Facile decoding of quantitative signatures from magnetic nanowire arrays

Abstract

Magnetic nanoparticles have been proposed as contact-free minimal-background nanobarcodes, and yet it has been difficult to rapidly and reliably decode them in an assembly. Here, high aspect ratio nanoparticles, or magnetic nanowires (MNWs), are characterized using first-order reversal curves (FORC) to investigate quantitative decoding. We have synthesized four types of nanowires (differing in diameter) that might be used for barcoding, and identified four possible “signature” functions that might be used to quickly distinguish them. To test this, we have measured the signatures of several combination samples containing two or four different MNW types, and fit them to linear combinations of the individual type signatures to determine the volume ratios of the types. We find that the signature which determines the ratios most accurately involves only the slope of each FORC at its reversal field, which requires only 2–4 data points per FORC curve, reducing the measurement time by a factor of 10 to 50 compared to measuring the full FORC.

Magnetic Nanowires toward Authentication

“…In contrast to the standard remanence measurements, such as isothermal and DC demagnetization methods, the BRM method saturated the magnetic nanobarcodes before applying and removing a progressively more negative field. This controlled the magnetic switching of the MNWs in a more restricted manner that improved the readout signal reproducibility, more details regarding the BRM have been discussed previously, [ 38 ] some details in the Supporting Information were added too.…”

Magnetic Nanowires for Nanobarcoding and Beyond

“…Moreover, the MNWs are dominantly fabricated using electrodeposition techniques that are cheap, fast, and scalable for mass production [ 30 , 31 , 32 , 33 ]. More importantly, their magnetic response can be readily extracted from the background signals, leading to a high signal-to-noise ratio–suitable for miniaturizing the barcodes size [ 7 ]; this is because the majority of materials are diamagnetic or paramagnetic, which do not produce magnetic signals, such as irreversible switching, which is exclusively a property of ferromagnetic materials [ 34 , 35 ]. Thus, as opposed to optical- or radio-frequency barcodes, magnetic signals are not contaminated by the background noise [ 36 , 37 , 38 , 39 ].…”

“…As a result, there has been much progress in the development of instruments for fast and repeatable DC measurements. The DC measurements include hysteresis loop measurements, the first-order reversal curve (FORC) method [ 42 , 43 , 44 ], remanence curve method [ 45 , 46 ], and, most recently, the projection method and the backward remanence method [ 34 , 47 ]. The AC measurements are magnetic particle spectroscopy and ferromagnetic resonance spectroscopy, as the most well-established and common methods that might be transferrable to daily applications [ 23 , 48 , 49 ].…”

Unlocking the decoding of unknown magnetic nanobarcode signatures

“…Therefore, to further enhance the reliability and reproducibility decoding using the remanence spectra, we propose to use a modified remanence measurement that is different from the standard remanence measurements. We reported our protocol for this method, named "backward remanence magnetization (BRM)", in our previous work [35]. Details about the BRM measurement and how it is beneficial compared to the IRM and DCD measurements are fully discussed in ESI using experimental comparison.…”