Search

In this study, CO₂ conversion to acetate and CH₄ was achieved in a flow-through laboratory-scale microbial electrosynthesis (MES) cell composed of a 3D conductive polylactic acid (cPLA) lattice cathode with electrodeposited metal electrocatalyst coatings. The MES cell with a bare cPLA cathode showed the poorest performance with the lowest H₂ and CH₄ production rates and low Coulombic efficiency. This was ascribed to a poor electrocatalytic activity of cPLA towards H₂ production and high electrode resistivity. When the cPLA electrode was modified with metal coatings, the CH₄, acetate and H₂ production rate increased significantly, with the following trend: cPLA < Ni < NiFe < NiFeMn. The better performance of the metal-coated cPLA in terms of CH₄ production was attributed to the lower electrical resistance, enhanced H₂ production and enhanced electron transfer between the cathode and the biofilm. At the cell potential of 2.8 V, the best-performing NiFeMn cPLA cathode showed stable production of CH₄ (50 ± 6 mL d⁻¹), acetate (185 ± 27 mg d⁻¹), and H₂ (545 ± 175 mL d⁻¹) at close to 100% Coulombic efficiency.

To unlock nature's potential for functional biomaterials, many efforts have been devoted to isolating the nanocrystalline domains within the supramolecular structure of polysaccharides. Yet, low reactivity and yield in aqueous systems along with excessive solvent usage hinders its development. In this report, the first solvent-free pathway to access carboxylated chitin and cellulose nanocrystals with excellent mass balance is described, relying on a new method coined high-humidity shaker aging (HHSA). The method involves a mild grinding of the polysaccharide with ammonium persulfate followed by an aging phase under high-humidity and on a shaker plate. Insights into the mechanism were uncovered, which highlighted the unique role of high humidity to afford a gradual uptake of water by the material up to deliquescence when the reaction is complete. This process was then validated for direct synthesis of nanocrystals from biomass sources including crab and soft wood pulp.

There is a desperate need for a solution to the ongoing waste management issues of the food processing industries. The demand for fish, including salmon, is higher than ever because of the growing global population and protein needs, however this results in large quantities of wasted by-products. This waste is problematic because it is potentially harmful to the environment and results in significant disposal costs for industries. The salmon frame (bones) is wasted once processed, however it is a potential feedstock for hydroxyapatite, a mineral for value-added applications. While other research has been done on accessing hydroxyapatite from animal wastes, these processes either use very high temperatures or chemicals that are more costly and hazardous for industrial purposes. In this study, we developed an enzymatic treatment using proteases and lipases simultaneously to clean the residual meat from salmon frames to isolate collagen-containing hydroxyapatite (sHAP) using Design of Experiment (DoE) under benign conditions. The variables were optimized using 2x3 and 2x4 factorial designs and it was determined by characterization techniques, weight loss calculations, and thermogravimetric analysis that the meat from the salmon frame was successfully hydrolyzed with 15 microliters/g Neutrase and 7.5 microliters/g Lipozyme CALB L in 40 degrees Celsius tap water for 6 h. We developed and propose a metric called Environment and Industry Hazard (EIH) for understanding the impact of such processing methods and compare the optimized procedure with existing techniques. The method reported herein is less impactful (environment, hazard, cost, carbon footprint) than others in the literature, as there are no solvents required, enzymes are easily disposed, and temperatures do not exceed 100 degrees Celsius during the entire process. Furthermore, we treated five salmon frames with the optimized conditions and determined it is possible to use this process on a larger scale.

Antimicrobial peptides (AMPs) offer a great promise in designing new therapeutics due to their ability to interfere in bacterial growth by penetrating the cell wall. The overuse of antibiotics has resulted into antibiotic-resistant bacteria and AMPs could be an alternative to circumvent this resistance. Chitosan nanocrystals (ChsNCs) are rod-shaped polysaccharide-based nanomaterials, formed by deacetylation of seafood waste. They possess primary amino groups on the surface of the nanoparticles which can be as used a scaffold due to the built-in morphology and ease in functionalization. Here, we developed a new methodology to functionalize ChsNCs with amino acids and peptides by using fundamentals of solid phase peptide synthesis. The resulting functionalized rod-shaped nanomaterials were characterized using nuclear magnetic resonance (NMR), dynamic light scattering (DLS), zeta potential measurements and microscopy imaging. This synthetic strategy could be used in designing ChsNC-based nanomaterials to target specific cells by attaching bioactive peptides to the nanomaterial surface.

