Kanet Wongravee

Characteristic fingerprint based on gingerol derivative analysis for discrimination of ginger (Zingiber officinale) according to geographical origin using HPLC-DAD combined with chemometrics

Chromatographic fingerprints of gingers from five different ginger-producing countries (China, India, Malaysia, Thailand and Vietnam) were newly established to discriminate the origin of ginger. The pungent bioactive principles of ginger, gingerols and six other gingerol-related compounds were determined and identified. Their variations in HPLC profiles create the characteristic pattern of each origin by employing similarity analysis, hierarchical cluster analysis (HCA), principal component analysis (PCA) and linear discriminant analysis (LDA). As results, the ginger profiles tended to be grouped and separated on the basis of the geographical closeness of the countries of origin. An effective mathematical model with high predictive ability was obtained and chemical markers for each origin were also identified as the characteristic active compounds to differentiate the ginger origin. The proposed method is useful for quality control of ginger in case of origin labelling and to assess food authenticity issues.

H2O2-triggered shape transformation of silver nanospheres to nanoprisms with controllable longitudinal LSPR wavelengths

A novel approach for the synthesis of colloidal silver nanoprisms (AgNPrs) with controllable localized surface plasmon resonance (LSPR) via a chemical shape transformation of silver nanospheres (AgNSs) is presented. The shape conversion is carried out by feeding hydrogen peroxide (H2O2) solution into a starch-stabilized AgNS colloid under ambient conditions. Oxidative dissolution and the mild reducing action of H2O2 under alkaline conditions serve as the principal reactions for the shape transformation process. After addition of H2O2, the instantaneous shape transformation events can be visualized by the naked eye through the color change of the colloid. Initial concentration of AgNSs, molar ratio of H2O2:AgNSs, H2O2 injection rate, and mixing efficiency are the key parameters for controlling the LSPR wavelengths of AgNPrs as the in-plane dipole plasmon resonance can be selectively tuned across visible and near infrared regions (i.e., 460–850 nm). The obtained AgNPrs exhibited mixed geometries e.g. hexagonal, truncated triangular, rounded-tip triangular prisms, and circular disks with average bisector lengths of 30 to 120 nm and the thickness of 10 to 20 nm. A colloid of highly concentrated AgNPrs having a final concentration up to 11 mM can be produced within 10 min.

Poly(N-isopropylacrylamide)-Stabilized Gold Nanoparticles in Combination with Tricationic Branched Phenylene-Ethynylene Fluorophore for Protein Identification

Gold nanoparticles stabilized by thermoresponsive polymer, poly(N-isopropylacrylamide) (PNIPAM-AuNPs) were prepared by surface grafting of thiol-terminated PNIPAM onto citrate-stabilized AuNPs. The color change of the PNIPAM-AuNPs solution from red to blue-purple without precipitation when the solution was heated to 40 °C, above the lower critical solution temperature (LCST) of PNIPAM, indicated the thermoresponsive property of the synthesized AuNPs. PNIPAM-AuNPs were used to detect proteins by chemical nose approach based on fluorescence quenching of fluorophore by AuNPs. An array-based sensing platform for detection of six proteins, namely bovine serum albumin, lysozyme, fibrinogen, concanavalin A, hemoglobin, holo-transferrin human can be successfully developed from the PNIPAM-AuNPs having different molecular weights (4 and 8 kDa) and conformation (varied heat treatment from 25 to 40 °C) in combination with a tricationic branched phenylene-ethynylene fluorophore. From principal component analysis (PCA) followed by linear discriminant analysis (LDA), 100% accuracy of protein classification using a leave-one-out (LOO) approach can be achieved by using only two types of PNIPAM-AuNPs.

