Revolutionize your particle measurement with OptoFluidic Force Induction

OF2i® stands for OptoFluidic Force Induction. This patented method for the characterization of nanoparticles is a game changer. For the first time you can get particle data continuously, seamlessly and in real-time, statistically relevant and representative of the whole particle population. OF2i® blasts through the limitations of conventional methods for particle characterization and revolutionizes your research and production.


This new principle uses light as a tool to manipulate nanoscaled objects in liquid pumped through a measuring cell. OptoFluidic Force Induction takes the “optical tweezers” principle pioneered by Arthur Ashkin a number of steps further: it focuses a donut-shaped laser through the liquid sample to exert optical force on the particles that pushes them forward and turns them around the beam’s center.

Table of contents

Making a movie – and the importance of a donut

Imagine your child is learning to walk. When they take their very first steps you will want to capture the moment. Will you take some photos or a video? A series of single snapshots will not tell the story as well as a film sequence. This is how the OF2i® method compares to the established methods for particle measurement. Whereas you only obtain short snapshots of the particle behavior using conventional methods (DLS, Laser Diffraction) or a short video of a limited number of particles (with NTA), OptoFluidic Force Induction delivers continuous measurement data in a seamless video stream. 

What does this continuous measurement mean?

This huge amount of data recorded by OF2i® over time gives insight into the concentration, size and size distribution of particle populations – and shows changes to these as they happen, in real-time. The online PAT sensor BRAVE B-Continuous can even be integrated directly into your production plant. Results are delivered continuously with single-particle sensitivity.
Being able to follow sample behavior as (nano)particles react and interact with each other and the sample environment is also groundbreaking for research and development applications. One of our very first research partners, Prof. Tobias Madl at the Medical University of Graz, used the prototype BRAVE B-Curious in his research and was able to directly monitor the processes involved in early biomolecular condensate formation for the very first time. He now has a new BRAVE B-Curious to help further his studies of age-related diseases.

And what about the donut?

The laser used by OF2i® is a vortex laser with a donut-shaped beam. Focusing this donut beam through the liquid sample causes the particles to spin around the beam’s center, moving the particles through the measuring cell on spiral trajectories without them bumping into each other.
(Movies are just better when donuts are involved).

Publication in Physical Review Applied: "Real-Time Nanoparticle Characterization Through Optofluidic Force Induction"
Šimić et al

OF2i® measures particle size and PSD of polydisperse samples

One of the major challenges in particle characterization is the handling of highly polydisperse and multimodal samples, which are frequently encountered in industrial processes. In our short white paper Analyzing polydisperse systems we demonstrate how the OptoFluidic Force Induction (OF2i®) method characterizes complex polydisperse systems in a continuous and seamless measurement spanning approximately one hour.
The corresponding figure shows:

(a) Measured diameters of a mixture of polystyrene spheres (n = 1.59) with nominal diameters of 203, 401, 600, 789, and 1040 nm over a large measurement time. The contribution of each ensemble is determined by a 1D Gaussian mixture model with five components applied to the histogram on top and highlighted by color.

(b) Total concentration (particles/mL) and

(c) count of each cluster, averaged over a period of tmeas = 180 s. For the smallest particles (203 nm), the concentration is divided by a factor of five for better representation.

Particle size histograms (∆d = 10 nm) obtained after (d) 55, (e) 25, and (f) 15 minutes, indicated by markers on the y-axis in panel (a).

Combining OF2i® with Raman analysis for detecting and identifying nano- and microplastics in liquids

BRAVE Analytics is working on an OF2i®-plus-Raman project with the goal of quantifying the amount and types of plastics in a fluidic environment. This will result in a Raman module for integration into the OF2i® platforms (one for benchtop laboratory analysis and one for the PAT sensor for production monitoring). This short white paper Raman analysis plus OF2i shows that Raman scattering is sufficient for identifying particles in the micrometer range. We are now concentrating on Raman detection of microparticles and nanoparticles.

The corresponding figure shows:
(a) P1 is a stably trapped single particle, P2 and P3 are agglomerations. The Raman spectra were obtained between the inserted squares
(b) The spectra of a single 5 µm particle sphere (P1), particle agglomerations (P2 and P3) and a reference spectrum of bulk polystyrene measured with a regular Raman microscope.