In this report, chitin and chitosan nanocrystals were used as biomass-based supports for Pd nanoparticles (NPs) used as a heterogeneous catalyst for the Heck coupling reaction. By using a one-pot fabrication method, a Pd salt precursor was directly reduced and deposited onto these nanocrystal catalysts. Characterization of these nanocomposites showed disperse Pd NPs on the surfaces of the chitinous nanocrystals. Heck coupling model reactions revealed full product yield in relatively benign conditions, outcompeting the use of other catalysts supported on biomass-based nanomaterials, including cellulose nanocrystals. These initial results show the potential for using chitinous nanomaterials as effective catalyst supports in cross-coupling reactions.

This study compares carbon felt (CF), granular activated carbon (GAC), and a conductive acrylonitrile butadiene styrene (cABS) polymer cathodes for CH

In this study, we demonstrate for the first time the fabrication of carboxylated chitosan nanocrystals (ChsNC) with high degree of deacetylation (DDA) at >80% and narrow size distribution. We also studied its application as a sustainable support material for metal-based catalysts. Carboxylated chitin nanocrystals (ChNCs) were initially prepared through partial cleavage of glycosidic bonds in chitin by ammonium persulfate, with concurrent oxidation of chitin C6 primary alcohols to produce carboxylate groups on the surface of the ChNCs. ChsNCs were subsequently prepared using an alkaline deacetylation procedure in the presence of NaBH4 to preserve the nanorod structure of the biomaterial. The resulting nanocrystals feature both carboxyl and amino functional groups. Transmission electron microscopy (TEM), X-ray diffraction (XRD), and Fourier-transform infrared (FTIR) spectroscopy were used to determine the morphology and composition of these carboxylated ChNCs and ChsNCs. Subsequently, we tested the ability of the as-made ChsNCs as a biomass-based catalyst support for Au nanoparticles (NPs) using the 4-nitrophenol reduction and the aldehyde-amine-alkyne (A3) coupling reactions to demonstrate its capabilities in regard to the ones of cellulose nanocrystals (CNCs). In particular, Au NPs over ChsNCs featured the highest turnover frequency (TOF) value for the 4-nitrophenol reduction reported for all Au-based catalysts supported on carbon-based systems. Spectroscopic and imaging techniques confirmed the importance of precisely controlling the redox state of Au as it is being deposited to afford a highly disperse active site on the bionano-support.

Polysaccharides have been shown to have immunomodulatory properties. Modulation of the immune system plays a crucial role in physiological processes as well as in the treatment and/or prevention of autoimmune and infectious diseases. Cellulose nanocrystals (CNCs) are derived from cellulose, the most abundant polysaccharide on the earth. CNCs are an emerging class of crystalline nanomaterials with exceptional physico-chemical properties for high-end applications and commercialization prospects. The aim of this study was to design, synthesize, and evaluate the cytotoxicity of a series of biocompatible, wood-based, cationic CNCs as potential immunomodulators. The anionic CNCs were rendered cationic by grafting with cationic polymers having pendant +NMe3 and +NH3 moieties. The success of the synthesis of the cationic CNCs was evidenced by Fourier transform infrared spectroscopy, dynamic light scattering, zeta potential, and elemental analysis. No modification in the nanocrystals rod-like shape was observed in transmission electron microscopy and atomic force microscopy analyses. Cytotoxicity studies using three different cell-based assays (MTT, Neutral Red, and LIVE/DEAD&reg, ) and three relevant mouse and human immune cells indicated very low cytotoxicity of the cationic CNCs in all tested experimental conditions. Overall, our results showed that cationic CNCs are suitable to be further investigated as immunomodulators and potential vaccine nanoadjuvants.

