Size-independent quantification of nanoplastics in various aqueous media using surfaced-enhanced Raman scattering.

In this work, we successfully developed an intriguing preparation strategy to reduce the size-dependent effect of nanoplastics (NPLs), which is the limitation of NPLs quantification by surface-enhanced Raman scattering (SERS). This simple and low-cost technique enabled us to quantify different sizes (i.e., 100, 300, 600, and 800 nm) of polystyrene nanospheres (PS NSs) in various aqueous media. The SERS substrate was simply prepared by sputtering gold particles to cover on a glass cover slide. By dissolving PS NSs in toluene and preconcentrating by coffee-ring effect, SERS measurement can quantify NPLs at a very low concentration with a limit of detection (LOD) of approximately 0.10-0.26 µg/mL. The experiment was also conducted in the presence of interferences, including salts, sugars, amino acids, and detergents. The method was validated for quantitative analysis using a mixture of 100-, 300-, 600-, and 800-nm PS NSs in a ratio of 1:1:1:1 in real-world media (i.e., tap water, mineral water, and river water), which successfully approaches the evaluation of PS NSs in the range of 10-40 µg/mL with an LOD of approximately 0.32-0.52 µg/mL.

Selection of cryoprotectants for freezing and freeze-drying of gold nanoparticles towards further uses in various applications.

Recently, cryopreservation of AuNPs without aggregation has been attempted to improve their long-term stability. This study investigated criteria to select cryoprotectants for AuNPs using a variety of materials, including sugar (sucrose), surfactant (Tween 20), polymers (polyvinyl alcohol (PVA) and polyvinylpyrrolidone (PVP)), and biopolymer (pectin). For cryoprotective performance, UV-vis spectroscopy reveals the potential of all cryoprotectants for preventing citrate-capped AuNPs (cit-AuNPs) from irreversible aggregation under freezing. While sucrose, PVP, and pectin were more suitable than Tween 20 and PVA as cryoprotectants for lyophilization of AuNPs with the maintained redispersability. For storage and further use, Luria-Bertani agar plate, dynamic light scattering (DLS), and transmission electron microscopy (TEM) results indicate impacts of the cryoprotectant coexisted with AuNPs after resuspension and imply that washing of the restored AuNPs is encouraged. Otherwise, running the restored AuNPs through applications, such as functionalization, protein conjugation, and surface-enhanced Raman scattering (SERS), without washing the cryoprotectant could lead to inaccurate results. This study also serves as a guideline for a comprehensive practice flow of AuNP handling, encompassing the synthesis step, cryopreservation, and use after resuspension.

MCR-ALS with sample insertion constraint to enhance the sensitivity of surface-enhanced Raman scattering detection.

The multivariate curve resolution-alternative least squares (MCR-ALS) algorithm was modified with sample insertion constraint to deconvolute the overlapping peaks in SERS spectra. The developed method was evaluated by the spectral data simulated using a Gaussian distribution function to generate two independent peaks corresponding to a capping agent and an analyte. The spectra were generated with different overlapping levels and various intensity ratios of the analyte to the capping agent. By using MCR-ALS with the sample insertion constraint, the peak of the capping agent was completely excluded to obtain a calibration model of the analyte with R2 > 0.95 under all conditions. Furthermore, our developed method was later applied to a real SERS measurement to quantify carbofuran (analyte) using the azo-coupling reaction with p-ATP (capping agent) on silver nanoparticles as a SERS substrate. A calibration model of derivative carbofuran phenol was generated with R2 = 0.99 and LOD = 28.19 ppm. To assess the performance of the calibration model, the model was used to estimate the concentration of carbofuran in an external validation set. It was found that the RMSE of prediction was only 2.109 with a promising R2 = 0.97.

Luminescent nanohybrid of ZnO quantum dot and cellulose nanocrystal as anti-counterfeiting ink.

