Jonathan D. Adams

Focused electron beam induced deposition: A perspective

Summary Background: Focused electron beam induced deposition (FEBID) is a direct-writing technique with nanometer resolution, which has received strongly increasing attention within the last decade. In FEBID a precursor previously adsorbed on a substrate surface is dissociated in the focus of an electron beam. After 20 years of continuous development FEBID has reached a stage at which this technique is now particularly attractive for several areas in both, basic and applied research. The present topical review addresses selected examples that highlight this development in the areas of charge-transport regimes in nanogranular metals close to an insulator-to-metal transition, the use of these materials for strain- and magnetic-field sensing, and the prospect of extending FEBID to multicomponent systems, such as binary alloys and intermetallic compounds with cooperative ground states. Results: After a brief introduction to the technique, recent work concerning FEBID of Pt–Si alloys and (hard-magnetic) Co–Pt intermetallic compounds on the nanometer scale is reviewed. The growth process in the presence of two precursors, whose flux is independently controlled, is analyzed within a continuum model of FEBID that employs rate equations. Predictions are made for the tunability of the composition of the Co–Pt system by simply changing the dwell time of the electron beam during the writing process. The charge-transport regimes of nanogranular metals are reviewed next with a focus on recent theoretical advancements in the field. As a case study the transport properties of Pt–C nanogranular FEBID structures are discussed. It is shown that by means of a post-growth electron-irradiation treatment the electronic intergrain-coupling strength can be continuously tuned over a wide range. This provides unique access to the transport properties of this material close to the insulator-to-metal transition. In the last part of the review, recent developments in mechanical strain-sensing and the detection of small, inhomogeneous magnetic fields by employing nanogranular FEBID structures are highlighted. Conclusion: FEBID has now reached a state of maturity that allows a shift of the focus towards the development of new application fields, be it in basic research or applied. This is shown for selected examples in the present review. At the same time, when seen from a broader perspective, FEBID still has to live up to the original idea of providing a tool for electron-controlled chemistry on the nanometer scale. This has to be understood in the sense that, by providing a suitable environment during the FEBID process, the outcome of the electron-induced reactions can be steered in a controlled way towards yielding the desired composition of the products. The development of a FEBID-specialized surface chemistry is mostly still in its infancy. Next to application development, it is this aspect that will likely be a guiding light for the future development of the field of focused electron beam induced deposition.

The bone diagnostic instrument II: Indentation distance increase

The bone diagnostic instrument (BDI) is being developed with the long-term goal of providing a way for researchers and clinicians to measure bone material properties of human bone in vivo. Such measurements could contribute to the overall assessment of bone fragility in the future. Here, we describe an improved BDI, the Osteoprobe IItrade mark. In the Osteoprobe IItrade mark, the probe assembly, which is designed to penetrate soft tissue, consists of a reference probe (a 22 gauge hypodermic needle) and a test probe (a small diameter, sharpened rod) which slides through the inside of the reference probe. The probe assembly is inserted through the skin to rest on the bone. The distance that the test probe is indented into the bone can be measured relative to the position of the reference probe. At this stage of development, the indentation distance increase (IDI) with repeated cycling to a fixed force appears to best distinguish bone that is more easily fractured from bone that is less easily fractured. Specifically, in three model systems, in which previous mechanical testing and/or tests reported here found degraded mechanical properties such as toughness and postyield strain, the BDI found increased IDI. However, it must be emphasized that, at this time, neither the IDI nor any other mechanical measurement by any technique has been shown clinically to correlate with fracture risk. Further, we do not yet understand the mechanism responsible for determining IDI beyond noting that it is a measure of the continuing damage that results from repeated loading. As such, it is more a measure of plasticity than elasticity in the bone.

Detection of proteins in serum by micromagnetic aptamer PCR (MAP) technology.

