Nam Ho Bae

Flexible and Disposable Sensing Platforms Based on Newspaper

The flexible sensing platform is a key component for the development of smart portable devices targeting healthcare, environmental monitoring, point-of-care diagnostics, and personal electronics. Herein, we demonstrate a simple, scalable, and cost-effective strategy for fabrication of a sensing electrode based on a waste newspaper with conformal coating of parylene C (P-paper). Thin polymeric layers over cellulose fibers allow the P-paper to possess improved mechanical and chemical stability, which results in high-performance flexible sensing platforms for the detection of pathogenic E. coli O157:H7 based on DNA hybridization. Moreover, P-paper electrodes have the potential to serve as disposable, flexible sensing platforms for point-of-care testing biosensors.

Fabrication of newspaper-based potentiometric platforms for flexible and disposable ion sensors

Paper-based materials have attracted a great deal of attention in sensor applications because they are readily available, biodegradable, inexpensive, and mechanically flexible. Although paper-based sensors have been developed, but important obstacles remian, which include the retention of chemical and mechanical stabilities when paper is wetted. Herein, we develop a simple and scalable process for fabrication of newspaper-based platforms by coating of parylene C and patterning of metal layers. As-prepared parylene C-coated newspaper (PC-paper) provides low-cost, disposable, and mechanically and chemically stable electrochemical platforms for the development of potentiometric ion sensors for the detection of electrolyte cations, such as, H+ and K+. The pH and K+ sensors produced show near ideal Nernstian sensitivity, good repeatability, good ion selectivity, and low potential drift. These disposable, flexible ion sensors based on PC-paper platforms could provide new opportunities for the development of point-of-care testing sensors, for diagnostics, healthcare, and environment testing.

Droplet-based digital PCR system for detection of single-cell level of foodborne pathogens

Recently, foodborne pathogen is a common and distressing disease around world to cause a threat to life and economic damages and it is urgent to develop a tools to diagnosis of such pathogens in the early stage to prevent potential outbreak. Although conventional cell extraction and recovery of DNA from pathogen and PCR method have been widely used, the methods require complex steps, experts, and expensive chemicals and instruments to improve the PCR performance. Herein, we report a droplet-based polymerase chain reaction (ddPCR) system which allows identifying single-cell level of foodborne pathogens. E. coli O157:H7 and Salmonella cells were selected as model bacterial foodborne pathogens. The ddPCR system could be a useful platform for the quantitative detection of foodborne pathogens without any pretreatment process.

A Disposable and Multi-Chamber Film-Based PCR Chip for Detection of Foodborne Pathogen

Since the increment of the threat to public health caused by foodborne pathogens, researches have been widely studied on developing the miniaturized detection system for the on-site pathogen detection. In the study, we focused on the development of portable, robust, and disposable film-based polymerase chain reaction (PCR) chip containing a multiplex chamber for simultaneous gene amplification. In order to simply fabricate and operate a film-based PCR chip, different kinds of PCR chambers were designed and fabricated using polyethylene terephthalate (PET) and polyvinyl chloride (PVC) adhesive film, in comparison with commercial PCR, which employs a stereotyped system at a bench-top scale. No reagent leakage was confirmed during the PCR thermal cycling using the film PCR chip, which indicates that the film PCR chip is structurally stable for rapid heat cycling for DNA amplification. Owing to use of the thin film to fabricate the PCR chip, we are able to realize fast thermal transfer from the heat block that leads to short PCR amplification time. Moreover, using the film PCR chip, we could even amplify the target pathogen with 10 CFU mL−1. The artificially infected milk with various concentration of Bacillus cereus was successfully amplified on a single film PCR chip. On the basis of the reliable results, the developed film PCR chip could be a useful tool as a POCT device to detect foodborne pathogens via genetic analysis.

Development of bufferless gel electrophoresis chip for easy preparation and rapid DNA separation

This work presents a handy, fast, and compact bufferless gel electrophoresis chip (BGEC), which consists of precast agarose gel confined in a disposable plastic body with electrodes. It does not require large volumes of buffer to fill reservoirs, or the process of immersing the gel in the buffer. It withstands voltages up to 28.4 V/cm, thereby allowing DNA separation within 10 min with a similar separation capability to the standard gel electrophoresis. The results suggest that our BGEC is highly suitable for in situ gel electrophoresis in forensic, epidemiological settings and crime scenes where standard gel electrophoresis equipment cannot be brought in while quick results are needed.

