Multistory Stairs-based, Fast and Point-of-care Testing for Disease Biomarker Using One-step Capillary Microfluidic Fluoroimmunoassay Chip via Continuous On-chip Labelling

CLICK-FLISA Based on Metal-Organic Frameworks for Simultaneous Detection of Fumonisin B1 (FB1) and Zearalenone (ZEN) in Maize

Mycotoxins are secondary products produced primarily by fungi and are pathogens of animals and cereals, not only affecting agriculture and the food industry but also causing great economic losses. The development of rapid and sensitive methods for the detection of mycotoxins in food is of great significance for livelihood issues. This study employed an amino-functionalized zirconium luminescent metal-organic framework (LOF) (i.e., UiO-66-NH2). Click chemistry was utilized to assemble UiO-66-NH2 in a controlled manner, generating LOF assemblies to serve as probes for fluorescence-linked immunoassays. The proposed fluoroimmunoassay method for Zearalenone (ZEN) and Fumonisin B1 (FB1) detection based on the UiO-66-NH2 assembled probe (CLICK-FLISA) afforded a linear response range of 1-20 μmol/L for ZEN, 20 μmol/L for FB1, and a very low detection limit (0.048-0.065 μmol/L for ZEN; 0.048-0.065 μmol/L for FB1). These satisfying results demonstrate promising applications for on-site quick testing in practical sample analysis. Moreover, the amino functionalization may also serve as a modification strategy to design luminescent sensors for other food contaminants.

A compact microfluidic laser-induced fluorescence immunoassay system using avalanche photodiode for rapid detection of alpha-fetoprotein

Alpha-fetoprotein (AFP), commonly employed for early diagnosis of liver cancer, serves as a biomarker for cancer screening and diagnosis. Combining the high sensitivity and specificity of fluorescence immunoassay (FIA), developing a low-cost and efficient immunoassay system for AFP detection holds significant importance in disease diagnosis. In this work, we developed a miniaturized oblique laser-induced fluorescence (LIF) immunoassay system, coupled with a microfluidic PMMA/paper hybrid chip, for rapid detection of AFP. The system employed an avalanche photodiode (APD) as the detector, and implemented multi-level filtering in the excitation light channel using the dichroic mirror and optical trap. At first, we employed the Savitzky-Golay filter and baseline off-set elimination methods to denoise and normalize the original data. Then the cutoff frequency of the low-pass filter and the reverse voltage of the APD were optimized to enhance the detection sensitivity of the system. Furthermore, the effect of laser power on the fluorescence excitation efficiency was investigated, and the sampling time during the scanning process was optimized. Finally, a four-parameter logistic (4PL) model was utilized to establish the concentration-response equation for AFP. The system was capable of detecting concentrations of AFP standard solution within the range of 1-500 ng/mL, with a detection limit of 0.8 ng/mL. The entire immunoassay process could be completed within 15 min. It has an excellent potential for applications in low-cost portable diagnostic instruments for the rapid detection of biomarkers.

A brief overview of passive microvalves in microfluidics: Mechanism, manufacturing, and applications

Microvalves play a crucial role in manipulating fluid states within a microfluidic system and are finding widespread applications in fields such as biology, medicine, and environmental preservation. Leveraging the characteristics and features of microvalves enables the realization of various complicated microfluidic functions. Continuous advancement in the manufacturing process contributes to more flexible control modes for passive microvalves. As a consequence, these valves are progressively shrinking in size while simultaneously improving in precision and stability. Although active microvalves have the benefits of low leakage, rapid response time, and wide adaptability range, the energy supply system limits the size and even their applicability in integration and miniaturization. In comparison, passive microvalves have the advantage of relying solely on the fluid flow or fluid driving pressure to control the open/close of fluid flow over active microvalves, in spite of having slightly reduced control accuracy. Their self-sustaining feature is highly consistent with the need for assembly and miniaturization in the point-of-care testing technology. Hence, these valves have attracted significant interest for research and application purposes. This review focuses on the recent literature on passive microvalves and details existing passive microvalves from three different aspects: operating principle, processing method, and applications. This work aims to increase the visibility of passive microvalves among researchers and enhance their comprehension by classifying them according to the aforementioned three aspects, facilitating the practical applications and further developments of passive microvalves. Additionally, this paper is expected to serve as a comprehensive and systematic reference for interdisciplinary researchers that intend to design related microfluidic systems.

