Since early 2013 I’m contributing to the SEPMAG blog. You can found there my last Posts about Biomagnetic Separation.
As Chief Scientific Officer of the company, I’m also helping our marketing department to edit several eBooks on the subject. You can download them at www.sepmag.eu/resources.
I hope you would enjoy the materials we are publishing the SEPMAG’s team!
Illustration: anatomyblue
Dr. Sylvain Martel explains at the last issue of the IEEE Spectrum (the journal of the Institute of Electric and Electronic Engineers) the research his team is doing at the École Polytechnique de Montréal.
The article describes how they use an MRI machine for robotic navigation. Using the extremely high and uniform field, they strongly magnetize the bead. As the field is uniform, the bead doesn’t move. Then, the gradient coils are activated and the bead pushed forward. By changing the direction of the gradient field, the bead moves through the artery.
The group of Dr. Martel plans to use as microbot the MC-1, a 2 µm diameter magnetotactic bacteria with a chain of iron oxide nanocrystals (magnetosomes). They can attach the drugs to the surface and, as the magnetic charge is big enough, use electromagnetic coils for orienting the magneic field by varying the current. The magnetostatic bacteria then navigates the twists and turns of the vascular network.
An online version of the article, with the title “Magnetic Microbots to Fight Cancer” can be found at the spectrum site http://spectrum.ieee.org/robotics/medical-robots/magnetic-microbots-to-fight-cancer
The major event on Diagnostics in Northamerica, the anual meeting of the American Association for Clinical Chemistry (AACC) will be held in Los Angeles Convention Centre the July 15–19. As part of the Conference Program, several Industry Workshops are organized and Sepmag has get approved its proposal.
The session, we have prepared with my colleague Dr. Maria Benelmekki, will review most of the topics we discussed since 2004 with large IVD-kits producers (see details)
We have already organized in-house seminars with our major European customers for trainning their staff. As it seems the content was useful for them (they are still buying our technology!!), we took the opportunity the AACC offered to share the content with the conference attendees. If you are interested in participate, just send an e-mail to AACCseminar@sepmag.eu.
And if you atttend the AACC, don’t forgot to visit us at booth 4557 (if you wish to book an appointment, this the e-mail address: AACCappointment@sepmag.eu)
As it has been announced at the News (www.sepmag.eu), SEPMAG is sponsoring the 9th International Conference on the Scientific and Clinical Applications of Magnetic Carriers. We will insert our flyers in the abstracts booklet, but the organizers also asked us for a 1 minute video to be projected during the meeting. We already have a corporative video, but it is near 4 minutes long. Then we needed to meet with the marketing&video guys, and condense the message in just a minute. You may see the result at the Sepmag Youtube channel
Biomagnetic Separation Equipment in 1 minute
and if you wish to compare the short Ad-like version (1 min), focused on the equipment, with the original one (which includes an introduction to Biomagnetic Separation, the Sepmag technology and the company background), here is the link.
Sepmag: Homogeneous Biomagnetic Separation (4 min version)
For additional information on the subject, just check the Sepmag website (www.sepmag,eu).
This week I would like to explain an unsuccessful project. By unsuccessful I mean we don’t achieve the original goal. Nevertheless, we have learned a lot on the way and we hope we will use the developed know-how elsewhere.
Fig1. Earth Magnetic Field and Heart Rate Signal
The project startsed with our neighbours, a medical electronic engineering company (www.advancare.com). We try to combine their expertise on biomedical signal processing and the Atipic magnetic background (www.atipic-pro.eu). As biomagnetic signals of the brain are very weak, we choosen try to measure the cardiographic signals. Magnetocardiography is a fancy subject, but for using it as substitute of electrocardiography, the use of cryogenic SQUID sensors is needed. As the two companies involved we were quite small, focus on developing an equipment on the Million Euro range was out of our reach.
However, if you are not a cardiologist (or even so), may be you don’t need to have the whole cardiographic wave. Just using the time between successive R-R peak (the higher peak in the wave) you can get a lot of medical interesting information, as it does the sport pulsemeter you use for monitor your efforts when running.
Looking for possible applications, we contacted an automotive supplier who was interested on drowsiness detection. As we, at ATIPIC we have experience with cars and magnetic sensors we start to work: heart rate was a physiologic signal that could, potentially, alert when people fall asleep. If we were able to place a sensor on the seat or the seat belt, and measure how the beat rate changes with time, we can potentially save the life of ¼ of 1/3 of the people killed in cars accidents! And for this application, being contactless is a pre-requisite (the system should not require the person to be wired)
Figure 2. Affordable low magnetic field sensors
First we focus on commercially available sensors (automotive will need a solution on the range of few euros by unit). We built a magnetic dipole and feed it wit a cardiographic signal. Our first target was to measure 1 nT on lab environement. As the Earth Magnetic Field is in the range of 50,000 nT, it was a nice challenge.
Figure 3. Values of the Earth Magnetic Field at several cities
As you probably have guessed, of-the-shelf sensors were not suitable. We revised different approaches, and my partner Dr. Maria Benelmekki (now at Universidade do Minho), provided us an elegant solution. We decide to call the sensor BEN, ‘officially’ for Barcelona Enhanced Noise, but also as a recognition to their contribution.
With this new, home-made, and cheap sensor, we were able to measure magnetic fields on the desired magnitude (1/50,000 the Earth). However we get a nice surprise. Due the low background noise, we were measuring the 50 Hz of the electrical wires of the lab. That was an interference we will not have in a car, but it was limiting our efforts to push the sensor sensitivity limits.
Fig 4. Magnetic signals for a magnetic dipol with a current simulating heart beat (top) and noise generated by ac current on the lab (50 Hz)
We solved easily using a zero gauss chamber (basically several concentric cylinders of permalloy, a very high permeability material). Once we see the sensor was working in the picoTesla range, the point was how to use it out of the chamber.
