Samuel M. Mugo

A porous layer open tubular monolith on microstructured optical fibre for microextraction and online GC-MS applications

A microextraction device comprising a porous layer open tubular (PLOT) polymer housed in a microstructured optical fiber has been shown to be an attractive tool for analyte extraction and coupling to GC-MS as a cost-effective alternative to traditional SPME. This paper details the fabrication of a poly(styrene-co-divinylbenzene) PLOT optical fibre microextraction device and its use in the extraction of polyaromatic hydrocarbons (PAHs) in aqueous solution. Good linear calibrations were obtained with R2 values above 0.970 for five PAHs analyzed, with percent relative standard deviation values of 22.2 to 43.6% for PAH standards with concentrations ranging from 0.1 to 100 ppm. In addition, the robust poly(styrene-co-DVB) PLOT optical fibre porous polymer microextraction (PPME) device appears to retain its effectiveness with repeated use over an extended period of time.

Multiresponsive Nanogels for Targeted Anticancer Drug Delivery

Nanogels with a biomolecular coating (biocoating) were shown to be capable of triggered delivery of anticancer drug Doxorubicin. The biocoating was formed utilizing binding between glycogen and the tetra-functional lectin Concanavalin A, which can be triggered to disassemble (and release) upon exposure to glucose and changes in solution pH. We also show the nanogels thermoresponsivity can be used to accelerate Doxorubicin release. Moreover, we showed that transferrin immobilized on the nanogel surface could accelerate nanogel uptake by cancer cells. In these experiments, we showed that Doxorubicin was able to be released to the nucleus of human liver cancer cell line (HepG2) within 3 h. Doxorubicin-loaded nanogels exhibit a strong growth inhibition ability toward HepG2. This investigation showcases how nanogel design and chemistry can be tuned to achieve useful biomedical applications.

An integrated carbon entrapped molecularly imprinted polymer (MIP) electrode for voltammetric detection of resveratrol in wine

A carbon entrapped molecularly imprinted polymer (CEMIP) electrode has been demonstrated as a sensitive and selective voltammetric sensor for the in situ detection of resveratrol in red wine. Using differential pulse voltammetry (DPV), the CEMIP was compared to the carbon entrapped non-imprinted polymer (CENIP), with the resveratrol imprinted format found to be 12 times more sensitive for the detection of resveratrol. The CEMIP and CENIP had a detection limit of 20 and ∼100 μg L−1, respectively, with both electrodes giving good linear standard addition calibrations with R2 ≥ 0.99 for concentrations between 0.1 and 5 mg L−1, which is the usual occurrence range of resveratrol in wine. Compared to the conventional carbon MIP composite (CMIPC), the CEMIP platform was 2.7 orders of magnitude more sensitive, which is attributed to the better electron transfer and unhindered access of the analyte to the responsive sites within the imprinted polymer. The CMIPC was only ∼2.5 times more sensitive than the CNIPC. The %RSD for CEMIP and CMIPC for ∼5.0 mg L−1 of resveratrol in spiked wine was determined to be 3.2% and 5.1%, respectively.

Arctic sea-ice proxies: Comparisons between biogeochemical and micropalaeontological reconstructions in a sediment archive from Arctic Canada:

Boxcore 99LSSL-001 from the southwest Canadian Arctic Archipelago (68.095°N, 114.186°W), studied by multiproxy approaches (sea-ice diatom biomarker IP25, phytoplankton-based biomarker brassicasterol, biogenic silica, total organic carbon, dinoflagellate cysts = dinocysts, diatoms) and their applications (sea-ice index PBIP25, modern analogue technique (MAT) transfer functions), provides a chronologically constrained (210Pb, 137Cs, two 14C dates) palaeoenvironmental archive spanning AD 1625–1999 with which to compare and evaluate proxies frequently used in sea-ice reconstructions. Whereas diatoms are rare, PBIP25, biogenic silica and qualitative dinocyst approaches show good agreement, suggesting that palaeo sea-ice histories based on biomarker and microfossil techniques are robust in this region. These combined approaches show fluctuating long open water to marginal ice zone conditions (AD 1625–1740), followed by high-amplitude oscillations between long open water and extended spring/summer sea ice (AD 1740–1870). Greater ice cover (AD 1870–1970) precedes recent reductions in seasonal sea ice (AD 1970–1999). Dinocyst-based MAT, however, produces a low-amplitude signal lacking the nuances of other proxies, with most probable sea-ice reconstructions poorly correlating with biomarker-based histories. Explanations for this disagreement may include limited spatial coverage in the modern dinocyst distribution database for MAT and the broad environmental tolerances of polar dinocysts. Overall, PBIP25 provides the most detailed palaeo sea-ice signal, although its use in a shallow polar archipelago downcore setting poses methodological challenges. This proxy comparison demonstrates the limitations of palaeo sea-ice reconstructions and emphasizes the need for calibration studies tying modern microfossil and biogeochemical proxies to directly measured oceanographic parameters, as a springboard for robust quantitative palaeo studies.

