BACKGROUND:
Notice is hereby given by the University of Ottawa of the intent to purchase an MFP-3D-BIO Atomic Force Microscope (“AFM”) system from Oxford Instruments Asylum Research for the nanomechanical characterization of tumourous tissues in physiological conditions. Equipped with a BioHeater liquid cell and a Nanorack attachment, the setup will permit researchers to alternate between force measurements and conventional AFM topographical imaging of fibrillar tissues when immersed in buffer at 37°C. Another key aspect of the intended research will consist in coupling the MFP-3D-BIO system with confocal microscopy to perform concomitant analysis of both nanomechanical and nanostructural properties of tissues when subjected to high stretching levels (as observed in tumours).
PROCESS:
Suppliers that consider their equipment functional, successfully tested, readily available and fully compliant to the ACAN minimum requirements may submit, in writing, a statement of specifications to the contact person identified in this Notice, on or before the closing date of this Notice. In the statement of specifications, the supplier must unequivocally demonstrate how their equipment, at minimum, equals, or exceeds the stated requirements.
If no other supplier submits a statement of specifications, on or before the closing date of this Notice, the competitive requirements of the University of Ottawa will be considered having been met. Following notification to any suppliers not successful in unequivocally demonstrating that their statement of specifications equals or exceeds the requirements set out in this Notice, the contract may then be awarded to the pre-identified supplier.
INTENDED USE:
A biophysics research project requires a way of (i) sub-nanometer resolution surface topography characterization and (ii) viscoelastic characterization of fibrillar matrices immersed in phosphate saline buffer and kept at 37°C. These properties will be measured via the MFP-3D-BIO (equipped with its liquid cell and stretching stage) either in relaxed (no strain) or pre-strained conditions, to mimic either the physiological or the tumour microenvironment.
Additionally, the instrument will be combined with an existing inverted confocal fluorescence microscope to simultaneously measure the structural variations occurring in the fibrillar tissues via Fluorescence Resonance Energy Transfer (FRET). Such unique setup will permit concomitant topographical (roughness, porosity), mechanical (Young modulus, viscosity) and structural (protein folding) characterization of the tissues across multiple length scales. Although significant, these variations will be miniscule and raise the requirement for the highest possible XYZ resolution.
FUNCTIONALITY:
The equipment must conform to the following minimum requirements:
I - Fundamental AFM Performance:
- XY Scan range of at least 110um with XY noise <500pm Adev.
- Vertical noise must be as follows: DC height noise <50 pm and cantilever deflection noise <15 pm using a Low coherence source Superluminescent diode (SLD) for ripple-free baseline
- Z scan range of at least 40um with system noise < 35pm Adev (in quiet imaging environment).
- Each scan axis of motion must be independently actuated using its own piezo stack and flexure stage.
- Must be able to move the stage with very high resolution (0.5nm) and repeatability.
- Must have integrated LVDT position sensors in XYZ to provide seamless closed loop operation. This eliminates and corrects position errors in the scanning system due to piezo hysteresis, creep, and non-linearity, and substantially reduces thermal drift effects. This feature is essential for accurate imaging and force measurements on biological samples.
- XY Scanner must be decoupled from the Z scanner. This eliminates bowing effect in images and improves the linearity of the XY scanning.
- Must have ability to accommodate sample sizes of greater than 80mm x 80 mm diameter, ≤27mm thick with optional leg extenders.
- Must have automatic calibration of the cantilever sensitivity (deflection sensitivity/INVOLS) and spring constant by simply selecting the probe type and clicking a button. To avoid tip damage, at no point during the calibration may the tip touch the sample. The feature uses the Sader method for accurate probe calibration without the need for probes in which the spring constant is pre-calibrated.
- System must be designed such that the probe (cantilever), laser module and photodetector move together in the Z axis such that it minimizes changes in sensitivity based on Z position. Systems that use tracking lenses or optics are subject to changes in the optical lever sensitivity based on absolute Z position or piezo extension, making quantitative measurements very difficult to perform
- Must have open-source software – Control and analysis must be user-programmable natively in an entirely open-source software programming language. This is necessary to allow novel or highly customized measurements.
