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Scanning probe microscopy and potentiometry using a junction field effect transistor based sensor
摘要： Scanning tunneling microscopy in its conventional form relies on a steady state tunneling current of 10?12–10?6 A. However, for various applications, it is desirable to reduce the current load to a minimum. Here, we present first experiments using a cooled junction field effect transistor in open gate operation, thereby reducing the DC-current to less than 10?19 A. This enables almost ideal measurements of the local electrochemical potential on a surface. Various methods applying dynamic modes can be used to maintain a constant distance between the scanning probe and the sample surface. Here, we use an AC-bias applied to the sample and a lock-in amplifier connected to the preamplifier to evaluate the conductance of the tunneling gap.
关键词： potentiometry,scanning probe microscopy,junction field effect transistor,sensor
更新于2025-09-09 09:28:46
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High-speed velocimetry in microfluidic protein mixers using confocal fluorescence decay microscopy
摘要： A method to measure fluid speeds on the order of 10,000 mm/s in microchannels is presented. A microfluidic protein mixer is manufactured with a 170 μm microscope coverslip bottom that interfaces with a confocal florescence microscope using a water-immersed Olympus UPLSAPO 60XW objective to create a diffraction-limited confocal volume. A diode laser with a repetition rate of 1 MHz is used to study Poiseuille flows at average speeds of 5000, 6000 and 7000 mm/s by exciting tris(2,2′-bipyridine)ruthenium(II) hexafluorophosphate solution at 1 μmol/L concentration flowing through the micro-mixer in the confocal volume. Decays collected using a time-correlated single photon counting card at each grid point are characterized by the first moment of the decay and curve fitted with the theoretical Poiseuille flow solutions. It was found that curve fitting with higher average speeds results in lower errors. A fluorescence correlation study was then carried out at different depths in the micro-mixer to understand the raw data profiles observed using the diode laser. A mixing study was then carried out using a Ti-Sapphire laser with a repetition rate of 3.8 MHz. A Poiseuille flow at 7000 mm/s was measured using the Ti-Sapphire laser and then curve fitted to the theoretical Poiseuille flow solution. The curve fit was then applied to the complicated flow region to determine speed. Results of the experimental mixing study are also compared to direct numerical simulation results.
关键词： Microfluidic protein mixers,High-speed velocimetry,Poiseuille flows,Fluorescence correlation spectroscopy,Confocal fluorescence decay microscopy
更新于2025-09-09 09:28:46
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Surface potential of meso-dimensional ZnS:Mn particles obtained using SHS method
摘要： The dependence of surface potential value on the particle size of micro- and meso-fractions for powdered ZnS:Mn obtained using self-propagating high-temperature synthesis has been investigated. Rather good agreement of model representations for the change in the value of surface potential for the particle with its size changed due to overlapping the space charge regions from opposite surfaces within the range ~ 1 ≤ R/Leff ≤ ~ 2.2 (R, particle radius; Leff, screening length) with experimental data obtained using the method of Kelvin probe microscopy has been shown. The value of Leff for ZnS:Mn particles is estimated as approximately 30 nm.
关键词： Surface potential,Nanoscale effects,ZnS:Mn,Particle size,Effective screening length,Kelvin probe force microscopy
更新于2025-09-09 09:28:46
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Excitation-multiplexed multicolor superresolution imaging with fm-STORM and fm-DNA-PAINT
摘要： Recent advancements in single-molecule-based superresolution microscopy have made it possible to visualize biological structures with unprecedented spatial resolution. Determining the spatial coorganization of these structures within cells under physiological and pathological conditions is an important biological goal. This goal has been stymied by the current limitations of carrying out superresolution microscopy in multiple colors. Here, we develop an approach for simultaneous multicolor superresolution imaging which relies solely on fluorophore excitation, rather than fluorescence emission properties. By modulating the intensity of the excitation lasers at different frequencies, we show that the color channel can be determined based on the fluorophore’s response to the modulated excitation. We use this frequency multiplexing to reduce the image acquisition time of multicolor superresolution DNA-PAINT while maintaining all its advantages: minimal color cross-talk, minimal photobleaching, maximal signal throughput, ability to maintain the fluorophore density per imaged color, and ability to use the full camera field of view. We refer to this imaging modality as “frequency multiplexed DNA-PAINT,” or fm-DNA-PAINT for short. We also show that frequency multiplexing is fully compatible with STORM superresolution imaging, which we term fm-STORM. Unlike fm-DNA-PAINT, fm-STORM is prone to color cross-talk. To overcome this caveat, we further develop a machine-learning algorithm to correct for color cross-talk with more than 95% accuracy, without the need for prior information about the imaged structure.
关键词： STORM,frequency multiplexing,multicolor imaging,DNA-PAINT,superresolution microscopy
更新于2025-09-09 09:28:46
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Noninvasive diagnostic imaging using machine-learning analysis of nanoresolution images of cell surfaces: Detection of bladder cancer
摘要： We report an approach in diagnostic imaging based on nanoscale-resolution scanning of surfaces of cells collected from body fluids using a recent modality of atomic force microscopy (AFM), subresonance tapping, and machine-leaning analysis. The surface parameters, which are typically used in engineering to describe surfaces, are used to classify cells. The method is applied to the detection of bladder cancer, which is one of the most common human malignancies and the most expensive cancer to treat. The frequent visual examinations of bladder (cytoscopy) required for follow-up are not only uncomfortable for the patient but a serious cost for the health care system. Our method addresses an unmet need in noninvasive and accurate detection of bladder cancer, which may eliminate unnecessary and expensive cystoscopies. The method, which evaluates cells collected from urine, shows 94% diagnostic accuracy when examining five cells per patient’s urine sample. It is a statistically significant improvement (P < 0.05) in diagnostic accuracy compared with the currently used clinical standard, cystoscopy, as verified on 43 control and 25 bladder cancer patients.