The effective diagnosis and prognosis of many diseases depends on the ability to quantitatively measure protein biomarkers from clinical samples at low concentrations. For example, fluctuations in serum concentrations of cytokines, such as platelet-derived growth factor-BB (PDGF-BB), can serve as indicators of tumor angiogenesis, whereas levels of virus-related proteins such as hemagglutinin can indicate progression of an infection. Accurate detection of diagnostic biomarkers in blood is often challenging because of its complex composition comprising thousands of proteins with concentrations ranging over 12 orders of magnitude. 5] Albumin, for example, constitutes approximately half of the total serum protein (30–50 mgmL ), while many important disease-related biomarkers exist at concentrations as low as 1 pg mL . 5] Enzyme-linked immunosorbent assay (ELISA) is a standard approach to detect protein biomarkers directly from blood. Unfortunately, this assay can suffer from a lengthy development period for specific antibodies, insufficient sensitivity, limited dynamic range, 8, 9] and long assay times involving multiple washing steps, thereby limiting its usefulness and making it impractical to implement at the point of care. Several groups have developed innovative approaches to improve the sensitivity and dynamic range of ELISAs by combining antibody-based molecular recognition with nucleic acid amplification-based detection, such as proximity ligation, immuno-PCR, and bio-barcode detection. However, because interferents in blood can inhibit many amplification reactions, there is a critical need for universal sample preparation systems that allow amplification-based detection of protein biomarkers from complex samples in a monolithic, disposable, and automated format. Herein, we report the micromagnetic aptamer PCR (MAP) detection system, which integrates high-gradient magnetic field sample preparation in a microfluidic device with aptamer-based real-time PCR readout, to achieve highly sensitive and quantitative detection of protein targets directly from complex samples. As a model, we demonstrate the capability to quantitatively detect the cancer biomarker PDGF-BB over a wide dynamic range (62 fm to 1 nm) in a complex background of serum with clearly discernable and reproducible PCR amplification signals. The detection assay starts with the incubation of a serum sample containing PDGF-BB target protein with magnetic beads coated with capture antibody and anti-PDGF PCR aptamers, which incorporate flanking PCR primer sequences (Figure 1A). As with ELISA, the use of dual-affinity reagents significantly increases the specificity of detection. After the incubation step, the sample was loaded into a micromagnetic separation (MMS) chip, in which magnetically labeled antibody–target–aptamer complexes were trapped by the high local magnetic field gradients generated by microfabricated ferromagnetic structures (MFSs) patterned within the microchannel. Meanwhile, nontarget serum proteins, unused reagents, and PCR contaminants were continuously washed out during separation (Figure 1B). After washing the trapped beads, the external magnetic field was removed, which demagnetized the MFSs thereby allowing magnetic target complexes to be eluted with phosphate-buffered saline containing 0.25 mm MgCl2 (PBSM; Figure 1C). The entire separation and purification process (trapping, washing, and bead release) required about 30 min. One microliter of collected eluent was directly subjected to real-time PCR analysis, which yielded a signal proportional to the concentration of target protein in the serum sample (Figure 1D). Note that real-time PCR calibration curves with and without magnetic beads verified that the presence of 1 10 antibodycoated magnetic beads per PCR reaction volume did not [*] S. S. Oh, Dr. Y. Xiao, Prof. H. T. Soh Materials Department, Department of Mechanical Engineering University of California, Santa Barbara Santa Barbara, CA 93106 (USA) E-mail: yixiao@physics.ucsb.edu tsoh@engr.ucsb.edu Dr. A. Csordas Institute for Collaborative Biotechnologies University of California, Santa Barbara (USA) Dr. A. E. Gerdon Department of Chemistry, Emmanuel College, Boston (USA)

Acoustophoretic Synchronization of Mammalian Cells in Microchannels

We report the first use of ultrasonic standing waves to achieve cell cycle phase synchronization in mammalian cells in a high-throughput and reagent-free manner. The acoustophoretic cell synchronization (ACS) device utilizes volume-dependent acoustic radiation force within a microchannel to selectively purify target cells of desired phase from an asynchronous mixture based on cell cycle-dependent fluctuations in size. We show that ultrasonic separation allows for gentle, scalable, and label-free synchronization with high G(1) phase synchrony (approximately 84%) and throughput (3 x 10(6) cells/h per microchannel).

Integrated acoustic and magnetic separation in microfluidic channels

With a growing number of cell-based biotechnological applications, there is a need for particle separation systems capable of multiparameter separations at high purity and throughput, beyond what is presently offered by traditional methods including fluorescence activated cell sorting and column-based magnetic separation. Toward this aim, we report on the integration of microfluidic acoustic and magnetic separation in a monolithic device for multiparameter particle separation. Using our device, we demonstrate high-purity separation of a multicomponent particle mixture at a throughput of up to 10(8) particleshr.

