[Show abstract][Hide abstract] ABSTRACT: Atomic force microscope infrared spectroscopy (AFM-IR) can perform IR spectroscopic chemical identification with sub-100 nm spatial resolution, but is relatively slow due to its low signal-to-noise ratio (SNR). In AFM-IR, tunable IR laser light is incident upon a sample, which results in a rise in temperature and thermomechanical expansion of the sample. An AFM tip in contact with the sample senses this nanometer-scale photothermal expansion. The tip motion induces cantilever vibrations, which are measured either in terms of the peak-to-peak amplitude of time-domain data or the integrated magnitude of frequency-domain data. Using a continuous Morlet wavelet transform to the cantilever dynamic response, we show that the cantilever dynamics during AFM-IR vary as a function of both time and frequency. Based on the observed cantilever response, we tailor a time-frequency-domain filter to identify the region of highest vibrational energy. This approach can increase the SNR of the AFM cantilever signal, such that the throughput is increased 32-fold compared to state-of-the art procedures. We further demonstrate significant increases in AFM-IR imaging speed and chemical identification of nanometer-scale domains in polymer films.
[Show abstract][Hide abstract] ABSTRACT: Nonlinear mechanical systems promise broadband resonance and instantaneous hysteretic switching that can be used for high sensitivity sensing. However, to introduce nonlinear resonances in widely used microcantilever systems, such as AFM probes, requires driving the cantilever to too large amplitude for any practical applications. We introduce a novel design for a microcantilever with a strong nonlinearity at small cantilever oscillation amplitude arising from the geometrical integration of a single BN nanotube. The dynamics of the system was modeled theoretically and confirmed experimentally. The system, besides providing a practical design of a nonlinear microcantilever-based probe, demonstrates also an effective method of studying the nonlinear damping properties of the attached nanotube. Beyond the typical linear mechanical damping, the nonlinear damping contribution from the attached nanotube was found to be essential for understanding the dynamical behavior of the designed system. Experimental results obtained through laser microvibrometry validated the developed model incorporating the nonlinear damping contribution.
[Show abstract][Hide abstract] ABSTRACT: We measure the infrared spectra of polyethylene nanostructures of height 15 nm using atomic force microscope infrared spectroscopy (AFM-IR), which is about an order of magnitude improvement over state of the art. In AFM-IR, infrared light incident upon a sample induces photothermal expansion, which is measured by an AFM tip. The thermomechanical response of the sample-tip-cantilever system results in cantilever vibrations that vary in time and frequency. A time-frequency domain analysis of the cantilever vibration signal reveals how sample thermomechanical response and cantilever dynamics affect the AFM-IR signal. By appropriately filtering the cantilever vibration signal in both the time domain and the frequency domain, it is possible to measure infrared absorption spectra on polyethylene nanostructures as small as 15 nm.
The Review of scientific instruments 02/2013; 84(2):023709. · 1.52 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The widely used dynamic mode atomic force microscopy (AFM) suffers severe sensitivity degradation and noise increase when operated in liquid. The large hydrodynamic drag between the oscillating AFM cantilever and the surrounding liquid overwhelms the dissipative tip-sample interaction forces that are employed for nanomechanical imaging. In this article, we show that the recently developed Trolling-Mode AFM based on a nanoneedle probe can resolve nanomechanical properties on soft samples in liquid, enabled by the significantly reduced hydrodynamic drag between the cantilever and the liquid. The performance of the method was demonstrated by mapping mechanical properties of the membrane of living HeLa cells.
Journal of Applied Physics 01/2013; 114(13):134313-134313-6. · 2.21 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We explore the use of a nonlinear cantilever system integrating geometric nonlinearity for AFM imaging, in contrast from the traditional linear cantilever system. The intrinsically nonlinear AFM cantilever system exhibits broadband resonance over a bandwidth several times of its linear resonant frequency and possesses an intrinsic stability that virtually eliminates the instability induced by the tip–sample interactions involved in a linear AFM system, thus the artifact of image contrast reversal. The ability to realize broadband operation may extend the application of AFM to spectral analysis of tip–sample interactions across a broad frequency range at the nanoscale.
[Show abstract][Hide abstract] ABSTRACT: Atomic force microscope (AFM) probe with a long and rigid needle tip was fabricated and studied for high Q factor dynamic (tapping mode) AFM imaging of samples submersed in liquid. The extended needle tip over a regular commercially available tapping-mode AFM cantilever was sufficiently long to keep the AFM cantilever from submersed in liquid, which significantly minimized the hydrodynamic damping involved in dynamic AFM imaging of samples in liquid. Dynamic AFM imaging of samples in liquid at an intrinsic Q factor of over 100 and an operational frequency of over 200 kHz was demonstrated. The method has the potential to be extended to acquire viscoelastic material properties and provide truly gentle imaging of soft biological samples in physiological environments.
