“…The purpose of this design is to transport analytes from the bulk solution closer to the sensor surface, thus locally increasing the analyte concentration. A similar electrode configuration has previously been reported to lower the detection time [ 45 ] from 60 to 1 min and increase the limit of detection of nanowire field effect transistors by a factor of 10 4 , reaching the aM range [ 46 ]. The mechanism was explained as a combination of AC electro-osmosis and streaming DEP, enabling a DEP interaction with proteins that cannot be immobilized against the electro-osmotic conveyance.…”
The combination of extreme miniaturization with a high sensitivity and the potential to be integrated in an array form on a chip has made silicon-based photonic microring resonators a very attractive research topic. As biosensors are approaching the nanoscale, analyte mass transfer and bonding kinetics have been ascribed as crucial factors that limit their performance. One solution may be a system that applies dielectrophoretic forces, in addition to microfluidics, to overcome the diffusion limits of conventional biosensors. Dielectrophoresis, which involves the migration of polarized dielectric particles in a non-uniform alternating electric field, has previously been successfully applied to achieve a 1000-fold improved detection efficiency in nanopore sensing and may significantly increase the sensitivity in microring resonator biosensing. In the current work, we designed microring resonators with integrated electrodes next to the sensor surface that may be used to explore the effect of dielectrophoresis. The chip design, including two different electrode configurations, electric field gradient simulations, and the fabrication process flow of a dielectrohoresis-enhanced microring resonator-based sensor, is presented in this paper. Finite element method (FEM) simulations calculated for both electrode configurations revealed ∇E2 values above 1017 V2m−3 around the sensing areas. This is comparable to electric field gradients previously reported for successful interactions with larger molecules, such as proteins and antibodies.
“…The purpose of this design is to transport analytes from the bulk solution closer to the sensor surface, thus locally increasing the analyte concentration. A similar electrode configuration has previously been reported to lower the detection time [ 45 ] from 60 to 1 min and increase the limit of detection of nanowire field effect transistors by a factor of 10 4 , reaching the aM range [ 46 ]. The mechanism was explained as a combination of AC electro-osmosis and streaming DEP, enabling a DEP interaction with proteins that cannot be immobilized against the electro-osmotic conveyance.…”
The combination of extreme miniaturization with a high sensitivity and the potential to be integrated in an array form on a chip has made silicon-based photonic microring resonators a very attractive research topic. As biosensors are approaching the nanoscale, analyte mass transfer and bonding kinetics have been ascribed as crucial factors that limit their performance. One solution may be a system that applies dielectrophoretic forces, in addition to microfluidics, to overcome the diffusion limits of conventional biosensors. Dielectrophoresis, which involves the migration of polarized dielectric particles in a non-uniform alternating electric field, has previously been successfully applied to achieve a 1000-fold improved detection efficiency in nanopore sensing and may significantly increase the sensitivity in microring resonator biosensing. In the current work, we designed microring resonators with integrated electrodes next to the sensor surface that may be used to explore the effect of dielectrophoresis. The chip design, including two different electrode configurations, electric field gradient simulations, and the fabrication process flow of a dielectrohoresis-enhanced microring resonator-based sensor, is presented in this paper. Finite element method (FEM) simulations calculated for both electrode configurations revealed ∇E2 values above 1017 V2m−3 around the sensing areas. This is comparable to electric field gradients previously reported for successful interactions with larger molecules, such as proteins and antibodies.