What do you get with OF2i®?

With OptoFluidic Force induction you get a number of benefits, including speed of results, continuous, real-time and online measurements, detection of extremely low particle concentrations and analysis which is statistically relevant as it considers up to 1000 particles per minute.

Benefit 1:
Enjoy faster particle analysis in real-time

The OF2i® method delivers faster results than conventional methods for particle characterization. Measurement data is available in real-time and can be monitored live. For the first time, you get insights into particle behavior, formation processes and sample stabilities and results are available instantly. Due to automated cleaning routines you will also save time and money.

Benefit 2:
Get representative data for the whole particle population

OF2i® also sets new standards in terms of accuracy. From now on it doesn’t matter whether you want to monitor particle behavior for a few seconds or for hours. OF2i® is able to measure around 1000 particles per minute at concentrations ranging from a few particles up to 10⁸ per milliliter. Particle sizes from 50 nm* to 5 µm* (*sample-dependent, a large-particle module up to 50 µm is planned) are detected, which means that measurement results deliver precise and representative data for the whole particle population. OF2i® delivers actual D-values, and even resolves complex, polydisperse samples.

Benefit 3:
Measure continuously during production

BRAVE B-Continuous is an online PAT sensor which integrates into the production plant to deliver insights into particle behavior in real-time. This leads to unprecedented benefits for quality control. As OF2i® is capable of monitoring and controlling the particle behavior during the production process the risk of out-of-spec product is reduced radically and waiting for results from the lab is no longer as critical. With OF2i® you can look inside your product to ensure high quality and monitor the health of your production plant.

Benefit 4:
Detect ultra-low particle concentrations

Particularly with ultra-low sample volumes as well as the detection of ultra-low particle concentrations OF2i® flexes its muscles. Thanks to the extreme sensitivity of the particle measurement technology OF2i® provides reliable and representative results for sample volumes starting at 20 µL and offers a detection range from 50 nm* to 5 µm* (*sample-dependent). Even a few particles per milliliter can be detected (e.g. for the detection of nanoplastics in water).

All the benefits of OptoFluidic Force Induction particle analysis

Send us your sample – and we’ll do the rest

OF2i® already simplifies work and optimizes outputs for selected partners

By using the OptoFluidic Force Induction particle size distributions, particle concentrations as well as particle sizes can be monitored in real-time and during production. This groundbreaking technology is used already in various industries, where OF2i® successfully complements or replaces established methods like DLS, NTA, TEM or Laser Diffraction.

OF2i® devices

Our revolutionary OF2i® method is currently available in two different products. BRAVE B-Curious is a benchtop nanoparticle analyzer for continuous, time-resolved characterization of nanoparticles in the lab. It also measures and captures ultra-low particle concentrations. BRAVE B-Continuous is an online PAT sensor which can be directly integrated into your production plant to monitor and control the manufacturing process. Both products provide new insights into particle behavior and will revolutionize your research and production.

See (nano)particles like never before with BRAVE B-Curious

If you characterize nanoparticles, do you want more meaningful and continuous insights into particle behavior? This is not easy to achieve with current methods. With BRAVE B-Curious you get a nanoparticle analyzer that shows you what is really happening inside your samples – as it occurs. Our benchtop nanoparticle analyzer even measures ultra-low concentrations and delivers representative results for the whole particle population. We are convinced that BRAVE B-Curious is on its way to revolutionize many fields of research.

Brave B-Curious - Sensormodul und Bildschirm mit H.A.N.S. Screen

Produce like never before with BRAVE B-Continuous

The OF2i® method can revolutionize production processes and increase the efficiency of production. As BRAVE B-Continuous directly integrates into the manufacturing process as an online PAT sensor it analyzes particle behavior seamlessly and in real-time. This leads to reduced costs, saves time and prevents out-of-spec production. Thanks to 24/7 production control, adjustments can be made immediately and directly. It is also easy to monitor the health of the production plant and carry out predictive maintenance. This heralds a new era for process monitoring, in-process quality control (IPQC), predictive maintenance, the identification of critical process parameters (CCP) and monitoring of critical quality attributes (CQA).
Brave Analytics - Aufnahme von Brave B-Continuous Rack

When is OF2i® a better alternative to DLS, NTA or laser diffraction?

