An electrochemical method for a rapid and sensitive immunoassay on digital microfluidics with integrated indium tin oxide electrodes coated on a PET film

Highly Efficient ITO-Free Quantum-Dot Light Emitting Diodes via Solution-Processed PEDOT:PSS Semitransparent Electrode

We present a study on the potential use of sulfuric acid-treated poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) as a viable alternative to indium tin oxide (ITO) electrodes in quantum dot light-emitting diodes (QLEDs). ITO, despite its high conductivity and transparency, is known for its disadvantages of being brittle, fragile, and expensive. Furthermore, due to the high hole injection barrier of quantum dots, the need for electrodes with a higher work function is becoming more significant. In this report, we present solution-processed, sulfuric acid-treated PEDOT:PSS electrodes for highly efficient QLEDs. The high work function of the PEDOT:PSS electrodes improved the performance of the QLEDs by facilitating hole injection. We demonstrated the recrystallization and conductivity enhancement of PEDOT:PSS upon sulfuric acid treatment using X-ray photoelectron spectroscopy and Hall measurement. Ultraviolet photoelectron spectroscopy (UPS) analysis of QLEDs showed that sulfuric acid-treated PEDOT:PSS exhibited a higher work function than ITO. The maximum current efficiency and external quantum efficiency based on the PEDOT:PSS electrode QLEDs were measured as 46.53 cd/A and 11.01%, which were three times greater than ITO electrode QLEDs. These findings suggest that PEDOT:PSS can serve as a promising replacement for ITO electrodes in the development of ITO-free QLED devices.

Microtrap-assisted microfluidic magnetic separation and concentration for ultrasensitive immunoassays of biomarkers

Precise and accurate quantitation of important biomarkers is significant, especially in early-stage diseases diagnosis. To realized effective biosample preparation and trace-level biomarker detection, a microtrap-assisted microfluidic magnetic immunoassays (μMI) method was developed in this work. A microtrap was fabricated inside the straight microchannel of μMI device to help magnetic separation and concentration of immunocomplexes. These immunocomplexes were enriched in microtrap of μMI device to accomplish selective and sensitive biomarker detection. Horseradish peroxidase-labeled magnetic beads were employed to evaluate assay feasibility and microtrap effect on assay sensitivity. The microtrap-assisted μMI was then applied for model biomarkers detection. The limits of detection of μMI were 0.025 pg/mL for monocyte chemoattractant protein-1 (MCP-1) and 0.021 pg/mL for matrix metalloproteinase-9 (MMP-9), which corresponded up to 2014-fold sensitivity improvement compared to their standard microwell enzyme-linked immunosorbent assay (ELISA) results. In addition, the selectivity and reproducibility of microtrap-assisted μMI were confirmed. In clinical serum sample analysis, recoveries of 91.3%-106.7% with relative standard deviations less than 6.1% were obtained for MCP-1 and MMP-9, and method accuracy was verified by commercial ELISA kit. The developed μMI can accomplish ultratrace biomarker detection offering practical tool for laboratorial and clinical research.

Dissolution-Enhanced Luminescence Enhanced Digital Microfluidics Immunoassay for Sensitive and Automated Detection of H5N1

Protein bioassay is a critical tool for the screening and detection of protein biomarkers in disease diagnostics and biological applications. However, the detection sensitivity and system automation of current immunoassays do not meet the emerging demands of clinical applications. Here, we developed a dissolution-enhanced luminescence-enhanced digital microfluidics immunoassay (DEL-DMF), which significantly improves the sensitivity and automation of the protein bioassay. In DEL-DMF, the sample and reagent droplets are controlled to complete the processes of sample transport, immunoreaction, and buffer washing, which not only minimizes sample consumption to 2 μL and enhances the binding efficiency of immunoreaction but also streamlines all the procedures and simplifies the process of immunoassay. Moreover, dissolution-enhanced luminescence using NaEuF₄ NPs as nanoprobes boosts the fluorescence and increases the sensitivity of the bioassay. We demonstrate the enhanced analytical performance of our DEL-DMF immunoassay to detect H5N1 hemagglutinin in human serum and saliva. A limit of detection of 1.16 pM was achieved in less than 0.5 h with only 2 μL sample consumption. Overall, our DEL-DMF immunoassay combines the merits of the microfluidics platform and dissolution-enhanced luminescence, thus affording superior detection sensitivity and system automation for protein biomarkers. This novel immunoassay microsystem holds great potential in clinical and biological applications.

