Electrokinetic Preconcentration and Detection of Neuropeptides at Patterned Graphene-Modified Electrodes in a Nanochannel

Abstract

Neuropeptides are vital to the transmission and modulation of neurological signals, with Neuropeptide Y (NPY) and Orexin A (OXA) offering diagnostic information on stress, depression, and neurotrauma. NPY is an especially significant biomarker, since it can be noninvasively collected from sweat, but its detection has been limited by poor sensitivity, long assay times, and the inability to scale-down sample volumes. Herein, we apply electrokinetic preconcentration of the neuropeptide onto patterned graphene-modified electrodes in a nanochannel by frequency-selective dielectrophoresis for 10 s or by electrochemical adsorptive accumulation for 300 s, to enable the electrochemical detection of NPY and OXA at picomolar levels from subnanoliter samples, with sufficient signal sensitivity to avoid interferences from high levels of dopamine and ascorbic acid within biological matrices. Given the high sensitivity of the methodology within small volume samples, we envision its utility toward off-line detection from droplets collected by microdialysis for the eventual measurement of neuropeptides at high spatial and temporal resolutions.

Nanoslit design for ion conductivity gradient enhanced dielectrophoresis for ultrafast biomarker enrichment in physiological media

“…Our prior work has implemented this methodology within various sensing paradigms for improving biomarker sensitivity. 22,23 A cross-section view of the device geometry used within this work is schematically presented in Figure 1(a) (device images in S1, supplementary material), wherein glassy carbon modified Pt electrodes within the reservoirs leading to a microchannel on each side are used to initiate the discussed electrokinetic effects under a DC-offset (2 V/cm) AC field (70 V rms /cm) that is set at the critical frequency required to cause optimal biomarker nDEP, which is 1 MHz for streptavidin, 3 MHz for Neuropeptide Y (NPY), 22 and 4-6 MHz for Prostate Specific Antigen (PSA). 23 The microchannels (5 lm depth) are connected by slit-shaped channels of 200 nm depth (henceforth called nanoslit).…”

“…In fact, our prior work quantified this at 10 4 -10 5 -fold concentration enhancement in the preconcentration region 19 and $10 3 -fold enhancement in analyte binding at capture probe surface. 22,23 This is apparent from the sharp rise in fluorescence signal to saturation levels in Figure 4 . (iii)).…”

“…[20][21][22][23] Furthermore, the highly localized nature of DEP behavior, due to its dependence on rE 2 , limits its spatial extent. 13,24 Herein, by initiating ICP at lateral perm-selective constrictions of large surface charge non-uniformity, we create conductivity differences across the nanoslit length to enhance the spatial extent for biomarker depletion.…”

Suspended particle transport through constriction channel with Brownian motion

“…There are many situations where small objects subject to Brownian motion in a fluid are introduced to the constriction of microscopic channels, for example, filtration of colloidal particles through porous media [1][2][3], translocation of DNA molecules through nanopore sequencers [4][5][6][7][8][9][10][11][12][13][14][15][16][17], and lab-on-achip (LOC) devices where analytes are introduced to various domains of nano-and microchannels for analysis [18][19][20][21][22][23][24][25]. It is now well known that the translocation phenomena of polymer molecules through nanopores with a diameter comparable to the monomer size have stochastic nature [5,6].…”

Quantifying spatio-temporal dynamics of biomarker pre-concentration and depletion in microfluidic systems by intensity threshold analysis

“…2 Micro/nanofluidic device methodologies are routinely applied towards enabling analyte preconcentration within physiologically relevant media [3][4][5] for reducing target diffusion time towards the sensor 6 and thereby enhancing detection sensitivity. 7 Selective pre-concentration also enables analyte enrichment over interfering proteins and small molecules, 8 which is especially relevant given the wide concentration range of proteomic biomarkers within typical biofluids (mg/ml-pg/ml). 9 In order to capitalize on the reduced diffusion lengths towards the sensor upon analyte pre-concentration within microfluidic and nanochannel geometries, there is a need to effectively overlap the pre-concentration and detection regions for ensuring enhanced target binding kinetics at the sensor.…”