Luminescent quantum dot (QD) ink is currently a powerful tool for generating hidden information on paper substrates. Herein, we fabricated a nanohybrid ink of bacterial cellulose nanocrystal (BCNC) and UV-responsive ZnO QD via electrostatic self-assembly for improving solvent resistance and message encryption process. Under investigations on the printed areas, the nanohybrid can slightly infiltrate into the paper fibers and form a thin layer on the top of paper substrates, conferring an enhanced print permanence against wetting conditions while maintaining the daylight unobservability and its luminescent stability. The water resistance of the proposed nanohybrid ink enables developing a higher security level that the prints can be submerged in CuCl2 aqueous solutions to quench the luminescent message. The concealed message can eventually be revealed under UV light again after submerging in EDTA solution. Our ZnO QD/BCNC nanohybrid with eco-friendly nature therefore exhibits great potential as security marking ink for counterfeit protection with sustainable uses.

Effects of Coagent Functionalities on Properties of Ultrafine Fully Vulcanized Powdered Natural Rubber Prepared as Toughening Filler in Rigid PVC.

Ultrafine fully vulcanized powdered natural rubber (UFPNR) has a promising application as a renewable toughening modifier in polymer matrices. In this work, the effects of acrylate coagents, which had different amounts of functional groups, on properties of UFPNR produced by radiation vulcanization and spray-drying was systematically investigated for the first time. Dipropylene glycol diacrylate (DPGDA), trimethylol propane trimethaacrylate (TMPTMA), and ditrimethylol propane tetraacrylate (DTMPTA) were used as coagents with two, three, and four acrylate groups, respectively. The radiation in the range of 250 to 400 kGy and coagent contents of up to 11 phr were used in the production process. Physical, chemical, and thermal properties of the UFPNR were characterized by swelling analysis, scanning electron microscopy, infrared spectroscopy, thermogravimetric analysis, and differential scanning calorimetry. The properties of UFPNR produced by using different type and content of coagents were compared and discussed. The results revealed that UFPNR with the smallest particle size of 3.6 ± 1.1 µm and the highest thermal stability (Td5 = 349 °C) could be obtained by using DTMPTA, which had the highest amount of functional group. It was proposed that the coagent with the greater number of acrylate groups enhanced the crosslinking of natural rubber as it had more reactive groups. Finally, an application of UFPNR as a toughening filler in rigid PVC was demonstrated with 34% improvement of impact strength.

Distinguishing Enantiomers by Tip-Enhanced Raman Scattering: Chemically Modified Silver Tip with an Asymmetric Atomic Arrangement.

Discrimination between enantiomers is achieved by tip-enhanced Raman scattering (TERS) using a silver tip that is chemically modified by an achiral para-mercaptopyridine (pMPY) probe molecule. Differences in the relative intensities of the pMPY spectra were monitored for three pairs of enantiomers containing hydroxy (-OH) and/or amino (-NH2 ) groups. The N: or N+ -H functionality of the pMPY-modified tip participates in hydrogen-bond interactions with a particular molecular orientation of each chiral isomer. The asymmetric arrangement of silver atoms at the apex of the tip induces an asymmetric electric field, which causes the tip to become a chiral center. Differences in the charge-transfer (CT) states of the metal-achiral probe system in conjunction with the asymmetric electric field produce different enhancements in the Raman signals of the two enantiomers. The near-field effect of the asymmetric electric field, which depends on the number of analyte functional groups capable of hydrogen-bond formation, improves the degree of discrimination.

Silver nanoparticle/bacterial nanocellulose paper composites for paste-and-read SERS detection of pesticides on fruit surfaces.

