Published by April Wong on September 16, 2020
The need for a simple, fast, and yet sensitive diagnostic, screening, and molecular characterization tool is indispensable in clinical and research applications. There is a demand for a portable device which is user-friendly, low cost, rapid, and portable. It should also provide a highly sensitive and specific assay in real-time . A portable surface plasmon resonance (SPR) instrument may be the answer. Ever since Biacore commercialized its first SPR instrument in 1990, there have been other manufacturers who have entered the SPR instrumentation area. SPR instruments have mostly been sold to large pharmaceutical companies for drug discovery purposes  . Many of these commercial instruments require trained personnel to operate and are not easily accessible, especially from the cost point of view. As a result, we have started to see in recent years more portable SPR instruments being introduced in the life science market. In this blog, we will discuss the differences and advantages of a portable SPR instrument over large and high throughput commercial SPR systems.
Large commercial instruments are commonly used to obtain binding kinetics of drug candidates at a high throughput screening (HTS) capacity. Although not designed for HTS, a portable SPR instrument has the advantage of being flexible that can be reconfigured for multiple purposes such as bio- and chemical sensing, characterization of binding interactions, and assay development. Therefore, one can use such a portable SPR to perform any of these tasks in a rapid and easy manner. Another advantageous feature of a portable SPR is its modularity. For example, a portable SPR can be integrated with other add-on accessories to simultaneously perform spectroscopy, electrochemistry, and chromatography . Table 1 gives an overview of the differences between a portable SPR and a large SPR system.
|Large SPR system||Portable SPR|
|Accessibility||Accessible often only in centralized labs through advanced booking||Any benchtop or even off-site, anytime|
|Consumable cost||High||Low cost sensor chips ranging from a few to tens of dollars per chip|
|Maintenance cost||High, yearly contract||Low to none|
|Type of operator||Trained personnel specifically for each SPR system||Any researcher, clinician, postdoc, or student|
|Applications||Binding kinetics of drug candidates||Bio-/chemosensing, characterization of binding interactions, assay development|
Affinité Instruments has developed a portable P4SPR (Figure 1) to make SPR much more accessible to researchers in various types of biomolecular labs. In order to make the instrument robust, optical components are specially designed to be fixed, non-moving parts. . In particular, P4SPR uses wavelength interrogation which significantly drives down manufacturing and maintenance cost . P4SPR is very compact with the size of a lunchbox, ideal for use in small areas or in rural settings. It allows researchers to do on-site, real-time testing without relying on the availability to centralized lab facilities. Table 2 below summarizes the benefits to researchers from having P4SPR in their disposal.
Figure 1. Image of a P4SPR instrument. Notice the easy-access injection ports and the four-channel microfluidic cell which accommodates 3 sample channels with an adjacent reference channel.
|Compact, size of a lunchbox||Portability|
|Thin-film sensor||Highly sensitive to region ~200 nm from sensor surface. Well established area as opposed to localized SPR (LSPR)|
|Wavelength interrogation mode||Low equipment and maintenance costs, robust, and user-friendly|
|Label-free sample preparation||No need to buy purification kits and reagents. No effect on sample for kinetics and affinity.|
|Setup time to first analysis in less than 10 minutes||Simple setup|
|Real-time output||Fast results|
|Triplicate multichannel microfluidic cell with separate reference channel||Simultaneous acquisition of triplicate measurements Reference corrects for any fluctuation in temperature and bulk refractive index changes Long contact time for slow kinetics|
|Direct injection with micropipette||Low sample volume|
|Integration with other techniques such as spectroscopy, microscopy, and electrochemistry||Flexibility in experimental setup and applications|
|Simplified software control with GUI||Real-time monitoring, data processing, and quantification|
P4SPR has been used in pre-clinical research in areas such as the detection of a breast cancer biomarker, small peptides, DNA, antibodies, explosives, and early-stage drug development screening . For instance, it helped elucidate a clear picture of the binding interactions between a transmembrane protein and small peptides by determining the equilibrium dissociation constants from the resultant affinity curves . Another example of P4SPR’s portability advantage is the outdoor detection of explosives traces near a grenade range at a military base in both summer and winter time . The need to prepare and transport the samples to a centralized facility was eliminated by allowing for continuous on-site, real-time monitoring over days and weeks. In this case, the time it took for site setup including sensor calibration, sample preparation, and data gathering and analysis can be as little as 1 hour in total, much less than the turnaround time of days with centralized testing . The application wheel below illustrates the many areas that a portable SPR can be applied.
Figure 2. The applications enabled by portable SPR instrument