Effendi Widjaja

DNA detection using nanostructured SERS substrates with Rhodamine B as Raman label

A technique is demonstrated to detect DNA hybridization at low concentrations, based on Surface-Enhanced Raman Scattering (SERS) using silicon nanostructures coated with gold-silver as substrate. Standard silicon process technologies were employed to fabricate the SERS substrates featuring nanogaps with a characteristic distance of 15+/-10nm. Target DNA was hybridized with cysteine-modified Peptide Nucleic Acids (PNA), which was previously fixed into the nanogaps as the capture sites. After hybridization, the introduced phosphate groups from the backbone of the target DNA showed strong affinity to an inorganic linker, Zr(4+), so that resulting in the assembly substrate-PNA-DNA-Zr. Since PNA does not possess phosphate groups, the linker is avoided when there is no hybridization from the complimentary DNA. Subsequently, the assembly of substrate-PNA-DNA-Zr was incubated with a Raman label, Rhodamine B (RB). The carboxylic acid group in RB reacted with the linker Zr(4+) allowing this Raman Label to be attached to the assembly substrate-PNA-DNA-Zr. The Raman peaks corresponding to RB were selected to detect the target DNA, with a detection limit of 1 x 10(-12)M.

Band-Target Entropy Minimization (BTEM) Applied to Hyperspectral Raman Image Data:

Band-target entropy minimization (BTEM) has been applied to extraction of component spectra from hyperspectral Raman images. In this method singular value decomposition is used to calculate the eigenvectors of the spectroscopic image data set. Bands in non-noise eigenvectors that would normally be used for recovery of spectra are examined for localized spectral features. For a targeted (identified) band, information entropy minimization or a closely related algorithm is used to recover the spectrum containing this feature from the non-noise eigenvectors, plus the next 5–30 eigenvectors, in which noise predominates. Tests for which eigenvectors to include are described. The method is demonstrated on one synthesized Raman image data set and two bone tissue specimens. By inclusion of small amounts of signal that would be unused in other methods, BTEM enables the extraction of a larger number of component spectra than are otherwise obtainable. An improvement in signal/noise ratio of the recovered spectra is also obtained.

Detection of trace crystallinity in an amorphous system using Raman microscopy and chemometric analysis

A novel analytical method to detect and characterize active pharmaceutical ingredient (API) trace crystallinity in an amorphous system using Raman microscopy and chemometric methods, namely band-target entropy minimization (BTEM) and target transformation factor analysis (TTFA) is developed. The method starts with Raman mapping measurements performed on some random areas of the amorphous system. This is followed by chemometric data analysis. In the case of a system without any a priori information, the BTEM algorithm is used to recover a set of pure component Raman spectral estimates followed by component and/or crystal structure identification. In the case of a system with some a priori information, TTFA is used to predict the presence or existence of a suspected component and/or crystal structure in the observed system. Four different amorphous systems were used as models. It is demonstrated that combined Raman microscopy and chemometric methods (BTEM or TTFA) outperformed powder X-ray diffraction (PXRD) in detecting trace crystallinity in amorphous systems. The spatial distributions of drug and polymer can also be directly obtained in order to study the homogeneity of the APIs in the solid dispersions. The present methodology appears very general and applicable to many other types of systems.

The effect of polyethylene glycol structure on paclitaxel drug release and mechanical properties of PLGA thin films.

