Genome Technology Center

Biomolecular Detection based on Micro-channel Gating


Mehdi Javanmard

We are focused on developing an inexpensive technique which can be applied to rapidly recognition of pathogenic bacteria and also target protein biomakers. Traditionally, microbiological techniques such as culture enrichment and various plating techniques have been used for detection of pathogens. These expensive and time consuming methods can take several days. More recently, the Cepheid GeneXpert automated sample preparation and real-time PCR detection system, has shown to be a rapid and reliable technology for detection of Bacillus Anthracis. Current microbiological techniques used for protein biomarker detection, involve time consuming methods based on sandwich immunoassays, requiring expensive labeling.

Our technique involves the use of a micro-channel functionalized with receptors specific to the target biomarker. Electrodes are integrated in the micro-channel for monitoring the impedance across the channel. For pathogenic bacteria detection, we monitor the impedance across the channel as bacterial cells pass through the channel. Bacterial cells captured by the receptors on the channel wall result in a steady-state increase in the impedance across the channel.

The same device is also used for detection of target biomarkers. For this application, we stain the target biomarker with polystyrene microspheres coated with primary receptors having an affinity to the biomarker. The functionalized beads are then incubated in the micro-channel. The beads which have captured the target biomarkers will then bind to the channel wall forming a sandwich assay. A flow is then applied to the channel causing the unbound beads in the channel to be flushed out. The percentage drop in the impedance across the channel is proportional to the percentage of beads remaining attached to the channel walls. Thus, in addition to detection, this technique can be used to quantify the biomarkers as well.

As a proof of principle, we have successfully demonstrated real-time detection of target yeast cells by measuring instantaneous changes in ionic impedance. We have also demonstrated the selectivity of our sensors in responding to target cells while remaining irresponsive to non-target cells. Using this technique, it can be possible to multiplex an array of these sensors onto a chip and probe a complex mixture for various types of bacterial cells.

We have also applied our biochip to the detection of target protein biomarkers using protein functionalized micro-channels for the rapid electrical detection and quantification of any type of target protein biomarker in a sample. We successfully demonstrate detection of anti-hCG antibody, at a concentration of 1ng/ml and a dynamic range of three orders of magnitude, in less than one hour.

In this proposal, we envision the use of this technique in a handheld device for multiplex high throughput analysis using an array of micro-channels for probing clinically relevant samples such as the human serum for various protein biomarkers for cancer detection, and also the detection of pathogenic bacteria in solution. For Pathogen detection we aim to achieve a detection limit of less than 10 CFU/ml. For target biomarker detection, we aim to achieve a detection limit of 1 pg/ml, lower than conventional detection methods like ELISA. Finally we will integrate our multiplexed biosensors and a CMOS integrated circuit into a portable handheld device, making the technology suitable for point-of-care diagnostics.

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