You know us for SPR instruments. Inside every P4SPR 2.0 and P4PRO is a Kretschmann SPR instrument with the complex optics taken out. Here is how it works, and why we built it that way.
One LED, one sensor, one detector. The dashed outlines mark where conventional SPR puts its lenses.
Lensless SPR is designed for a different user and a different measurement: the researcher at their own bench, running binding experiments on larger targets in real, complex samples. Those experiments produce larger shifts, so maximum sensitivity isn't the goal; a dependable reading of where the resonance moves is.
We got there with three design decisions.
Light reflects under a thin gold film on a prism by total internal reflection. At resonance, part of that light couples into surface plasmons in the gold and a dip appears in the reflected light. Its position depends on what binds to the surface.
This is the same physics as conventional SPR, on purpose. Sensor surfaces, immobilization chemistries, published methods and the way data is interpreted all carry over. Only the instrument around it changed.
Light shining straight onto a metal can't excite a surface plasmon; it needs extra momentum along the surface. There are three classic ways to give it that.
A small gap, about one wavelength, separates the prism from the metal. Light reflecting in the prism excites plasmons across the gap. The gap is hard to control, so it is rarely used for biosensing.
A thin gold film sits directly on the prism. Light reflects under the gold and excites plasmons on the other side, where the sample is. The standard configuration for biosensing.
No prism: a patterned metal surface diffracts the light to excite plasmons. The light usually has to pass through the sample, and the grating must be precisely fabricated.
Starting from that configuration, we took out every component the measurement didn't need and replaced the rest with fixed geometry.
| Conventional SPR | Lensless SPR |
|---|---|
| Collimating and focusing lenses | Aperture tunnels machined into the light path shape the LED light |
| Rotating stage and angle scanning | Wavelength interrogation at a fixed angle: a broadband LED and a spectrometer read the resonance by colour |
| Hemispherical prism, source and detector on angled arms | Dove prism: light leaves on the same axis it enters, so the whole path is one straight line |
| Polarizer | Polarizer, kept |
| A full optical train for each channel | One LED and one sensing area per channel, with fibres feeding one shared spectrometer |
Fewer optical components means a less refined raw signal. We offset that where it is cheaper and more flexible to do so:
Data processing. Peak tracking follows the resonance position across the full spectrum, rather than the intensity at a single wavelength. Reference channels subtract bulk refractive-index changes and drift.
Assay strategy. Surface chemistries and experimental designs chosen for the larger shifts that larger targets give in complex samples.
Nothing to align, nothing to move, and every channel is a copy of the first.
When the light path is a machined part, an SPR instrument can be small, simple, and identical from one channel to the next. The lensless optical module fits within the footprint of an earbud case; add the detector and the whole measurement is about the size of a pipette-tip box. A full instrument can even travel in a carry-on and run on arrival.
That moves the real challenge to where your biology is. It's also where we now put most of our effort, alongside you.
What you capture on the gold, and how, decides what you can measure in a real sample.
Surface chemistry guide →References, concentrations and regeneration set your data quality. Ready-made sensors and kits give you a head start.
Sensors & kits →Peak tracking, referencing and fitting turn the signal into answers, in Affilabs.core.
Software →
Patented lensless surface plasmon resonance technology.