Sabahudin Hrapovic

Characteristics and properties of carboxylated cellulose nanocrystals prepared from a novel one-step procedure.

Cellulose nanocrystals (CNCs) have emerged as a new class of nanomaterials for polymer reinforcement and nanocomposite formulation owing to their exceptionally high mechanical strength (modulus of 100–140 GPa), low density (1.6 g cm − 3 ), chemical tunability, environmental sustainability, and anticipated low cost. [ 1 ] CNCs have also been fostered for a myriad of applications including enzyme immobilization, [ 2 ]

Effect of Surface Charge on the Cellular Uptake and Cytotoxicity of Fluorescent Labeled Cellulose Nanocrystals

Probing of cellular uptake and cytotoxicity was conducted for two fluorescent cellulose nanocrystals (CNCs): CNC-fluorescein isothiocyanate (FITC) and newly synthesized CNC-rhodamine B isothiocyanate (RBITC). The positively charged CNC-RBITC was uptaken by human embryonic kidney 293 (HEK 293) and Spodoptera frugiperda (Sf9) cells without affecting the cell membrane integrity. The cell viability assay and cell-based impedance spectroscopy revealed no noticeably cytotoxic effect of the CNC-RBITC conjugate. However, no significant internalization of negatively charged CNC-FITC was observed at physiological pH. Indeed, the effector cells were surrounded by CNC-FITC, leading to eventual cell rupture. As the surface charge of CNC played an important role in cellular uptake and cytotoxicity, facile surface functionalization together with observed noncytotoxicity rendered modified CNC as a promising candidate for bioimaging and drug delivery systems.

Assessment of Cytotoxicity of Quantum Dots and Gold Nanoparticles Using Cell-Based Impedance Spectroscopy

A continuous online technique based on electric cell-substrate impedance sensing (ECIS) was demonstrated for measuring the concentration and time response function of fibroblastic V79 cells exposed to nanomaterials such as quantum dots (QDs) and fluorescent gold nanoparticles. The half-inhibition concentration, (ECIS50), the required concentration to attain 50% inhibition of the cytotoxic response, was estimated from the response function to ascertain cytotoxicity during the course of measurement. The ECIS50 values agreed well with the results obtained using the standard neutral red assay. Cadmium selenide quantum dots showed direct cytotoxicity with the ECIS assay. For the cadmium telluride quantum dots, significant toxicity could be assigned to free cadmium, although additional toxicity could be attributed to the QDs per se. The QDs synthesized with indium gallium phosphide and the fluorescent gold nanoparticles were not cytotoxic.

Immobilization of Antibodies and Enzymes on 3-Aminopropyltriethoxysilane-Functionalized Bioanalytical Platforms for Biosensors and Diagnostics

3‐Aminopropyltriethoxysilane-Functionalized Bioanalytical Platforms for Biosensors and Diagnostics Sandeep Kumar Vashist,*,†,‡ Edmond Lam, Sabahudin Hrapovic, Keith B. Male, and John H. T. Luong †HSG-IMIT Institut für Mikround Informationstechnik, Georges-Koehler-Allee 103, 79110 Freiburg, Germany ‡Laboratory for MEMS Applications, Department of Microsystems Engineering IMTEK, University of Freiburg, Georges-Koehler-Allee 103, 79110 Freiburg, Germany National Research Council Canada, Montreal, Quebec H4P 2R2, Canada Innovative Chromatography Group, Irish Separation Science Cluster (ISSC), Department of Chemistry and Analytical, Biological Chemistry Research Facility (ABCRF), University College Cork, Cork, Ireland

Catalysis using gold nanoparticles decorated on nanocrystalline cellulose

A novel nanocomposite was prepared by deposition of carbonate-stabilized Au nanoparticles (AuNPs) onto the surface of poly(diallyldimethyl ammonium chloride) (PDDA)-coated carboxylated nanocrystalline cellulose (NCC). The hybrid material possessed AuNPs (1.45% by weight) with an average diameter of 2.95 ± 0.06 nm. The catalytic activity of AuNP/PDDA/NCC for reducing 4-nitrophenol to 4-aminophenol was compared to other Au-supported composites. An activation energy of 69.2 kJ mol(-1) was obtained for the reaction. Indeed, the reaction rate constant k of (5.1 ± 0.2) × 10(-3) s(-1) was comparable to the benchmark literature value obtained using AuNPs (<5 nm in diameter) decorated on a network of crystalline cellulose fibers. Our strategy promotes the use of natural resources to prepare reusable hybrid inorganic-organic materials for important reactions with facilitated product isolation/purification.

Cellulose nanocrystal/gold nanoparticle composite as a matrix for enzyme immobilization.