关键词： diagnostic imaging,cancer diagnostics,atomic force microscopy,machine learning,noninvasive methods
更新于2025-09-09 09:28:46
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Growth, Morphology and Stability of Au in Contact with the Bi2Se3(0001) Surface
摘要： We report a combined microscopy and spectroscopy study of Au deposited on the Bi2Se3(0001) single crystal surface. At room temperature Au forms islands, according to the Volmer–Weber growth mode. Upon annealing to 100° C the Au deposits are not stable and assemble into larger and thicker islands. The topological surface state of Bi2Se3 is weakly affected by the presence of Au. Contrary to other metals, such as Ag or Cr, a strong chemical instability at the Au/Bi2Se3 interface is ruled out. Core level analysis highlights Bi diffusion toward the surface of Au islands, in agreement with previous findings, while chemical interaction between Au and atomic Se is limited at the interfacial region. For the investigated range of Au coverages, the Au/Bi2Se3 heterostructure is inert towards CO and CO2 exposure at low pressure (10-8 mbar) regime.
关键词： metal to topological insulator contact,chemical properties,photoemission spectroscopy,growth mode,electronic properties,microscopy
更新于2025-09-09 09:28:46
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Exciting vibrons in both frontier orbitals of a single hydrocarbon molecule on graphene
摘要： Vibronic excitations in molecules are key to the fundamental understanding of the interaction between vibrational and electronic degrees of freedom. In order to probe the genuine vibronic properties of a molecule even after its adsorption on a surface appropriate bu?er layers are of paramount importance. Here, vibrational progression in both molecular frontier orbitals is observed with submolecular resolution on a graphene-covered metal surface using scanning tunnelling spectroscopy. Accompanying calculations demonstrate that the vibrational modes that cause the orbital replica in the progression share the same symmetry as the electronic states they couple to. In addition, the vibrational progression is more pronounced for separated molecules than for molecules embedded in molecular assemblies. The entire vibronic spectra of these molecular species are moreover rigidly shifted with respect to each other. This work unravels intramolecular changes in the vibronic and electronic structure owing to the e?cient reduction of the molecule–metal hybridization by graphene.
关键词： single molecules,quantum chemistry,density functional theory,vibrational progression,graphene,scanning tunnelling microscopy,frontier orbitals
更新于2025-09-09 09:28:46
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Improving gas sensing by CdTe decoration of individual aerographite microtubes
摘要： Novel gas sensors have been realized by decorating clusters of tubular Aerographite with CdTe using magnetron sputtering techniques. Subsequently, individual microtubes were separated and electrically contacted on a SiO2/Si substrate with pre-patterned electrodes. Cathodoluminescence, electron microscopy and electrical characterization prove the successful formation of a polycrystalline CdTe thin film on Aerographite enabling an excellent gas response to ammonia. Furthermore, the dynamical response to ammonia exposure has been investigated, highlighting the quick response and recovery times of the sensor, which is highly beneficial for extremely short on/off cycles. Therefore, this gas sensor reveals a large potential for cheap, highly selective, reliable and low-power gas sensors, which are especially important for hazardous gases such as ammonia.
关键词： ammonia,electron microscopy,nanocomposite,hybrid material,gas sensing
更新于2025-09-09 09:28:46
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An approach to spin-resolved molecular gas microscopy
摘要： Ultracold polar molecules are an ideal platform for studying many-body physics with long-range dipolar interactions. Experiments in this field have progressed enormously, and several groups are pursuing advanced apparatus for manipulation of molecules with electric fields as well as single-atom-resolved in situ detection. Such detection has become ubiquitous for atoms in optical lattices and tweezer arrays, but has yet to be demonstrated for ultracold polar molecules. Here we present a proposal for the implementation of site-resolved microscopy for polar molecules, and specifically discuss a technique for spin-resolved molecular detection. We use numerical simulation of spin dynamics of lattice-confined polar molecules to show how such a scheme would be of utility in a spin-diffusion experiment.
关键词： quantum gas microscopy,quantum simulation,ultracold molecules,single-molecule control,dipolar spin models,optical lattices
更新于2025-09-09 09:28:46
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Label-free imaging of amyloid plaques in Alzheimer’s disease with stimulated Raman scattering microscopy
摘要： One of the key pathological features of Alzheimer’s disease (AD) is the existence of extracellular deposition of amyloid plaques formed with misfolded amyloid-β (Aβ). The conformational change of proteins leads to enriched contents of β sheets, resulting in remarkable changes of vibrational spectra, especially the spectral shifts of the amide I mode. Here, we applied stimulated Raman scattering (SRS) microscopy to image amyloid plaques in the brain tissue of an AD mouse model. We have demonstrated the capability of SRS microscopy as a rapid, label-free imaging modality to differentiate misfolded from normal proteins based on the blue shift (~10 cm?1) of amide I SRS spectra. Furthermore, SRS imaging of Aβ plaques was verified by antibody staining of frozen thin sections and fluorescence imaging of fresh tissues. Our method may provide a new approach for studies of AD pathology, as well as other neurodegenerative diseases associated with protein misfolding.
关键词： amyloid plaques,protein misfolding,Alzheimer’s disease,stimulated Raman scattering microscopy,label-free imaging
更新于2025-09-09 09:28:46