This study aimed to develop an eco-friendly flexible surface-enhanced Raman scattering (SERS) substrate for in-situ detection of pesticides using biodegradable bacterial nanocellulose (BNC). Plasmonic silver nanoparticle- bacterial nanocellulose paper (AgNP-BNCP) composites were prepared by vacuum-assisted filtration. After loading AgNPs into BNC hydrogel, AgNPs were trapped firmly in the network of nanofibrous BNCP upon ambient drying process, resulting in 3D SERS hotspots within a few-micron depth on the substrate. The fabricated AgNP-BNCPs exhibited high SERS activity with good reproducibility and stability as demonstrated by the detection of 4-aminothiophenol and methomyl pesticide. Due to the optical transparency of BNCP, a direct and rapid detection of methomyl on fruit peels using AgNP-BNCPs can be achieved, demonstrating a simple and effective 'paste-and-read' SERS approach. These results demonstrate potential of AgNP-BNCP composites for user-friendly in-situ SERS analysis.

Characterisation of insoluble α-1,3-/α-1,6 mixed linkage glucan produced in addition to soluble α-1,6-linked dextran by glucansucrase (DEX-N) from Leuconostoc citreum ABK-1.

Glucansucrases catalyse the formation of glucans from sucrose. The glucansucrase-encoding gene from Leuconostoc citreum ABK-1, dex-N, was successfully cloned and expressed in E. coli BL21 Star (DE3). DEX-N produces 2 types of glucans: soluble (S-dextran) and insoluble (I-glucan) glucans. The S-dextran was determined to be ca. 10 kDa in size and contained >90% α-1,6 linkages; along with its water solubility, this is similar to commercial dextran. On the other hand, I-glucan was water-insoluble, harbouring a block-wise pattern of α-1,3 and α-1,6 linkages in its structure. Notably, the FTIR and powder X-ray diffraction pattern of I-glucan exhibited a combination of features found in α-1,6-linked dextran and α-1,3-linked mutan. Although both I-glucan and mutan are insoluble glucans, their physical characteristics are notably dissimilar.

Plasmonic-Enhanced Photocurrent Generation of Organic Photovoltaics Induced by 1D Grating and 2D Crossed Grating Structures.

In this work, plasmonic-enhanced photocurrent generation in organic photovoltaic (OPV) devices is demonstrated. One-dimensional (1D) and two-dimensional (2D) crossed grating structures are created on the active-layer surface composed of a blend of poly(3-hexylthiophene-2,5-diyl) (P3HT) and [6,6]-phenyl C61 butyric acid methyl ester (PC61BM) via a nanoimprinting technique using a template of a Blu-ray disc recordable (BD-R) grating structure. After formation of aluminum back electrodes, the grating-coupled surface plasmon (GCSPR) and light scattering observed in the devices with grating structures provide a 12.3% and 11.0% enhancement of the photocurrent for the devices with 1D grating and 2D crossed grating structures, respectively. The OPV devices with the 2D crossed grating show a plasmonic-enhanced photocurrent under irradiation with light with all polarization directions, whereas those with the 1D grating provide plasmonic enhancement only under illumination with p-polarized light.

Fabrication of Miniature Surface Plasmon Resonance Sensor Chips by Using Confined Sessile Drop Technique.

In this study, we demonstrate a simple and efficient method to fabricate miniature surface plasmon resonance (SPR) sensor chips by using confined sessile drop technique. A liquid optical adhesive (NOA 61) was dropped on the circular flat surface of cylindrical substrates made of poly(dimethylsiloxane) (PDMS). The formation of hemispherical optical prisms was accomplished by taking advantage of the sharp edges of cylindrical PDMS substrates that prevented the overflow of liquid NOA 61 at the edge of substrates. The size of the hemispherical optical prisms can be controlled by changing the diameter of the cylindrical PDMS substrates. After UV curing, the SPR sensor chips were obtained by the deposition of 3 nm thick chromium and 47 nm thick gold on the flat side of the prisms. The fabricated miniature SPR sensor chips were then mounted on a three-dimensional-printed flow cell to complete the microfluidic SPR sensor module. The miniature SPR sensor chips provided a comparable sensitivity to the conventional high-refractive-index glass SPR chips. To demonstrate the detection capability of nanometer-sized materials, we applied the miniature microfluidic SPR system for monitoring the deposition of layer-by-layer ultrathin films of poly(diallyldimethylammonium chloride)/poly(sodium 4-styrenesulfonate) and for detecting human immunoglobulin G.

