Sample Preconcentration Utilizing Nanofractures Generated by Junction Gap Breakdown Assisted by Self-Assembled Monolayer of Gold Nanoparticles

Abstract

The preconcentration of proteins with low concentrations can be used to increase the sensitivity and accuracy of detection. A nonlinear electrokinetic flow is induced in a nanofluidic channel due to the overlap of electrical double layers, resulting in the fast accumulation of proteins, referred to as the exclusion-enrichment effect. The proposed chip for protein preconcentration was fabricated using simple standard soft lithography with a polydimethylsiloxane replica. This study extends our previous paper, in which gold nanoparticles were manually deposited onto the surface of a protein preconcentrator. In the present work, nanofractures were formed by utilizing the self-assembly of gold-nanoparticle-assisted electric breakdown. This reliable method for nanofracture formation, involving self-assembled monolayers of nanoparticles at the junction gap between microchannels, also decreases the required electric breakdown voltage. The experimental results reveal that a high concentration factor of 1.5×104 for a protein sample with an extremely low concentration of 1 nM was achieved in 30 min by using the proposed chip, which is faster than our previously proposed chip at the same conditions. Moreover, an immunoassay of bovine serum albumin (BSA) and anti-BSA was carried out to demonstrate the applicability of the proposed chip.

A simple electrokinetic protein preconcentrator utilizing nano-interstices

“…Two junction gaps were designed along the main microchannel for the formation of nano-interstices via the AuNP-based SAM. The layout and fabrication of the proposed protein preconcentrator herein are basically the same as those in our previous work, 21 which is shown in Figs. 1(a) and 1(b).…”

“…Furthermore, a selfassembled monolayer (SAM) of gold NPs (AuNPs) was employed to reduce the required voltage for electric breakdown. 21 The method for nanofracture formation involving the use of the SAMs of AuNPs at the junction gap between microchannels could be well controlled and was reliable. However, a voltage of hundreds of volts was still required.…”

A compact microfluidic chip with integrated impedance biosensor for protein preconcentration and detection

“…In our preview work, protein detection was implemented based on an immunoassay that utilized antibodies and fluorescence spectroscopy. 24 In this approach, proteins trapped by antibodies are detected using the impedance method, where the impedance between electrodes is changed due to the presence of the targeted protein. The impedance method is adopted in this study due to its low cost and ease of integration with microfluidic channel structures.…”

“…12 In our previous work, protein preconcentration was implemented in a biochip based on the exclusion enrichment method and nanofractures were created by breaking down the junction gap between two microfluidic channels activated by gold nanoparticles. 24 Recently, a simple protein preconcentrator was proposed, 25 in which the EEE is achieved in nanointerstices via a self-assembled monolayer (SAM) of Au nanoparticles. This simple and reliable method does not require a high voltage or time-consuming fabrication.…”

“…The layout and fabrication of the proposed protein preconcentrator herein are basically the same as those in our previous work. 24,25 After PDMS is bonded to glass to form microchannels, surface modification is implemented to immobilize antibodies on the sensing electrodes. The details of the structure are presented in Fig.…”