Get more particle analytics than ever before

First came the OptoFluidic Force (OF2i) method, inspired by Arthur Ashkin’s optical tweezers. As a unique way of measuring the size and concentration of particles continuously, OF2i raised the bar on online (nano)particle characterization, providing single-particle accuracy and insights into complex polydisperse systems. After the launch of the first OF2i benchtop instrument, BRAVE B-Curious, the BRAVE team began working on additional particle analytics modules – and the idea for a Raman module, BRAVE B-Elementary, was born. Read on to learn how this optical trapping technique coupled with flow-through Raman spectroscopy will revolutionize the way you analyze particles.

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Bringing Raman analysis in-flow for continuous results

Is it possible to adapt the fundamentals of optical tweezers to hold particles in flow steady enough to read out their Raman spectra?  The answer is Yes. Using our knowledge of optical trapping (OF2i), we created a laser setup which either slows down or stops particles for a short time as they flow through the measuring cell. The resulting Raman analyzer works in-flow and identifies up to 120 particles per minute via their Raman spectra – with automated sample handling and almost no sample preparation.

How does combined OF2i®-Raman work?

Let’s look at the schematic of the OF2i®-Raman setup, here showing measurement of 5 µm polystyrene (PS) beads.
(a) Fluidic forces transport the particles through the cell; a focused laser beam optically manipulates the particles.
(b) A SCMOS camera records the scattered Raman signal of individual particles at up to 30 frames per second. The camera image shows the recorded light of three 5 µm polystyrene beads. (see Reference 1)
(c) The analysis of the camera signal (Raman spectra) is compared with a reference spectrum. (see Reference 1)
(d) The OF2i® signal uses the speed of each particle to calculate particle size. (see Reference 2)

Reference publications

1. Šimić M, Neuper, C, Hohenester, U, & Hill, C. (2023). Optofluidic force induction as a process analytical technology. Analytical and Bioanalytical Chemistry, 451(21), 5181-5191.
2. Neuper C, Šimić M, Lockwood T, Gonzalez de Vega R, Hohenester U, Fitzek H, et al. Optofluidic Force Induction meets Raman Spectroscopy and Inductively Coupled Plasma – Mass Spectrometry: A new hyphenated technique for comprehensive and complementary characterisations of single particles. ChemRxiv. 2023; doi:10.26434/chemrxiv-2023-hwgll This content is a preprint and has not been peer-reviewed.

Publication "OptoFluidic Force Induction meets Raman Spectroscopy and Inductively Coupled Plasma - Mass Spectrometry: A new hyphenated technique for comprehensive and ocmplementary characterisation of single particles"

Analysis of inorganic particles with phases / polymorphism

In a proof of concept (see Reference 2) for the combined OF2i-Raman measurement, titanium dioxide particles (P1, P2) were trapped and the phases analyzed to distinguish between rutile and anatase.

2. Neuper C, Šimić M, Lockwood T, Gonzalez de Vega R, Hohenester U, Fitzek H, et al. Optofluidic Force Induction meets Raman Spectroscopy and Inductively Coupled Plasma – Mass Spectrometry: A new hyphenated technique for comprehensive and complementary characterisations of single particles. ChemRxiv. 2023;
doi:10.26434/chemrxiv-2023-hwgll This content is a preprint and has not been peer-reviewed.

Analysis of microplastics

As a further proof of concept (see Reference 2), three microplastic particles were trapped by OF2i and the Raman spectra were analyzed by the BRAVE B-Elementary module.  

2. Neuper C, Šimić M, Lockwood T, Gonzalez de Vega R, Hohenester U, Fitzek H, et al. Optofluidic Force Induction meets Raman Spectroscopy and Inductively Coupled Plasma – Mass Spectrometry: A new hyphenated technique for comprehensive and complementary characterisations of single particles. ChemRxiv. 2023;
doi:10.26434/chemrxiv-2023-hwgll This content is a preprint and has not been peer-reviewed.

What are the benefits of OF2i®-Raman?

The combination of OF2i and Raman spectroscopy is unique and brings special benefits for your chemical analysis and particle characterization. 

When is OF2i® a better alternative to conventional Raman microscopes?

OF2i® + Raman has a number benefits compared to commercially available Raman microscopes.

OF2i® + Raman is for high-throughput screening.

OF2i-Raman is ideal for the chemical analysis of large volumes of liquid sample. Even non-specialists can operate the device: sample loading and cleaning are automated; operation requires significantly less user interaction than with Raman microscopes.

OF2i® + Raman measures in-flow.

Whereas Raman microscopes provide one-off analysis of a sample, the OF2i-Raman setup provides continuous analysis directly in-flow and over minutes or even hours. The combined method is also sensitive to ultra-low concentrations.

OF2i® + Raman has single-particle sensitivity.

The OF2i-Raman setup detects and traps individual particles as they flow through the measuring cell. A Raman spectra is recorded for each passing particle.

OF2i® + Raman requires minimum sample preparation.

With OF2i-Raman you do not need to prepare a substrate. Depending on your sample, you may not even need to filter the sample beforehand. The setup reads out Raman spectra from particles directly in liquid.

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Fields of use for the correlative OF2i®-Raman method

Combining optical trapping and size determination via OF2i with in-flow Raman analysis has the potential to revolutionize the following areas:

How Arthur Ashkin inspired OF2i®-Raman

The many uses of optical tweezers

Christian Hill, now CEO and CTO of BRAVE Analytics, first discovered the pioneering work of Arthur Ashkin during frustrating work on his dissertation. Chris was looking for a better way to measure particle sizes as part of his PhD at the Institute for Biophysics (Medical University of Graz).  Reading about the principle of optical tweezers led to many, many experiments in the small laser laboratory on the Medical University campus, eventually culminating in a “Eureka” moment – and the birth of the Optofluidic Force Induction (OF2i) principle.

Trapping particles on the donut beam
OF2i makes use of light’s capability to manipulate, move and “trap” particles to create the optimal conditions to determine number-based particle size and particle concentration from the speed of each individually trapped particle. OF2i® measurements are available as a PAT device BRAVE B-Continuous and for the lab: BRAVE B-Curious.

Using optical trapping for Raman analysis

Trapping particles in a laser beam not only has benefits for particle size determination. The setup for the BRAVE B-Elementary Raman module uses this capability to decelerate or even stop particles during continuous flow in order to read out a Raman spectra. The analysis is quick, user-independent and highly sensitive to ultra-low concentrations.

What the future holds

And because we know light can do so much more, the BRAVE team is already working on further projects to expand and complement our existing devices. Stay tuned for the launch of a separate measuring cell for determining the exact size of large particles (up to 5 µm) and much more in the pipeline.

Send us your sample - and we'll do the rest

Find out whether OF2i®-Raman analysis is 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!