Freestanding high-aspect-ratio gold masks for low-energy, phase-based x-ray microscopy.

High-resolution, x-ray phase contrast microscopy, a key technique with promising potential in biomedical imaging and diagnostics, is based on narrow-slit high-aspect-ratio gold gratings. We present the development, fabrication details, and experimental testing of the freestanding 10µm thick gold membrane masks with an array of 0.9-1.5µm void slit apertures for a novel low-energy x-ray microscope. The overall mask size is 4 mm × 4 mm, with a grating pitch of 7.5µm, 6.0-6.6µm wide gold bars are supported by 3µm wide crosslinks at 400µm intervals. The fabrication process is based on gold electroplating into a silicon mold coated with various thin films to form a voltage barrier, plating base, and sacrificial layer, followed by the mold removal to obtain the freestanding gold membrane with void slit apertures. We discuss key aspects for the materials and processes, including gold structures homogeneity, residual stresses, and prevention of collapsing of the grid elements. We further demonstrate the possibility to obtain high-resolution, high contrast 2D images of biological samples using an incoherent, rotating anode x-ray tube.

Brain-Implantable Multifunctional Probe for Simultaneous Detection of Glutamate and GABA Neurotransmitters.

Glutamate (GLU) and gamma-aminobutyric acid (GABA) are neurotransmitters (NTs) with an essential role in signal transmission in the brain. Brain disorders, such as epilepsy, Alzheimer's and Parkinson's diseases, and traumatic brain injury can be linked to imbalances in the GLU-GABA homeostasis that occurs in sub-second to seconds time frames. Current measurement techniques can detect these two NT concentrations simultaneously only in vitro. The present work reports on the fabrication of a silicon multifunctional biosensor microarray probe for sub-second simultaneous GLU-GABA detection in real-time, with excellent analyte sensitivity and selectivity and in vivo capabilities. The novel Si probes feature four surface-functionalized platinum ultramicroelectrodes (UMEs) for simultaneous amperometric detection of GLU and GABA with a sentinel, and a built-in microfluidic channel for the introduction of neurochemicals in the proximity of the UMEs. The microchannel also allows functioning of an On-Demand In-situ Calibrator that runs in-situ biosensor calibration. The probe exhibited excellent robustness at insertion in agarose-gel brain-tissue-mimicking test, and remarkably high hydrogen peroxide sensitivity (a by-product of GLU-GABA enzyme biosensor) with values on the order of 5000 nA µM -1 cm -2 and maximum sensitivities of 204±15 nA µM -1 cm -2 and 37±7 nA µM -1 cm -2 for GLU and GABA, respectively. Furthermore, the limit of detection of the biosensors reached as low as 7 nM, 165 nM and 750 nM for H 2 O 2, GLU and GABA, respectively and a temporal resolution of hundreds of milliseconds during in vivo studies using freely moving rats.

Approaching the Strain-Free Limit in Ultrathin Nanomechanical Resonators.

Ultrathin mechanical structures are ideal building platforms to pursue the ultimate limit of nanomechanical resonators for applications in sensing, signal processing, and quantum physics. Unfortunately, as the thickness of the vibrating structures is reduced, the built-in strain of the structural materials plays an increased role in determining the mechanical performance of the devices. As a consequence, it is very challenging to fabricate resonators working in the modulus-dominant regime, where their dynamic behavior is exclusively determined by the device geometry. In this Letter, we report ultrathin doubly clamped nanomechanical resonators with aspect ratios as large as L/t ∼5000 and working in the modulus-dominant regime. We observed room temperature thermomechanically induced motion of multiple vibration modes with resonant frequencies closely matching the predicted values of Euler-Bernoulli beam theory under an axial strain of 6.3 × 10-8. The low strain of the devices enables a record frequency tuning ratio of more than 50 times. These results illustrate a new strategy for the quantitative design of nanomechanical resonators with unprecedented performance.

Nonlinear Mode Coupling and One-to-One Internal Resonances in a Monolayer WS2 Nanoresonator.

