Sejin Park

Nonenzymatic continuous glucose monitoring in human whole blood using electrified nanoporous Pt.

This paper describes the first devised method for the nonenzymatic and electrochemical glucose monitoring in 100% human whole blood and serum. The nanoporous Pt electrode allows for the selective amplification of glucose oxidation in the presence of electroactive interfering species without the need for enzymatic reaction. The outer membrane was particularly optimized to allow glucose molecules to be electrochemically detected against the numerous constituents of human blood. The proposed sensor provided reproducible amperometric responses to glucose in human serum and whole blood. Its sensitivity was maintained for at least 7h under constantly electrified conditions, and continued to work properly after 30 days of storage in human whole blood and serum. Unlike the enzyme-based glucose sensors, it was found to be minimally affected by thermal fluctuation, so as to remain successful even after steam sterilization at high temperature (134 °C) and pressure (0.22 Mpa). The unprecedented long-term stability and sterilization compatibility observed herein suggest a promising alternative to conventional enzymatic glucose sensors for many analytical and clinical applications, particularly for continuous glucose monitoring devices designed to potentially lead to a closed-loop artificial pancreas by combining them with an insulin pump.

Single Gold Microshell Tailored to Sensitive Surface Enhanced Raman Scattering Probe

We finely tuned the Au shell on a polystyrene microsphere of 2 microm in diameter to achieve a strong surface enhanced raman scattering (SERS)-active platform so that the molecules on a single microspherical shell surface produce their own fingerprint SERS spectra. The proposed microshells can be easily and individually manipulated under a conventional optical microscope using a micropipet and act as a sensitive probe to obtain the SERS spectra of the monolayer of molecules on Pt as well as Au surfaces without any requirement of special surface morphology or modification for inducing SERS activity. Well-defined SERS spectra can be obtained at a very short acquisition time of milliseconds, suggesting useful applications of the present system based on the decoding of the SERS-active barcodes on individually functionalized microshells.

In vivo calibration of the subcutaneous amperometric glucose sensors using a non-enzyme electrode.

A new two-point calibration method for the subcutaneous amperometric continuous glucose sensor is reported. The proposed method is based on direct measurement of the background current (I(o)) using a non-enzyme electrode. For in vivo test, three electrodes were implanted in rabbits. Two of the three were identical needle-type enzyme electrodes with perfluorinated polymer outer layers (Pt/enzyme layer/Kel-F/PTFE/Kel-F/Nafion) that were placed in subcutaneous tissue and in a vessel (ear artery), respectively. And one non-enzyme electrode with exactly the same membrane composition as those of other two was in the subcutaneous layer to measure the background current. Implantation in the subcutaneous layer generated many crevices on the protecting layers of the electrodes. The signals from enzyme electrodes were effectively corrected by the measured background current from the non-enzyme electrode. In addition, a telemetric monitoring system was developed and evaluated for in vivo continuous glucose monitoring in order to alleviate the problems of motion artifact.

Nanoporous platinum thin films synthesized by electrochemical dealloying for nonenzymatic glucose detection

Nanoporous Pt thin films were prepared by simultaneous deposition of Pt and Si and subsequent dealloying of Si out of the Pt(x)Si(1-x) films. The x values were easily controlled in the range of 0.10 to 0.90 by the distances between the sample position and the target positions and by the plasma power for the targets. With a roughness factor of around 40, the nanoporous Pt films showed enough sensitivity, selectivity, and detection limit for glucose and interfering species. Multiple nanoporous Pt films with similar roughness factors were easily fabricated using this method, which showed good enough and similar performance to other reported glucose sensors, suggesting a simple and quality controlled manufacturing method for nanoporous Pt films as nonenzymatic glucose sensors.

SERS decoding of micro gold shells moving in microfluidic systems

In this study, in situ surface‐enhanced Raman scattering (SERS) decoding was demonstrated in microfluidic chips using novel thin micro gold shells modified with Raman tags. The micro gold shells were fabricated using electroless gold plating on PMMA beads with diameter of 15 μm. These shells were sophisticatedly optimized to produce the maximum SERS intensity, which minimized the exposure time for quick and safe decoding. The shell surfaces produced well‐defined SERS spectra even at an extremely short exposure time, 1 ms, for a single micro gold shell combined with Raman tags such as 2‐naphthalenethiol and benzenethiol. The consecutive SERS spectra from a variety of combinations of Raman tags were successfully acquired from the micro gold shells moving in 25 μm deep and 75 μm wide channels on a glass microfluidic chip. The proposed functionalized micro gold shells exhibited the potential of an on‐chip microfluidic SERS decoding strategy for micro suspension array.

Enhancement in Selectivity of Nonenzymatic Glucose Sensors Based on Mesoporous Platinum by A.C. Impedance

Improvement of the selectivity of nonenzymatic glucose based on mesoporous platinum (-ePt) by using A.C. impedance is reported. The idea of the present work is based on the novel effect of the mesoporous electrode that the apparent exchange current due to glucose oxidation remarkably grows although the reaction kinetics on the surface is still sluggish. It is expected that the enlarged apparent exchange current on the mesoporous electrode can raise the sensitivity of admittance in A.C. impedance to glucose concentration. At a low frequency, A.C. impedance could become more powerful. The admittance at 0.01 Hz is even more sensitive to glucose than to ascorbic acid while amperometry exhibits the inverse order of sensitivity. This is the unique behavior that is neither observed by A.C. impedance on flat platinum electrode nor obtained by amperometry. The study shows how the combination of A.C. impedance and nano-structured surface can be applied to the detection of sluggish reaction such as electrochemical oxidation of glucose.

Determination of Fluoroquinolone Antibacterial Agents by Square Wave Adsorptive Stripping Voltammetry

Electrochemical behavior of fluoroquinolone antibacterial agents on carbon paste electrode (CPE) were investigated by cyclic voltammetry and square wave adsorptive stripping voltammetry. The fluoroquinolone antibacterial agents tested in this study were Enrofloxacin (ENR), Norfloxacin (NOR), Ciprofloxacin (CIP), Ofloxacin (OFL) and Levofloxacin (LEV). In acetate buffer at pH 4.5, the oxidation peak potentials of the fluoroquinolone antibacterial agents of ENR, NOR, CIP, OFL, and LEV were 0.952 V, 1.052 V, 1.055 V, 0.983 V, and 0.990 V (vs. Ag/AgCl), respectively. And their oxidation peak currents from square wave adsorptive stripping voltammograms are proportional to the concentration of each antibacterial agent over the range from 0.2 µM to 1 µM.

Regulation of Electrochemical Oxidation of Glucose by lonic Strength-Controlled Virtual Area of Nanoporous Platinum Electrode

Electrochemical reaction of glucose was regulated by the electrochemically active area of nanoporous platinum, which is controlled by ionic strength. The profile of the oxidation current of glucose vs. ionic strength was identical with that of the electrochemically active area. This result confirms that the nanopores are virtually opened for the electrochemical reaction of glucose when the ionic strength climbs over a specific concentration and implies that the electrochemical reactions on nanoporous electrode surfaces can be controlled by concentration of electrolyte.