OF2i® outpaces established particles analysis technologies in a number of ways. Although established methods like DLS, NTA or laser diffraction are well-suited for certain tasks each method has its limits. If you want to understand dynamic processes, resolve complex polydisperse systems or take a closer look at all the particle populations in your sample (with additional in-flow Raman analysis available), OF2i® is an excellent choice. For production processes OF2i® has many benefits as well. OF2i® delivers true online process control with the ultimate goal of achieving real-time release testing and saving time, waste and preventing out-of-spec formulations.

OF2i® is fast.

With OptoFluidic Force Induction results are available in seconds. OF2i® measures up to 1000 particles per minute so results are statistically relevant.

OF2i® measures continuously.

Whereas other methods for particle characterization deliver one-off "snaphots" of particle behavior, OF2i® delivers live measurement data continuously over seconds, minutes or even hours (and 24/7 with the PAT sensor).

OF2i® has single-particle sensitivity.

With OF2i® you can detect and analyze single nanoparticles trapped in the laser beam. The results for particle size, particle size distributions and particle concentration are highly accurate and statistically relevant, even for ultra-low concentrations and ultra-low sample volumes. The results are representative of the entire particle population.

OF2i® measures in real-time.

All measurement results are available as a live data stream in a matter of seconds and allow continuous monitoring of particle behavior. While established methods for the analysis of particles are typically not able to measure online during production, OF2i® delivers true process monitoring 24/7.

Method DLS NTA LD OF2i®
Integrable into the production process
Continuous measurement in a lab
Measurement of particle concentration
yes, clearly defined active measuring volume
Measurement of particle size distribution for monodisperse samples
Measurement of particle size distribution for polydisperse samples
Detection range (particle size)
1 nm to 10 µm (sample-dependent)
10 nm to 1 µm (sample-dependent)
10 nm to 3 mm (sample-dependent)
50 nm to 5 µm (sample-dependent)
Monitoring of dynamic processes
Continuous particle identification with in-flow Raman analysis

How OF2i® was invented

It started with a problem
Christian Hill, now CEO and CTO of BRAVE Analytics, was frustrated with the particle analysis methods he was using in experiments for his PhD research. Looking around for alternatives, he found research by Arthur Ashkin describing the “optical tweezers” principle Ashkin invented to trap particles using a tightly focused laser beam. Chris began to wonder how this idea might be used to get a better look at particles. After spending many hours thinking about this theory, reading and thinking some more, Chris was motivated to create a laser setup in a small laboratory on the Medical University of Graz campus.

What started with the answer
The end result was a new and patented method for particle analysis: OF2i® (OptoFluidic Force Induction) method. OF2i® is a completely new approach to characterizing particles and nanoparticles. It delivers measurement results for nanoparticle size, nanoparticle size distribution as well as nanoparticle concentration – in a continuous and time-resolved way – and BRAVE B-Continuous even measures online during production processes. 

How OF2i® overcomes the limits of Brownian motion

OptoFluidic Force Induction takes the “optical tweezers” principle pioneered by Arthur Ashkin a number of steps further: it focuses a donut-shaped laser through the liquid sample to exert optical force on the particles that pushes them forward and turns them around the beam’s center.
Why trap and accelerate?
OF2i® traps the nanoparticles but allows them to continue moving along their spiral trajectories. Accelerating the particles means they are no longer displaying Brownian motion, their movement is much faster and, in fact, the speed of their movement correlates with their particle size. Keeping the particles on their own trajectories minimizes interparticle collisions that would disrupt measurement and makes it easy to follow the particles as they accelerate. In the OF2i® setup a microscope records the velocity change due to these optical forces which is used to calculate the particle size.

Publication in Physical Review Applied: "Theoretical Description of Optofluidic Force Induction"
Šimić et al

How does OptoFluidic Force Induction work?

