(37b) Dielectrophoretic Preconcentration and Detection of Neuropeptides at Graphene-Modified Electrodes in a Nanochannel

Neuropeptides offer information on the chemistry, biology and pharmacology of the nervous system. However, their presence at picomolar levels within nanoliter-scale microdialysis samples poses analytical challenges due to interferences from other biomolecules at far higher levels. NPY is an especially significant biomarker, since it can be non-invasively collected from sweat, but its detection has been limited by poor sensitivity, long assay times and the inability to scale-down sample volumes. Herein, based on our prior work on dielectrophoretic trapping of proteins within nanochannels [1-3], we apply electrokinetic preconcentration of the neuropeptide onto patterned graphene-modified electrodes [4] in a nanochannel [5] by frequency-selective dielectrophoresis (DEP). While DEP has been extensively applied previously to sort micron-sized biological cells based on their electrophysiology, its application to separate nanoscale biomolecules in physiological media is limited by the cube-fold drop in trapping force with size of the polarized particle and an increase in disruptive electrothermal flow due to non-uniform Joule heating. We have overcome this limitation by using a nano-slit device design with sharp constrictions to enhance trapping forces, while reducing Joule heating due to enhanced heat dissipation at nanochannel interfaces. In this manner, through localized concentration enhancement of NPY on graphene-modified electrodes in a nanochannel that were optimized for high conductivity and fast adsorption kinetics, we demonstrate picomolar detection sensitivities within seconds from sub-nanoliter micro-dialysates. In follow-up work, we are exploring the coupling of this paradigm with aptamers for improving detection selectivity for electrochemical detection of neuropeptides within bio-fluid matrices including interfering electroactive peptides. Based on the ability of this methodology for detection sensitivities comparable to immunoassays, but with far more rapid assay times than immunoassays and with far less sample volumes, we envision its application within off-line detection from dialysates for measurement of neuropeptides at high spatial and temporal resolutions.

References

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