Watching molecules meet - in real time, without a single label - on the physics of trapped light.
Most tools for studying how molecules bind ask you to tag them first - attach a fluorescent dye, a radioactive marker, or a second detection antibody, then read the signal. Resonant Sensors Incorporated (RSI) took a different route. Its instruments watch the binding happen directly, using an optical effect called guided-mode resonance, and add nothing to the sample at all.
The company was founded in 2004 in Arlington, Texas, out of optics research tied to the University of Texas at Arlington. Its co-founders pair two disciplines that rarely share a bench: Debra Wawro Weidanz, an immunologist who serves as CEO and chief scientist, and Robert Magnusson, the optics researcher whose work on resonant waveguide gratings underpins the technology. That combination - physics that can see, biology that needs seeing - is the whole company in miniature.
Today RSI sells a benchtop instrument, the ResoSens Ultra-Mab Pro, alongside disposable sensor plates and analysis software. The pitch is simple to state and hard to build: label-free binding data, in real time, on a plate format labs already know, using less than a drop of sample. The rest of this dossier explains how that works, who buys it, and where RSI sits in a market full of much larger names.
Strip away the jargon and the mechanism is elegant: a nanostructured grating traps light so precisely that only one exact color reflects back. When a molecule lands on the surface, that color shifts - and the shift is your data.
White light hits a zeroth-order waveguide grating built into the plate surface.
The nanostructure reflects back a single, sharp resonant wavelength - highly sensitive to the surface.
As a bioreaction occurs, tiny density changes at the surface alter the local refractive index.
The reflected color shifts. ResoVu software turns that shift into kinetics, affinity and specificity.
A semi-automated benchtop plate reader with integrated buffer dispensing and incubation. Runs label-free detection in a disposable 96-well format, with run times measured in minutes rather than hours.
Captures spectral shifts from the reader and converts them into binding kinetics, affinity and specificity data - the analysis layer that makes the raw optics usable.
Proprietary disposable sensor plates in 96- and 384-well formats. Available untreated (bare TiO2) or pre-activated with standard attachment chemistries for biotinylated reagents.
Fee-for-service label-free assay work: antibody characterization, epitope binning, hybridoma screening, affinity and specificity testing, and assay development support.
RSI's customers are teams for whom binding is the whole game. Antibody discovery and immunotherapy groups use the system to characterize candidates - how tightly they bind, how selectively, and to which epitope. Hybridoma and monoclonal antibody labs use it to screen large panels quickly. Diagnostics developers, academic research groups and contract research organizations round out the base.
The design choices reveal the intended user. Sub-50-microliter samples suit precious biologics. Tolerance for crude samples - not just purified ones - matches the messy reality of early screening. The standard 96-well footprint means adopting RSI doesn't force a lab to rebuild its workflow. These are the details that separate a physics demonstration from a working instrument.
Applications the platform is marketed for include antibody characterization (kinetics, selectivity and specificity), epitope binning, hybridoma screening, protein-protein and small-molecule interaction analysis, and cell-based assays - the recurring measurement problems of immunotherapy R&D.
Label-free binding analysis is an established, competitive field. The incumbents are large: Sartorius/ForteBio's Octet (bio-layer interferometry), Cytiva's Biacore (surface plasmon resonance), and high-throughput SPR systems from Carterra and Bruker/Sierra Sensors. Many of these instruments carry six-figure price tags and demanding footprints.
RSI's angle is accessibility. A benchtop reader paired with disposable plates aims at teams that cannot justify a full SPR suite but still need real-time, label-free kinetics. Its differentiators, as the company frames them: a standard disposable plate format, very small sample volumes, tolerance for crude samples, and multi-point microarray detection per well.
The trade-off is scale. This is a roughly four-person company competing against divisions of multibillion-dollar tools vendors. Its strategy has been focus and endurance - deep specialization in one physics platform, sustained by NIH and NSF SBIR/STTR grants and private venture funding, rather than a race to breadth.
An immunologist who leads the company and its science. Her work on GMR biosensor applications is cited across the field, and she anchors RSI's focus on antibody and immunotherapy use cases.
An optics researcher whose foundational work on guided-mode resonance and resonant waveguide gratings provides the physics behind RSI's sensors, including patented sensor designs.
Debra Weidanz and Robert Magnusson establish RSI to commercialize guided-mode resonance sensing.
Patents on guided-mode resonance sensors using angular, spectral, modal and polarization diversity enter the record.
The platform advances with NIH and NSF small-business research grants.
GMR biosensor research demonstrates roughly 0.1 pM detection of neuropeptide Y in sandwich assays.
RSI closes a Series B round of about $2.63M to advance commercialization.
The company rolls out the ResoSens Ultra-Mab Pro reader, ResoVu software and Bionetic disposable plates.
The core trick - guided-mode resonance - means a nanostructured grating reflects back just one precise color of light, and that color shifts the instant a molecule binds.
The system needs less than 50 microliters - roughly a single drop - per run.
It can read binding in crude samples, not just purified ones, which is unusual for label-free tools.
The whole company runs on a team of about four people out of Arlington, Texas.
Label-free optical biosensor systems - the ResoSens Ultra-Mab Pro benchtop plate reader, ResoVu software and disposable Bionetic microarray plates - that measure molecular binding interactions in real time using guided-mode resonance technology.
A nanostructured waveguide grating reflects back one precise wavelength of light. When molecules bind at the sensor surface, that wavelength shifts; measuring the spectral shift reveals binding events without any fluorescent or radioactive labels.
Antibody discovery and immunotherapy labs, hybridoma and monoclonal antibody teams, diagnostics developers, and academic and CRO research groups needing kinetics, affinity, specificity and epitope-binning data.
Arlington, Texas, at 416 Yates St - with roots in optics research at the University of Texas at Arlington.
It delivers label-free, real-time results in a standard disposable 96-well plate format, uses very small sample volumes (under 50 microliters), tolerates crude samples, and aims to be more accessible than large SPR instruments.