Optical Sensing Platform for the Colorimetric Determination of Silver Nanoprisms and Its Application for Hydrogen Peroxide and Glucose Detections Using a Mobile Device Camera.

Silver nanoprisms (AgNPrs) have a unique localized surface plasmon resonance, resulting in strong absorption and scattering within the visible light region. In this work, we propose image acquisition from colloidal solutions of AgNPrs using a combination of transmitted and scattered light. The developed measurement technique could be carried out by separately recording transmitted and scattering images of the solutions, using a mobile device camera prior to a calculation of the empirical absorption value (IA). The IA value of green for AgNPrs solutions was found to be in agreement with the absorption spectra obtained using a conventional spectroscopic technique. This technique was utilized for the quantifications of hydrogen peroxide and glucose. Good linearities between ΔIA and those typical analytes were observed. The limit of detection for the typical biosensor of glucose was 19.8 µM. As such, we expect the methodology herein developed for hydrogen peroxide and glucose determinations by means of monitoring the color change of transmitted and scatting images from solutions to contribute to the development of simple, rapid, and reliable detection systems to be further applied to biochemical analysis and clinical diagnosis, as well as to household biosensor applications.

Local structural changes in graphene oxide layers induced by silver nanoparticles.

Structural changes of graphene oxide (GO) in silver/graphene oxide (AGO) nanocomposites are investigated using tip-enhanced Raman scattering (TERS). Because of markedly high spatial resolution of the TERS technique, the measurements of molecular information at specific nano-scaled positions can be achieved by constructing line-profile TERS spectra straight from the center of silver nanoparticles (AgNPs) on GO layers. The results show evidences that AgNPs cause shortening of C-C bonds beneath AgNPs, flattening of GO layers, and critical bending on GO layers. Additionally, a connection of carbon atoms via a C-C network subsequently expands structural changes with a distance of 200-250 nm from the center of AgNPs, even though this distance is larger than the size of AgNPs. The proposed model of GO structural changes unveils new understanding about changes in properties from GO to AGO nanocomposites, which will contribute to a development of advanced nanostructures/nanocomposites in the near future.

Analysis of cosmetic residues on a single human hair by ATR FT-IR microspectroscopy.

In this work, ATR FT-IR spectra of single human hair and cosmetic residues on hair surface are successfully collected using a homemade dome-shaped Ge µIRE accessary installed on an infrared microscope. By collecting ATR spectra of hairs from the same person, the spectral patterns are identical and superimposed while different spectral features are observed from ATR spectra of hairs collected from different persons. The spectral differences depend on individual hair characteristics, chemical treatments, and cosmetics on hair surface. The "Contact-and-Collect" technique that transfers remarkable materials on the hair surface to the tip of the Ge µIRE enables an identification of cosmetics on a single hair. Moreover, the differences between un-split and split hairs are also studied in this report. These highly specific spectral features can be employed for unique identification or for differentiation of hairs based on the molecular structures of hairs and cosmetics on hairs.

Transmission surface plasmon resonance techniques and their potential biosensor applications.

Transmission surface plasmon resonance (TSPR) is an unusual extraordinary optical transmission that is more transparent at certain wavelengths than expected by classical theory. The three main plasmonic structures that providing this phenomenon are nanohole arrays, diffraction gratings, and nanoslit arrays. This extraordinary optical transmission phenomenon is produced as a result of surface plasmon excitations. The shifting in TSPR responses upon changing of dielectric environment at the surface of a metallic film was observed. After TSPR was discovered from metallic nanohole arrays in 1998, the number of papers about this topic rapidly increased. In the 20 years since, TSPR has been utilized to improve the detection limits, sensitivity, selectivity, and dynamic range of biosensing devices, resulting in them having greater potential for commercialization. This review gives a broad overview of the TSPR phenomenon, the development of this technique, and the typical experimental setups used to acquire TSPR signals; it also describes how they are applied in the field of research into biosensors.

