Microfluidic sensors based on two-dimensional materials for chemical and biological assessments

There has been an exponential increase in the number of studies of two-dimensional (2D) layered materials for sensing applications since the isolation of graphene in 2004. These materials serve as...

Manufacturing of Microfluidic Sensors Utilizing 3D Printing Technologies: A Production System

3D integrated microfluid devices are a group of engineered microelectromechanical systems (MEMS) whereby the feature size and operating range of the components are on a microscale. These devices or systems have the ability to detect, control, activate, and create macroscale effects. On this basis, microfluidic chips are systems that enable microliters and smaller volumes of fluids to be controlled and moved within microscale-sized (one-millionth of a meter) channels. While this small scale can be compared to microfluid chips of larger applications, such as pipes or plumbing practices, their small size is commonly useful in controlling and monitoring the flow of fluid. Through such applications, microfluidic chip technology has become a popular tool for analysis in biochemistry and bioengineering with their most recent uses for artificial organ production. For this purpose, microfluidic chips can be instantly controlled by the human body, such as pulse, blood flow, blood pressure, and transmitting data such as location and the programmed agents. Despite its vast uses, the production of microfluidic chips has been mostly dependent upon conventional practices that are costly and often time consuming. More recently, however, 3D printing technology has been incorporated in rapidly prototyping microfluid chips at microscale for major uses. This state-of-the-art review highlights the recent advancements in the field of 3D printing technology for the rapid fabrication, and therefore mass production, of the microfluid chips.

Scalable All-Printed Microwave Microfluidic Sensor for Multi-Liquid Characterization based on a Stub-Loaded Microstrip Line

Microwave microfluidic sensors are typically designed with a channel in vicinity of a resonator's fringing electric (<i>E</i>)-fields, to characterize the material properties of a single fluid. This paper leverages hybrid 3D and dispenser printing to realize a scalable microfluidic sensor utilizing the parallel-plate capacitance of an open-ended microstrip stub, enabling, for the first time, a tunable sensitivity. A stub-loaded microstrip line is then proposed for characterizing multiple microfluidic samples simultaneously using a simple two-port multi-band resonator. The physical constrains which limit the scalability of the proposed sensors have been analyzed analytically and numerically, prior to implementing a three-channel triple-band sensor. The microfluidic channels have been fabricated using stereolithography 3D printing with the microstrip line directly dispenser printed on a conformable polyimide substrate. To accommodate varying channel thicknesses, a tapered microstrip line is proposed to maintain the impedance matching. The fabricated sensor is characterized using binary water-IPA mixtures to evaluate its sensitivity, comparing favorably with reported 3D-printed sensors. The proposed sensor achieves over 90% accuracy in determining the real permittivity following a simple water-based calibration across the different channels, for samples with 16 oC temperature sensitivity across all channels.

Scalable All-Printed Microwave Microfluidic Sensor for Multi-Liquid Characterization based on a Stub-Loaded Microstrip Line

Microwave microfluidic sensors are typically designed with a channel in vicinity of a resonator's fringing electric (<i>E</i>)-fields, to characterize the material properties of a single fluid. This paper leverages hybrid 3D and dispenser printing to realize a scalable microfluidic sensor utilizing the parallel-plate capacitance of an open-ended microstrip stub, enabling, for the first time, a tunable sensitivity. A stub-loaded microstrip line is then proposed for characterizing multiple microfluidic samples simultaneously using a simple two-port multi-band resonator. The physical constrains which limit the scalability of the proposed sensors have been analyzed analytically and numerically, prior to implementing a three-channel triple-band sensor. The microfluidic channels have been fabricated using stereolithography 3D printing with the microstrip line directly dispenser printed on a conformable polyimide substrate. To accommodate varying channel thicknesses, a tapered microstrip line is proposed to maintain the impedance matching. The fabricated sensor is characterized using binary water-IPA mixtures to evaluate its sensitivity, comparing favorably with reported 3D-printed sensors. The proposed sensor achieves over 90% accuracy in determining the real permittivity following a simple water-based calibration across the different channels, for samples with 16 oC temperature sensitivity across all channels.

A Perovskite-Based Paper Microfluidic Sensor for Haloalkane Assays

Detection of haloalkanes is of great industrial and scientific importance because some haloalkanes are found serious biological and atmospheric issues. The development of a flexible, wearable sensing device for haloalkane assays is highly desired. Here, we develop a paper-based microfluidic sensor to achieve low-cost, high-throughput, and convenient detection of haloalkanes using perovskite nanocrystals as a nanoprobe through anion exchanging. We demonstrate that the CsPbX3 (X = Cl, Br, or I) nanocrystals are selectively and sensitively in response to haloalkanes (CH2Cl2, CH2Br2), and their concentrations can be determined as a function of photoluminescence spectral shifts of perovskite nanocrystals. In particular, an addition of nucleophilic trialkyl phosphines (TOP) or a UV-photon-induced electron transfer from CsPbX3 nanocrystals is responsible for achieving fast sensing of haloalkanes. We further fabricate a paper-based multichannel microfluidic sensor to implement fast colorimetric assays of CH2Cl2 and CH2Br2. We also demonstrate a direct experimental observation on chemical kinetics of anion exchanging in lead-halide perovskite nanocrystals using a slow solvent diffusion strategy. Our studies may offer an opportunity to develop flexible, wearable microfluidic sensors for haloalkane sensing, and advance the in-depth fundamental understanding of the physical origin of anion-exchanged nanocrystals.