SPR: A powerful tool for real-time, label-free analysis of biomolecular interactions
The study and characterization of molecular interactions is essential to explore biomolecular structure-function relationships, and it aids our understanding of biological systems in life sciences. Surface Plasmon Resonance (SPR) biosensors analyze macromolecular interactions in real-time and label-free. They have proven to be a valuable tool for scientists in many disciplines including immunology, molecular biology, cell biology and biochemistry. Compared to conventional techniques, SPR biosensors speed up such investigations as drug development, immunoreagent quality control, cell adhesion studies and polymer- biomolecule interactions.
Listed below are some examples of biomolecular interactions which have been successfully studied using SPR:
Peptide/protein - protein
DNA/RNA - protein
protein - cell
receptor - cell
protein - virus/phage
carbohydrate - protein
carbohydrate - cell
liposome - protein
artificial materials - biological matter
drugs - protein
drugs - DNA/RNA.
In addition to biomolecular interaction studies, SPR sensors can be used to quantify adsorption and desorption processes in non-biological systems or to follow the course of solid phase-based chemical reactions on the chip surface.
SPR Biosensor SR7000DC: An affordable and versatile system that’s easy to configure and modify with off-the-shelf components that you select
With the SR7000DC, fundamental data on biomolecular interactions is easily accessible to labs of any size, as the system is affordable, compact and easy to configure or modify with off-the-shelf components. The instrument’s sensitivity equals even the most high-end instruments, and it provides about three times the dynamic range. A wide selection of sensorchips and modules combine superior technology with complementary analytical techniques making the SR7000DC a truly flexible and versatile instrument. For cost-effective operation, the open design of the SR7000DC allows easy access to all serviceable components. Fast and efficient technical service and a competent support team help to accelerate your work and minimize downtime.
The SR7000DC biosensors, which use Surface Plasmon Resonance (SPR), measure refractive index changes close to the interface of a sensor chip in real-time. Such changes occur when biomolecules interact with immobilized ligands and replace water from binding sites on the sensor surface. The refractive index differences are detected via angle changes of reflected light from an LED source and are directly related to the amount of sensor surface-bound biomolecules. Using an ultrasensitive Kretschmann geometry with 3700 pixel CCD array, our SPR sensors are able to detect protein densities down to 0.1 pg / mm².
Key features optics:
Dual channel including real-time referencing
Full reflectivity curves downloadable
Widest dynamic range: 1.32 – 1.43 (with high RI glass chips up to 1.6. 175.000 RU or 17.500 mdeg).
Excellent baseline stability: Maximum drift 0.6 µRIU/hour (0.38 RU/h or 0.038 mdeg/h)
Robust: No moving parts and virtually indestructible sapphire prism
For general information on SPR detectors please check the chapters "SPR principle" and “Optics” in our Tech Note section.
Flexible liquid handling system
For the SR7000(DC), both flow-through and static cuvette SPR biosensor systems are available. The user thus has the possibility to choose the optimal liquid handling system for each experiment. The dead volume of the flow cell is below 1 µl which results in a sharp flow profile.
The liquid handling system is designed to use low cost off-the-shelf HPLC valves and tubing. This allows for easy change-over if contamination or damage occurs. Additionally, a range of options allows for selection of the most appropriate materials and tube sizes for the biomolecules and chemicals to be used. For even buffer flow, a high quality syringe pump provides the lowest noise and most stable baselines for kinetic and equilibrium analysis. Alternatively, a peristaltic pump can be used as a lower cost option, to flow cleaning solutions, or to continually recirculate analytes for long time span equilibrium experiments.
Fully automated operation with optional autosampler
The robotic autosampler is designed to maximize the performance and throughput of the SR7000 Surface Plasmon Resonance instrument. It is specifically designed for life science related applications and is excellently suited for use with SPR biosensors. Features include sample cooling and heating (4°C – 40°C) and metal-free biocompatible PEEK Fluidics. Minimal sample carryover and excellent repeatability ensure high quality, reproducible kinetic data.
The autosampler is extremely flexible: It has the capability to inject small volumes – down to 25 µL - when sample quantity is limited or large volumes – up to 1 mL - when long term equilibrium analysis is required. The sample loop and syringe sizes can be varied for micro to macro injections. The autosampler is compatible with 1.5 mL sample vials, 96 and 384 well plates.
Highly versatile reagent addition and mixing routines automate complex sensor surface derivatizations, dilutions, pH changes, etc. In addition, the programmable sampling height allows aspiration from two-phase samples such as liquid-liquid extracts or samples containing a precipitate. An additional solvent selection valve (optional) provides almost unlimited volumes for reagent addition and needle wash. With the optional extra switching valve, you have a powerful tool for fully automated sample enrichment and clean-up controlled from a single keyboard.