Thin films of poly(lactic acid-co-glycolic acid) (PLGA) incorporating paclitaxel typically have slow release rates of paclitaxel of the order of 1 μg day(-1) cm(-2). For implementation as medical devices a range of zero order release rates (i.e. 1-15 μg day(-1) cm(-2)) is desirable for different tissues and pathologies. Eight and 35 kDa molecular weight polyethylene glycol (PEG) was incorporated at 15%, 25% and 50% weight ratios into PLGA containing 10 wt.% paclitaxel. The mechanical properties were assessed for potential use as medical implants and the rates of release of paclitaxel were quantified as per cent release and the more clinically useful rate of release in μg day(-1) cm(-2). Paclitaxel quantitation was correlated with the release of PEG from PLGA, to further understand its role in paclitaxel/PLGA release modulation. PEG release was found to correlate with paclitaxel release and the level of crystallinity of the PEG in the PLGA film, as measured by Raman spectrometry. This supports the concept of using a phase separating, partitioning compound to increase the release rates of hydrophobic drugs such as paclitaxel from PLGA films, where paclitaxel is normally homogeneously distributed/dissolved. Two formulations are promising for medical device thin films, when optimized for tensile strength, elongation, and drug release. For slow rates of paclitaxel release an average of 3.8 μg day(-1) cm(-2) using 15% 35k PEG for >30 days was achieved, while a high rate of drug release of 12 μg day(-1) cm(-2) was maintained using 25% 8 kDa PEG for up to 12 days.

Altering the drug release profiles of double-layered ternary-phase microparticles.

Double-layered ternary-phase microparticles composed of a poly(D,L-lactide-co-glycolide) (50:50) (PLGA) core and a poly(L-lactide) (PLLA) shell impregnated with poly(caprolactone) (PCL) particulates were loaded with ibuprofen (IBU) and metoclopramide HCl (MCA) through a one-step fabrication process. MCA and IBU were localized in the PLGA core and in the shell, respectively. The aim of this study was to study the drug release profiles of these double-layered ternary-phase microparticles in comparison to binary-phase PLLA(shell)/PLGA(core) microparticles and neat microparticles. The particle morphologies, configurations and drug distributions were determined using scanning electron microscopy (SEM) and Raman mapping. The presence of PCL in the PLLA shell gave rise to an intermediate release rate of MCA between that of neat and binary-phase microparticles. The ternary-phase microparticles were also shown to have better controlled release of IBU than binary-phase microparticles. The drug release rates for MCA and IBU could be altered by changing the polymer mass ratios. Ternary-phase microparticles, therefore, provide more degrees of freedom in preparing microparticles with a variety of release profiles and kinetics.

Template-free low temperature hydrothermal synthesis and characterization of rod-shaped manganese oxyhydroxides and manganese oxides

Single-crystalline MnOOH (γ-MnOOH) and MnO2 nanorods (β-MnO2 and α-MnO2) were synthesized by redox reaction of a mixture of KMnO4 and Mn(CH3COO)2 at various pH levels at a temperature range of 120–180 °C. The products were characterized by powder x-ray diffraction (XRD), x-ray photoelectron spectroscopy (XPS), Raman and infra-red spectroscopy, field-emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM). It is interesting to find that the prepared MnOOH and MnO2 all have one-dimensional nanostructures. The catalytic activity of MnO2 nanorods was studied for selective catalytic sulfur oxidation of model diesel containing 4,6-dimethyl dibenzothiophene in the presence of air as oxidant.

Nanoparticle Formation and Growth During In Vitro Dissolution of Ketoconazole Solid Dispersion

The aim of this study is to examine the physical mechanisms during the dissolution of a solid dispersion, so as to provide further understanding behind the enhanced dissolution properties. X-ray amorphous solid dispersions of ketoconazole (KC), a poorly aqueous soluble drug, were prepared by melt extrusion with polyvinlypyrrolidone 17 (PVP 17) and PVP-vinyl acetate (PVP-VA64) copolymer. Prior to dissolution, Raman mapping showed a fully homogeneous spatial distribution of KC in polymer and possible drug dispersion at molecular level, whereas Fourier transform infrared spectroscopy revealed no drug-polymer chemical interaction. During in vitro dissolution test, a burst release followed by a gradual decline in dissolution could be explained by the release of KC in molecular form followed by formation of drug nanoparticles and their subsequent growth to micron size range as shown by dynamic light scattering analysis. Observations using transmission electron microscopy and cryogenic scanning electron microscopy provided support to the suggested mechanisms. The results suggested that the release of KC from the solid dispersions was carrier controlled initially, and PVP 17 PF is more efficient in inhibiting particle growth as compared with PVP-VA64. The particle growth inhibition during dissolution may be an important consideration to achieve the full benefits of dissolution enhancement of solid dispersions.