This study demonstrated the removal of selenite and selenate in flow-through permeable bioelectrochemical barriers (microbial electrolysis cells, MECs). The bioelectrochemical barriers consisted of cathode and anode electrode compartments filled with granular carbon or metallurgical coke. A voltage of 1.4 V was applied to the electrodes to enable the bioelectrochemical removal of selenium species. For comparison, a similarly designed permeable anaerobic biobarrier filled with granular carbon was operated without voltage. All biobarrier setups were fed with water containing up to 5,000 µg L−1 of either selenite or selenate and 70 mg L−1 of acetate as a source of organic carbon. Significant removal of selenite and selenate was observed in MEC experimental setups, reaching 99.5–99.8% over the course of the experiment, while in the anaerobic biobarrier the removal efficiency did not exceed 88%. By simultaneously operating several setups and changing operating parameters (selenium species, influent Se and acetate concentrations, etc.) we demonstrated enhanced removal of Se species under bioelectrochemical conditions.

Chitin nanocrystals (ChNCs) were prepared by partial cleavage of glycosidic bonds in chitin with concurrent oxidation of chitin C6 primary alcohols to produce carboxylate groups on the surface of the ChNCs. Following alkaline deacetylation of the ChNCs in the presence of NaBH4 to inhibit “end-peeling” afforded chitosan nanocrystals (ChsNCs) with a degree of deacetylation (DDA) >80%. Transmission electron microscopy (TEM), X-ray diffraction (XRD) and Fourier-transform Infrared (FTIR) spectroscopy were used to determine the morphology and composition of these carboxylated ChNCs and ChsNCs. Subsequently, two methods were used to deposit Au onto the nanocrystals, and the catalytic activities of the resulting biomass-based nanocatalysts were tested for the 4-nitrophenol reduction and the aldehyde-amine-alkyne (A3) coupling reaction. In particular, Au nanoparticles over ChsNCs featured the highest turnover frequency value for the 4-nitrophenol reduction reported to date. Spectroscopic and imaging techniques confirmed the importance of controlling precisely the redox state of Au as it is being deposited to afford highly disperse active site on the bio-nano-support.

A one-pot green procedure for the treatment of cellulosic biomass with ammonium persulfate (APS) was developed for the synthesis of highly crystalline carboxylated nanocrystalline cellulose (NCC–COOH), an emerging nanomaterial with a plethora of diversified applications. Raman spectroscopy proved applicable for monitoring the fate of APS and its two byproducts during the production of NCC–COOH from microcrystalline cellulose (MCC). The two main byproducts were then identified and quantified as ammonium sulfate (AS) and H₂SO₄ with the latter accounted for 60% of the total sulfate ions in solution. On the basis of such findings, one-step neutralization of H₂SO₄ and NCC with NH₄OH immediately after reaction was implemented for the formation of additional AS, followed by its quantitative recovery by precipitation. This was a very effective and critical step in waste stream management and cost reduction for the large scale production of NCC. In addition, the process resulted in highly crystalline NCC with COO⁻NH₄⁺ groups, a nanomaterial with improved dispersion and thermal characteristics over NCC with COOH and COO⁻Na⁺ groups.

Graphene, graphene oxide, sulfonated graphene, and sulfonated graphene oxide (SGO) have been prepared, characterized and tested for the dehydration of xylose to furfural in water. In particular, SGO was proven to be a rapid and water-tolerant solid acid catalyst even at very low catalyst loadings down to 0.5 wt. percent vs xylose, maintaining its initial activity after 12 tested repetitions at 200 °C, with an average yield of 61 percent in comparison to 44 percent for the uncatalyzed system. Raman spectroscopy, energy dispersive X-ray spectroscopy, thermogravimetric analysis, X-ray photoelectron spectroscopy, 13C solid state nuclear magnetic resonance spectroscopy, Fourier transform infrared spectroscopy and surface area analysis suggested that the aryl sulfonic acid groups were the key active sites for high temperature production of furfural in water. They were more thermally stable under the reaction conditions and acidic than other functional groups attached to the graphene surface.

High quality cellulose nanocrystals are synthesized using a simple one-step procedure with ammonium persulfate. This versatile method processes a variety of cellulosic biomass without the need for pretreatments to remove non- cellulosic plant contents.

