A laboratory preprint reports that electroplated cobalt-platinum magnets on a flexible Kapton circuit board had an in-plane remanence reading of 0.24 tesla before annealing and 1.4 tesla afterward, while a separate microfluidic demonstration trapped some magnetic beads. The work presents the arrangement as a possible permanent-magnet platform for biosensors, but the reported evidence is a materials and device-engineering proof of concept rather than a validated biological device.
The manuscript is an arXiv preprint, version 1, dated 26 August 2026. The magnets were electroplated on copper pads on Kapton in three reported footprint variants: 9, 13.5 and 18 square millimetres. X-ray diffraction and vibrating-sample magnetometry were used for comparisons before and after annealing.
From copper pads to a thin CoPt layer
The reported manufacturing trials used current densities from 50 to 200 milliamps per square centimetre and plating times of two to four hours. The deposited magnets were then annealed under argon at 600 degrees Celsius for 30 minutes. That sequence describes how the samples were prepared; the supplied comparison does not by itself establish which process step accounted for the later magnetic readings.
The electroplating bath had a reported volume of 100 millilitres. Its listed concentrations were 0.0500 moles per litre of dinitrodiammine-platinum, 0.0515 moles per litre of cobalt sulfamate hydrate and 0.1000 moles per litre of ammonium citrate.
Three-dimensional microscopy measured the deposited layer at about 6.0 plus or minus 0.2 micrometres. In the COMSOL simulation, magnetic nanoparticles flowed in water through a microfluidic channel beside a CoPt magnet. The modeled magnet measured 2 millimetres by 4.5 millimetres and was 6 micrometres thick.
The before-and-after magnetic readings
Remanence is the magnetisation left after an external field is removed. In the in-plane VSM comparison, the reported value was 0.24 tesla before annealing and 1.4 tesla after it; the paper described the difference as about six times. The result is a before-and-after comparison, with no replicate uncertainty reported in the supplied analysis.
The out-of-plane VSM result was 5.7 millitesla before annealing and 470 millitesla after it. The in-plane result was stronger, and the reported easy magnetisation axis — the direction in which the material most readily stays aligned — ran parallel to the substrate.
XRD reported the disordered A1 and crystalline L10 structures, with lattice parameters of 0.3858 nanometres for a and 0.3727 nanometres for c. The reported axial ratio, a divided by c, was 0.966. EDX at 10 kilovolts measured 45.9 plus or minus 1.2 per cent platinum and described the cobalt-to-platinum composition as close to 50:50.
Model thresholds and a physical test
In the model, some particles were trapped at a remanence of 0.5 tesla, the majority at 1 tesla and all modeled particles at approximately 1.4 tesla. These are simulation thresholds, not measured capture rates in a working channel.
The physical channel demonstration showed some magnetic beads being captured, and reported no macroparticles developing and blocking the channel. The authors also reported that a 500-millitesla simulation showing some trapping matched an experiment using 470-millitesla out-of-plane remanence. No quantitative metric for that agreement was supplied.
A proof of concept, not a validated device
The size of the experimental and modeled sets is not clear from the supplied results: the number of fabricated magnets, measured specimens, simulated particles, channels and replicate measurements is not reported. The bead endpoint is qualitative; there are no reported figures for capture efficiency, throughput, precision, recovery, flow rate or blockage rate. The experiment therefore shows some beads being trapped, while all-particle trapping appears only as a model result.
The comparison before and after annealing does not isolate annealing from other uncontrolled influences. The results also do not experimentally establish manufacturing yield, repeatability, long-term stability, adhesion or thermal durability. And because the demonstration used magnetic beads rather than cells, clinical samples or a validated DNA workflow, it does not demonstrate cell capture, cell sorting, DNA extraction, DNA amplification or clinical performance.
The conclusion states that the process created a scalable permanent magnet suitable for biosensors and says that coercivity increased nearly tenfold. But absolute coercivity values and supporting measurements are not reported in the supplied results, and the scalability statement is not accompanied by manufacturing-yield, throughput or durability data.
Further work would need to test reproducibility across independently fabricated devices, quantify capture efficiency, throughput, recovery and operating flow limits, and examine stability during long-term or repeated thermal and fluidic exposure. The acknowledgements state that the research was supported by EPSRC funding EP/S019960/1.
Paper data and sources
Original title: PCB-Integrated CoPt Micromagnets for Magnetophoresis
Authors: Melissa Mitchell, Henrique Mira, Simon Bending et al.
Journal/Repository: arXiv
Status: Preprint, not yet peer-reviewed
First online: 2026-08-26
DOI: Not available
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