Nanomechanical resonators make exquisite force sensors due to their small footprint, low dissipation, and high frequencies. Because the lowest resolvable force is limited by ambient thermal noise, resonators are either operated at cryogenic temperatures or coupled to a high-finesse optical or microwave cavity to reach sub aN Hz-1/2 sensitivity. Here, we show that operating a monolayer WS2 nanoresonator in the strongly nonlinear regime can lead to comparable force sensitivities at room temperature. Cavity interferometry was used to transduce the nonlinear response of the nanoresonator, which was characterized by multiple pairs of 1:1 internal resonance. Some of the modes exhibited exotic line shapes due to the appearance of Hopf bifurcations, where the bifurcation frequency varied linearly with the driving force and forms the basis of the advanced sensing modality. The modality is less sensitive to the measurement bandwidth, limited only by the intrinsic frequency fluctuations, and therefore, advantageous in the detection of weak incoherent forces.

Ultrananocrystalline Diamond Integration with Pyrolytic Carbon Components of Mechanical Heart Valves.

In this report, an idea of integrating ultrananocrystalline diamond (UNCD) with pyrolytic carbon (PyC) -based mechanical heart valves, has been demonstrated. The report addresses the strategies to avoid graphitization and film delamination during the diamond coating. Raman and scratch tests showed that a UNCD film with high purity could adhere to the PyC substrate strongly. A thrombin generation study demonstrated an excellent biocompatibility of UNCD towards fresh human platelets. These results suggest that UNCD could be a good candidate of surface material for next generation heart valves and other implantable devices.

Diamond coated artificial cardiovascular devices.

Ultrananocrystalline diamond (UNCD), an extremely smooth, low cost diamond coating was successfully developed herein for antithrombogenic application which requires high biocompatibility, low wear, low friction, and chemical inertness. The substrate materials utilized in the Jarvik 2000 ventricular assist device (VAD), silicon carbide and titanium alloy, provide an excellent substrate match for UNCD integration. The paper addresses the development of medical-quality UNCD films to significantly improve the knowledge base regarding the defect mechanisms of UNCD films, to reduce or eliminate known wear-inducing imperfections in the film, and to thoroughly characterize and test the films as well as assembled UNCD-coated VADs. After the defect reduction and seeding experiments to improve film adhesion and coating quality, the best candidate deposition method has been down-selected for coating and assembly of VAD parts from Jarvik Heart. The coated and assembled devices have been tested with mechanical and blood-simulating fluid hydrodynamic testing at Jarvik Heart for full verification of the new coating technology. UNCD interface takes advantage of combining unmatched durability and antithrombogenicity.

Ultrananocrystalline diamond tip integrated onto a heated atomic force microscope cantilever.

We report a wear-resistant ultrananocrystalline (UNCD) diamond tip integrated onto a heated atomic force microscope (AFM) cantilever and UNCD tips integrated into arrays of heated AFM cantilevers. The UNCD tips are batch-fabricated and have apex radii of approximately 10 nm and heights up to 7 µm. The solid-state heater can reach temperatures above 600 °C and is also a resistive temperature sensor. The tips were shown to be wear resistant throughout 1.2 m of scanning on a single-crystal silicon grating at a force of 200 nN and a speed of 10 µm s(-1). Under the same conditions, a silicon tip was completely blunted. We demonstrate the use of these heated cantilevers for thermal imaging in both contact mode and intermittent contact mode, with a vertical imaging resolution of 1.9 nm. The potential application to nanolithography was also demonstrated, as the tip wrote hundreds of polyethylene nanostructures.

Brain-Implantable Multifunctional Probe for Simultaneous Detection of Glutamate and GABA Neurotransmitters: Optimization and In Vivo Studies.

Imbalances in levels of glutamate (GLU) and gamma-aminobutyric acid (GABA) and their sub-second signaling dynamics occur in several brain disorders including traumatic brain injury, epilepsy, and Alzheimer's disease. The present work reports on the optimization and in vivo testing of a silicon (Si) multifunctional biosensor probe for sub-second simultaneous real-time detection of GLU and GABA. The Si probe features four surface-functionalized platinum ultramicroelectrodes (UMEs) for detection of GLU and GABA, a sentinel site, and integrated microfluidics for in-situ calibration. Optimal enzyme concentrations, size-exclusion phenylenediamine layer and micro spotting conditions were systematically investigated. The measured GLU sensitivity for the GLU and GABA sites were as high as 219 ± 8 nA µM-1 cm-2 (n = 3). The measured GABA sensitivity was as high as 10 ± 1 nA µM-1 cm-2 (n = 3). Baseline recordings (n = 18) in live rats demonstrated a useful probe life of at least 11 days with GLU and GABA concentrations changing at the levels of 100's and 1000's of µM and with expected periodic bursts or fluctuations during walking, teeth grinding and other activities and with a clear difference in the peak amplitude of the sensor fluctuations between rest (low) and activity (higher), or when the rat was surprised (a reaction with no movement). Importantly, the probe could improve methods for large-scale monitoring of neurochemical activity and network function in disease and injury, in live rodent brain.