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.

Colored passive layers on Ti can be prepared by electrochemical means and their coloration can be switched reversibly between several colors by increasing or decreasing the AC voltage (VAC) in a stepwise manner. The coloration, which originates from iridescence, is directly related to the passive layer’s thickness (d) achieved at each VAC value. Two concurrently occurring processes, the passive layer growth and passive layer dissolution, control the passive layer thickness. At a given AC voltage, the passive layer reaches a steady-state thickness at which the growth rate (υgrowth) equals the dissolution rate (υdiss). An increase or decrease in VAC modifies the values of υgrowth and υdiss until a new steady-state thickness, and new coloration, is achieved.

A biosensor for arsenite has been developed using molybdenum-containing arsenite oxidase, prepared from the chemolithoautotroph NT-26 that oxidizes arsenite to arsenate. The enzyme was galvanostatically deposited for 10 min at 10 microA onto the active surface of a multiwalled carbon nanotube modified glassy carbon electrode. The resulting biosensor enabled direct electron transfer, i.e., effecting reduction and then reoxidization of the enzyme without an artificial electron-transfer mediator. Arsenite was detected within 10 s at an applied potential of 0.3 V with linearity up to 500 ppb and a detection limit of 1 ppb. The biosensor exhibited excellent reproducibility, 2% at 95% confidence interval for 12 repeated analyses of 25 ppb arsenite. Copper, a severe interfering species commonly found in groundwater, did not interfere, and the biosensor was applicable for repeated analysis of spiked arsenite in tap water, river water, and a commercial mineral water.

Biosensing and diagnostic platforms with high sensitivity, specificity, and fast response time are based on immobilized biomolecules such as antibodies (Abs), aptamers, enzymes, nucleic acids, receptors, and whole cells for the detection of target analytes. Such sensing biomolecules should be bound to the surface of a signal transducer with a required specific chemical, electrical, or optical property. The biological recognition event generates a quantifiable signal, which is equated to the amount or concentration of the analyte. APTES can be deposited on solid materials, electrode materials, nanomaterials, and nanocomposites under variable conditions of concentration, solvent, temperature, and time. In addition, curing conditions such as air/heat drying might be necessary depending upon the intended application. Pertinent information on the thickness, morphology, and conformation of the APTES layer reported in the literature is often different and conflicting.

Boron doped diamond (BDD) macro- and microelectrodes were modified by electrodeposition of platinum nanoparticles using a multipotential step electrodeposition technique and used for the oxidative determination of arsenite, As(III). The formation of Pt nanoparticles was evident from cyclic voltammetry measurement, whereas AFM and SEM revealed the size and size distribution of deposited Pt nanoparticles. Raman spectroscopy illustrated a correlation between the typical BDD signature and the number of platinum deposition cycles. Linear sweep voltammetry performed with the modified BDD microelectrode outperformed its macrocounterpart and resulted in very low detecting currents with enhanced signal-to-noise ratios. With linearity up to 100 ppb and a detection limit of 0.5 ppb, the electrochemical system was applicable for processing tap and river water samples. Over 150 repetitive runs could be performed, and electrochemical etching of platinum allowed the reuse of the BDD microelectrode. The presence of copper and chloride ions, the two most severe interferents at levels commonly found in groundwater, did not interfere with the assay.

Metal nanoparticles (Pt, Au, or Cu) together with multiwalled and single-walled carbon nanotubes (MWCNT and SWCNT) solubilized in Nafion have been used to form nanocomposites for electrochemical detection of trinitrotoluene (TNT) and several other nitroaromatics. Electrochemical and surface characterization by cyclic voltammetry, AFM, TEM, SEM, and Raman spectroscopy confirmed the presence of metal nanoparticles on CNTs. Among various combinations tested, the most synergistic signal effect was observed for the nanocomposite modified glassy carbon electrode (GC) containing Cu nanoparticles and SWCNT solubilized in Nafion. This combination provided the best sensitivity for detecting TNT and other nitroaromatic compounds. Adsorptive stripping voltammetry for TNT resulted in a detection limit of 1 ppb, with linearity up to 3 orders of magnitude. Selectivity toward the number and position of the nitro groups in different nitroaromatics was very reproducible and distinct. Reproducibility of the TNT signal was within 7% (n = 8) from one electrode preparation to another, and the response signal was stable (+/-3.8% at 95% confidence interval) for 40 repeated analyses with 10 min of preconditioning. The Cu-SWCNT-modified GC electrode was demonstrated for analysis of TNT in tap water, river water, and contaminated soil.