The role of calcium and magnesium in the concrete tubes of the sandcastle worm

SUMMARY Sandcastle worms Phragmatopoma californica build mound-like reefs by sticking together large numbers of sand grains with cement secreted from the building organ. The cement consists of protein plus substantial amounts of calcium and magnesium, which are not invested in any mineral form. This study examined the effect of calcium and magnesium depletion on the structural and mechanical properties of the cement. Divalent ion removal by chelating with EDTA led to a partial collapse of cement architecture and cement dislodgement from silica surfaces. Mechanical properties examined were sand grain pull-out force, tube resistance to compression and cement adhesive force. EDTA treatment reduced sand grain pull-out forces by 60% and tube compressive strength by 50% relative to controls. EDTA lowered both the maximal adhesive force and energy dissipation of cement by up to an order of magnitude. The adhesiveness of calcium- and magnesium-depleted cement could not be restored by re-exposure to the ions. The results suggest that divalent ions play a complex and multifunctional role in maintaining the structure and stickiness of Phragmatopoma cement.

Effect of Ca2+ ions on the adhesion and mechanical properties of adsorbed layers of human osteopontin.

Using an atomic force microscope and a surface force apparatus, we measured the surface coverage, adhesion, and mechanical properties of layers of osteopontin (OPN), a phosphoprotein of the human bones, adsorbed on mica. OPN is believed to connect mineralized collagen fibrils of the bone in a matrix that dissipates energy, reducing the risk of fractures. Atomic force microscopy normal force measurements showed large adhesion and energy dissipation upon retraction of the tip, which were due to the breaking of the many OPN-OPN and OPN-mica bonds formed during tip-sample contact. The dissipated energy increased in the presence of Ca(2+) ions due to the formation of additional OPN-OPN and OPN-mica salt bridges between negative charges. The forces measured by surface force apparatus between two macroscopic mica surfaces were mainly repulsive and became hysteretic only in the presence of Ca(2+): adsorbed layers underwent an irreversible compaction during compression due to the formation of long-lived calcium salt bridges. This provides an energy storage mechanism, which is complementary to energy dissipation and may be equally relevant to bone recovery after yield. The prevalence of one mechanism or the other appears to depend on the confinement geometry, adsorption protocol, and loading-unloading rates.

High-throughput, temperature-controlled microchannel acoustophoresis device made with rapid prototyping

We report a temperature-controlled microfluidic acoustophoresis device capable of separating particles and transferring blood cells from undiluted whole human blood at a volume throughput greater than 1 L h −1 . The device is fabricated from glass substrates and polymer sheets in microscope-slide format using low-cost, rapid-prototyping techniques. This high-throughput acoustophoresis chip (HTAC) utilizes a temperature-stabilized, standing ultrasonic wave, which imposes differential acoustic radiation forces that can separate particles according to size, density and compressibility. The device proved capable of separating a mixture of 10- and 2-μm-diameter polystyrene beads with a sorting efficiency of 0.8 at a flow rate of 1 Lh −1 . As a first step toward biological applications, the HTAC was also tested in processing whole human blood and proved capable of transferring blood cells from undiluted whole human blood with an efficiency of 0.95 at 1 Lh −1 and 0.82 at 2 Lh −1 . (Some figures may appear in colour only in the online journal)

Tunable acoustophoretic band-pass particle sorter.

Acoustophoretic separation in microchannels offers a promising avenue for high-throughput, label-free, cell and particle separation for many applications. However, previous acoustophoretic separation approaches have been limited to a single size separation threshold, analogous to a binary filter, (i.e., high-pass or low-pass). Here, we describe a tunable acoustophoretic separation architecture capable of sorting cells and particles based on a range of sizes, analogous to a band-pass filter. The device is capable of sorting an arbitrary range of particle sizes between 3 and 10 mum in diameter with high efficiency (transfer fraction=0.98+/-0.02) at a throughput of approximately 10(8) particleshmicrochannel.

Molecular energy dissipation in nanoscale networks of Dentin Matrix Protein 1 is strongly dependent on ion valence

The fracture resistance of biomineralized tissues such as bone, dentin, and abalone is greatly enhanced through the nanoscale interactions of stiff inorganic mineral components with soft organic adhesive components. A proper understanding of the interactions that occur within the organic component, and between the organic and inorganic components, is therefore critical for a complete understanding of the mechanics of these tissues. In this paper, we use Atomic Force Microscope (AFM) force spectroscopy and dynamic force spectroscopy to explore the effect of ionic interactions within a nanoscale system consisting of networks of Dentin Matrix Protein 1 (DMP1) (a component of both bone and dentin organic matrix), a mica surface, and an AFM tip. We find that DMP1 is capable of dissipating large amounts of energy through an ion-mediated mechanism, and that the effectiveness increases with increasing ion valence.