A rapid and simple thermally-solvent assisted method of bonding was introduced for poly(methyl methacrylate) (PMMA) based microfluidic substrates. The technique is a low-temperature (), and rapid () bonding technique; in addition, only a fan-assisted oven with some paper clamps are used. Two different solvents (ethanol and isopropyl alcohol) with two different methods of cooling (one-step and three steps) were employed to determine the best solvent and method of cooling (residual stresses may be released in different cooling methods) by considering bonding strength and quality. In this bonding technique, a thin film of solvent between two PMMA sheets disperses tends to dissolve a thin film of PMMA sheet surface, then evaporate, and finally reconnect monomers of the PMMA sheets at the specific operating temperature. The operating temperature of this method comes from the coincidence of the solubility parameter graph of PMMA with the solubility parameter graph of the solvents. Different tests such as tensile strength test, deformation test, leakage tests, and surface characteristics tests were performed to find the optimum conditions for this bonding strategy. The best bonding quality and the highest bonding strength () occurred when 70% isopropyl alcohol solution was employed with the one-step cooling method. Furthermore, the bonding reversibility was taken into account and critical percentages for irreversible bonding were obtained for both of the solvents and methods. This method provides a perfect bonding quality for PMMA substrates, and can be used in laboratories without needing any expensive and special instruments, because of its merits such as lower bonding time, lower-cost, and higher strength etc in comparison with the majority of other common bonding techniques.
A facile and digital do‐it‐yourself technique is proposed to fabricate inexpensive sensors on flexible substrates (paper, cloth, and plastic film). A set of office‐grade equipment (i.e., laserjet printer, thermal laminator, computer‐aided paper cutter), and commercially available supplies (i.e., baking wax paper, furniture restoration metal‐leaf) are used. Forming electrodes through traditional printing and defining a fluidic confinement region through crafting practice enable fabrication of a wide range of devices without requiring customized specialty instruments, costly infrastructure, and complicated fabrication steps, unlike previously introduced methods. Three different levels of experiments are designed to assess the comprehensiveness and responsiveness of the proposed method to the needs of existing research fields. The performances of the fabricated features at each level are evaluated to cover various application domains in environmental monitoring and biomedical diagnostics utilizing conductometric, colorimetric, biochemical, and chemoresistive detection principles. Devices with varying size of features, from nanometers to centimeters, are fabricated and characterized. This method provides an alternative route to decentralized production of low‐cost flexible sensors and other devices, with a minimal step, time, and facilities. The operation of such devices is simple and can be further empowered by smartphones for data analysis and transmission.
In this study, a capillary-based micro-optofluidic viscometer, which is capable of measuring dynamic viscosity in a range of 0.5 mPa s-50 mPa s with only a small volume of liquid (26 µl) in just a few seconds (less than 15 s for most of the samples used) with an acceptable accuracy (99.56%), has been designed, fabricated, and tested. This device consists of two different parts, namely a poly(methyl methacrylate) (PMMA) microfluidic chip and an electro-optical detection system. The viscometer determines viscosity by measuring the time that the liquid travels between two specific points of a rectangular microchannel. The microchannel has been micro-milled on a PMMA substrate, which has been bonded to another PMMA sheet. The fluid flow inside the microfluidic chip has been created by the capillary driven flow; hence, there is no need for any external devices to generate fluid flow. The resolution of this microviscometer is approximately 0.001 mPa s. An ADC circuit has been added to the electro-optical detection system, which is an optically-activated stopwatch circuit, to enhance accuracy, sensitivity, resolution, and to make this viscosity measurement device applicable and efficient for a wide range of applications. This integrated microviscometer automatically notices entry of liquid and completion of the experiment, and finally gives the result. In this study, only Newtonian fluids were tested via this microviscometer, but this device is also capable of measuring non-Newtonian liquids. This portable microviscometer has applications in different fields such as point-of-care diagnosis, chemical and food industries, pharmaceutical industries, research laboratories, etc.
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