Palladium Nanoparticles Immobilized on Individual Calcium Carbonate Plates Derived from Mussel Shell Waste: An Ecofriendly Catalyst for the Copper-Free Sonogashira Coupling Reaction.

The conversion of waste into high-value materials is considered an important sustainability strategy in modern chemical industries. A large volume of shell waste is generated globally from mussel cultivation. In this work, mussel shell waste (Perna viridis) is transformed into individual calcium carbonate plates (ICCPs) and is applied as a support for a heterogeneous catalyst. Palladium nanoparticles (3-6 nm) are deposited with an even dispersion on the ICCP surface, as demonstrated by X-ray diffraction and scanning electron microscopy. Using this system, Sonogashira cross-coupling reactions between aryl iodides and terminal acetylenes were accomplished in high yields with the use of 1 % Pd/ICCP in the presence of potassium carbonate without the use of any copper metal or external ligand. The Pd/ICCP catalyst could also be reused up to three times and activity over 90 % was maintained with negligible Pd-metal leaching. This work demonstrates that mussel shell waste can be used as an inexpensive and effective support for metal catalysts in coupling reactions, as demonstrated by the successful performance of the Pd-catalyzed, copper-free Sonogashira cross-coupling process.

Self-assembly of Gd3+/SDS/HEPES complex and curcumin entrapment for enhanced stability, fluorescence image in cellular system.

At present, strategies to disperse hydrophobic molecules in water without altering their chemical structures include conventional surfactant-based micellar and vesicular systems, encapsulation into water dispersible polymeric nanoparticles, and loading onto the surface of various metal nanoparticles. Here, we report a simple and low cost platform to incorporate hydrophobic molecules into a stable water dispersible nanostructure that can significantly increase the stability of the encapsulated materials. The platform is based on the incorporation of hydrophobic molecules into the self-assembled complex of gadolinium ion (Gd3+), sodium dodecyl sulfate (SDS), and 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid (HEPES) called GdSH. After being incorporated, the two model hydrophobic dyes, curcumin and curcumin borondifluoride show approximately 50% and 30% improved stability, respectively. Investigation of the self-assembled 10-14 multilayered 60nm spheres with inter-layer distances of 4.25nm indicates coordination of SDS and HEPES with Gd3+. Incorporation of the hydrophobic molecules into the multilayered spheres results in reduction of the interlayer distance of the multilayer spheres to 4.17nm, suggesting enhanced packing of the hydrophobic chain of SDS and HEPES around the Gd3+. The incorporation of the two curcuminoids into the self-assembled complex also causes an increase in fluorescence quantum yield of the two dyes, thus suggesting spatial confinement of the packed dye molecules. The better cellular uptake of the nanoparticles is responsible for the expected enhancement in fluorescence image of the encapsulated materials.

Grating-coupled surface plasmon resonance enhanced organic photovoltaic devices induced by Blu-ray disc recordable and Blu-ray disc grating structures.

In this work, we studied the performance enhancement of organic thin-film solar cells (OSCs) originating from the presence of diffraction gratings on the surface of the active layer. Two types of diffraction gratings, periodic gratings (Blu-ray disc recordable: BD-R) and quasi-random gratings (Blu-ray disc: BD), were employed as master templates for grating structures. The grating structures were introduced to the surfaces of poly(3-hexylthiophene) (P3HT):phenyl-C61-butyric acid methyl ester (PCBM) films, which were the active layers of the solar cells. The addition of the grating structures led to an increase of light absorption in the absorption region of P3HT:PCBM induced by light scattering. Furthermore, the grating-coupled surface plasmon resonance generated additional light absorption peaks. With illumination of non-polarized light at a normal incident angle, the short-circuit current densities of the BD-R and BD solar cells improved by 11.05% and 10.6%, respectively. Efficiency improvements of 19.28% and 3.21% were also observed for the BD-R and BD devices, respectively. Finally, the finite-difference time-domain simulation results revealed an enhanced electric field in the P3HT:PCBM layer, especially in the BD-R OSC devices.