Colorimetric determination of hydrogen peroxide by morphological decomposition of silver nanoprisms coupled with chromaticity analysis

A novel colorimetric method with image colour analysis for highly sensitive and accurate detection of hydrogen peroxide using starch-stabilized silver nanoprisms (AgNPrs) is proposed. AgNPrs were morphologically decomposed by a low concentration of hydrogen peroxide revealed by UV-visible absorption spectroscopy and transmission electron microscopy (TEM). The morphological changes of AgNPrs led to an appreciable colour change in the AgNPr solution from red to orange, and finally yellow. A good linear relationship between the wavelength shift of AgNPrs and the H2O2 concentration can be obtained. The solution phase detection of H2O2 by the direct morphological change can be accomplished without any surface modification of AgNPrs. In addition to the conventional determination of the H2O2 concentration utilizing spectroscopic data, a new and simple colorimetric strategy based on the chromaticity analysis of AgNPr solution was demonstrated. The strategy can be employed not only for visual detection of H2O2 by the naked eye but also for reliable and convenient methods for quantification of H2O2. The hydrogen peroxide concentration at 1.57 μM can be recognized by naked-eye observation with good accuracy, stability and reproducibility. Furthermore, the proposed protocol can be applied to determine the glucose concentration through the glucose-oxidase system. A good linearity between the red chromaticity of the solution colour and the glucose concentrations was observed. The new colorimetric determination of hydrogen peroxide utilizing digital image analysis on colour changes from AgNPr shape decomposition will open up an alternative method for simple, rapid and reliable detection of hydrogen peroxide and can realize its future applications in biochemical analysis or clinical diagnosis.

Enhancement of the reduction efficiency of soluble starch for platinum nanoparticles synthesis

In this work, the efficiency of soluble starch as a reducing and a stabilizing agent in the synthesis of platinum nanoparticles under acidic-alkaline treatment is systematically studied. The degraded intermediates with reducing potential (i.e., small molecules containing aldehyde and α-hydroxy ketone moieties) are concomitantly generated when the alkaline concentration is greater than 0.025 M. The in situ generated species could completely reduce platinum ions (20 mM) and sufficiently stabilize the obtained platinum nanoparticles (5 mM) of uniform particle size (2-4 nm). The reduction is efficient and rapid as a complete conversion is achieved within 5 min. In a stronger alkaline condition, the platinum nanoparticles tend to aggregate and form a bigger domain because extensive degradation generates small starch fragments with less stabilization efficiency. This observation suggests that starch is a promising green material which could be chemically treated and transformed to a powerful reducing agent and stabilizer for the synthesis of metal nanoparticles.

3D SERS Imaging Using Chemically Synthesized Highly Symmetric Nanoporous Silver Microparticles

3D surface-enhanced Raman scattering (SERS) imaging with highly symmetric 3D silver microparticles as a SERS substrate was developed. Although the synthesis method is purely chemical and does not involve lithography, the synthesized nanoporous silver microparticles possess a regular hexapod shape and octahedral symmetry. By using p-aminothiophenol (PATP) as a probe molecule, the 3D enhancement patterns of the particles were shown to be very regular and predictable, resembling the particle shape and exhibiting symmetry. An application to the detection of 3D inhomogeneity in a polymer blend, which relies on the predictable enhancement pattern of the substrate, is presented. 3D SERS imaging using the substrate also provides an improvement in spatial resolution along the Z axis, which is a challenge for Raman measurement in polymers, especially layered polymeric systems.

Nanoporous silver microstructure for single particle surface-enhanced Raman scattering spectroscopy

The potential of a nanoporous Ag microstructure (np-AgMs) for use as a single particle for surface-enhanced Raman scattering spectroscopy (SERS), with the added advantages of being easy to manipulate and reusable, was successfully demonstrated. The np-AgMs with interconnected pore and controllable pore size were fabricated from symmetric hexapod AgCl via a galvanic replacement reaction in NaCl solution with zinc (Zn) as the sacrificed metal. The clean surface of np-AgMs enables rapid surface functionalization with easy handling and sample preparation as no particle aggregation occurs. The SERS acquisition spots on the np-AgMs can be visually selected using a normal Raman microscope. SERS spectra of p-aminothiophenol (PATP) with a concentration range of 10−8–10−3 M can be achieved. The position-dependent enhancement of np-AgMs was expendably evaluated. The signal-position correlation was confirmed by electric filed enhancement obtained from Finite-difference time-domain (FDTD) calculation. In addition, the highly stable substrate showed insignificant loss of the enhanced Raman signal after several cycles of chemical re-generation. Finally, the potential application of np-AgMs in label-free detection of biomolecules including hemoprotein, protein without chromophore and DNA strains at low concentration of 500 μg mL−1 was demonstrated.