The capabilities of using boron-doped diamond (BDD) thin films as electrode materials for analysis of the 16 US Environmental Protection Agency (EPA) priority polyaromatic hydrocarbons (PAHs) after a liquid chromatographic separation were evaluated. The BDD electrode was able to detect all 16 PAHs with high sensitivity due to the low background current and wide potential window. The method provided detection limits ranging from 12-40 nM (3-10 ppb) and repeatable results over consecutive analysis. Calibration curves were linear up to at least 10 microM for all PAHs. The work shows the promising use of diamond as an amperometric detector in high performance liquid chromatography (HPLC), especially for PAHs and other hydrophobic aromatic compounds.

A flow analysis electrochemical system has been developed, characterized, and optimized for the determination of arsenite (As(III)). Sensitivity was significantly improved by the electrochemical deposition of gold nanoparticles on a dual glassy carbon electrode, which was inserted into a cross-flow thin-layer electrochemical cell. The electrochemical system was linear up to 15 ppb with a detection limit of 0.25 ppb. Gold deposition was evident from cyclic voltammetry measurements, whereas atomic force microscopy and scanning electron microscopy revealed the size and distribution of deposited gold nanoparticles. The size and density of the nanoparticles were related to the gold salt concentration, deposition time, and potential as well as the electrode position. The response to arsenite was directly related to the frequency, increment, and amplitude of the square wave voltammetry as well as the deposition time and potential. Estimated reproducibility was +/-1.1% at 95% confidence interval for 40 repeated analyses of 8 ppb arsenite during continuous analysis. The reproducibility was far superior if the electrochemical reduction of arsenite was performed in nitric acid instead of hydrochloric or sulfuric acid. The electrochemical system was applicable for analysis of spiked arsenic in mineral water containing a significant amount of various ion elements.

Copper (Cu) nanoparticles (4–8 nm in diameter), prepared by using sodium borohydride to reduce copper dodecyl sulfate (Cu(DS)2), were used with single-wall carbon nanotubes (SWCNTs) to fabricate electrochemical sensors. Nafion, a perfluorosulfonated polymer, was able to solubilize SWCNTs and displayed interactions with Cu nanoparticles to form a network, connecting Cu nanoparticles to a glassy carbon (GC) or Cu electrode surface. Cyclic voltammetry confirmed an electrical contact through SWCNTs between Cu nanoparticles and the GC backing whereas TEM micrographs illustrated the deposition of Cu nanoparticles on the carbon nanotubes. The response time and the detection limit (S/N=3) of the sensor for glucose were 10 s and 250 nM, respectively, i.e. a four-fold increase in the sensitivity compared to a bare Cu disk electrode. The response to interferents, such as acetaminophen, ascorbic acid and uric acid was suppressed in the presence of the SWCNT/Cu nanoparticle composite.

A simple procedure has been described for the fabrication of multi-wall carbon nanotube (CNT) based electrochemical sensors. 3-Aminopropyltriethoxysilane (APTES) induced solubilization of CNTs allowed for the modification of electrode surfaces. With glucose oxidase (GOx), a flavin (FAD) containing enzyme as a model system, APTES was used as a solubilizing agent for CNTs as well as an immobilization matrix for GOx to construct a mediatorless biosensor. Our biosensor was able to efficiently monitor direct electroactivity of GOx at the electrode surface. A well-defined glucose response was observed at -0.45?V (vs. Ag/AgCl) whereas relevant physiological levels (0.1?mM) of three common interfering species, uric acid, ascorbic acid, and acetaminophen, resulted in no response. Although CNTs modified by APTES acted as semiconductors to reduce the exposed sensing surface, we reasoned nanoscale ldquodendritesrdquo of CNTs modified by APTES formed a network and projected outwards from the electrode surface and acted like bundled ultra-microelectrodes that allowed access to the active FAD site and facilitated direct electron transfer to the immobilized enzyme. The glucose biosensor prepared using a carbon fiber (11?mum) exhibited picoamperometric current response within 5?s with detection limits of 5-10?muM.