High purity silver microcrystals recovered from silver wastes by eco-friendly process using hydrogen peroxide.

A simple, rapid, and environmentally friendly process using hydrogen peroxide, was developed for recovering high purity silver directly from industry and laboratory wastes. Silver ammine complex, [Ag(NH3)2]+Cl-, derived from AgCl were generated and then directly reduced using H2O2 to reliably turn into high purity microcrystalline silver (99.99%) examined by EDS and XRD. Morphology of the recovered silver microcrystals could be selectively tuned by an addition of poly(vinyl pyrrolidone). The main parameters in the recovering process including pH, concentration of Ag+ and the mole ratio of H2O2:Ag+ were carefully optimized though the central composite design (CCD). The optimized condition was employed for a trial recovery of 50 L silver ammine complex prepared from a collection of silver-wastes during 3-year research on industrial nanoparticle production. The recovered silver microcrystals >700 g could be recovered with 91.27%. The remaining solution after filtering of the recovered silver microcrystals can be used repeatedly (at least 8 cycles) without losing recovery efficiency. Matrix interferences including Pb2+ and Cl- play a minimal role in our silver recovery process. Furthermore, the direct usage of the recovered silver microcrystals was demonstrated by using as a raw material of silver clay for creating a set of wearable silver jewelries.

Facile and Sensitive Detection of Carbofuran Carbamate Pesticide in Rice and Soybean Using Coupling Reaction-based Surface-Enhanced Raman Scattering.

In this research, a sensitive and selective method for detecting one of the most toxic insecticides, "carbofuran", in rice and soybean is presented. This method is based on the coupling reaction of diazonium ion combined with a surface-enhanced Raman scattering technique. Diazonium ion produced from p-aminothiophenol reacts specifically with carbofuran phenol from the hydrolysis of carbofuran. The generated azo compounds attach to the surface of silver nanoparticles via the Ag-S bond. Therefore, a strong Raman intensity can be obtained. The concentration of carbofuran can be determined by following the intensity of the peak at 1201 cm-1, attributed to the C-N stretching vibration of the azo compound. The result shows a good linear correlation (R2 = 0.9786) against carbofuran concentrations (0.1 - 5 ppm) with a detection limit of 0.452 ppm. Our proposed protocol is insignificantly influenced by various common interferences. Moreover, this method has been successfully validated to determine carbofuran concentrations in rice and soybean with detection limits of 0.446 and 0.520 ppm, respectively.

Nanogold-Gallate Chitosan-Targeted Pulmonary Delivery for Treatment of Lung Cancer.

Lung cancer is one of the most of cancer type founds and a leading cause of death worldwide. Through the development of new candidate compound (3,4,5-tribenzyloxybenzoic acid (GAOBn)) and a drug delivery system of our design of quaternized chitosan-gallic acid-folic acid stabilized gold nanoparticles (Au@QCS-GA-FA) as the targeted nanocarrier for treatment of lung cancer, we have found that GAOBn not only showed high cytotoxicity against lung cancer cells (CHAGO) with more than tenfold than cisplatin, but also showed low toxicity against normal cells (CRL-1947). The combination Au@QCS-GA-FA/GAOBn showed highly efficient cellular uptake and localization of gold nanoparticles via the active targeting of cancer cells. This established the potential of Au@QCS-GA-FA as a nanocarrier for anticancer agent-targeted delivery for treatment of lung cancer.