[Show abstract][Hide abstract] ABSTRACT: a b s t r a c t Micro/nanomechanical resonators often exhibit nonlinear behaviors due to their small size and their ease to realize relatively large amplitude oscillation. In this work, we design a nonlinear micromechanical can-tilever system with intentionally integrated geometric nonlinearity realized through a nanotube cou-pling. Multiple scales analysis was applied to study the nonlinear dynamics which was compared favorably with experimental results. The geometrically positioned nanotube introduced nonlinearity effi-ciently into the otherwise linear micromechanical cantilever oscillator, evident from the acquired responses showing the representative hysteresis loop of a nonlinear dynamic system. It was further shown that a small change in the geometry parameters of the system produced a complete transition of the nonlinear behavior from hardening to softening resonance.
International Journal of Solids and Structures 04/2012; 49:2059-2065. · 2.04 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: A direct-write nanofabrication technique was applied to fabricate high aspect ratio Pt needle electrodes for site specific electrochemistry and electrophysiology. Non-passivated and passivated (with a 10 nm thin insulating film) Pt needles having uniform radii as small as 100 nm and lengths over 30 μm were deposited on the exposed conductive ends of ultramicroelectrodes to form extended needle electrodes. Diffusion limited current and its dependence on the radius of the Pt needle were measured with linear sweep voltammetry. Model fittings validated the function of such needle electrodes for effective microscale electrochemical studies and potentially electrophysiological applications.
[Show abstract][Hide abstract] ABSTRACT: Accessing the interior of live cells with minimal intrusiveness for visualizing, probing, and interrogating biological processes has been the ultimate goal of much of the biological experimental development.
The recent development and use of the biofunctionalized nanoneedles for local and spatially controlled intracellular delivery brings in exciting new opportunities in accessing the interior of living cells. Here we review the technical aspect of this relatively new intracellular delivery method and the related demonstrations and studies and provide our perspectives on the potential wide applications of this new nanotechnology-based tool in the biological field, especially on its use for high-resolution studies of biological processes in living cells.
Different from the traditional micropipette-based needles for intracellular injection, a nanoneedle deploys a sub-100-nm-diameter solid nanowire as a needle to penetrate a cell membrane and to transfer and deliver the biological cargo conjugated onto its surface to the target regions inside a cell. Although the traditional micropipette-based needles can be more efficient in delivery biological cargoes, a nanoneedle-based delivery system offers an efficient introduction of biomolecules into living cells with high spatiotemporal resolution but minimal intrusion and damage. It offers a potential solution to quantitatively address biological processes at the nanoscale.
The nanoneedle-based cell delivery system provides new possibilities for efficient, specific, and precise introduction of biomolecules into living cells for high-resolution studies of biological processes, and it has potential application in addressing broad biological questions. This article is part of a Special Issue entitled Nanotechnologies - Emerging Applications in Biomedicine.
Biochimica et Biophysica Acta 03/2011; 1810(3):330-8. · 4.66 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Recent demonstration of shear piezoelectricity in an isolated collagen fibril, which is the origin of piezoelectricity in bone, necessitates investigation of shear piezoelectric behavior in bone at the nanoscale. Using high resolution lateral piezoresponse force microcopy (PFM), shear piezoelectricity in a cortical bone sample was studied at the nanoscale. Subfibrillar structure of individual collagen fibrils with a periodicity of 60–70 nm were revealed in PFM map, indicating the direct contribution of collagen fibrils to the shear piezoelectricity of bone.
[Show abstract][Hide abstract] ABSTRACT: Continued progress in the electronics industry depends on downsizing, to a few micrometers, the wire bonds required for wiring integrated chips into circuit boards. We developed an electrodeposition method that exploits the thermodynamic stability of a microscale or nanoscale liquid meniscus to "write" pure copper and platinum three-dimensional structures of designed shapes and sizes in an ambient air environment. We demonstrated an automated wire-bonding process that enabled wire diameters of less than 1 micrometer and bond sizes of less than 3 micrometers, with a breakdown current density of more than 10(11) amperes per square meter for the wire bonds. The technology was used to fabricate high-density and high-quality interconnects, as well as complex three-dimensional microscale and even nanoscale metallic structures.
