Bioaerosol monitoring by integrating DC impedance microfluidic cytometer with wet-cyclone air sampler.

The recent outbreak of COVID-19 has highlighted the seriousness of airborne diseases and the need for a proper pathogen detection system. Compared to the ample amount of research on biological detection, work on integrated devices for air monitoring is rare. In this work, we integrated a wet-cyclone air sampler and a DC impedance microfluidic cytometer to build a cyclone-cytometer integrated air monitor (CCAM). The wet-cyclone air sampler sucks the air and concentrates the bioaerosols into 10 mL of aqueous solvent. After 5 min of air sampling, the bioaerosol-containing solution was conveyed to the microfluidic cytometer for detection. The device was tested with aerosolized microbeads, dust, and Escherichia coli (E. coli). CCAM is shown to differentiate particles from 0.96 to 2.95 µm with high accuracy. The wet cyclone air-sampler showed a 28.04% sampling efficiency, and the DC impedance cytometer showed 87.68% detection efficiency, giving a total of 24.59% overall CCAM efficiency. After validation of the device performance, CCAM was used to detect bacterial aerosols and their viability without any separate pretreatment step. Differentiation of dust, live E. coli, and dead E. coli was successfully performed by the addition of BacLight bacterial viability reagent in the sampling solvent. The usage could be further extended to detection of specific species with proper antibody fluorescent label. A promising strategy for aerosol detection is proposed through the constructive integration of a DC impedance microfluidic cytometer and a wet-cyclone air sampler.

In Situ Real-Time Monitoring of ITO Film under a Chemical Etching Process Using Fourier Transform Electrochemical Impedance Spectroscopy.

As a novel approach to the in situ real-time investigation of an ITO electrode during the wet etching process, step-excitation Fourier-transform electrochemical impedance spectroscopy (FT-EIS) was implemented. The equivalent circuit parameters (e.g., Rct, Cdl) continuously obtained by the FT-EIS measurements during the entire etching process showed an electrode activation at the initial period as well as the completion of etching. The FT-EIS results were further validated by cyclic voltammograms and impedance measurements of partially etched ITO films using ferri- and ferrocyanide solution in combination with FESEM imaging, EDS, XRD analyses, and COMSOL simulation. We also demonstrated that this technique can be further utilized to obtain intact interdigitated array (IDA) electrodes in a reproducible manner, which is generally considered to be quite tricky due to delicacy of the pattern. Given that the FT-EIS allows for instantaneous snapshots of the electrode at every moment, this work may hold promise for in situ real-time examination of structural, electrokinetic, or mass transfer-related information on electrochemical systems undergoing constantly changing, transient processes including etching, which would be impossible with conventional electroanalytical techniques.

Sensitivity-Tunable and Disposable Ion-Sensing Platform Based on Reverse Electrodialysis.

The detection of ions is of critical importance for environmental, industrial, and physiological applications, where sensitive and disposable ion sensing is still challenging. Herein, we present a sensitivity-tunable ion-sensing platform based on reverse electrodialysis, which is suitable for convenient and sensitive on-site analysis of various ions. It is revealed that this sensing system does not require any external power supply, and the sensitivities can be modulated by altering the number of stacks, possibly higher than the theoretical limitation, the Nernstian slope. The sensing system is integrated with a multicolor detection system via the introduction of polyaniline as a reporting material, which enables direct quantitative analysis based on a continuous color change gradient observable with the naked eye. Overall, the adopted approach by introducing reverse electrodialysis represents remarkable progress toward self-powered and disposable ion sensors with high and easily tunable potentiometric sensitivity.

Multiplex immunoassays using virus-tethered gold microspheres by DC impedance-based flow cytometry.

Bead-based multiplex immunoassays for common use require enhanced sensitivity and effective prevention of non-specific adsorption, as well as miniaturization of the detection device. In this work, we have implemented virus-tethered gold microspheres for multiplex immunoassay applications, employing a DC impedance-based flow cytometer as a detection element. The advantages of virus-tethered gold microspheres, including excellent prevention of non-specific adsorption, are extended to signal enhancement arising from the large quantity of antibody loading on each virion, and to flexible movement of filamentous virus. Individual virus-tethered beads generate their own DC impedance and fluorescence signals, which are simultaneously detected by a chip-based microfluidic flow cytometer. This system successfully realized multiplex immunoassays involving four biomarkers: cardiac troponin I (cTnI), prostate specific antigen (PSA), creatine kinase MB (CK-MB), and myoglobin in undiluted human sera, elevating sensitivity by up to 5.7-fold compared to the beads without virus. Constructive integration between filamentous virus-tethered Au-layered microspheres and use of a microfluidic cytometer suggests a promising strategy for competitive multiplex immunoassay development based on suspension arrays.

3D interdigitated electrode array in the microchannel free of reference and counter electrodes.

We demonstrate the three-dimensional (3D) interdigitated array (IDA) chip that operates without reference and counter electrodes, which are necessary components to apply enough potential to trigger the intended redox process, but used unwieldy for chip-based electrochemical detection. Using the electrode configuration, we propose a unique electrochemical system that is capable of controlling applied potential to a pair of working electrodes despite absence of reference and counter electrodes by fixing the electron transfer mediator on the electrodes in a microchannel. The electrochemical potential of the 2-electrode (2E) system is defined by the potential of the electron transfer mediator, poly(methylene green) (PMG), immobilized with poly(dopamine) (PDA) on the ITO surface by electropolymerization. The 3D IDA chip in the 2E system successfully acts as an electrochemical immunosensing platform. Creatine Kinase-MB in human serum was measured down to ~ pg / mL level. Therefore, the 3D IDA in the 2E system constitutes a simple and scalable platform that needs only nL level of sample volume for sensitive electrochemical detection in miniaturized multiplex immunoassay field.