A vertically paired electrode for redox cycling and its application to immunoassays

An electrochemical immunoassay based on the redox cycling method was presented using vertically paired electrodes (VPEs), which were fabricated using poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) as an electrode material and parylene-C as a dielectric layer. For the application to immunoassays, different electrochemical properties of PEDOT:PSS were analyzed for the redox reaction of 3,3',5,5'-tetramethylbenzidine (TMB, the chromogenic substrate for enzyme-immunoassays) at different pH conditions, including the conductivity (σ), electron transfer rate constant (k_app), and double-layer capacitance (C_dl). The influencing factors on the sensitivity of redox cycling based on VPE based on PEDOT:PSS were analyzed for the redox reaction of TMB, such as the electrode gap and number of electrode pairs. Computer simulation was also performed for the redox cycling results based on VPEs, which had limitations in fabrication, such as VPEs with an electrode gap of less than 100 nm and more than five electrode pairs. Finally, the redox cycling based on VPE was applied to the medical diagnosis of human hepatitis-C virus (hHCV) using a commercial ELISA kit. The sensitivity of the redox cycling method for the medical diagnosis of hHCV was compared with conventional assay methods, such as TMB-based chromogenic detection, luminol-based chemiluminescence assay, and a rapid test kit (lateral flow immunoassay).

Fabrication of a Cell-Friendly Poly(dimethylsiloxane) Culture Surface via Polydopamine Coating

In this study, we fabricated a poly(dimethylsiloxane) (PDMS) surface coated with polydopamine (PDA) to enhance cell adhesion. PDA is well known for improving surface adhesion on various surfaces due to the abundant reactions enabled by the phenyl, amine, and catechol groups contained within it. To confirm the successful surface coating with PDA, the water contact angle and X-ray photoelectron spectroscopy were analyzed. Human umbilical vein endothelial cells (HUVECs) and human-bone-marrow-derived mesenchymal stem cells (MSCs) were cultured on the PDA-coated PDMS surface to evaluate potential improvements in cell adhesion and proliferation. HUVECs were also cultured inside a cylindrical PDMS microchannel, which was constructed to mimic a human blood vessel, and their growth and performance were compared to those of cells grown inside a rectangular microchannel. This study provides a helpful perspective for building a platform that mimics in vivo environments in a more realistic manner.

Electrochemical One-Step Immunoassay Based on Switching Peptides and Pyrolyzed Carbon Electrodes

Switching peptides were designed to bind reversibly to the binding pocket of antibodies (IgG) by interacting with frame regions (FRs). These peptides can be quantitatively released when antigens bind to IgG. As FRs have conserved amino acid sequences, switching peptides can be used as antibodies for different antigens and different source animals. In this study, an electrochemical one-step immunoassay was conducted using switching peptides labeled with ferrocene for the quantitative measurement of analytes. For the effective amperometry of the switching peptides labeled with ferrocene, a pyrolyzed carbon electrode was prepared by pyrolysis of the parylene-C film. The feasibility of the pyrolyzed carbon electrode for the electrochemical one-step immunoassay was determined by analyzing its electrochemical properties, such as its low double-layer capacitance (C_dl), high electron transfer rate (k_app), and wide electrochemical window. In addition, the factors influencing the amperometry of switching peptides labeled with ferrocene were analyzed according to the hydrodynamic radius, the number of intrahydrogen bonds, dipole moments, and diffusion coefficients. Finally, the applicability of the electrochemical one-step immunoassay for the medical diagnosis of the human hepatitis B surface antigen (hHBsAg) was assessed.

Ion-selective electrode-based potentiometric immunoassays for the quantitative monitoring of alpha-fetoprotein by coupling rolling cycle amplification with silver nanoclusters

This work reports an ion-selective electrode-based potentiometric immunoassay for AFP detection coupling rolling cycle amplification with silver nanoclusters.