the matrix of NFs. After their electrospinning, the prepared nanowebs were submitted to a heat post-treatment at 160 °C which was shown to trigger the PVA crystallization. In addition, the physical crosslinking of PVA chains by NaBO2 resulting from NaBH4 oxidation in the precursor suspension was also observed. Interestingly, an SEM study evidenced that the thermal post-treatment in combination with the presence of NaBO2 clearly improved the thermal stability of the synthesized composite nanowebs. Finally, catalytic hydrogenation tests showed the absence of Ru NPs leaching from NFs in the reaction medium, and displayed good conversion of styrene into ethylbenzene.

Polycaprolactone-Based, Porous CaCO3 and Ag Nanoparticle Modified Scaffolds as a SERS Platform With Molecule-Specific Adsorption

Surface-enhanced Raman scattering (SERS) is a high-performance technique allowing detection of extremely low concentrations of analytes. For such applications, fibrous polymeric matrices decorated with plasmonic metal nanostructures can be used as flexible SERS substrates for analysis of analytes in many application. In this study, a three-dimensional SERS substrate consisting of a CaCO₃-mineralized electrospun (ES) polycaprolactone (PCL) fibrous matrix decorated with silver (Ag) nanoparticles is developed. Such modification of the fibrous substrate allows achieving a significant increase of the SERS signal amplification. Functionalization of fibers by porous CaCO₃ (vaterite) and Ag nanoparticles provides an effective approach of selective adsorption of biomolecules and their precise detection by SERS. This new SERS substrate represents a promising biosensor platform with selectivity to low and high molecular weight molecules.

Atomic layer deposition of palladium nanoparticles on a functional electrospun poly-cyclodextrin nanoweb as a flexible and reusable heterogeneous nanocatalyst for the reduction of nitroaromatic compounds

We here show a rational approach for the fabrication of a flexible, insoluble catalytic electrospun nanoweb of cross-linked cyclodextrin (CD) for the reduction of nitroaromatics. CD nanofibers were produced by electrospinning an aqueous HP-β-CD solution containing a multifunctional cross-linker (i.e., 1,2,3,4-butanetetracarboxylic acid, BTCA) and were subsequently cross-linked by heat treatment, which led to an insoluble electrospun poly-CD nanoweb. The poly-CD nanoweb was decorated with Pd nanoparticles (Pd-NPs) by atomic layer deposition (ALD) technique over 20 cycles to give rise to a catalytic electrospun nanoweb (i.e., Pd@poly-CD). The formation of the Pd-NPs on the poly-CD nanofiber surface was clearly evidenced by TEM and STEM imaging, which displayed the homogeneously distributed Pd-NPs with a mean size of 4.34 nm. ICP-MS analysis revealed that the Pd content on the Pd@poly-CD nanoweb was 0.039 mg per mg of nanoweb. The catalytic performance of the Pd@poly-CD nanoweb was tested for the reduction of a nitroaromatic compound (i.e., 4-nitrophenol (4-NP)), and high catalytic performance of the Pd@poly-CD nanoweb was observed with a corresponding TOF value of 0.0316 min-1. XPS was used to explore the oxidation state of Pd atoms before and after the catalytic reduction of 4-NP, and no significant change was observed after catalytic reactions. In brief, the Pd@poly-CD nanoweb having handy, flexible, structural stability and reusability can be effectively used in environmental applications as a heterogeneous nanocatalyst for the reduction of toxic nitroaromatics.

Naturally-derived electrospun wound dressings for target delivery of bio-active agents

Electrospun nanofibers are known as the advanced means for wound dressing. They have represented remarkable potency to encapsulate and deliver biomolecules promoting the wound healing process. Compared to synthetic polymers, naturally derived polymers (NDP) are more qualified candidates for fabrication of biomedical electrospun scaffolds. Not only nanofibers of NDP illustrate higher biocompatibility and biodegradability rates, but also they mimic the native extracellular matrix more closely, which leads to the wound closure acceleration by enhancing tissue regeneration. Aside, incorporation of bioactive molecules and therapeutic agents into the nanofibers can generate innovative bioactive wound dressings with significantly improved healing potentials. This paper starts with a brief discussion on the steps and factors influencing the wound healing process. Then, the recent applications of electrospun nanofibers as wound dressing with healing accelerating properties are reviewed. Further, the various healing agents and alternative strategies for modification and functionalization of bioactive naturally-derived electrospun nanofibers are discussed.