Platinum nanoparticles with a diameter of 2-3 nm were prepared and used in combination with single-wall carbon nanotubes (SWCNTs) for fabricating electrochemical sensors with remarkably improved sensitivity toward hydrogen peroxide. Nafion, a perfluorosulfonated polymer, was used to solubilize SWCNTs and also displayed strong interactions with Pt nanoparticles to form a network that connected Pt nanoparticles to the electrode surface. TEM and AFM micrographs illustrated the deposition of Pt nanoparticles on carbon nanotubes whereas cyclic voltammetry confirmed an electrical contact through SWCNTs between Pt nanoparticles and the glassy carbon (GC) or carbon fiber backing. With glucose oxidase (GOx) as an enzyme model, we constructed a GC or carbon fiber microelectrode-based biosensor that responds even more sensitively to glucose than the GC/GOx electrode modified by Pt nanoparticles or CNTs alone. The response time and detection limit (S/N = 3) of this biosensor was determined to be 3 s and 0.5 microM, respectively.

This paper describes a new strategy for fabricating continuous gold films based on the self-assembly of the gold colloid monolayer on a poly(diallyldimethylammonium chloride)-modified glass slide, followed by electroless plating. Hydroxylamine-mediated reduction was proven as an excellent route to enlargement of immobilized nanoparticles on polymer-coated glass substrates in comparison to formaldehyde-mediated reduction. Au colloidal surface-catalyzed reduction of Au3+ by hydroxylamine exhibited very fast kinetics as monitored and confirmed by UV-vis spectroscopy in real time. The nanoscale morphology of the gold film was dependent on the initial coverage of gold nanoparticles and thermal annealing. Atomic force micrographs further revealed that enlarged particles were neither spherical nor cyclindrical, but highly complex in shape. The gold film thickness and its corresponding surface roughness could be easily controlled by setting the electroless deposition time. X-ray diffraction certified uniformity of deposits with the Au(111) crystallographic structure as the predominant one. No organic contamination during the course of electroless plating was observed as confirmed by both X-ray photoelectron spectroscopy and contact angle measurements. The stable and continuous gold films were used as electrodes for electrochemical experiments.

An improved enzyme-linked immunosorbent (ELISA) assay using one-step antibody immobilization has been developed for the detection of human fetuin A (HFA), a specific biomarker for atherosclerosis and hepatocellular carcinoma. The anti-HFA formed a stable complex with 3-aminopropyltriethoxysilane (APTES) by ionic and hydrophobic interactions. The complex adsorbed on microtiter plates exhibited a detection range of 4.9 pg mL(-1) to 20 ng mL(-1) HFA, with a limit of detection of 7 pg mL(-1). Furthermore, an analytical sensitivity of 10 pg mL(-1) was achieved, representing a 51-fold increase in sensitivity over the commercial sandwich ELISA kit. The results obtained for HFA spiked in diluted human whole blood and plasma showed the same precision as the commercial kit. When stored at 4°C in 0.1 M phosphate-buffered saline (PBS, pH 7.4), the anti-HFA bound microtiter plates displayed no significant decrease in their functional activity after two months. The new ELISA procedure was extended for the detection of C-reactive protein, human albumin and human lipocalin-2 with excellent analytical performance.

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.

Nanocrystalline cellulose (NCC), a rigid rod-like nanoscale material, can be produced from cellulosic biomass in powder, liquid, or gel forms by acid and chemical hydrolysis. Owing to its unique and exceptional physicochemical properties, the incorporation of a small amount of NCC into plastic enhances the mechanical strength of the latter by several orders of magnitudes. Carbohydrate-based NCC poses no serious environmental concerns, providing further impetus for the development and applications of this green and renewable biomaterial to fabricate lightweight and biodegradable composites and aerogels. Surface functionalization of NCC remains the main focus of NCC research to tailor its properties for dispersion in hydrophilic or hydrophobic media. It is of uttermost importance to develop tools and protocols for imaging of NCC in a complex matrix and quantify its reinforcement effect.

