Honest Makamba - Academia.edu (original) (raw)

Papers by Honest Makamba

Ga onmiddellijk naar paginanavigatie. Determination of diffusion coefficients of platinum chloro ... more Ga onmiddellijk naar paginanavigatie. Determination of diffusion coefficients of platinum chloro complexes using the Taylor dispersion and the electrophoretic stopped flow methods. Please use this identifier to cite or link to this item: Record Details. Record ID, 372219. ...

calibration curve obtained from PDMS protein chip, the concentration of the spiked sample was det... more calibration curve obtained from PDMS protein chip, the concentration of the spiked sample was determined to be around 103(±3) pg/mL from 3 replicates. The 10% positive deviation from the exact amount (90 pg/mL) added into the mouse serum is likely due to the endogenous TGF β already present in the healthy mouse serum. The arithmetic difference between the spiked and non spiked sample shows that the chip can be used to accurately determine the endogenous TGF β in serum. Results indicate that the modified surface was hydrophilic and reactive for bio-species up to more than 7 days in its dry form. The chips were also applied for the detection of low abundant proteins in the cell lysates. Innovative aspects • Bio-affinity Surface on PDMS substrate with long-term stability and reactivity.

Molecules, 2019

Carbon dots (CDs) are fluorescent nanomaterials used extensively in bioimaging, biosensing and bi... more Carbon dots (CDs) are fluorescent nanomaterials used extensively in bioimaging, biosensing and biomedicine. This is due in large part to their biocompatibility, photostability, lower toxicity, and lower cost, compared to inorganic quantum dots or organic dyes. However, little is known about the utility of CDs as separation adjuvants in capillary electrophoresis (CE) separations. CDs were synthesized in-house according to a ‘bottom-up’ method from citric acid or other simple carbon precursors. To demonstrate the applicability of CDs as separation adjuvants, mixtures of holo- (metallated) and apo- (demetallated) forms of transferrin (Tf, an iron transport protein) were analyzed. In the absence of CDs, the proteins were not resolved by a simple CE method; however, upon addition of CDs to the separation buffer, multiple forms of Tf were resolved indicating that CDs are valuable tools to facilitate the separation of analytes by CE. CE parameters including sample preparation, buffer ident...

Journal of Chromatography A, 2006

Protein phosphorylation is one of the most important known posttranslational modifications and th... more Protein phosphorylation is one of the most important known posttranslational modifications and the strategy to enrich phosphopeptides becomes a critical issue for mapping protein phosphorylation sites. In this study, nano-titanium dioxide (TiO2) composites were synthesized, characterized, and demonstrated to have high loading capacity and high capture efficiency for enriching phosphopeptides. TiO2 nanoparticles were first silanized with methacryloxypropyltrimethoxysilane (MPTMS) and then were photopolymerized in the presence of a diacrylate crosslinker. The chemical bonds formed by the reaction were confirmed by both FT-IR and X-ray photoelectron spectroscopy (XPS). Scanning electron microscopy (SEM) further reveals that agglomeration of the particles was created by the crosslinking, which allowed the nanocomposites to be well retained within the cartridge and used as the chromatographic packing material. Titration with phenyl phosphate indicated that the TiO2 nanocomposites have two times as much phosphate binding capacity compared with 5 microm TiO2 particles. Moreover, based on repetitive analyses of the tryptic digest deduced from pure proteins as well as from protein mixtures containing phospho and non-phospho proteins, the capture efficiency of TiO2 nanocomposites was determined to be two to five times larger compared with 5 microm TiO2 particles. The cost for preparing nanocomposite TiO2 is low and it holds great promises to be used as chromatographic materials for phosphopeptide enrichment.