While established particle analysis technologies are based on Brownian motion and therefore subject to restrictions and irregularities, OF2i® goes one step further and accelerates nanoparticles with defined fluidic and optically induced forces. With OF2i® a laser beam propagates through a flow cell. In this case it only takes minimal photonic forces to accelerate, decelerate or redirect the nanoparticles regardless of their Brownian motion. By using an ultramicroscopic setup OF2i® can obtain the intensities from single particle light scattering, the single particle trajectories and the particle number per transported volume. With the obtained data the opto-fluidic force induction technology is able to determine particle sizes, particle size distributions and particle concentration continuously and in real-time – and all this with a throughput of up to 1000 particles per minute.

Structure and working principle of the OF2i® method

The basic structure of the OF2i® nanoparticle measurement technology consists of a laser (532 nm linear polarized CW DPSS with a maximum output power of 2W), a microfluidic channel and an ultramicroscope (10x PLAN microscope objective). First nanoparticles are pumped through a liquid in a cylindrical flow cell. Then a weakly focused vortex or Laguerre-Gaussian laser beam with an orbital angular momentum (OAM) is focused through the sample. The laser exerts optical forces on the nanoparticles so they move along spiral-shaped trajectories, this reduces collisions between particles to a minimum. The nanoparticles excited by the laser beam scatter the light, which is monitored by the ultramicroscope objective and recorded by a CCD camera at a rate of 200 frames per second. In addition OF2i® gathers information about the scattering cross-sections and uses particle tracking to determine the velocities of the individual particles. A computer controls laser output power and the fluidic flow.

The theory of the OF2i® principle based on Mie scattering

Mie theory describes the scattering phenomena of electromagnetic waves on spheric particles. For the OF2i® principle we have developed a theoretical model for Mie scattering of a spherical nanoparticle excited by a Laguerre-Gaussian laser beam. This requires a multipole expansion of the electromagnetic fields in terms of spherical Bessel and Hankel functions as well as vector spherical harmonics. The electromagnetic fields outside of the nanosphere can then be represented by the multipole coefficients an, bn, where n labels the different spherical degrees and orders. Against this background the theoretical principle of OF2i® can be described in three steps.

Step 1:

First, we compute the coefficients aincn, bincn for the incoming fields of the Laguerre-Gaussian beam following the approach of A. D. Kiselev and D. O. Plutenko, Phys. Rev. A 89, 043803 (2014).

Step 2:

By employing the usual Mie coefficients we compute the coefficients an, bn for the scattered electromagnetic fields.

Step 3:

Finally, from the sum of incoming and scattered electromagnetic fields, we compute the force acting on the spherical nanoparticle using the analytic expressions given in R. Gutierrez-Cuevas, N. J. Moore, and M. A. Alonso, Phys. Rev. A 97, 053848 (2018).

As input for the OF2i® principle we only require the refractive indices of the nanosphere and the embedding medium. As the vortex field is known, we obtain the optical force Fopt(r) acting on the nanosphere at some position r. Using Newton’s equation of motion and Stoke’s equation for viscous flows, the exact velocity distribution in the nanosphere v field can be calculated.

With this formula we can start a brave venture into a new era of nanoparticle characterization:

v(r) = vfluid + Fopt(r)/6πR

The theoretical model of the OF2i® principle contains no free parameters. This means it only requires calibration of the predetermined video image scale and the measured input laser intensity. OF2i® is a calibration-free method for our customers.

The three types of trajectories of the OF2i® principle

As soon as the laser beam reaches the nanoparticles in the sample, they are trapped and move along the intensity maxima of the vortex beam. Nanoparticles that have not been trapped by the beam are transported by the fluid in the transverse direction. With OptoFluidic Force Induction we can distinguish three types of trajectories.


If nanoparticles are trapped from the beginning and are accelerated by the optical forces their velocity curves are in almost perfect agreement with the maxima of the experimental velocity histograms.


There are also nanoparticles that initially do not move along the intensity maxima but these are deflected by the optical forces and finally become trapped while propagating down the flow channel.


Finally there are nanoparticles that are not trapped by the laser or the optical forces. They do not scatter light and remain dark in the analysis algorithms.

Send us your sample – and we’ll do the rest

Find out whether OF2i® measurements are the answer to your particle challenges!
Get in touch, we’ll organize measurements on your sample(s) and send you a detailed measurement report.
This is the first (non-binding) step to a feasibility study. Open the door to deeper insights today!

