Paper and thread are widely used as the substrates for fabricating low-cost, disposable, and portable microfluidic analytical devices used in clinical, environmental, and food safety monitoring. Concerning separation methods including chromatography and electrophoresis, these substrates provide unique platforms for developing portable devices. This review focuses on summarizing recent research on the miniaturization of the separation techniques using paper and thread. Preconcentration, purification, desalination, and separation of various analytes are achievable using electrophoresis and chromatography methods integrated with modified or unmodified paper/thread wicking channels. A variety of 2D and 3D designs of paper/thread platforms for zone electrophoresis, capillary electrophoresis, and modified/unmodified chromatography are discussed with emphasis on their limitation and improvements. The current progress in the signal amplification strategies such as isoelectric focusing, isotachophoresis, ion concentration polarization, isoelectric focusing, and stacking methods in paper-based devices are reviewed. Different strategies for chromatographic separations based on paper/thread will be explained. The separation of target species from complex samples and their determination by integration with other analytical methods like spectroscopy and electrochemistry are well-listed. Furthermore, the innovations for plasma and cell separation from blood as an important human biofluid are presented, and the related paper/thread modification methods are explored.
Isotachophoresis , Microfluidic Analytical Techniques , Humans , Microfluidics , Electrophoresis, Capillary/methods , Isoelectric Focusing/methods , Isotachophoresis/methods , Chromatography
An origami three-dimensional design of a paper-based potentiometric sensor is described. In its simplest form, this electrochemical paper-based analytical device (ePAD) is made from three small parts of the paper. Paper layers are folded on each other for the integration of a solid contact ion selective electrode (here a carbon-paste composite electrode) and a solid-state pseudo-reference electrode (here writing pencil 6B on the paper), which are in contact with a hydrophilic channel fabricated on the middle part (third part) of the paper. In this case, the pseudo-reference and working electrodes are connected to the two sides of the hydrophilic channel and hence the distance between them is as low as the width of paper. The unmodified carbon paste electrode (UCPE) and modification with the crown ether benzo15-crown-5 (B15C5) represented a very high sensitivity to Cu (II) and Cd2+ ions, respectively. The sensor responded to H2O2 using MnO2-doped carbon paste electrode (CPE). Furthermore, a biosensor was achieved by the addition of glucose oxidase to the MnO2-doped CPE and hence made it selective to glucose with ultra-sensitivity. In addition to very high sensitivity, our device benefits from consuming a very low volume of sample (10.0 µL) and automatic sampling without need for sampling devices.
Biosensing Techniques/instrumentation , Microfluidic Analytical Techniques , Potentiometry/methods , Carbon , Electrochemical Techniques , Electrodes , Glucose Oxidase , Hydrogen Peroxide , Ion-Selective Electrodes , Manganese Compounds , Microfluidics , Oxides
A disposable paper-based bipolar electrochemical biosensor is reported for determination of glucose. The closed bipolar electrochemical cell is fabricated on a small part of paper using a laser printing-based process for paper hydrophobization. The bipolar and driving electrodes are provided by pressing the writing pencil HB on the paper. The mechanism of sensing of glucose is oxidation of the analyte in the sensing cell using glucose oxidase followed by reduction of the produced H2O2 by application of an external potential (10.0 V). This causes the oxidation of K4Fe(CN)6 in the presence of Fe(II) ions and subsequent formation of Prussian Blue (PB) particles in the reporting cell. The intensity of the blue color in the reporting cell is used as a visual and colorimetric signal that can be digitally read using a scanner of digital camera. The parameters affecting the performance of the device were optimized using experimental design and chemometrics modeling. The P-BPE represents a very wide response range that extends from 0.1 mmol.L-1 to 4.0 mol.L-1 in the case of hydrogen peroxide, and from 0.1 to 50 mmol.L-1 in the case of glucose. The limit of detections for hydrogen peroxide and glucose are 4.9 µmol.L-1 and 70 µmol.L-1 respectively. Graphical abstract Analyte solution (H2O2) and deionized water is injected to the sensing and the reporting cells respectively. By applying of an external potential, H2O2 reduction and potassium ferrocyanide (K4Fe(CN)6) oxidation is performed. This provides the appropriate condition for Prussian blue (PB) production (dark blue) in the reporting cell.
