A Review on Microfluidic Paper-Based Analytical Devices for Glucose Detection.

Glucose, as an essential substance directly involved in metabolic processes, is closely related to the occurrence of various diseases such as glucose metabolism disorders and islet cell carcinoma. Therefore, it is crucial to develop sensitive, accurate, rapid, and cost effective methods for frequent and convenient detections of glucose. Microfluidic Paper-based Analytical Devices (µPADs) not only satisfying the above requirements but also occupying the advantages of portability and minimal sample consumption, have exhibited great potential in the field of glucose detection. This article reviews and summarizes the most recent improvements in glucose detection in two aspects of colorimetric and electrochemical µPADs. The progressive techniques for fabricating channels on µPADs are also emphasized in this article. With the growth of diabetes and other glucose indication diseases in the underdeveloped and developing countries, low-cost and reliably commercial µPADs for glucose detection will be in unprecedentedly demand.

Recent Progresses in Electrochemical DNA Biosensors for MicroRNA Detection.

MicroRNAs (miRNAs), as the small, non-coding, evolutionary conserved, and post-transcriptional gene regulators of the genome, have been highly associated with various diseases such as cancers, viral infections, and cardiovascular diseases. Several techniques have been established to detect miRNAs, including northern blotting, real-time polymerase chain reaction (RT-PCR), and fluorescent microarray platform. However, it remains a significant challenge to develop sensitive, accurate, rapid, and cost-effective methods to detect miRNAs due to their short size, high similarity, and low abundance. The electrochemical biosensors exhibit tremendous potential in miRNA detection because they satisfy feature integration, portability, mass production, short response time, and minimal sample consumption. This article reviewed the working principles and signal amplification strategies of electrochemical DNA biosensors summarized the recent improvements. With the development of DNA nanotechnology, nanomaterials and biotechnology, electrochemical DNA biosensors of high sensitivity and specificity for microRNA detection will shortly be commercially accessible.

Typography-Like 3D-Printed Templates for the Lithography-Free Fabrication of Microfluidic Chips.

Typography-like templates for polydimethylsiloxane (PDMS) microfluidic chips using a fused deposition modeling (FDM) three-dimensional (3D) printer are presented. This rapid and fast proposed scheme did not require complicated photolithographic fabrication facilities and could deliver resolutions of ~100 µm. Polylactic acid (PLA) was adopted as the material to generate the 3D-printed units, which were then carefully assembled on a glass substrate using a heat-melt-curd strategy. This craft of bonding offers a cost-effective way to design and modify the templates of microfluidic channels, thus reducing the processing time of microfluidic chips. Finally, a flexible microfluidic chip to be employed for cell-based drug screening was developed based on the modularized 3D-printed templates. The lithography-free, typography-like, 3D-printed templates create a modularized fabrication process and promote the prevalence of integrated microfluidic systems with minimal requirements and improved efficiency.

Manufacturing of an electrochemical biosensing platform based on hybrid DNA hydrogel: Taking lung cancer-specific miR-21 as an example.

DNA hydrogel garnered increasing attention in the sensing and medical field owing to its native biocompatibility and mechanical stability. While electrochemistry serves as a quantitative and sensitive detection technique, electrochemical DNA hydrogel biosensor is rarely reported. Here, for the first time, we report an electrochemical biosensor based on hybrid DNA hydrogel immobilized on indium tin oxide/polyethylene terephthalate (ITO/PET) electrode for the detection of lung cancer-specific microRNA, miR-21. The biosensor is capable of detecting miR-21 at a concentration as low as 5nM (1 pmol) and linear read-out from 10nM to 50µM. Ferrocene-tagged recognition probes were cross-linked with DNAs grafted on the polyacrylamide backbones to form the hybrid DNA hydrogel, which was further immobilized on 3-(trimethoxysilyl)propyl methacrylate (KH 570) treated ITO electrode. When the recognition probe was hybridized with the target miR-21, the hydrogel dissolved, producing a loss of ferrocene tags and a reduction in current, detected by Cyclic Voltammetry (CV) and Differential Pulse Voltammetry (DPV). The material characteristics of the biosensor were verified using contact angle meter and Energy Dispersive Spectrometer (EDS). This novel biosensor holds great promise in early sensitive clinical diagnosis for a variety of cancer-specific biomarkers due to the flexible sequence design of the recognition probe.

An electrochemical biosensor based on DNA tetrahedron/graphene composite film for highly sensitive detection of NADH.

Dihydronicotinamide adenine dinucleotide (NADH) is a major biomarker correlated with lethal diseases such as cancers and bacterial infection. Herein, we report a graphene-DNA tetrahedron-gold nanoparticle modified gold disk electrode for highly sensitive NADH detection. By assembling the DNA tetrahedron/graphene composite film on the gold disk electrode surface which prior harnessed electrochemical deposition of gold nanoparticles to enhance the effective surface area, the oxidation potential of NADH was substantially decreased to 0.28V (vs. Ag/AgCl) and surface fouling effects were successfully eliminated. Furthermore, the lower detection limit of NADH by the presented platform was reduced down to 1fM, with an upper limit of 10pM. Both the regeneration and selectivity of composite film-modified electrode are investigated and proved to be robust. The novel sensor developed here could serve as a highly sensitive probe for NADH detection, which would further benefit the field of NADH related disease diagnostics.

Electrochemical detection of lung cancer specific microRNAs using 3D DNA origami nanostructures.

Recent reports have indicated that aberrant expression of microRNAs is highly correlated with occurrence of lung cancer. Therefore, highly sensitive detection of lung cancer specific microRNAs provides an attractive approach in lung cancer early diagnostics. Herein, we designed 3D DNA origami structure that enables electrochemical detection of lung cancer related microRNAs. The 3D DNA origami structure is constituted of a ferrocene-tagged DNA of stem-loop structure combined with a thiolated tetrahedron DNA nanostructure at the bottom. The top portion hybridized with the lung cancer correlated microRNA, while the bottom portion was self-assembled on gold disk electrode surface, which was modified with gold nanoparticles (Au NPs) and blocked with mercaptoethanol (MCH). The preparation process and the performance of the proposed electrochemical genosensor were characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM), cyclic voltammetry (CV) and differential pulse voltammetry (DPV). Under the optimal conditions, the developed genosensor had a detection limit of 10 pM and a good linearity with microRNA concentration ranging from 100 pM to 1 µM, which showed a great potential in highly sensitive clinical cancer diagnosis application.