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.

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.

Gas diffusion cathodes with electrodeposited nickel (Ni) particles have been developed and tested for hydrogen production in a continuous flow microbial electrolysis cell (MEC). A high catalytic activity of electrodeposited Ni particles in such a MEC was obtained without a proton exchange membrane, i.e. under direct cathode exposure to anodic liquid. Co-electrodeposition of Pt and Ni particles did not improve any further hydrogen production. The maximum hydrogen production rate was 5.4 L/LR/day, corresponding to Ni loads between 0.2 and 0.4 mg cm−2. Continuous MEC operation demonstrated stable hydrogen production for over one month. Owing to the fast hydrogen transport through the cathodic gas diffusion layer, the loss of hydrogen production to methanogenic activity was minimal, generally with less than 5% methane in the off-gas. Overall, gas diffusion cathodes with electrodeposited Ni particles demonstrated excellent stability for hydrogen production compared to expensive Pt cathodes.

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.

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.

The reinforcement effect of carbon nanotubes (CNTs) has been examined as a function of their loading and aspect ratio in poly(vinyl alcohol) (PVA) based hybird fibers. Lignosulfonic acid sodium salt (LSA) was used to disperse CNTs to produce consistently high CNT loaded PVA-LSA-CNT hybrid fibers using an electrospinning process. The elastic modulus of individual fibers was measured using atomic force microscopy. The presence of CNTs significantly increased the average elastic modulus of PVA-LSA-CNT fibers compared to PVA-LSA fibers. The elastic modulus, however, exhibited no fiber diameter dependency. Transmission electron microscopy (TEM) was used to determine the loading and the aspect ratio of CNTs in each hybrid fiber. The CNT loading in PVA-LSA-CNT fibers varied widely due to non-uniform CNT dispersion and displayed no relationship with the elastic modulus. Our results also demonstrated that the average value of CNT aspect ratio significantly affected the elastic modulus of the hybrid fibers. Such a result was in agreement with theoretical prediction in which the stress transfer efficiency in a composite matrix is strongly dependent on the CNT aspect ratio.

An effective and robust electrochemical approach has been developed for selective detection of dopamine in the presence of 3,4-dihydroxyphenylalanine (l-DOPA), ascorbic acid, uric acid and other dopamine metabolites. A 'layer-by-layer' film of tyramine and pyrrole-1-propionic acid (PPA) was formed by subsequent electropolymerization on a boron-doped diamond (BDD) electrode with an overall thickness of approximately 33 nm as estimated by AFM. The formation of the electropolymerized homogeneous film was also confirmed by SEM and Raman spectroscopy. The modified BDD electrode exhibited rapid response to dopamine within 6 s and a detection limit of 50 nM with excellent reproducibility. The stable electropolymerized film was capable of excluding electroactive interference from 20 microM l-DOPA, 20 microM 3,4-dihydroxyphenylacetic acid (DOPAC), and ascorbic and uric acids at normal physiological conditions (100 microM each). The modified electrode could be used for several repeated analyses of dopamine at 5 microM, without noticeable surface fouling. A plausible mechanism for permselectivity was suggested and supported by pertinent experimental data.

Rapid detection of microorganisms is highly desirable. A procedure has been developed based on interactions between gold nanoparticles and proteins of microorganisms (Escherichia coli, Rhodococcus rhodochrous, and Candida sp.) followed by scanning electron microscopy (SEM). The nanoparticle-cell interaction was confirmed by ultraviolet resonance Raman spectroscopy (UVRS) in the SEM focus. Cell suspensions in a buffer were interacted with gold nanoparticles (