[Show abstract][Hide abstract] ABSTRACT: A nanomechanical resonator incorporating intrinsically geometric nonlinearity and operated in a highly nonlinear regime is modeled and developed. The nanoresonator is capable of extreme broadband resonance, with tunable resonance bandwidth up to many times its natural frequency. Its resonance bandwidth and drop frequency (the upper jump-down frequency) are found to be very sensitive to added mass and energy dissipation due to damping. We demonstrate a prototype nonlinear mechanical nanoresonator integrating a doubly clamped carbon nanotube and show its broadband resonance over tens of MHz (over 3 times its natural resonance frequency) and its sensitivity to femtogram added mass at room temperature.
[Show abstract][Hide abstract] ABSTRACT: Studying biology in living cells is methodologically challenging but highly beneficial. Recent advances in nanobiotechnology offer exciting new opportunities to address this challenge. The nanoneedle technology, as an emerging technology that uses a cell membrane-penetrating nanoneedle to probe and manipulate biological processes in living cells, is expected to play an important role in this endeavor. Here we review the recent development and future direction of the nanoneedle technology for biological studies in living cells. The nanoneedle technology is shown to be powerful and versatile, and can offer numerous new ways to explore biological processes and biophysical properties of living cells with high spatial and temporal precision potentially reaching molecular resolution.
[Show abstract][Hide abstract] ABSTRACT: Recent advance has seen the development of nanomechanical resonators operated in the linear regime that are capable of detecting extremely small physical quantities and even quantum interactions. However, the reduced device size reduces its dynamic range (down to nanometer) for linear operation, which makes developing the required measurement system difficult and accordingly limits their sensitivity, especially in ambient and room temperature environments. We design and develop a conceptually new nanomechanical resonator integrating an essential nonlinearity, which consists of a simple doubly clamped carbon nanotube driven with an oscillating concentrated force. We demonstrate the RF broadband nanoresonator that realizes a tunable bandwidth over three times its natural frequency and a room temperature mass sensitivity up to 0.1 zg/ Hz, over two orders of magnitude better than the corresponding linear nanoresonator. This intrinsically nonlinear design can be readily integrated into the ongoing development of nanoscale electromechanical systems to extend their practical operation for ultrahigh sensitivity sensing.
[Show abstract][Hide abstract] ABSTRACT: The microstructure of type I collagen, consisting of alternating gap and overlap regions with a characteristic D period of approximately 67 nm, enables multifunctionalities of collagen fibrils in different tissues. Implementing near-surface dynamic and static nanoindentation techniques with atomic force microscope, we reveal mechanical heterogeneity along the axial direction of a single isolated collagen fibril from tendon and show that, within the D period, the gap and overlap regions have significantly different elastic and energy dissipation properties, correlating the significantly different molecular structures in these two regions. We further show that such subfibrillar heterogeneity holds in collagen fibrils inside bone and might be intrinsically related to the excellent energy dissipation performance of bone.
[Show abstract][Hide abstract] ABSTRACT: Understanding piezoelectricity, the linear electromechanical transduction, in bone and tendon and its potential role in mechanoelectric transduction leading to their growth and remodeling remains a challenging subject. With high-resolution piezoresponse force microscopy, we probed piezoelectric behavior in relevant biological samples at different scale levels: from the subfibrillar structures of single isolated collagen fibrils to bone. We revealed that, beyond the general understanding of collagen fibril being a piezoelectric material, there existed an intrinsic piezoelectric heterogeneity within a collagen fibril coinciding with the periodic variation of its gap and overlap regions. This piezoelectric heterogeneity persisted even for the collagen fibrils embedded in bone, bringing about new implications for its possible roles in structural formation and remodeling of bone.
[Show abstract][Hide abstract] ABSTRACT: Studying molecular dynamics inside living cells is a major but highly rewarding challenge in cell biology. We present a nanoscale mechanochemical method to deliver fluorescent quantum dots (QDs) into living cells, using a membrane-penetrating nanoneedle. We demonstrate the selective delivery of monodispersed QDs into the cytoplasm and the nucleus of living cells and the tracking of the delivered QDs inside the cells. The ability to deliver and track QDs may invite unconventional strategies for studying biological processes and biophysical properties in living cells with spatial and temporal precision, potentially with molecular resolution.
[Show abstract][Hide abstract] ABSTRACT: Piezoresponse force microscopy was applied to directly study individual type I collagen fibrils with diameters of approximately 100 nm isolated from bovine Achilles tendon. It was revealed that single collagen fibrils behave predominantly as shear piezoelectric materials with a piezoelectric coefficient on the order of 1 pm V(-1), and have unipolar axial polarization throughout their entire length. It was estimated that, under reasonable shear load conditions, the fibrils were capable of generating an electric potential up to tens of millivolts. The result substantiates the nanoscale origin of piezoelectricity in bone and tendons, and implies also the potential importance of the shear load-transfer mechanism, which has been the principle basis of the nanoscale mechanics model of collagen, in mechanoelectric transduction in bone.