Gold Nanoparticle-Integrated Scaffolds for Tissue Engineering and Regenerative Medicine

The development of scaffolding materials that recapitulate the cellular microenvironment and provide cells with physicochemical cues is crucial for successfully engineering functional tissues that can aid in repairing damaged organs. The use of gold nanoparticles for tissue engineering and regenerative medicine has raised great interest in recent years. In this mini review, we describe the shape-dependent properties of gold nanoparticles, and their versatile use in creating tunable nanocomposite scaffolds with improved mechanical and electrical properties for tissue engineering. We further describe using gold nanoparticle-integrated scaffolds to achieve improved stem cells proliferation and differentiation. Finally, we discuss the main challenges and prospects for clinical translation of gold nanoparticles-hybrid scaffolds.

Fabrication of Electrospun Polymer Nanofibers with Diverse Morphologies

Fiber structures with nanoscale diameters offer many fascinating features, such as excellent mechanical properties and high specific surface areas, making them attractive for many applications. Among a variety of technologies for preparing nanofibers, electrospinning is rapidly evolving into a simple process, which is capable of forming diverse morphologies due to its flexibility, functionality, and simplicity. In such review, more emphasis is put on the construction of polymer nanofiber structures and their potential applications. Other issues of electrospinning device, mechanism, and prospects, are also discussed. Specifically, by carefully regulating the operating condition, modifying needle device, optimizing properties of the polymer solutions, some unique structures of core⁻shell, side-by-side, multilayer, hollow interior, and high porosity can be obtained. Taken together, these well-organized polymer nanofibers can be of great interest in biomedicine, nutrition, bioengineering, pharmaceutics, and healthcare applications.

Ag-Nanoparticle-Bearing Poly(vinylidene fluoride) Nanofiber Mats as Janus Filters for Catalysis and Separation

Hydrophilic Ag nanoparticles were pattern-deposited onto one side of an electrospun poly(vinylidene fluoride) (PVDF) nanofiber mat, yielding a Janus filter. The filter was used to separate a receiver cell from a reactor cell that contained an aqueous 4-nitrophenol/NaBH₄ solution. Upon contact with this solution, the Ag nanoparticles catalyzed the reduction of 4-nitrophenol to 4-aminophenol. After the reaction reached completion, ethyl acetate was added into the reactor to extract the product. During this process, the ethyl acetate containing 4-aminophenol also selectively permeated regions of the hydrophobic yet oleophilic PVDF mat that were not covered by Ag nanoparticles. The product was obtained after the evaporation of ethyl acetate. This paper demonstrates the first use of a Janus filter in a catalytic separatory reactor that catalyzes a chemical reaction and then facilitates the eventual separation of the formed product via filtration.

Production of electrospun nanofibers based on graphene oxide/gum Arabic

Over the last few years, the electrospinning technique has attracted significant attention for the production of novel nanofibrous materials. At the same time, the use of graphene oxide and the natural products extracted from plants and/or trees have become very popular in various fields of science. In this work, a new method for the production of nanofibers based on a combination of Gum Arabic (GA), as a natural tree gum exudate, PVA, as an environmentally-friendly stabilizer, and graphene oxide (GO) has been developed and characterized. SEM analysis showed fundamental differences on the surface of bare nanofibers with and without GO, and also significantly smaller fiber diameters in the case of the presence of GO (fibers <100 nm present). Raman spectroscopy confirmed and TGA analysis approximated the content of GO in the nanofibers. Adsorption of methylene blue on the produced nanofibrous membrane was about 50% higher in the presence of GO, which opens the possibility to use GO/GA/PVA fibers in several applications, for example for the removal of dyes.

Preparation of Quasi-Three-Dimensional Porous Ag and Ag-NiO Nanofibrous Mats for SERS Application

In this study, two new quasi-three-dimensional Surface Enhanced Raman Scattering (SERS) substrates, namely porous Ag and Ag-NiO nanofibrous mats, were prepared using a simple, electrospinning-calcination, two-step synthetic process. AgNO₃/polyvinyl pyrrolidone (PVP) and AgNO₃/Ni(NO₃)₂/PVP composites serving as precursors were electrospun to form corresponding precursory nanofibers. Porous Ag and Ag-NiO nanofibers were successfully obtained after a 3-h calcination at 500 °C under air atmosphere, and analyzed using various material characterization techniques. Synthesized, quasi-three-dimensional porous Ag and Ag-NiO nanofibrous mats were applied as SERS substrates, to measure the model compound Rhodamine 6G (R6G), and investigate the corresponding signal enhancement. Furthermore, porous Ag and Ag-NiO nanofibrous mats were employed as SERS substrates for melamine and methyl parathion respectively. Sensitive detection of melamine and methyl parathion was achieved, indicating their feasibility as an active SERS sensing platform, and potential for food safety and environmental monitoring. All the results suggest that the electrospinning-calcination, two-step method offers a new, low cost, high performance solution in the preparation of SERS substrates.

Plasma-treated electrospun nanofibers as a template for the electrostatic assembly of silver nanoparticles

Silver nanoparticles assembled on a plasma treated electrospun nanofiber membrane could show excellent SERS effect.