Biosensors can be considered as a most plausible and exciting application area for nanobiotechnology. The recent bloom of nanofabrication technology and biofunctionalization methods of carbon nanotubes (CNTs) has stimulated significant research interest to develop CNT-based biosensors for monitoring biorecognition events and biocatalytic processes. The unique properties of CNTs, rolled-up sheets of carbon atoms with a diameter less than 1 nm, offer excellent prospects for interfacing biological recognition events with electronic signal transduction. CNT-based biosensors could be developed to sense only a few or even a single molecule of a chemical or biological agent. Both hydrogen peroxide and NADH, two by-products of over 300 oxidoreductases, are efficiently oxidized by CNT-modified electrodes at significantly lower potentials with minimal surface fouling. This appealing feature enables the development of useful biosensors for diversified applications. Aligned CNT “forests” can act as molecular wires to allow efficient electron transfer between the detecting electrode and the redox centers of enzymes to fabricate reagentless biosensors. Electrochemical sensing for DNA can greatly benefit from the use of CNT based platforms since guanine, one of the four bases, can be detected with significantly enhanced sensitivity. CNTs fluoresce, or emit light after absorbing light, in the near infrared region and retain their ability to fluoresce over time. This feature will allow CNT-based sensors to transmit information from inside the body. The combination of micro/nanofabrication and chemical functionalization, particularly nanoelectrode assembly interfaced with biomolecules, is expected to pave the way to fabricate improved biosensors for proteins, chemicals, and pathogens. However, several technical challenges need to be overcome to tightly integrate CNT-based platforms with sampling, fluidic handling, separation, and other detection principles. The biosensing platform must function well in a real-world sample environment where selectivity, sensitivity, detection limits, and ruggedness are the four prerequisites. Carbon nanotube patents look more controversial in electronics but are less problematical in energy, health care, and cosmetics. The use of CNTs in biosensing looks very promising as reflected by some significant patents in this area and other research and developement endeavors.

Platinum nanoparticles were electrodeposited by a multi-potential step technique onto a multi-walled carbon nanotube (MWCNT) film pre-casted on a glassy carbon (GC) or boron-doped diamond (BDD) electrode. The MWCNT network consisted of Pt nanoparticles with an average diameter of 120 nm after an optimization of 36 deposition cycles. The resulting electrochemical sensors were capable of detecting hydrogen peroxide as low as 25 nM. Five different enzymes: glucose, lactate, glutamate, amino acid and xanthine oxidases, respectively, were deposited by a constant current technique for 5–10 min to form a stable and active biolayer for the analysis of their corresponding analytes. The glucose oxidase-based biosensor was linear up to 10 mM glucose with a detection limit of 250 nM and a response time of 5 s. Similar response times and detection limits were observed with glutamate, lactate, and amino acid oxidase despite the fact that the linear ranges were noticeably narrower. The mechanism of deposition was attributed to the decrease of local pH, created by oxygen evolution and effected enzyme precipitation.

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. Graphical abstract image for this article

This communication reveals new and unique optical properties with respect to enhanced fluorescence of gold nanorods as they elongate; a novel strategy for DNA hybridization studies based on monitoring the fluorescence intensity of gold nanorods has been demonstrated.

Pt-Zn porphyrin nanocomposites have been synthesized using zinc porphyrin and dihydrogen hexachloroplatinate in the presence of light and ascorbic acid. TEM and AFM imaging revealed that Pt nanoparticles with an average diameter of approximately 3.5 nm were embedded within the Zn porphyrin matrix. The glassy carbon electrode was modified with Nafion-stabilized Pt-Zn porphyrin nanocomposites and used for dehalogenation of carbon tetrachloride, chloroform, pentachlorophenol, chlorobenzene, and hexachlorobenzene as five test models. The Pt-Zn porphyrin nanocomposite-modified electrode exhibited catalytic activity for the reduction of organohalides at -1.0 V versus Ag/AgCl. Raman signatures confirmed the dehalogenation of chlorobenzene by the nanocomposite-modified electrode. The above two aliphatic and three aromatic organohalides had detection limits of 0.5 microM with linearity up to 8 microM. The modified electrode was good for at least 80 repeated measurements of 4 microM chlorobenzene with a storage stability of 1 month at room temperature. The deactivation of the electrode activity was associated with the loss of platinum nanoparticles from the nanocomposite structure.