Visual and user-friendly software
The SR7000DC Data Acquisition and Analysis software acquires and presents the data from both sensing channels in real-time. The data from the second channel can be subtracted during the acquisition process but also at a later stage to provide a referenced sensorgram. Alternatively, it is possible to run the second channel independently. The option to set markers and make notes helps to document the course of an experiment and identify individual injections at a later time. For control of the data quality, full reflectivity curves may be downloaded from the instrument at any time.
After completion of the experiment, the raw sensorgram is transferred to the post process screen, where an aligned overlay plot may be created from the individual injections. For further analysis, the resulting data can be exported into Excel, Origin, GraphPad Prism or a number of other programs like SCRUBBER and CLAMP (Center for Biomolecular Interaction Analysis, Univ. of Utah) or WINSPALL (WINSPALL, Juergen Worm, MPIP Mainz).
Additional modules
The value of a Surface Plasmon Resonance instrument can be significantly enhanced when it is combined with complementary analytical techniques or upgraded with components that open up additional applications. XanTec bioanalytics is constantly developing interfaces and modules that make most of your SR7000DC. You can design experiments which are not possible with any other instrument and produce unique data. Currently, the following modules are available:
- MALDI flow cell. As invaluable SPR is to quantify interaction processes at the molecular level, it cannot identify an unknown ligand that may have been bound, for example during a ligand fishing experiment. These qualitative data can be provided by complementary techniques such as Matrix Assisted Laser Desorption and Ionization (MALDI). This method is increasing in popularity as it allows identifying not only the molecular weight of bound species, but also provides valuable sequence information via enzymatic on-chip digestion as well. The MALDI flow cell contains removable hydrogel coated pins with high immobilization capacities, which are located opposite to the sensorchip surface.
MALDI flowcell with pin handling tool
After binding of an unknown ligand has been detected with SPR, these pins - then carrying a high ligand density - can be removed and transferred to a modified MALDI target, where the ligand can be directly analyzed or be subjected to a digestive treatment. Alternatively, the pins may also be transferred to vials for ligand recovery, analysis by other analytical techniques or PCR in the case of DNA-DNA interactions. The pin system is compatible with MALDI targets / spectrometers from all major manufacturers.
- E-SPR flow cell. The combination of electrochemistry and SPR can visualize processes on the surface of an electrode at the molecular level. It is therefore a useful tool to study electrolysis, corrosion processes or to develop electrochemical biosensors. A potential application of particular interest is the investigation of transmembrane proteins as the technique allows measurement of conductivity changes in ion channel containing membrane systems upon interaction with specific signalling molecules. The E-SPR module can be used to study such electrochemical processes with the SR7000DC as it incorporates a working and a reference electrode in the flow cell and uses the surface of the gold chip as counter electrode. A standard coax connector connects the electrodes to a potentiostat or similar devices.
- Photo flow cell. During the past years, numerous light-induced immobilization techniques have been developed. Further, photopolymerization on surfaces or the interaction of adsorbed species with radiation may be effectively studied with transparent SPR devices. XanTec’s photo flow cell with UV transparent quartz windows allows irradiation of the sensor chip surface with light of a broad wavelength spectrum and thus a variety of experimental setups.
- High temperature flow cell. Although most biomolecular processes proceed between 10 and 40 °C, some systems may require significantly higher temperatures. One example are thermophilic microorganisms which live at temperatures above 80 °C. The study of heat-induced stress reactions is another example of such experimental conditions. Yet another field is the investigation of temperature dependant adsorption and desorption processes or catalysis at surfaces. All these experiments can be conducted with the insulated high temperature flow cell which can be thermostatized from 4 °C to 90 °C. Beside the high temperature working range, this flow cell is solvent resistant and tolerates corrosive media such as concentrated acids and bases.
Wide variety of sensor chips
The surface of a sensor chip is the central part of a biosensor. It is here where the biomolecular interaction takes place and where the biochemical binding event is transduced into an opto-electronic signal. Therefore the quality of the sensor surface determines the quality of the sensorgrams. As different chemical structures of the immobilized biomolecules require adapted coupling strategies, XanTec bioanalytics offers the market-wide largest choice of SPR sensorchips derivatized with various chemical and biochemical functionalities. These functional groups are either linked to planar surfaces or attached to grafted hydrogels which are available in different thicknesses. The surfaces are available on various chip sizes so it is possible to compare data from different instruments or to directly transfer protocols, even to other analytical formats like microarray slides.
