Affordable Fabrication of Conductive Electrodes and Dielectric Films for a Paper-based Digital Microfluidic Chip

In order to fabricate a digital microfluidic (DMF) chip, which requires a patterned array of electrodes coated with a dielectric film, we explored two simple methods: Ballpoint pen printing to generate the electrodes, and wrapping of a dielectric plastic film to coat the electrodes. For precise and programmable printing of the patterned electrodes, we used a digital plotter with a ballpoint pen filled with a silver nanoparticle (AgNP) ink. Instead of using conventional material deposition methods, such as chemical vapor deposition, printing, and spin coating, for fabricating the thin dielectric layer, we used a simple method in which we prepared a thin dielectric layer using pre-made linear, low-density polyethylene (LLDPE) plastic (17-μm thick) by simple wrapping. We then sealed it tightly with thin silicone oil layers so that it could be used as a DMF chip. Such a treated dielectric layer showed good electrowetting performance for a sessile drop without contact angle hysteresis under an applied voltage of less than 170 V. By using this straightforward fabrication method, we quickly and affordably fabricated a paper-based DMF chip and demonstrated the digital electrofluidic actuation and manipulation of drops

Paper-based sensors for rapid detection of virulence factor produced by Pseudomonas aeruginosa

Pyocyanin is a toxin produced by Pseudomonas aeruginosa. Here we describe a novel paper-based electrochemical sensor for pyocyanin detection, manufactured with a simple and inexpensive approach based on electrode printing on paper. The resulting sensors constitute an effective electrochemical method to quantify pyocyanin in bacterial cultures without the conventional time consuming pretreatment of the samples. The electrochemical properties of the paper-based sensors were evaluated by ferri/ferrocyanide as a redox mediator, and showed reliable sensing performance. The paper-based sensors readily allow for the determination of pyocyanin in bacterial cultures with high reproducibility, achieving a limit of detection of 95 nM and a sensitivity of 4.30 μA/μM in standard culture media. Compared to the similar commercial ceramic based sensors, it is a 2.3-fold enhanced performance. The simple in-house fabrication of sensors for pyocyanin quantification allows researchers to understand in vitro adaptation of P. aeruginosa infections via rapid screenings of bacterial cultures that otherwise are expensive and time-consuming

Paper-based sensors for rapid detection of virulence factor produced by <i>Pseudomonas aeruginosa</i>

<div><p>Pyocyanin is a toxin produced by <i>Pseudomonas aeruginosa</i>. Here we describe a novel paper-based electrochemical sensor for pyocyanin detection, manufactured with a simple and inexpensive approach based on electrode printing on paper. The resulting sensors constitute an effective electrochemical method to quantify pyocyanin in bacterial cultures without the conventional time consuming pretreatment of the samples. The electrochemical properties of the paper-based sensors were evaluated by ferri/ferrocyanide as a redox mediator, and showed reliable sensing performance. The paper-based sensors readily allow for the determination of pyocyanin in bacterial cultures with high reproducibility, achieving a limit of detection of 95 nM and a sensitivity of 4.30 μA/μM in standard culture media. Compared to the similar commercial ceramic based sensors, it is a 2.3-fold enhanced performance. The simple in-house fabrication of sensors for pyocyanin quantification allows researchers to understand <i>in vitro</i> adaptation of <i>P</i>. <i>aeruginosa</i> infections via rapid screenings of bacterial cultures that otherwise are expensive and time-consuming.</p></div

Electrochemical characterization of the paper-based sensors.

<p>Evaluation of electrochemical sensor performance by (a) cyclic voltammograms (CV) at various scan rates in ferri/ferrocyanide. (b) The extracted peak currents are linearly proportional with the square roots of the scan rates denoting a quasi-reversible system suitable for analyte quantification. Measurements are conducted against the reference electrode.</p

Sensor fabrication process.

<p>(a) Placement of the mask on top of the photo paper. (b) Manual scrapping of ink on top of the shadow mask. (c) shadow mask removal. (d) Photo paper with carbon screen printed electrodes.</p

Pyocyanin quantification.

<p>Detection of pyocyanin in lysogeny broth (LB) using the paper-based sensors. (a) Square wave voltammograms of increasing pyocyanin concentrations from 1–40 μM in LB. (b) Standard curve using the extracted peak currents as function of the pyocyanin concentration.</p