Adjustable Methacrylate Porous Monolith Polymer Layer Open Tubular Silica Capillary Microextraction for the Determination of Polycyclic Aromatic Hydrocarbons

ABSTRACT A novel adjustable porous polymer monolith layer open tubular silica capillary microextraction (PLOT-ME) device was fabricated by thermal polymerization of a poly(glycidylmethacrylate-co-ethylene glycol dimethacrylate) (GMA-co-EDMA) polymer film (∼20 µm) within a 250 µm internal diameter silica capillary initiated with 4,4′-azobis(4-cyanopentanoyl chloride). The polymer film thickness and morphology were controlled by the polymerization time and temperature. The length of the microextraction platform immersed in the sample was adjusted by the sample concentration and sample matrix. Furthermore, since the microextraction platform performance typically degraded with use, the PLOT-ME device affords a new microextraction zone that may be exposed by cleaving off the end. This ability significantly reduces the cost of microextraction for academic and research environments. The performance of the PLOT-ME device was tested for microextraction of polycyclic aromatic hydrocarbons (PAHs): naphthalene, 2,6-dimethylnaphthalene, anthracene, 9-methylanthracene, and phenanthrene in aqueous media. Linear calibration curves for the PAHs were obtained with correlation coefficients near unity and relative standard deviations from 2 to 20% for PAH standards from 100 to 0.1 µg/L. The limits of detection for the PAHs were between 0.02 and 0.06 µg/L, while the recoveries were from 97 to 104% in lake water. The precision between different PLOT-ME devices was 11%.

A flow-through enzymatic microreactor for the rapid conversion of triacylglycerols into fatty acid ethyl ester and fatty acid methyl ester derivatives for GC analysis

A flow-through enzymatic microreactor for the rapid conversion of triacylglycerols (TAG) into fatty acid ethyl ester (FAEE) or fatty acid methyl ester (FAME) derivatives was developed. The microreactor was a porous silica monolith fabricated within a 320 μm ID fused silica capillary with lipase from Candida antarctica immobilized onto the large surface area of the monolith. The microreactor was used for the room temperature ethanolysis of TAG from edible oils including canola, sesame, soybean and refined-bleached-deodorized palm oil. GC/MS-NCI and GC/FID were used to prove the identification of the FAEE and FAME products. The microreactor completely transformed the starting oils into FAEEs or FAMEs, without the use of any reagents other than alcohol, in quantities suitable for GC analysis. The prototype microreactors were reusable >5 times with ethanol and 2 times with methanol. The FAEE products obtained using the microreactor were similar to those produced using commercial Novozyme 435 enzyme beads as well as by catalysis with ethanolic H2SO4.

Porous Polymer Monolith Microextraction Platform for Online GC-MS Applications

One of the key steps in chemical analysis is sample preparation. It is a very important step prior to analysis, otherwise the analyte signal could be suppressed by sample matrix interference. In most cases sample preparation entails some form of extraction of the analyte(s) of interest from the interfering species. Conventional extraction techniques include liquid-liquid extraction (LLE) and solid phase extraction (SPE). LLE involves mixing two immiscible solvent together, and based on solubility equilibria the analyte or the interfering species partitions preferentially in the organic solvent. Ideally, the partition coefficient is very high to allow for efficient extraction (Park et al., 2001). In SPE, analytes of interest are extracted from solution by passing the liquid through a solid phase, such as a C18 SPE cartridge. Based on different physical and chemical properties, the desired solute either is adsorbed onto the solid phase, from whence it can later be eluted, or remains in solution while impurities are retained on the solid phase (Korner et al., 2000). The LLE and SPE extraction methods are laborious and demand the use of copious amounts of samples and solvents, therefore driving up the cost of chemical analysis. For LLE, emulsion formation can be a nuisance. These methods are also limited by factors like cartridge clogging in SPE, single use of the SPE and the need for toxic and polluting solvents (such as halogenated solvents like chloroform and dichloromethane) in LLE.