Journal of Chromatography A, 1998

The effect of the chiral diamine sparteine as a cationic mobile phase modifier on the retention a... more The effect of the chiral diamine sparteine as a cationic mobile phase modifier on the retention and enantioseparation of five hydrophobic basic drugs on an α1-acid glycoprotein column was studied. Sparteine produced good results over the whole range of its concentration (1–15 mM) in the phosphate buffer mobile phase at pH 6.0 for the selected drugs (alprenolol, propranolol, promethazine, chlorpheniramine

ELECTROPHORESIS, 2006

The binding of estrogen receptor (ER) to estrogen response element (ERE) is essential for genomic... more The binding of estrogen receptor (ER) to estrogen response element (ERE) is essential for genomic pathways of estrogens and gel‐based electrophoretic mobility shift assay (EMSA) is commonly used for analyzing ERE binding. Gel‐based EMSA, however, requires the use of hazard radio isotopes and they are slow, labor‐intensive and difficult to quantify. Here, we present quantitative affinity assays based on microchip electrophoresis using PEG‐modified glass microchannels, which bear neutral surfaces against the adsorption of acidic DNA molecules and basic ER proteins. We first demonstrated the feasibility of the method by measuring binding constants of recombinant ERα and ERβ with a consensus ERE sequence (cERE, 5'‐GGTCAGAGTGACC‐3') as well as with an ERE‐like sequence (ERE 1576, 5'‐GACCGGTCAGCGGACTCAC‐3'). Changes in mobility as a function of protein‐DNA molar ratios were plotted and the dissociation constants were determined based on non‐linear curve fitting. The minimu...

ELECTROPHORESIS, 2008

We report on the photopatterning of single carbon nanotube composites with soft hydrogel polymers... more We report on the photopatterning of single carbon nanotube composites with soft hydrogel polymers in glass microchannels. Since the hydrogels by themselves are able to withstand liquid flow within the microchannels, we covalently combined them with single‐walled carbon nanotubes to impart mechanical strength. We attempted this approach by patterning the gels within the microchannels without prior surface modifications. Our results show that the 1‐cm nanocomposite hydrogels are far stronger than the free hydrogels. Moreover, the nanocomposites were able to concentrate and separate proteins within a 1.5‐cm distance using gel‐free buffers. The separation cannot only be tuned by changing the running buffer; the lack of gels in the running buffer reduces the chance of channel blockage and thus the lifetime of the device is prolonged. The usefulness of the patterned nanocomposites may be extended by a wide selection of nanocomposite properties and monomers to find a broad range of applica...

ELECTROPHORESIS, 2005

Chip-based microfluidic devices coupled with electrospray ionization-mass spectrometry We present... more Chip-based microfluidic devices coupled with electrospray ionization-mass spectrometry We present the current status of the development of microfluidic devices fabricated on different substrates for coupling with electrospray ionization-mass spectrometry (ESI-MS). Until now, much success has been gained in fabricating the ESI chips, which show better performances due to miniaturization when compared with traditional methods. Integration of multiple steps for sample preparation and ESI sample introduction, however, remains a great challenge. This review covers the main technical development of electrospray device that were published from 1997 to 2004. This article does not attempt to be exclusive. Instead, it focuses on the publications that illustrated the breath of the development and applications of microchip devices for MS-based analysis.

Chromatographia, 1998

ABSTRACT Reversed-phase HPLC separations of basic compounds have been optimized by use of mobile ... more ABSTRACT Reversed-phase HPLC separations of basic compounds have been optimized by use of mobile phases containing 1,8-diaminooctane (DAO) as amine modifier and heptanesulfonate as counter-ion. Such studies have demonstrated the high resolution and selectivity of this chromatographic system compared with mobile phases prepared with the more widely used primary amines. With the aim of clarifying the retention mechanism involved, three sets of compounds with different structures and properties were analyzed: sulfamidics and trimethoprim, aromatic diamines and aminophenols, and a standard mixture of lipophilic basic drugs. The conditions investigated were: diaminoalkane modifier concentration, diaminoalkane modifier alkyl-chain length, nature and concentration of the counter-ion, pH of the mobile phase, concentration of the organic modifer, and the nature of the stationary phase as characterized by percentage carbon loading. Analysis of chromatographic behavior as a function of the chromatographic conditions has enabled the proposal of a mechanism of retention of the three classes of compounds.