Droplet-based glucosamine sensor using gold nanoparticles and polyaniline-modified electrode.

A droplet-based electrochemical sensor for direct measurement of D-glucosamine was developed using carbon paste electrodes (CPEs) modified with gold nanoparticles (AuNPs) and polyaniline (PANI). Central composition design (CCD) was employed as a powerful method for optimization of parameters for electrode fabrication. The optimized amounts of AuNPs and PANI obtained from the response surface were determined as 300 and 3000mgL(-1), respectively. Coupled with a droplet microfluidic system, the analysis of glucosamine was performed in a high-throughput manner with a sample throughput of at least 60 samples h(-1). In addition, the adsorption of the analyte on the electrode surface was prevented due to compartmentalization in droplets. Linearity of the proposed system was found to be in the range of 0.5-5mM with a sensitivity of 7.42×10(-3)Amol(-1)Lcm(-2) and limits of detection and quantitation of 0.45 and 1.45mM, respectively. High intraday and interday (evaluated among 3 days) precisions for the detection of 50 droplets containing glucosamine were obtained with relative standard deviation less than 3%. The system was successfully used to determine the amounts of glucosamine in supplementary products with error percentage and relative standard deviation less than 3%. In addition, the amounts of glucosamine measured using the developed sensor were in good agreement with those obtained from a CE method. These indicate high accuracy and precision of the proposed system.

Comparison of multivariate analysis methods for extracting the paraffin component from the paraffin-embedded cancer tissue spectra for Raman imaging

This study aimed to extract the paraffin component from paraffin-embedded oral cancer tissue spectra using three multivariate analysis (MVA) methods; Independent Component Analysis (ICA), Partial Least Squares (PLS) and Independent Component - Partial Least Square (IC-PLS). The estimated paraffin components were used for removing the contribution of paraffin from the tissue spectra. These three methods were compared in terms of the efficiency of paraffin removal and the ability to retain the tissue information. It was found that ICA, PLS and IC-PLS could remove the paraffin component from the spectra at almost the same level while Principal Component Analysis (PCA) was incapable. In terms of retaining cancer tissue spectral integrity, effects of PLS and IC-PLS on the non-paraffin region were significantly less than that of ICA where cancer tissue spectral areas were deteriorated. The paraffin-removed spectra were used for constructing Raman images of oral cancer tissue and compared with Hematoxylin and Eosin (H&E) stained tissues for verification. This study has demonstrated the capability of Raman spectroscopy together with multivariate analysis methods as a diagnostic tool for the paraffin-embedded tissue section.

Gold microsheets having nano/microporous structures fabricated by ultrasonic-assisted cyclic galvanic replacement

A novel technique for the fabrication of nano/microporous gold (Au) microsheets using an ultrasonic-assisted cyclic galvanic replacement reaction between a sacrificial silver (Ag) plate and gold ions (AuCl4−) is reported. First of all, AuCl4− is reduced on the surface of sacrificial Ag via a galvanic replacement reaction. Then, the epitaxial growth of the Au film on the Ag surface is disturbed by the precipitated AgCl by-product of this galvanic replacement reaction. The co-precipitated AgCl and galvanic-generated Au nanostructures induce the formation of an interpenetrated Au/AgCl nanocomposite film on the surface of the sacrificial Ag plate. Finally, ultrasonic radiation enables auto-detachment of the galvanic-generated film along the AgCl/Ag interface. The galvanic replacement and auto-detachment processes continuously occur as a cycle until the scarified Ag is totally consumed. The coral-like Au nanostructures with nano/microporous morphologies are realized after removing AgCl by NH3 treatment. The hierarchical nano/microporous structures have micropores and nanopores with sizes of 0.15–0.30 μm and 30–60 nm, respectively, separated by chain-like Au structures. The complex porous structures, through which liquids can easily flow, can potentially be used in applications such as high-efficiency free-standing catalysts, super capacitors, electrochemical sensors and surface-enhanced Raman scattering (SERS) substrates. A SERS application of the Au microsheets is also demonstrated.