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Abstract
Many researchers have fabricated micro and nanofluidic devices incorporating optical, chemical, and electrical detection systems with the aim of achieving on-chip analysis of macromolecules. The present study demonstrates a label-free detection of DNA using a nanofluidic device based on impedance measurements that is both sensitive and simple to operate. Using this device, the electrophoresis and dielectrophoresis effect on DNA conformation and the length dependence were examined. A low alternating voltage was applied to the nanogap electrodes to generate a high intensity field (>0.5 MV/m) under non-faradaic conditions. In addition, a 100 nm thick gold electrode was completely embedded in the substrate to allow direct measurements of a solution containing the sample passing through the gap, without any surface modification required. The high intensity field in this device produced a dielectrophoretic force that stretched the DNA molecule across the electrode gap at a specific frequency, based on back and forth movements between the electrodes with the DNA in a random coil conformation. The characteristics of 100 bp, 500 bp, 1 kbp, 5 kbp, 10 kbp, and 48 kbp λ DNA associated with various conformations were quantitatively analyzed with high resolution (on the femtomolar level). The sensitivity of this system was found to be more than about 10 orders of magnitude higher than that obtained from conventional linear alternating current (AC) impedance for the analysis of bio-polymers. This new high-sensitivity process is expected to be advantageous with regard to the study of complex macromolecules and nanoparticles.
Highlights
Recent advances in nanotechnology have led to rapid growth in nanofluidics research based on fluid manipulations [1,2,3,4], reactions [5,6], analyses [7,8,9], and other processes in which the unique characteristics of nanometer-scale spaces and interfaces are utilized [7,10]
Unidimensional nanochannels are of special interest since they represent the only practical approach to the continuous processing of miniscule fluid samples, which may be necessary for the preparation, detection, separation, and reaction of samples in a single flow stream
We developed a novel sensing method for single biomolecules based on electrical impedance spectroscopy (EIS) enhanced by taking advantage of the electric field in a nanospace
Summary
Recent advances in nanotechnology have led to rapid growth in nanofluidics research based on fluid manipulations [1,2,3,4], reactions [5,6], analyses [7,8,9], and other processes in which the unique characteristics of nanometer-scale spaces and interfaces are utilized [7,10]. We developed a novel sensing method for single biomolecules based on electrical impedance spectroscopy (EIS) enhanced by taking advantage of the electric field in a nanospace The advantages of this method include the facile generation of a very strong electric field in response to an applied voltage, which is sufficiently low so as to avoid electrode reactions, the induction of a high electric field by electrostatic forces to control changes in the motion, and conformation of the sample molecule as a means of amplifying the impedance signal, a short transit distance across the inter-electrode space that promotes good high frequency characteristics and reduces the faradaic current, and the minimal diffusion effects resulting from a unique measurement environment. The measurements were conducted under stopped flow conditions to maintain a uniform concentration
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