Lab-on-a-disc agglutination assay for protein detection by optomagnetic readout and optical imaging using nano- and micro-sized magnetic beads

Abstract

We present a biosensing platform for the detection of proteins based on agglutination of aptamer coated magnetic nano- or microbeads. The assay, from sample to answer, is integrated on an automated, low-cost microfluidic disc platform. This ensures fast and reliable results due to a minimum of manual steps involved. The detection of the target protein was achieved in two ways: (1) optomagnetic readout using magnetic nanobeads (MNBs); (2) optical imaging using magnetic microbeads (MMBs). The optomagnetic readout of agglutination is based on optical measurement of the dynamics of MNB aggregates whereas the imaging method is based on direct visualization and quantification of the average size of MMB aggregates. By enhancing magnetic particle agglutination via application of strong magnetic field pulses, we obtained identical limits of detection of 25pM with the same sample-to-answer time (15min 30s) using the two differently sized beads for the two detection methods. In both cases a sample volume of only 10µl is required. The demonstrated automation, low sample-to-answer time and portability of both detection instruments as well as integration of the assay on a low-cost disc are important steps for the implementation of these as portable tools in an out-of-lab setting.

Rotating magnetic particles for lab-on-chip applications – a comprehensive review

“…The cluster assay was accelerated by the magnetic chain formation, to a time on the order of 5 min. The formation of chains can also be measured by recording the modulation of scattered light in a rotating magnetic field, as demonstrated around 2010 by Park et al 123 and Donolato et al 36,38 who monitored the transmission of light, and by Ranzoni et al [41][42][43] who monitored the scattered light under an angle (see Fig. 6B).…”

“…Another way to measure the concentration of target molecules is by a cluster assay. Here MPs are provided with capture molecules and form clusters in the presence of target molecules [30][31][32][33][34][35][36][37][38][39][40][41][42][43][44][45][46] (Fig. 1C).…”

“…One year later the same group published a paper showing that these rotating magnetic particle chains can be used to capture biological molecules. 9 This principle has been extensively studied in the years thereafter 11 and was used in many bio-sensing applications 35,37,38,42,43 (Fig. 1B and C) to significantly shorten assay times, typically from 60-120 min to 15-30 min.…”

“…BluSense combines magnetic actuation with existing bluray technology, where the rotational motion of a disk-shaped cartridge gives microfluidic actuation and optical detection is used to measure cluster formation. 38 With a detection angle of the scattered light at 90 degrees, Ranzoni et al 43 demonstrated that the concentration of PSA in undiluted blood plasma could be measured in the low picomolar range, by recording the amplitude of the 2f signal (at twice the driving frequency). Vliembergen et al 124,125 have extended the optical detection method by analyzing the rotation-angle dependent scattering signals.…”

A primary SERS-active interconnected Si-nanocore network for biomolecule detection with plasmonic nanosatellites as a secondary boosting mechanism

“…Of the available techniques used for biosensing with nanomaterials, which include electrochemical, 1 pyroelectric 2 and optical techniques, 3 SERS-based biomolecule detection offers distinctive advantages compared to the other methods including ultrahigh sensitivity 4 and high specicity. 5 For biomolecule detection with SERS, most sensing platforms utilize the surface plasmon resonance (SPR) mechanism characteristic of noble metal nanostructures (NMNs) as the primary source for SERS enhancement.…”