Integrated Microcentrifuge Carbon Entrapped Glucose Oxidase Poly (N-Isopropylacrylamide) (pNIPAm) Microgels for Glucose Amperometric Detection

Abstract This study demonstrates a miniaturized integrated glucose biosensor based on a carbon microbeads entrapped by glucose oxidase (GOx) immobilized on poly (N-isopropylacrylamide) (pNIPAm) microgels. Determined by the Lowry protein assay, the pNIPAm microgel possesses a high enzyme loading capacity of 31 mg/g. The pNIPAm GOx loaded on the microgel was found to maintain a high activity of approximately 0.140 U determined using the 4-aminoantipyrine colorimetric method. The integrated microelectrochemical cell was constructed using a microcentrifuge vial housing packed with (1:1, w/w) carbon entrapped by pNIPAm GOx microgels, which played the dual role of the microbioreactor and the working electrode. The microcentrifuge vial cover was used as a miniaturized reference electrode and an auxiliary electrode holder. The device can work as biosensor, effectively converting glucose to H2O2, with subsequent amperometric detection at an applied potential of −0.4 V. The microelectrochemical biosensor was used to detect glucose in wide linear range from 30 µM to 8.0 mM, a low detection limit of 10 µM, a good linear regression coefficient (R2) of 0.994, and a calibration sensitivity of 0.0388 µA/mM. The surface coverage of active GOx, electron transfer rate constant (ks), and Michaelis–Menten constant (KMapp) of the immobilized GOx were 4.0 × 10−11 mol/cm2, 5.4 s−1, and 0.086 mM, respectively. To demonstrate the applicability and robustness of the biosensor for analysis of high sample matrix environment, glucose was analyzed in root beer. The microelectrochemical device was demonstrated for analysis of small sample (<50 µL), while affording high precision and fast signal measurement (≤5 s).

Stimuli Responsive Polymer-Based 3D Optical Crystals for Sensing

3D optical crystals have found their applications in sensing, actuation, optical devices, batteries, supercapacitors, etc. The 3D optical crystal devices are comprised of two main components: colloidal gels and nanoparticles. Nanoparticles self-assemble into face center cubic structures in colloidal gels. The inherent 3D optical crystal structure leads to display of structural colors on these devices following light impingement. As such, these optical properties have led to the utilization of these 3D optical crystals as self-reporting colorimetric sensors, which is the focus of this review paper. While there is extensive work done so far on these materials to exhaustively be covered in this review, we focus here in on: mechanism of color display, materials and preparation of 3D optical crystals, introduction of recent sensing examples, and combination of 3D optical crystals with molecular imprinting technology. The aim of this review is to familiarize the reader with recent developments in the area and to encourage further research in this field to overcome some of its challenges as well as to inspire creative innovations of these materials.

Candida antarctica B Lipase-Loaded Microreactor for the Automated Derivatization of Lipids

ABSTRACT A key bottleneck in the profiling of lipids is the multistep derivatization required prior to gas chromatography (GC) analysis. A single in-vial lipid derivatization and analysis may significantly minimize sample loss and improve analytical sensitivity. A cotton fiber-supported poly(glycidylmethacrylate-co-ethylene glycol dimethacrylate) polymer microbrush microreactor loaded with Candida antarctica lipase B was developed for the facile conversion of triacylglycerols into fatty acid ethyl ester derivatives for gas chromatograph–mass spectrometry (GC–MS) analysis. The polymer microbrush microreactor was fabricated in effort to provide efficient, simplified, cost effective, and high-throughput GC–MS determination of triacylglycerols. The polymer microbrush microreactor was used as an in-vial triacylglycerol transesterification platform, with economical sample consumption of less than or equal to 100 µL and significant reduction of reagents. To evaluate the polymer microbrush microreactor performance for lipids, a triolein standard and camelina oil triacylglycerols were quantitatively transformed into ethyl oleate and fatty acid ethyl esters, respectively, following a 3 h reaction time. The lipase-loaded cotton fiber-supported poly(glycidylmethacrylate-co-ethylene glycol dimethacrylate) polymer microbrush microreactors were reusable for up to five times for quantitative transesterification with minimal loss of lipase activity.