Analytical Chemistry, 2008

Poly(dimethylsiloxane) (PDMS) possesses many advantages, such as biocompatibility and high oxygen... more Poly(dimethylsiloxane) (PDMS) possesses many advantages, such as biocompatibility and high oxygen permeability, which makes it an attractive material for fabricating biodevices. Creating an affinity surface with long-term stability and reactivity for biomolecular interactions on a PDMS substrate, however, is difficult due to its inherent hydrophobicity. In this study, an affinity surface on a PDMS substrate with long-term hydrophilicity and affinity reactivity is reported. This modification is composed of two parts. The bottom part is made of polyelectrolyte multilayers and is capable of providing long-term hydrophilic stability. The top part consists of three protein layers, bovine serum albumin (BSA), anti-BSA, and protein G, and offers an affinity surface for antibody binding and, more importantly, provides favorable orientation and minimum nonspecific binding. The chemical modification for the different stages was monitored by atomic force microscopy (AFM), attenuated total reflection Fourier transform infrared spectroscopy (ATR-FT-IR), and contact angle and fluorescence measurements. A longterm PDMS immunodevice (LPID) based on polyelectrolyte multilayers and protein layers was fabricated and applied to the detection of transforming growth factor (TGF-) protein in mouse serum by the enzyme-linked immunosorbent assay (ELISA) method. Results show that a linear calibration curve was obtained in the concentration range from 500 to 15.125 pg/mL, and the relative standard deviation was less than 3%. Also, the amount of TGF-spiked in mouse serum was precisely determined. Results indicate that the modified surface was hydrophilic and reactive to biospecies up to more than 7 days in its dry form. Moreover, the blocking reagent used to reduce nonspecific binding was found to be not necessary for the LPID. Thus, the reported method is expected to hold a great potential for fabricating PDMS-based affinity devices such as protein chips. Poly(dimethylsiloxane) (PDMS) possesses many advantages, like high optical transparency, biocompatibility, chemical stability, and high oxygen permeability, which makes it an attractive material. This has resulted in many applications of this material in biological and chemical analysis.

Analytical Chemistry, 2009

In order to investigate the resistance to non-specific binding on different PDMS surfaces, we inc... more In order to investigate the resistance to non-specific binding on different PDMS surfaces, we incubated 100 µg/mL FITC-labeled protein (BSA and IgG) solutions in the bare, BSA-coated and PEMS-coated PDMS channel surfaces. After two-hour

Analytical Chemistry, 2007

of 17α-Cy3-estradiol The synthesis procedure was depicted in Figure S1 and described in below. An... more of 17α-Cy3-estradiol The synthesis procedure was depicted in Figure S1 and described in below. An amount of 2.4 g of t-Butyldimethylsilyl chloride (ALDRICH, St. Louis, MO, USA) and 2.8 g of imidazole (Fluka, Buchs, Switzerland) were add to a solution of the 2.0 g estrone (Fluka, Buchs, Switzerland) dissolved in 20 mL dry dimethylformamide (J.T. Baker, Phillipsburg, NJ, USA). The mixture was stirred at room temperature overnight and then diluted with ether. The organic phase was washed with brine and the organic solvents were evaporated to afford 2 (84%).

Analytical Chemistry, 2002

Figure 5. Electrophoresis on oxidized-PDMS and PEG-grafted-PDMS devices. (A) Shown is a schematic... more Figure 5. Electrophoresis on oxidized-PDMS and PEG-grafted-PDMS devices. (A) Shown is a schematic of the channels on the microfluidic devices. (B) The two halves of a PDMS device were oxidized by exposure to an oxygen plasma. F-PKC and F-src were injected from the double-T (v-vi) into the main electrophoresis channel (vi-iv) and electrophoresed. Shown is a typical electropherogram. (C) Conditions are identical to that in (B) except that the two halves of a PDMS device were grafted with PEG (25 µg/cm 2). Also shown is a typical electropherogram.