Fig 5. Biomagnetic signals measured by BEN sensor in a shielded environment. Single sensor (left) and differential configuration (rigth)
We builded a differential configuration, some digital filtering, and, voilà!!! The heart-like signal appeared. (OK, it was not so straightforward, but my goal is encourage you to use magnetic sensors).
Fig 6. Biomagnetic signals measured with BEN differential sensor in unshielded environment
By this time, the parallel experiments to determine how to use beat rate as drowsiness detector were unconclusive, and the industrial partner cancelled the project due the technical risk (it was the right decision: their goal was to have a potential product in 3 years, and the results proved we will need additional basic research far beyond their budget and timing).
Then this is by now the end of the story: we have a very nice sensor we can still improve, we have proved it works fine measuring magnetic fields below 1 nanoTesla, but we have not application to working on.
If you have some ideas, just contact me… we will be glad to discuss how to cooperate!!! (martinez@atipic-pro.eu)
Will my magnetic particles separate so fast?
Commercial magnetic beads separate in seconds when you approach a magnet. The micrometer size and an appropriate magnetic charge do the job. However, when the size and/or the magnetic content decreases, separation time can increase to many hours.
I have been travelling around the globe on scientific meetings, sales call, workshop and seminars related with magnetic beads. There I was showing the performance of precision magnetophoresis systems my company was producing (www.sepmag.eu). After the demo, the people working on new applications of magnetic beads and/or producing nanobeads always asked me ‘Will my magnetic particles separate so fast?’
The answer is not easy. Fortunately my former colleagues at Universitat Autonoma de Barcelona campus are working hard on finding the answer (honestly, the discussion started at a lunch initially planned to talk about family, films and football).
We first we focused on understanding how the magnetic beads are separated: in short, when a big magnetic field is applied, the magnetic beads become saturated and, as any small magnet, align with the neighbour beads. This large chains gains magnetic moment as a whole and move faster than an isolated magnetic bead will do. If the beads are superparamagnetic, once the magnetic field disappears, the chains dissolved and the beads disaggregate by simple thermal diffusion.
The answer to a question opened a lot of new ones: Which parameters determine the chain-like aggregate formations? Or in simple words, when my beads will move fast (seconds) or slow (hours).
The short answer is that it will depend mainly on the magnetic moment of each single bead and their diameter, and slightly on the beads concentration.
With these three parameters, we can estimate the number of magnetic beads in the chains: if N>>1 your beads will separate quickly. If N<1 your beads will separate as isolated particles, then separation time will be large. I’ll not come on details on the simulations and calculations, if you are interested you can have a look on the published papers. But we can have a look on the resulting formula:
Number of magnetic beads on a chain when a magnetic field is applied
The number of beads will depend on the volume fraction, of dispersed solids in the suspension (easily calculated from concentration). Increasing the concentration a factor 4, the N* will double. But if your beads are slow (N<<1), it will be difficult in practice to change the concentration by several orders of magnitude.
The second part of the expression, is the gamma factor. As N depends exponentially on it, any small change will affect a lot to the N.
But what is gamma? My colleagues described as
Factors affecting exponentially the number of magnetic beads on chains, original formula
Apart of physical constants m0 and kB, we have temperature, something we can’t vary too much in Life Sciences, the saturation magnetic moment of the bead and their diameter. Note we are assuming the bead is saturated, i.e. the magnetic field applied is big enough (we have did the calculations for not-saturated case, but has less practical use for biomagnetic separation as the process time are much more longer…)
As experimental physicist, I prefer to express gamma as function of saturation magnetisation, Ms the value we can measure experimentally (Note Ms with capital ‘M’, is the magnetisation by unit of volume. If you measure magnetisation by unit of mass –emu/g-, just multiply by the beads density)
Factors affecting exponentially the number of magnetic beads on a chain, as I prefer to express
With this expression you can see the quantitative dependence of gamma: it growths as the cube of the bead diameter and the square of Ms.
How to take advantage of the theory to increase the performance of your beads?
We can calculate our N* using the above expressions. If the value is below 1, we can estimate the increase on diameter need to reach N>>1.
As probably, the resultant diameter will exceed the needs of your application, we should play with the magnetic properties. Increase a 10% the content of magnetic pigment will increase N* by a factor 3 (remember N is proportional to exp(d3Ms2)). It is worth a try!!
Of course, if you can change your magnetic charge by one with higher magnetisation saturation it will be better, but most probably it will affect the chemistry necessary for your beads.
I hope to have been able to help you to use the work of my colleagues for practical applications. If you wish go through the details, have a look on the references or send me an e-mail (martinez@sepmag.eu) if you need help to determine your N*.
References:
J. Andreu, J. Camacho, J. Faraudo. Aggregation of superparamagnetic colloids in magnetic fields: the quest for the equilibrium state. Soft Matter 7, 2336 (2011).
J. Andreu, J. Camacho, J. Faraudo, M. Benelmekki, C. Rebollo, Ll.M. Martinez. Simple analytical model for the magnetophoretic separation of superparamagnetic dispersions in a uniform magnetic field. Phys. Rev. E 84, 021402 (2011).
Since I started working on industrial applications of magnetism, different customers asked me the same questions. This blog will try to answer these doubts and, hopefully, show you the amazing possibilities of magnetism on several fields. From Life Sciences to Aerospace, from In Vitro Diagnostics to Automotive Components, I hope to help you to learn something new and, time to time, generate a spark that will start a new magnetic application.
Let us start next week with the most recurrent question when I show some one our Sepmag’s systems…”Will my magnetic particles separate so fast?”