By utilizing a high-temperature superconducting quantum
interference
device (high-T
c SQUID) magnetometer, an
alternating current (AC) magnetosusceptometer, referred to as an analyzer,
was developed for ultrasensitive immunoassays. The analyzer has been
applied to assay biomarkers in human plasma associated with Alzheimer’s
disease (AD) and Parkinson’s disease (PD). The involved assay
methodology is the so-called immunomagnetic reduction (IMR). Such
an analyzer has been approved for clinical use in Taiwan and Europe.
The mass production of the analyzer is needed for clinical utilities.
The issue of exploring analyzer-to-analyzer variations in the performances
becomes critical. Unfortunately, there is no standard characterization
to determine the variations in performances among analyzers. In this
study, key characterizations, such as output signal stability, signal-to-noise
ratio, measured concentrations of a control sample, etc., are proposed.
In total, three analyzers are characterized in this work. The detected
biomarkers include amyloid peptides, total tau protein, phosphorylated
tau protein, and α-synuclein protein for AD and PD. Through
one-way ANOVA for any of the characterizations among the three analyzers,
it was found that there was no significant difference in any of these
characterizations among the analyzers (p > 0.05).
Furthermore, the three analyzers are applied to assay biomolecules
for AD and PD in reference samples. High correlations (r > 0.8) in measured concentrations of any of these biomarkers
in
reference samples were obtained among the three analyzers. The results
demonstrate that the proposed characterizations are feasible for achieving
consistent performance among high-T
c SQUID-based
AC magnetosusceptometers for assaying biomolecules.