Euna Ko

Large-Scale Plasma Patterning of Transparent Graphene Electrode on Flexible Substrates

Graphene, a two-dimensional carbon material, has attracted significant interest for applications in flexible electronics as an alternative transparent electrode to indium tin oxide. However, it still remains a challenge to develop a simple, reproducible, and controllable fabrication technique for producing homogeneous large-scale graphene films and creating uniform patterns with desired shapes at defined positions. Here, we present a simple route to scalable fabrication of flexible transparent graphene electrodes using an oxygen plasma etching technique in a capacitively coupled plasma (CCP) system. Ascorbic acid-assisted chemical reduction enables the large-scale production of graphene with solution-based processability. Oxygen plasma in the CCP system facilitates the reproducible patterning of graphene electrodes, which allows controllable feature sizes and shapes on flexible plastic substrates. The resulting graphene electrode exhibits a high conductivity of 80 S cm(-1) and a transparency of 76% and retains excellent flexibility upon hard bending at an angle of ±175° and after repeated bending cycles. A simple LED circuit integrated on the patterned graphene film demonstrates the feasibility of graphene electrodes for use in flexible transparent electrodes.

Determination of glycated albumin using boronic acid-derived agarose beads on paper-based devices

Self-monitoring of glycated albumin (GA), a useful glycemic marker, is an established method for preventing diabetes complications. Here, the paper-based lateral flow assay devices were developed for the sensitive detection of GA and the total human serum albumin (tHSA) in self-monitoring diabetes patients. Boronic acid-derived agarose beads were packed into a hole on a lateral flow channel. These well-coordinated agarose beads were used to capture GA through specific cis-diol interactions and to enhance the colorimetric signals by concentrating the target molecules. The devices exhibited large dynamic ranges (from 10 μg/ml to 10 mg/ml for GA and from 10 mg/ml to 50 mg/ml for tHSA) and low detection limits (7.1 μg/ml for GA and 4.7 mg/ml for tHSA), which cover the range of GA concentration in healthy plasma, which is 0.21-1.65 mg/ml (0.6%-3%). In determining the unknown GA concentrations in two commercial human plasma samples, the relative percentage difference between the values found by a standard ELISA kit and those found by our developed devices was 2.62% and 8.80%, which are within an acceptable range. The measurements of GA and tHSA were completed within 20 min for the total sample-to-answer diagnosis, fulfilling the demand for rapid analysis. Furthermore, the recovery values ranged from 99.4% to 110% in device accuracy tests. These results indicate that the developed paper-based device with boronic acid-derived agarose beads is a promising platform for GA and tHSA detection as applied to self-monitoring systems.