Ultrasonic fabrication of flexible antibacterial ZnO nanopillar array film

Antibacterial activity is essential and highly demanded in worldwide to prevent potential bacterial infection. Here in this work, we report a new approch for the fabrication of flexible zinc oxide nanopillar arrays (ZG-NPA) film with an efficient antibacterial activity. A flexible NPA film served as a substrate for the rapid formation of ZnO by using ultrasound-assisted method. The enhancement of antibacterial activity were induced by cellular damages because of nano topological effects and electrostatic interaction between bacteria and ZG-NPA. Owing to the benefits of combination with flexibility, high surface areas from nano-features and excellent antibacterial efficiency (>80%) of ZG-NPA, the film can show great potential for use as novel biomaterials for preventing bacterial infections.

A microfluidic electrochemical aptasensor for enrichment and detection of bisphenol A.

Bisphenol A (BPA) is an organic monomer used to make common consumer goods such as plastic containers, sports equipment, and cosmetics which are heavily produced worldwide. A growing interest has been drawn to general public as BPA is one of the major endocrine disrupting chemicals threating human health. To date, numerous BPA sensors have been attempted to be developed but important challenges still remained such as limited linearity range, easy to use, and long term response time. To address the present issues, a microfluidic channel should be integrated into an electrochemical aptasensor and it is called Geometrically Activated Surface Interaction (GASI) chip. The vigorous generation of the micro-vortex in the GASI fluidic chamber provides the high collision chances between BPA and anti-BPA aptamer (BPAPT) and consequently more BPA molecules can be captured on the aptasensor surface, which finally results in high sensitivity of the aptasensor. To construct the integrated aptasensor, a miniaturized gold electrode is fabricated using shadow mask and e-beam evaporation process. Afterward, BPAPT is immobilized on a nanostructured gold electrode via thiol chemistry, and other terminus of the aptamer is labeled with a ferrocene (Fc) redox probe. Then, the microfluidic channel is mounted over the miniaturized gold electrode to introduce and enrich BPA to the aptasensor. Upon the specific interaction between BPA and its aptamer, configuration of aptamer is changed so that Fc tag approaches to the electrode surface and direct oxidation signal of Fc and BPA are followed as analytical signals. The unique microfluidic integrated electrochemical aptasensor delivers a wide linear dynamic range over 5 × 10-12 to 1 × 10-9 M, with a limit of detection 2 × 10-13 M. This aptasensor provides a precise platform for simple, selective and more importantly rapid detection of BPA. Such kind of sensing platforms can serve as a fertile ground for designing miniaturized portable sensors.

A film-based integrated chip for gene amplification and electrochemical detection of pathogens causing foodborne illnesses

Given the increased interest in public hygiene due to outbreaks of food poisoning, increased emphasis has been placed on developing novel monitoring systems for point-of-care testing (POCT) to evaluate pathogens causing foodborne illnesses. Here, we demonstrate a pathogen evaluation system utilizing simple film-based microfluidics, featuring simultaneous gene amplification, solution mixing, and electrochemical detection. To minimize and integrate the various functionalities into a single chip, patterned polyimide and polyester films were mainly used on a polycarbonate housing chip, allowing simple fabrication and alignment, in contrast to conventional polymerase chain reaction, which requires a complex biosensing system at a bench-top scale. The individual integrated sensing chip could be manually fabricated in 10 min. Using the developed film-based integrated biosensing chip, the genes from the pathogens causing foodborne illnesses were simultaneously amplified based on multiple designed microfluidic chambers and Hoechst 33258, which intercalates into double-stranded DNA, to generate the electrochemical signal. The target pathogen gene was accurately analyzed by square wave voltammetry (SWV) within the 25 s, while the gel electrophoresis required about 30 min. Based on the developed integrated biosensing chip, the 1.0 × 101 and 1.0 × 102 colony-forming unit (CFU) of Staphylococcus aureus and Escherichia coli were sensitively detected with high reproducibility in the 25 s. On the basis of the significant features of the film-based molecular analysis platform, we expect that the developed sensor could be applied to the screening of various pathogens as a POCT device.