PicoMolar level detection of protein biomarkers based on electronic sizing of bead aggregates: theoretical and experimental considerations

Abstract

We demonstrate a novel method for electronically detecting and quantifying protein biomarkers using microfluidic impedance cytometry. Our biosensor, which consists of gold electrodes micro-fabricated in a microchannel, detects the differences between bead aggregates of varying sizes in a micro-pore sandwiched between two micro channels. We perform a sandwich immunoassay, where the complementary antibody pairs are immobilized on two different bead types, and the presence of antigen results in bead aggregation, the amount of which depends on antigen quantity. When single beads or bead aggregates pass through the impedance sensor, differences in impedance change are detected. In this manuscript, we perform a comprehensive theoretical study on the limits imposed on sensitivity of this technique due to electronic noise and also mass transfer and reaction limits. We also experimentally characterize the performance of this technique by validating the technique on an IgG detection assay. A detection limit at the picoMolar level is demonstrated, thus comparable in sensitivity to a sandwich ELISA.

Towards low-power wearable wireless sensors for molecular biomarker and physiological signal monitoring

“…2. The molecules passing the electrode will produce pulses in the voltage output as described in [2], [9]. The physiological signal sensing continuously acquires signals from electrical measurement.…”

“…The use of integrated and embedded computing power has enabled wearable electronic systems for monitoring various physiological signals [1]. Meanwhile, we have also demonstrated the detection of various biomolecules in blood using impedance-based biodetection, which has the potential to enable truly miniaturized wearable diagnostic platforms [2]. The combination of wearable devices for continuous biomolecular measurements and physiological parameter acquisition can provide a more accurate understanding of the physiological state of millions of individuals and enable the new paradigm of "crowd-sourced" biomarker discovery and validation.…”

A portable battery powered microfluidic impedance cytometer with smartphone readout: towards personal health monitoring

“…We used the exact same sensor fabrication process as we did previously (Lin et al 2015), however, we briefly describe the process here. The microfluidic channel was constructed by casting polydimethylsiloxane (PDMS) on the master mold.…”

“…Impedance cytometry (Emaminejad et al 2015), which is based on electrical detection, is advantageous over optical readout because of the potential for developing instrumentation with a small footprint. We have previously shown how electrical impedance cytometry can be used towards detection of proteins (Mok et al 2014), cells (Emaminejad et al 2015), and nucleic acids (Javanmard et al 2011) with high specificity and sensitivity (Lin et al 2015). Significant improvements in wireless technology have also made it possible for hand-held medical devices to wirelessly connect with miniaturized computing devices like smart phones and tablets, thus making results readily available for both the patient and medical professionals.…”

Rapid Assessment of Surface Markers on Cancer Cells Using Immuno-Magnetic Separation and Multi-frequency Impedance Cytometry for Targeted Therapy

“…Previously, we demonstrated the feasibility of using digital electronic detection of protein biomarkers 22 and also the ability to fully miniaturize the footprint of the readout instrumentation to portable and wearable platforms 23,23 . We also demonstrated electronic bead aggregate sizing for protein biomarker detection and quantification of soluble proteins 25 . We also demonstrated label-free classification of drug sensitive cells using multi-frequency impedance cytometry in conjunction with supervised machine learning 26 .…”