Pure component spectral reconstruction from mixture data using SVD, global entropy minimization, and simulated annealing. Numerical investigations of admissible objective functions using a synthetic 7-species data set.

A combination of singular value decomposition, entropy minimization, and simulated annealing was applied to a synthetic 7‐species spectroscopic data set with added white noise. The pure spectra were highly overlapping. Global minima for selected objective functions were obtained for the transformation of the first seven right singular vectors. Simple Shannon type entropy functions were used in the objective functions and realistic physical constraints were imposed in the penalties. It was found that good first approximations for the pure component spectra could be obtained without the use of any a priori information. The present method out performed the two widely used routines, namely Simplisma and OPA‐ALS, as well as IPCA. These results indicate that a combination of SVD, entropy minimization, and simulated annealing is a potentially powerful tool for spectral reconstructions from large real experimental systems.

Use of Raman Microscopy and Band-Target Entropy Minimization Analysis To Identify Dyes in a Commercial Stamp. Implications for Authentication and Counterfeit Detection

Raman microscopy was used in mapping mode to collect more than 1000 spectra in a 100 microm x 100 microm area from a commercial stamp. Band-target entropy minimization (BTEM) was then employed to unmix the mixture spectra in order to extract the pure component spectra of the samples. Three pure component spectral patterns with good signal-to-noise ratios were recovered, and their spatial distributions were determined. The three pure component spectral patterns were then identified as copper phthalocyanine blue, calcite-like material, and yellow organic dye material by comparison to known spectral libraries. The present investigation, consisting of (1) advanced curve resolution (blind-source separation) followed by (2) spectral data base matching, readily suggests extensions to authenticity and counterfeit studies of other types of commercial objects. The presence or absence of specific observable components form the basis for assessment. The present spectral analysis (BTEM) is applicable to highly overlapping spectral information. Since a priori information such as the number of components present and spectral libraries are not needed in BTEM, and since minor signals arising from trace components can be reconstructed, this analysis offers a robust approach to a wide variety of material problems involving authenticity and counterfeit issues.

Influence of polymer content on stabilizing milled amorphous salbutamol sulphate.

The study investigates the influence of polyvinyl pyrrolidone (PVP) concentration on stabilizing the amorphous form of salbutamol sulphate (SS) before and after storage under ambient and elevated humidity conditions. Different mass ratios of SS and PVP (0-90wt%) were co-milled using a planetary ball mill. X-ray powder diffraction (XRPD), high sensitivity differential scanning calorimetry (HSDSC), dynamic vapor sorption (DVS), infrared spectroscopy (FT-IR), scanning electron microscopy (SEM) and Raman microscopy (RM) were used to analyze the stability of the co-milled mixtures against heat and humidity treatments as well as storage at different humidity conditions. Prior storage, DSC and DVS analyses revealed that re-crystallization of amorphous SS was suppressed above PVP content of 33 wt%. Probable hydrogen bond interaction between SS and PVP was found in FT-IR analysis. XRPD diffractograms and SEM analysis showed stability against re-crystallization was achieved in the co-milled mixtures with a minimum PVP content of 80 wt% after storage. Homogeneous distribution of SS and PVP from RM analysis showed fine clustering of SS and PVP, suggesting the formation of an amorphous dispersion at molecular level. The results provide insights on the application of thermal and humidity treatments, accelerated stability testing and investigations on drug-excipient interactions to predict the minimum ratio of an excipient for stabilizing the amorphous state of a milled API.