| lifeScan One-Touch™ AFM System
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A Radically New Mode of Operation of
Existing AFMs for
High Resolution Biological Structure
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True computer control of the cantilever
throughout the approach/one-touch/withdraw
cycle by a patented, proven technology
Low molecular damage, high lateral resolution, and
immediate adhesion force make lifeScan the best
imaging instrument for the Life Sciences
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What lifeScan Does
- lifeScan examines the deflection of the cantilever Angstrom by Angstrom during approach to the specimen and halts the approach at the smallest detectible deflection, i.e. at a single touch, effectively inhibiting damage to in situ molecular structure.
The cantilever force constant used for scanning can be as low as can be found commercially (typically 20 picoNewtons/nm) since energy stored in the cantilever motion is not required to unbind the tip.
Low force constant is desirable because it can be shown to be approximately equal to the compressive force that occurs in detecting contact.
- lifeScan then breaks the newly formed bond between tip and sample using a calibrated magnetic liftoff force of whatever strength is required.
Magnetic liftoff enables a direct, quantitative measure of adhesion force in picoNewtons, replacing the semi-quantitative estimate derived from phase of oscillation.
Intra-Pixel Feedback to the Specimen Piezo for High Resolution
- Height is measured digitally in approach steps each pixel.
Feedback to the specimen piezo maintains a preset approach count by digital addition to the specimen piezo voltage before the next pixel.
Therefore the feedback is necessarily fast enough and cannot limit the lateral resolution.
- There are no feedback gains for the operator to adjust, unlike the analog feedback of all previous atomic force microscopy.
There is no bandwidth limitation and no oscillation induced by increasing feedback gains.
Lateral Resolution
- Lateral resolution is determined by the tip diameter used: 1-2 nm for single-wall nanotubes, 3-5 nm for super sharp silicon, 5-10 nm for standard silicon.
The low detect force of lifeScan preserves nanotube and super sharp silicon tips and permits repeat scanning of proteins at increasing magnification.
Magnetic Micro-particle Cantilever Tips
- The highest performance commercial tips with lowest force constants and smallest diameter tips are fitted with samarium cobalt magnetic microparticles by LifeAFM for customer use.
Data Acquisition
- Data acquisition rate for all signals is 200 kHz (400 kHz possible).
Scanning can be chosen at 2n pixels per line and 2m lines per frame, where n, m are arbitrary positive integers.
Typically, scanning is at 256 pixels x 256 lines and at 0.8 to 1.2 lines per second.
- Complete force curves for all pixels are recorded automatically, each force curve showing cantilever deflection in volts vs. approach distance in counts where each count is typically 0.1 nm. Resulting file size is 25 megabytes per field.
- Fields of different data are simultaneously displayed and recorded during the scan:
- high resolution topography (flattened height map) in nm
- differential height between successive pixels, in nm, for an edge-sharpened image
- adhesion force in picoNewtons, at the same lateral resolution as topography
- compressibility in selectable units
- unflattened height map, in nm, for evaluating specimen flatness and tilt
Magnetic Lift-off
- After detection of specimen surface, with the cantilever stationary and minimally deflected, a linear magnetic force ramp of 50 steps is initiated.
The ramp amplitude is adjusted so tip separation occurs at about 2/3 of the 50-step range.
- Magnetic force is calibrated in terms of cantilever force constant at the beginning of each run, so the force at lift-off (adhesion force) is known in picoNewtons.
- The adhesion force map and the height map are in register at the pixel level, owing to their concurrent determination within each approach/withdraw cycle.
lifeScan Software: lifeProcessor and lifeView
- lifeProcessor DSP program written in C and executing on a high-speed processor controls the detailed state of the AFM proper. The Veeco MultiMode™ AFM provides excellent stable operation.
Data from each complete scan line is stored in the processor and transmitted to the host PC between scan lines.
Computer-intelligent search procedure for initial engagement is free of false detection of sample surface.
Current scan parameters are stored for later re-use.
Highly stable operation requires little or no adjustment of machine parameters over many hours of data collection.
- lifeView, a Windows program written in C++ provides the interface to the experimenter, accepting new parameters for the entire run and for the next field, carrying out calibrations as needed, and collecting and displaying data.
A true multi-user environment on a standard PC uses a standard Windows operating system.
Force curves are displayed each scan line during data collection with exact replay always available.
Online measurement capabilities include x, y, z, distance, and angles with histogram capability, and correlation and Fourier analyses.
Multiple palette and color display options are available.
All signals required for LifeScan operation are on the operator screen.
Accuracy of Height Measurement
- Machine RMS error in Z is <0.1 nm. RMS error in Z for a full scan line measuring mica is 0.1 nm.
Data Analysis: IDL and lifeAnalysis
- The powerful data analysis and display program, IDL (Interactive Display Language, Research Systems Inc.), is provided to lifeScan users for refined and quantitative display of height and adhesion force data.
- All data are available in EPS, JPEG, TIFF and many other formats.
- An extensive set of display and measurement operations is preprogrammed in the lifeAnalysis package for the lifeScan customer.
These include 2 and 3-dimensional displays with a variety of quantitative color representation and contouring, sectioning through structures, nanometer height and lateral distance measurement including contour length for DNA.
Comprehensive statistical analysis and a wide range of mathematical operations are features of IDL.
- To exploit fully the high resolution available from lifeScan, local Gaussian averages of the data can be selected for any trade-off desired between statistical accuracy of the data at each pixel and lateral resolution.
- As indicated by its name, IDL is a programming language, but a very intuitive one so no special training is required to create new, specialized analysis programs for any given experiment.
- IDL is normally run on a separate analysis computer. Each field as it finishes scanning is shipped to it and is ready for in depth analysis at any time.
Signal Access
- Main signals and triggers required for lifeScan operation are brought to BNC’s on the front panel where they are conveniently monitored by oscilloscope. Most of these signals are already displayed on the lifeView screen, but having them also available to an oscilloscope means they can be observed at any time and in a variety of time formats.
- Additional input BNC’s on the control panel allow changes to the machine logic for special purpose experiments.
Scanners
- lifeScan drives the MultiMode™ AFM produced by the Veeco Metrology Subdivision in Santa Barbara, CA. The MultiMode uses several Scanners, capable of different field sizes, z-range and resolution.
- lifeScan, focused on high resolution biological structure problems, normally uses the E or EV scanners of the MultiMode, with X-Y range of 10 µm x 10 µm and Z range of 2.5 µm. It is also able to drive the A scanner (0.4 µm x 0.4 µm x 0.4 µm) and the J or JV scanners (125 µm x 125 µm x 5 µm).
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