Sample preconcentration utilizing nanofractures generated by junction gap breakdown assisted by self-assembled monolayer of gold nanoparticles.

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 1.5×10(4) 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

Single-Cell Electric Lysis on an Electroosmotic-Driven Microfluidic Chip with Arrays of Microwells

Accurate analysis at the single-cell level has become a highly attractive tool for investigating cellular content. An electroosmotic-driven microfluidic chip with arrays of 30-µm-diameter microwells was developed for single-cell electric lysis in the present study. The cellular occupancy in the microwells when the applied voltage was 5 V (82.4%) was slightly higher than that at an applied voltage of 10 V (81.8%). When the applied voltage was increased to 15 V, the cellular occupancy in the microwells dropped to 64.3%. More than 50% of the occupied microwells contain individual cells. The results of electric lysis experiments at the single-cell level indicate that the cells were gradually lysed as the DC voltage of 30 V was applied; the cell was fully lysed after 25 s. Single-cell electric lysis was demonstrated in the proposed microfluidic chip, which is suitable for high-throughput cell lysis

Protein Preconcentration Using Nanofractures Generated by Nanoparticle-Assisted Electric Breakdown at Junction Gaps - Figure 2

<p>(a) Schematic diagram of depositing nanoparticles to assist electric breakdown on the chip; (b) image of fabricated chip (optical microscopy image in inset) and (c) illustrations of nanofracture formation for protein preconcentration.</p

(a) Measured <i>I-V</i> curves for region between junction gaps before application of electric breakdown for cases with 0.5, 1.0, and 2.0 nM gold nanoparticles for self-assembly; (b) <i>I-V</i> curves before and after nanofracture formation for case with 0.5 nM gold nanoparticles for self-assembly compared with case without SAM.

<p>Simple equivalent circuit for measurement is shown in inset.</p

Schematic diagram of operations of electrokinetic protein preconcentration.

<p>Schematic diagram of operations of electrokinetic protein preconcentration.</p

Fluorescence images of 100 nM FITC labeled BSA in 1 mM PBS buffer solution (pH 7.4) taken at various time points.

<p>Chip with 2 nM of gold nanoparticles at the junction gaps had a DC voltage of 300 V applied to it for 5 min to create nanofractures.</p