A novel nanocomposite consisting of cellulose nanocrystals (CNCs) functionalized with gold nanoparticles (AuNPs) serving as an excellent support for enzyme immobilization with phenomenally high loading is presented in this work. As testing models, cyclodextrin glycosyl transferase (CGTase) and alcohol oxidase were conjugated on an activated CNC/AuNP matrix. This catalytic platform exhibits significant biocatalytic activity with excellent enzyme stability and without apparent loss of the original activity. The recovered specific activities were approximately 70% and 95% for CGTase and alcohol oxidase, respectively. This novel and inexpensive material is anticipated to extend to other enzymes, enhancing the enzyme loading and activity as well as the stability in both operation and storage.

Picomolar Detection of Protease Using Peptide/Single Walled Carbon Nanotube/Gold Nanoparticle-Modified Electrode

Picomolar electrochemical detection of human immunodeficiency virus type-1 protease (HIV-1 PR) using ferrocene (Fc)-pepstatin-modified surfaces has been presented. Gold electrode surface was modified with gold nanoparticles (AuNP) or thiolated single walled carbon nanotubes/gold nanoparticles (SWCNT/AuNP). Thiol-terminated Fc-pepstatin was then self-assembled on such surfaces as confirmed by Raman spectroscopy and scanning electron microscope. The interaction between the Fc-pepstatin-modified substrates and HIV-1 PR was studied by cyclic voltammetry and electrochemical impedance spectroscopy. Both electrode materials showed enhanced electrochemical responses to increasing concentrations of HIV-1 PR with shifting to higher potentials as well as decrease in the overall signal intensity. However, the sensing electrode modified with thiolated SWCNTs/AuNPs showed remarkable detection sensitivity with an estimated detection limit of 0.8 pM.

Raman-based detection of bacteria using silver nanoparticles conjugated with antibodies

Surface enhanced Raman scattering (SERS) has been used to detect bacteria captured by polyclonal antibodies sorbed onto protein-A-modified silver nanoparticles. The selectivity and discrimination of the technique were assured by using a specific antibody to the model bacterium, Escherichia coli. As the SERS enhancement mechanism depends upon the metal surface proximity, 8 nm was considered as the optimum distance between the bacterium and the nanoparticle surface. Spectral reproducibility was verified using Principal Components Analysis to differentiate the clusters corresponding to the biomolecules and/or bacteria sorbed onto nanoparticles. Compared to the normal Raman spectrum, the SERS technique resulted in an intensity enhancement of over 20-fold.

Preparation of well-dispersed gold/magnetite nanoparticles embedded on cellulose nanocrystals for efficient immobilization of papain enzyme

A nanocomposite consisting of magnetite nanoparticles (Fe3O4NPs) and Au nanoparticles (AuNPs) embedded on cellulose nanocrystals (CNCs) was used as a magnetic support for the covalent conjugation of papain and facilitated recovery of this immobilized enzyme. Fe3O4NPs (10-20 nm in diameter) and AuNPs (3-7 nm in diameter) were stable and well-dispersed on the CNC surface. Energy-dispersive spectroscopy, X-ray diffraction, and Fourier transform infrared spectroscopy were used to evaluate the surface composition and structure of CNC/Fe3O4NPs/AuNPs. The nanocomposite was successfully used for the immobilization and separation of papain from the reaction mixture. The optimal enzyme loading was 186 mg protein/g CNC/Fe3O4NPs/AuNPs, significantly higher than the value reported in the literature. The activity of immobilized papain was studied by electrochemical detection of its specific binding to the Thc-Fca-Gly-Gly-Tyr-Arg inhibitory sequence bound to an Au electrode. The immobilized enzyme retained 95% of its initial activity after 35 days of storage at 4 °C, compared to 41% for its free form counterpart.

Selective Nanomolar Detection of Dopamine Using a Boron-Doped Diamond Electrode Modified with an Electropolymerized Sulfobutylether-β-cyclodextrin-Doped Poly(N-acetyltyramine) and Polypyrrole Composite Film

N-acetyltyramine was synthesized and electropolymerized together with a negatively charged sulfobutylether-beta-cyclodextrin on a boron-doped diamond (BDD) electrode followed by the electropolymerization of pyrrole to form a stable and permselective film for selective dopamine detection. The selectivity and sensitivity of the formed layer-by-layer film was governed by the sequence of deposition and the applied potential. Raman results showed a decrease in the peak intensity at 1329 cm(-1) (sp(3)), the main feature of BDD, upon each electrodeposition step. Such a decrease was correlated well with the change of the charge-transfer resistance derived from impedance data, i.e., reflecting the formation of the layer-by-layer film. The polycrystalline BDD surface became more even with lower surface roughness as revealed by scanning electron and atomic force microscopy. The modified BDD electrode exhibited rapid response to dopamine within 1.5-2 s and a low detection limit of 4-5 nM with excellent reproducibility. Electroactive interferences caused by 4-dihydroxyphenylalanine, 3,4-dihydroxyphenylacetic acid, ascorbic acid, and uric acid were completely eliminated, whereas the signal response of epinephrine and norepinephrine was significantly suppressed by the permselective film.