These industries can be revolutionized by OF2i®

Initial use cases
have shown that OptoFluidic Force Induction can provide unprecedented insights into particle activity. These include applications in pharma and biotech, cosmetics, medical research and water analysis. We also see potential in microelectronics, coatings and environmental analysis. The applications of the groundbreaking OF2i® method are almost limitless.

Brave Analytics - OF2i OptoFluidic Force Induction Prinzip Illustration

Applications of the OF2i® principle in the pharmaceutical and biotech industries

Especially in the production and monitoring of pharmaceutical emulsions, infusions, vaccines or pain killers, exact particle size distributions have be monitored and guaranteed. The BRAVE B-Continuous PAT sensor is already delivering results in a pilot plant for optimizing the production of total parenteral nutrition (TPN) formulations produced in high-pressure homogenization steps. The lab device BRAVE B-Curious is successfully used for research on liposomes, proteins, vaccines and virus-like particles.

Why OF2i®?

Due to OF2i’s single-particle sensitivity and its ability to resolve even complex, polydisperse systems it is delivering pioneering results in biotech and pharmaceutical applications.

Applications of the OF2i® method in the beauty and cosmetics industry

When producing cosmetics products such as sunscreens, the EU requires nanoparticles below a certain size to be declared on the labeling. With OF2i® you can produce cosmetics that just contain particle sizes up to the limit and not below.

Why OF2i®?

Due to its single-particle accuracy and the possibility to measure directly in the production process, OF2i® can ensure that the particle size limit is not exceeded.

OF2i® applications for environmental analysis

Waste water that is led back into rivers or seas must be analyzed meticulously to ensure it has no negative affects on the environment. Bottled and tap water also have to comply with strict regulations. Whether waste water, bottle water or tap water, OF2i® detects even the smallest nanoplastic particles, viruses, bacteria, antibiotics or other contaminations.

Why OF2i®?

No other method for particle characterization is capable of detecting ultra-low concentrations in waste water or drinking water with this degree of sensitivity.

OF2i® revolutionizes basic research

Whether researching biomolecular condensate formation, drug dissociation and dissolution or the production of virus-like particles OF2i® gives insights into the processes unlike anything seen before. OF2i® makes it possible to monitor kinetic processes such as the formation and size distribution of proteins, lipids and extracellular vesicles over time.

Why OF2i®?

Of all the methods for particle characterization only OF2i® is able to monitor sample kinetics seamlessly and continuously over time.

Applications in industrial research

The possibilities of OF2i® are endless for industrial research. In the case of chemical-mechanical-planarization and polishing, for example, the particle size distribution of the CMP slurry is a critical parameter for the success of the process. OF2i® is well-suited to detecting large-particle tails in the slurry. OF2i® also contributes to online quality control of nanocomposite electroplating processes in order to obtain a more homogeneous particle size distribution, reduced particle size, and upgraded final products. 

Why OF2i®?

With OF2i® you obtain more accurate measurement results of particle sizes, particle size distributions and representative data for the whole particle population. This minimizes critical problems during production processes and reduces rejects. In the field of electroplating OF2i® can monitor nanoparticle concentrations continuously in the electrolytic bath.

Using OF2i® for dental medicine and for the treatment of bone defects

Hydroxyapatite nanocrystals are used for the treatment of bone defects and for the remineralization of tooth enamel. For online quality control during the production of these crystals the OF2i® method has been implemented as a PAT sensor. 

Why OF2i®?

OF2i® has many benefits in the field of online quality control. Hydroxyapatite nanocrystals can be monitored and controlled during production. The gathered measurement results are representative for the whole particle population and are displayed continuously. 

Benefits of the OF2i® method and groundbreaking features

We already collaborate with selected companies and universities which now use OF2i® technology to achieve groundbreaking results in their production and research. These brave pioneers use our patented method for nanoparticle characterization to get a step ahead of their competitors and reach new levels in their research. If the conventional methods for particle measurement limit your research or you want to increase the efficiency of your production, we are happy to present our revolutionary method in a live demonstration. Our experts will answer all your questions and discuss further steps.

Learn more about OF2i® and become a first mover.

Brave Analytics - Graph zu Methodenvergleich OF2iBrave Analytics - Graph zu Methodenvergleich OF2i