Nanofountain-probe-based high-resolution patterning and single-cell injection of functionalized nanodiamonds.

Nanodiamonds are rapidly emerging as promising carriers for next-generation therapeutics and drug delivery. However, developing future nanoscale devices and arrays that harness these nanoparticles will require unrealized spatial control. Furthermore, single-cell in vitro transfection methods lack an instrument that simultaneously offers the advantages of having nanoscale dimensions and control and continuous delivery via microfluidic components. To address this, two modes of controlled delivery of functionalized diamond nanoparticles are demonstrated using a broadly applicable nanofountain probe, a tool for direct-write nanopatterning with sub-100-nm resolution and direct in vitro single-cell injection. This study demonstrates the versatility of the nanofountain probe as a tool for high-fidelity delivery of functionalized nanodiamonds and other agents in nanomanufacturing and single-cell biological studies. These initial demonstrations of controlled delivery open the door to future studies examining the nanofountain probe's potential in delivering specific doses of DNA, viruses, and other therapeutically relevant biomolecules.

Novel ultrananocrystalline diamond probes for high-resolution low-wear nanolithographic techniques.

A hard, low-wear probe for contact-mode writing techniques, such as dip-pen nanolithography (DPN), was fabricated using ultrananocrystalline diamond (UNCD). Molding within anisotropically etched and oxidized pyramidal pits in silicon was used to obtain diamond tips with radii down to 30 nm through growth of UNCD films followed by selective etching of the silicon template substrate. The probes were monolithically integrated with diamond cantilevers and subsequently integrated into a chip body obtained by metal electroforming. The probes were characterized in terms of their mechanical properties, wear, and atomic force microscopy imaging capabilities. The developed probes performed exceptionally well in DPN molecular writing/imaging mode. Furthermore, the integration of UNCD films with appropriate substrates and the use of directed microfabrication techniques are particularly suitable for fabrication of one- and two-dimensional arrays of probes that can be used for massive parallel fabrication of nanostructures by the DPN method.

A quantitative study of detection mechanism of a label-free impedance biosensor using ultrananocrystalline diamond microelectrode array.

It is well recognized that label-free biosensors are the only class of sensors that can rapidly detect antigens in real-time and provide remote environmental monitoring and point-of-care diagnosis that is low-cost, specific, and sensitive. Electrical impedance spectroscopy (EIS) based label-free biosensors have been used to detect a wide variety of antigens including bacteria, viruses, DNA, and proteins due to the simplicity of their detection technique. However, their commercial development has been hindered due to difficulty in interpreting the change in impedance upon antigen binding and poor signal reproducibility as a result of surface fouling and non-specific binding. In this study, we develop a circuit model to adequately describe the physical changes at bio functionalized surface and provide an understanding of the detection mechanism based on electron exchange between electrolyte and surface through pores surrounding antibody-antigen. The model was successfully applied to extract quantitative information about the bio surface at different stages of surface functionalization. Further, we demonstrate boron-doped ultrananocrystalline diamond (UNCD) microelectrode array (3 × 3 format, 200 µm diameter) improves signal reproducibility significantly and increases sensitivity by four orders of magnitude. This study marks the first demonstration of UNCD array based biosensor that can reliably detect a model Escherichia coli K12 bacterium using EIS, positioning this technology for rapid adoption in point-of-use applications.

Direct deposition and assembly of gold colloidal particles using a nanofountain probe.

We report the direct delivery and assembly of negatively charged gold colloidal particles atop positively charged amino-terminated silicon oxide surfaces using a nanofountain atomic force microscopy probe. The experimental results and fluid simulations indicate that the flow of nanoparticles is confined to the core tip region of the probe. This leads to the assembly of high-resolution submicron patterns (200 nm) on the substrate with feature sizes dependent on the tip-substrate contact time. A diffusion mechanism for the patterning is proposed and discussed.