Analytical Letters, 2016

ABSTRACT The detection of organophosphate compounds was demonstrated using sol–gel materials made... more ABSTRACT The detection of organophosphate compounds was demonstrated using sol–gel materials made of zirconia composite films. The detection was performed via inclusion complexes of the organophosphates of paraoxon-ethyl and parathion-ethyl with the zirconium dioxide-β-cyclodextrin composite film. The formation of sol–gel thin film process was investigated and optimized. The morphology of zirconium dioxide with β-cyclodextrin gel was characterized by scanning electron microscopy and energy-dispersive spectroscopy. Attenuated total reflectance Fourier transform infrared spectroscopy was used for the characterization of the inclusion complexes of paraoxon-ethyl and parathion-ethyl on zirconium dioxide with β-cyclodextrin film. The hydrolysis of paraoxon-ethyl by zirconium dioxide with the β-cyclodextrin gel thin film caused peak shifts in the attenuated total reflectance Fourier transform infrared spectra. The increase in absorption intensity correlated with increasing paraoxon-ethyl concentration, but this trend was not observed for parathion-ethyl. The hydroxyl vibration band of the intermolecular and intramolecular hydrogen bonds was observed to decline with increasing paraoxon-ethyl concentration. Quantitative analysis of paraoxon-ethyl using attenuated total reflectance Fourier transform infrared spectra provided a linear calibration relationship from 1 to 7 µM with a limit of detection as low as 30 nM.

Analytical Chemistry, 2005

Poly(dimethylsiloxane) (PDMS) is a biomaterial that presents serious surface instability characte... more Poly(dimethylsiloxane) (PDMS) is a biomaterial that presents serious surface instability characterized by hydrophobicity recovery. Permanently hydrophilic PDMS surfaces were created using electrostatic self-assembly of polyethyleneimine and poly(acrylic acid) on top of a hydrolyzed poly(styrene-alt-maleic anhydride) base layer adsorbed on PDMS. Cross-linking of the polyelectrolyte multilayers (PEMS) by carbodiimide coupling and covalent attachment of poly(ethylene glycol) (PEG) chains to the PEMS produced stable, hydrophilic, protein-resistant coatings, which resisted hydrophobicity recovery in air. Attenuated total reflection Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy revealed that the thin films had excellent chemical stability and resisted hydrophobicity recovery in air over 77 days of measurement. The spectra also showed a dense coverage for PEG dialdehyde and excellent resistance to protein adsorption from undiluted rat serum. Atomic force microscopy revealed dense coverage with PEG dialdehyde and PEG diamine. Contact angle measurements showed that all films were hydrophilic and that the PEG dialdehyde-topped thin film had a virtually constant contact angle (∼20°) over the five months of the study. Electrokinetic analysis of the coatings in microchannels always exposed to air also gave good protein separation and constant electroosmotic flow during the five months that the measurements were done. We expect that the stable, hydrophilic, protein-resistant thin-film coatings will be useful for many applications that require long-term surface stability. Historically, poly(dimethylsiloxane) (PDMS) has been used in medicine for making devices such as implants, 1,2 catheters, pacemaker encapsulants, and ocular lenses. 3 More recently, the use of PDMS has been extended to the fabrication of microfluidic chips. 4-7 The application of PDMS has been driven by its good properties, which include low toxicity and flexibility. Despite the many advantages that PDMS has, its applications in microfluidics and medicine have been problematic because PDMS is highly hydrophobic. Even when the surface is made hydrophilic, PDMS gradually reverts to the hydrophobic state due to surface rearrangements. The surface instability of PDMS has not been fully addressed to date. Various approaches have been used to modify PDMS surfaces for various applications. Modification procedures include exposure to energy sources such as plasma, 9,10 corona discharge, 11 and ultraviolet light, 12 polyelectrolyte multilayers (PEMS), 13 radiationinduced graft polymerization, 14,15 silanization, 16 atom-transfer radical polymerization, 17,18 chemical vapor deposition, 19 cerium(IV) catalysis, 20,21 phospholipid bilayer modification, 22-24 and more recently, sol-gel modifications. 7 Most of these approaches do not solve the problem of hydrophobicity recovery via the silica-like layer or deformations since the hydrophilic groups are directly