Scalable economic extracellular synthesis of CdS nanostructured particles by a non-pathogenic thermophile.

We report microbially facilitated synthesis of cadmium sulfide (CdS) nanostructured particles (NP) using anaerobic, metal-reducing Thermoanaerobacter sp. The extracellular CdS crystallites were <10 nm in size with yields of ~3 g/L of growth medium/month with demonstrated reproducibility and scalability up to 24 L. During synthesis, Thermoanaerobacter cultures reduced thiosulfate and sulfite salts to H2S, which reacted with Cd²âº cations to produce thermodynamically favored NP in a single step at 65 °C with catalytic nucleation on the cell surfaces. Photoluminescence (PL) analysis of dry CdS NP revealed an exciton-dominated PL peak at 440 nm, having a narrow full width at half maximum of 10 nm. A PL spectrum of CdS NP produced by dissimilatory sulfur reducing bacteria was dominated by features associated with radiative exciton relaxation at the surface. High reproducibility of CdS NP PL features important for scale-up conditions was confirmed from test tubes to 24 L batches at a small fraction of the manufacturing cost associated with conventional inorganic NP production processes.

Crystallite sizes and lattice parameters of nano-biomagnetite particles.

Average crystallite sizes of microbially synthesized pure, metal-, and lanthanide-substituted magnetite (bio-magnetite) were determined for a variety of incubation times and temperatures, substitutional elements and amounts, bacterial species, and precursor types. The intriguing difference between nanoparticle bio-magnetite and chemically synthesized magnetite (chem-magnetite) was that powder X-ray diffraction (XRD) data showed that the bio-magnetite exhibited slightly smaller lattice parameters, however, Raman Spectroscopy exhibited no difference in Fe-O bonding. These results indicate that bio-magnetite likely exhibits a more compact crystal structure with less uncoordinated iron on the surface suppressing negative pressure effects. The bio-magnetite with decreased lattice parameters could have potential technological advantages over current commercial chemically synthesized magnetites.

Large-scale production of magnetic nanoparticles using bacterial fermentation.

Production of both nano-sized particles of crystalline pure phase magnetite and magnetite substituted with Co, Ni, Cr, Mn, Zn or the rare earths for some of the Fe has been demonstrated using microbial processes. This microbial production of magnetic nanoparticles can be achieved in large quantities and at low cost. In these experiments, over 1 kg (wet weight) of Zn-substituted magnetite (nominal composition of Zn(0.6)Fe(2.4)O4) was recovered from 30 l fermentations. Transmission electron microscopy (TEM) was used to confirm that the extracellular magnetites exhibited good mono-dispersity. TEM results also showed a highly reproducible particle size and corroborated average crystallite size (ACS) of 13.1 ± 0.8 nm determined through X-ray diffraction (N = 7) at a 99% confidence level. Based on scale-up experiments performed using a 35-l reactor, the increase in ACS reproducibility may be attributed to a combination of factors including an increase of electron donor input, availability of divalent substitution metal ions and fewer ferrous ions in the case of substituted magnetite, and increased reactor volume overcoming differences in each batch. Commercial nanometer sized magnetite (25-50 nm) may cost $500/kg. However, microbial processes are potentially capable of producing 5-90 nm pure or substituted magnetites at a fraction of the cost of traditional chemical synthesis. While there are numerous approaches for the synthesis of nanoparticles, bacterial fermentation of magnetite or metal-substituted magnetite may represent an advantageous manufacturing technology with respect to yield, reproducibility and scalable synthesis with low costs at low energy input.

Microbial formation of lanthanide-substituted magnetites by Thermoanaerobacter sp. TOR-39.

The potentially toxic effects of soluble lanthanide (L) ions, although microbially induced mineralization can facilitate the formation of tractable materials, has been one factor preventing the more widespread use of L-ions in biotechnology. Here, we propose a new mixed-L precursor method as compared to the traditional direct addition technique. L (Nd, Gd, Tb, Ho and Er)-substituted magnetites, L( y )Fe(3 - y )O(4) were microbially produced using L-mixed precursors, L( x )Fe(1 - x )OOH, where x = 0.01-0.2. By combining lanthanides into the akaganeite precursor phase, we were able to mitigate some of the toxicity, enabling the microbial formation of L-substituted magnetites using a metal reducing bacterium, Thermoanaerobacter sp. TOR-39. The employment of L-mixed precursors enabled the microbial formation of L-substituted magnetite, nominal composition up to L(0.06)Fe(2.94)O(4), with at least tenfold higher L-concentration than could be obtained when the lanthanides were added as soluble salts. This mixed-precursor method can be used to extend the application of microbially produced L-substituted magnetite, while also mitigating their toxicity.

Force reflecting teleoperation with adaptive impedance control.

Experimentation and a survey of the literature clearly show that contact stability in a force reflecting teleoperation system requires high levels of damping on the master robot. However, excessive damping increases the energy required by an operator for commanding motion. The objective of this paper is to describe a new force reflecting teleoperation methodology that reduces operator energy requirements without sacrificing stability. We begin by describing a new approach to modeling and identifying the remote environment of the teleoperation system. We combine a conventional multi-input, multi-output recursive least squares (MIMO-RLS) system identification, identifying in real-time the remote environment impedance, with a discretized representation of the remote environment. This methodology generates a time-varying, position-dependent representation of the remote environment dynamics. Next, we adapt the target impedance of the master robot with respect to the dynamic model of the remote environment. The environment estimation and impedance adaptation are executed simultaneously and in real time. We demonstrate, through experimentation, that this approach significantly reduces the energy required by an operator to execute remote tasks while simultaneously providing sufficient damping to ensure contact stability.

A magnetocaloric pump for microfluidic applications.

A magnetocaloric pump provides a simple means of pumping fluid using only external thermal and magnetic fields. The principle, which can be traced back to the early work of Rosensweig, is straightforward. Magnetic materials tend to lose their magnetization as the temperature approaches the material's Curie point. Exposing a column of magnetic fluid to a uniform magnetic field coincident with a temperature gradient produces a pressure gradient in the magnetic fluid. As the fluid heats up, it loses its attraction to the magnetic field and is displaced by cooler fluid. The impact of such a phenomenon is obvious: fluid propulsion with no moving mechanical parts. Until recently, limitations in the magnetic and thermal properties of conventional materials severely limited practical operating pressure gradients. However, recent advancements in the design of metal substituted magnetite enable fine control over both the magnetic and thermal properties of magnetic nanoparticles, a key element in colloidal-based magnetic fluids (ferrofluids). This paper begins with a basic description of the process and previous limitations due to material properties. This is followed by a review of existing methods of synthesizing magnetic nanoparticles as well as an introduction to a new approach based on thermophilic metal-reducing bacteria. We compare two compounds and show, experimentally, significant variation in specific magnetic and thermal properties. We develop the constitutive thermal, magnetic, and fluid dynamic equations associated with a magnetocaloric pump and validate our finite-element model with a series of experiments. Preliminary results show a good match between the model and experiment as well as approximately an order of magnitude increase in the fluid flow rate over conventional magnetite-based ferrofluids operating below 80 degrees C. Finally, as a practical demonstration, we describe a novel application of this technology: pumping fluids at the "lab-on-a-chip" microfluidic scale.