ABSTRACT
This work describes a new method for fabrication of enclosed channel porous-media microfluidic analytical devices using selective laser ablation. Microfluidic structures can be readily produced inside the enclosed devices within two fabrication steps. A sheet of porous material was first sandwiched and bonded between two sheets of polymeric film. The porous substrate inside the film layers was then selectively ablated using a laser cutter to create hollow barriers for microfluidic channels. Selective ablation of only the porous layer was achieved because the porous substrate layer is susceptible to ablation by the laser beam, whereas the film layer is resistant to laser ablation due to its light transmission properties. This selective laser ablation processing is not limited by laser type. As a proof-of-concept, two different laser systems, a 10.6 µm CO2 laser and a 455 nm diode laser, were employed for this purpose. A variety of porous materials, including cellulose, nitrocellulose, and glass microfiber, were combined with a wide variety of polymeric films to fabricate enclosed microfluidic devices. The developed method is versatile; depending on material combination and number of layers of materials in the devices, enclosed microfluidic devices with 2D, passive 3D, or compression-activated 3D fluid flow can be created. Quantitative assays for albumin, glucose, and cholesterol in human serum performed using devices produced via this method demonstrated the utility of this fabrication approach. This unique, simple, and scalable method for fabrication of enclosed microfluidic devices not only ensures protection of devices from contamination and prevention of fluid evaporation, but also offers a method for commercial fabrication of porous-media analytical devices.
ABSTRACT
A novel approach to building a membrane-based disposable well-plate, here applied to cyanide detection, is described. Chitosan encapsulated CdTe quantum dots with a maximum emission at 520 nm (CS-QD520) were used as fluorophores. The CS-QD520 nanoparticle was specifically quenched by copper(II), and the quenched CS-QD520 (Cu-CS-QD520) was deposited onto a glass microfiber filter (GF/B). Subsequent introduction of cyanide ion resulted in fluorescence recovery. The "signal-ON" fluorescence linearly correlated to cyanide concentrations in the range of 38.7 to 200 µM with a limit of detection of 11.6 µM. The assay was incorporated into a membrane-based well-plate format to enhance sample throughput. A three-layer paper/glass microfiber well plate design was cut using a laser cutter and assembled using a polycaprolactone (PCL) as a bonding agent in a low-cost laminator. The experimental conditions were optimized and applied to detect cyanide in drinking water with rapid, high-throughput, low-cost analysis.
Subject(s)
Cadmium Compounds/chemistry , Chitosan/chemistry , Cyanides/analysis , Fluorescent Dyes/chemistry , Quantum Dots/chemistry , Tellurium/chemistry , Reproducibility of Results , Spectrometry, FluorescenceABSTRACT
This work presents new chemical sensing devices called "membraneless gas-separation microfluidic paper-based analytical devices" (MBL-GS µPADs). MBL-GS µPADs were designed to make fabrication of the devices simple and user-friendly. MBL-GS µPADs offer direct quantitative analysis of volatile and nonvolatile compounds. Porous hydrophobic membrane is not needed for gas-separation, which makes fabrication of the device simple, rapid and low-cost. A MBL-GS µPAD consists of three layers: "donor layer", "spacer layer", and "acceptor layer". The donor and acceptor layers are made of filter paper with a printed pattern. The donor and acceptor layers are mounted together with a spacer layer in between. This spacer is a two-sided mounting tape, 0.8 mm thick, with a small disc cut out for the gas from the donor zone to diffuse to the acceptor zone. Photographic image of the color that is formed by the reagent in the acceptor layer is analyzed using the ImageJ program for quantitation. Proof of concept of the MBL-GS µPADs was demonstrated by analyzing standard solutions of ethanol, sulfide, and ammonium. Optimization of the MBL-GS µPADs was carried out for direct determination of ammonium in wastewaters and fertilizers to demonstrate the applicability of the system to real samples.