- The system’s software must include contact mechanics models for interpreting the sample modulus from a wide range of force-curve tip-sample interactions (Hertz, DMT, JKR and Oliver-Pharr contact mechanics models).
- Must have lateral drift of at least 10s pm per minute and software based drift correction that can measure and eliminate the effect of lateral drift in the AFM measurements.
- Must include a vibration isolation table and noise enclosure with window designed for inverted optical microscope-mounted AFMs. The enclosure must provide an acoustically quiet environment for low-noise AFM imaging.
- Must include on-site installation, training and at least one year standard warranty.
II - BioHeater Performance:
- The BioHeater must consist of a closed fluid cell with an immersed heating element that symmetrically heats the surrounding fluid. The fluid cell must have a total of ten ports (seven are available for liquid and gas exchange and electrical access to the sample; the remaining three are used by the heating element).
- Must heat from ambient to 80°C.
- Must have 0.02°C precision; 0.1°C accuracy; 0.1°C overshoot.
- Must be compatible with all high NA objectives (0.17mm cover slip bottom recommended).
- Must have top and bottom optical access
- Must accommodate sample sizes: 25mm maximum; 2mm thickness; 10mm sample travel within cell when open; 1-3mm sample travel within cell when closed and scanning.
- Fluid volume: 5ml before engage; 1.5ml-2.55ml after engage, clamped and sealed.
- Must have closed loop operation
- Must operate at 110 or 220 VAC
- Must have built-in microprocessor for temperature control
- Must be fully programmable through the MFP-3D software
III - Accessories for Nanomechanics:
- Nanorack: Must have fundamental accessory that enables application of tensile strain to a sample while it is in the AFM under measurement. Strain must be symmetric about the sample observation area to minimize displacement of the region of interest. Device must be capable of applying strain in excess of 400%, with the extension measured with precision of ≤ 5µm. The maximum applied load must be at least 80N and monitored by a strain gauge with < 1N resolution.
- Multiple Spring Constant Calibration Methods: Quick, push-button non-destructive determination of (in air) cantilever spring constant using thermal noise and Sader hydrodynamic methods. Thermal tune measurements on cantilevers must be up to 2.5MHz.
- AM-FM Viscoelastic Mapping: The system must support AM-FM viscoelastic mapping mode. Tapping mode AFM is a gentle imaging mode with widespread applications. Quantification of tip−sample mechanical properties such as stiffness is challenging with tapping mode AFM. Bimodal tapping mode keeps the advantages of single frequency tapping mode while extending the technique by driving and measuring an additional resonant mode of the cantilever.
IV – Compatibility of the MFB-3D-BIO (Oxford Instruments) with LSM-880 (Zeiss)
The MFP-3D-BIO AFM scanning head must be fully compatible with the LSM 880 inverted confocal microscope Axio Observer 7 stand from Zeiss (already a property of our group at uOttawa), which will allow the researchers to combine both instruments to perform simultaneous viscoelastic measurements and FRET conformational/structural mapping of tumourous tissues when they are under high strain.
Justification of Pre-Selected Supplier:
Supplier: Oxford Instruments Asylum Research Inc, 6310 Hollister Ave., Santa Barbara, CA, 93117, USA
Justification:
The system offered by Oxford Instruments Asylum Research is the highest resolving AFM available on the market and the only one accommodating open source software development. The ability to write custom code for this piece of equipment is required as it will allow for future incorporation of more involved measurement schemes.
The combination of both the performance of the AFM itself and its unique accessories are unique to this vendor. The required Nanorack and AM-FM viscoelastic mapping modules are made exclusively by Oxford Instruments Asylum Research. Additionally, no other vendor on the market offers an AFM with comparable vertical noise, vibration immunity, lateral drift figures and XYZ scan ranges. Since the intended use involves topographic and force measurements at the nanoscale, it’s paramount to use an instrument that is capable of performing at these extremely small scales in liquid environments, even when samples are large, rough, and extremely viscous. The system is also able to move the stage with unmatched high resolution and repeatability.
Lastly, no other supplier’s AFM is based on a modular design for the scanning head, allowing its use either in stand-alone configuration or in combination with an existing Zeiss inverted confocal microscope.