Optimization of Electrode Patterns for an ITO-Based Digital Microfluidic through the Finite Element Simulation

Indium tin oxide (ITO)-based digital microfluidics (DMF) with unique optical and electrical properties are promising in the development of integrated, automatic and portable analytical systems. The fabrication technique using laser direct etching (LDE) on ITO glass has the advantages of being rapid, low cost and convenient. However, the fabrication resolution of LDE limits the minimum line width for patterns on ITO glasses, leading to a related wider lead wire for the actuating electrodes of DMF compared with photolithography. Therefore, the lead wire of electrodes could affect the droplet motion on the digital microfluidic chip due to the increased contact line with the droplet. Herein, we developed a finite element model of a DMF with improved efficiency to investigate the effect of the lead wire. An optimized electrode pattern was then designed based on a theoretical analysis and validated by a simulation, which significantly decreased the deformation of the droplets down to 0.012 mm. The performance of the optimized electrode was also verified in an experiment. The proposed simulation method could be further extended to other DMF systems or applications to provide an efficient approach for the design and optimization of DMF chips.

A Digital Microfluidic Device Integrated with Electrochemical Impedance Spectroscopy for Cell-Based Immunoassay

The dynamic immune response to various diseases and therapies has been considered a promising indicator of disease status and therapeutic effectiveness. For instance, the human peripheral blood mononuclear cell (PBMC), as a major player in the immune system, is an important index to indicate a patient's immune function. Therefore, establishing a simple yet sensitive tool that can frequently assess the immune system during the course of disease and treatment is of great importance. This study introduced an integrated system that includes an electrochemical impedance spectroscope (EIS)-based biosensor in a digital microfluidic (DMF) device, to quantify the PBMC abundance with minimally trained hands. Moreover, we exploited the unique droplet manipulation feature of the DMF platform and conducted a dynamic cell capture assay, which enhanced the detection signal by 2.4-fold. This integrated system was able to detect as few as 104 PBMCs per mL, presenting suitable sensitivity to quantify PBMCs. This integrated system is easy-to-operate and sensitive, and therefore holds great potential as a powerful tool to profile immune-mediated therapeutic responses in a timely manner, which can be further evolved as a point-of-care diagnostic device to conduct near-patient tests from blood samples.

Detection Efficiency of Ag Nanoparticle Labels for a Heart Failure Marker Using Linear and Square-Wave Anodic Stripping Voltammetry

In this article, we compare linear sweep anodic stripping voltammetry (LASV) and square-wave anodic stripping voltammetry (SWASV) for detection of a nano metalloimmunoassay. Two separate immunoassays were examined: a model assay, based on interactions between antibodies, and a sandwich assay for the heart failure marker NT-proBNP. In both cases, one antibody is linked to a magnetic microbead, and one is linked to a spherical Ag nanoparticle label. Electrochemical detection is carried out on a paper device. The three analytical figures of merit studied were the precision of the measurements, the calibration sensitivity, and the limit of detection (LOD). For the NT-proBNP assay, the results show that after optimization of the pulse amplitude and frequency of the potential input for SWASV, the detection efficiency is substantially higher compared to LASV. Specifically, the calibration sensitivity increased by up to ~40 fold, the average coefficient of variation decreased by ~40%, and the (LOD) decreased to 300.0 pM. Finally, for a model immunoassay, a ~10-fold decrease in the LOD was observed for SWASV compared to LASV.