(381b) Enabling Ultrafast Immunoassays By Dielectrophoretic Biomarker Enrichment on a Nanoslit Device Platform

Heterogeneous immunoassays usually require long incubation times to promote specific target binding and several wash steps to eliminate non-specific binding. Hence, signal saturation is rarely achieved at detection limit analyte levels, leading to significant errors in analyte quantification due to the extreme sensitivity of the signals to incubation time and methodology.  Additionally, conventional immunoassay methodologies are not well suited for working with the sub-nanoliter level sample volumes often encountered within point-of-care diagnostic and therapeutic applications, such as for the serial monitoring of cells from liquid biopsies. The poor binding kinetics of immunoassays at detection limit levels can be alleviated through creating a highly concentrated analyte plug that is localized in the vicinity of immobilized capture probes. A commonly investigated methodology for achieving highly concentrated analyte plugs from dilute samples is through electrokinetic enrichment due to ion depletion at the micro/nanochannel interface for coupling with pre-immobilized antibodies. An alternate methodology to enhance biomarker binding kinetics is by immobilizing antibodies inside nano-slit channels, since this device geometry significantly reduces the extent of the diffusion layer. However, no prior work has applied electrokinetic enrichment of the biomarkers inside nano-slit device geometries with immobilized capture probes, to explore the enhancement in analyte binding kinetics obtained by combining these two approaches. Herein, we present a device to achieve this outcome by coupling frequency-selective dielectrophoretic enrichment of the target biomarker in physiological media to capture probes immobilized in a nano-slit channel to enable ultrafast immunoassays that exhibit near-instantaneous (< 2 minutes) signal saturation with dilute biomarker samples (picomolar levels) within ultra-low sample volumes (picoliters). By coupling dielectrophoretic biomarker enrichment with electrochemical detection methods, we are able to eliminate the need for wash steps to remove excess secondary antibody or reporter molecules, since electron transfer rates steeply drop-off for electroactive molecules localized beyond a few nanometers from the electrode surface. Based on the reduced signal variations at early time points with detection limit levels of Prostate Specific Antigen, and the relative insensitivity of the signals to incubation time at later time points, we envision a method for carrying out more accurate immunoassays using analyte enrichment in nano-slits.

References:

B. Sanghavi, W. Varhue, J. Chavez, C.F. Chou, N. S. Swami; “Electrokinetic preconcentration and detection of neuropeptides at patterned graphene-modified electrodes in a nano-channel device”, Anal. Chem. (2014), 86 (9), pp 4120–4125.