“…The superimposed signals provided the advantages of both DEP and EO, first moving distant particles toward the region between the electrodes with EO flow, and then capturing the moved particles at a particular position, where the largest electric field occurs, against the flow with pDEP. This superimposition can be employed to enhance the sensor sensitivity and reduce the detection time when used with biosensors 18 . In fact, the amount of DEP-assisted attachment of cTnI (cardiac troponin I) after 1 min was less than that due to sedimentation for 1 h 18 in a cTnI sensor, because the proteins far from the electrode might not be attracted toward the electrode rapidly with DEP alone.…”
Section: Resultsmentioning
confidence: 99%
“…This superimposition can be employed to enhance the sensor sensitivity and reduce the detection time when used with biosensors 18 . In fact, the amount of DEP-assisted attachment of cTnI (cardiac troponin I) after 1 min was less than that due to sedimentation for 1 h 18 in a cTnI sensor, because the proteins far from the electrode might not be attracted toward the electrode rapidly with DEP alone. Figure 4 Amounts of particles collected within the RoIs using different electrical signals.…”
Section: Resultsmentioning
confidence: 99%
“…This technique allowed for a relatively large gap between two electrodes and short electric field exposure time, and high capture efficiency. We believe that the superimposition of AC EO and DEP can be applied to many biosensors requiring the rapid detection of biological particles with simple coplanar electrodes 17 , 18 .…”
Section: Discussionmentioning
confidence: 99%
“…In this regard, DEP and EO need to be combined to enable the selective and rapid concentration of particles far from the electrodes as well as near the electrodes onto a particular spot, such as a sensing element, thereby increasing the sensitivity of a sensor to biological particles such as bacteria, proteins, and viruses 17 , 18 . Few studies have been conducted using both EO and DEP on planar electrodes; in those studies, two electrodes generating DEP were implemented in the gaps between two outer electrodes inducing EO 19 , 20 .…”
Dielectrophoresis (DEP) is usually effective close to the electrode surface. Several techniques have been developed to overcome its drawbacks and to enhance dielectrophoretic particle capture. Here we present a simple technique of superimposing alternating current DEP (high-frequency signals) and electroosmosis (EO; low-frequency signals) between two coplanar electrodes (gap: 25 μm) using a lab-made voltage adder for rapid and selective concentration of bacteria, viruses, and proteins, where we controlled the voltages and frequencies of DEP and EO separately. This signal superimposition technique enhanced bacterial capture (Escherichia coli K-12 against 1-μm-diameter polystyrene beads) more selectively (>99%) and rapidly (~30 s) at lower DEP (5 Vpp) and EO (1.2 Vpp) potentials than those used in the conventional DEP capture studies. Nanometer-sized MS2 viruses and troponin I antibody proteins were also concentrated using the superimposed signals, and significantly more MS2 and cTnI-Ab were captured using the superimposed signals than the DEP (10 Vpp) or EO (2 Vpp) signals alone (p < 0.035) between the two coplanar electrodes and at a short exposure time (1 min). This technique has several advantages, such as simplicity and low cost of electrode fabrication, rapid and large collection without electrolysis.
Metabolites are essential molecules involved in various metabolic processes, and their deficiencies and excessive concentrations can trigger significant physiological consequences. The detection of multiple metabolites within a non‐invasively collected biofluid could facilitate early prognosis and diagnosis of severe diseases. Here, a metal oxide heterojunction transistor (HJ‐TFT) sensor is developed for the label‐free, rapid detection of uric acid (UA) and 25(OH)Vitamin‐D3 (Vit‐D3) in human saliva. The HJ‐TFTs utilize a solution‐processed In2O3/ZnO channel functionalized with uricase enzyme and Vit‐D3 antibody for the selective detection of UA and Vit‐D3, respectively. The ultra‐thin tri‐channel architecture facilitates strong coupling between the electrons transported along the buried In2O3/ZnO heterointerface and the electrostatic perturbations caused by the interactions between the surface‐immobilized bioreceptors and target analytes. The biosensors can detect a wide range of concentrations of UA (from 500 nm to 1000 µM) and Vit‐D3 (from 100 pM to 120 nm) in human saliva within 60 s. Moreover, the biosensors exhibit good linearity with the physiological concentration of metabolites and limit of detections of ≈152 nm for UA and ≈7 pM for Vit‐D3 in real saliva. The specificity is demonstrated against various interfering species, including other metabolites and proteins found in saliva, further showcasing its capabilities.
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