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.
This work presents a fully disposable
microchamber for gas generation
of a sample solution. The microchamber consists of a cylindrical well-reactor
and a paper-based microfluidic lid (μFluidic lid), which also
serves as the reagent loading and dispensing unit. The base of the
reactor consists of a hydrophobic membrane covering an in-house graphene
electrochemical gas sensor. Fabrication of the gas sensor and the
three-layer μFluidic lid is described. The μFluidic lid
is designed to provide a steady addition of the acid reagent into
the sample solution instead of liquid drops from a disposable syringe.
There are three steps in the procedure: (i) acidification of the sample
in the reactor to generate SO2 gas by the slow dispensing
of the acid reagent from the μFluidic lid, (ii) diffusion of
the liberated SO2 gas through the hydrophobic membrane
at the base of the reactor, and (iii) in situ detection of SO2 by cathodic reduction at the graphene electrode. The device
was demonstrated for quantitation of the sulfite preservative in wine
without heating or stirring. The selectivity of the analysis is ensured
by the combination of the gas-diffusion membrane and the selectivity
of the electrochemical sensor. The linear working range is 2–60
mg L–1 SO2, with a limit of detection
(3SD of intercept/slope) of 1.5 mg L–1 SO2. This in situ method has the shortest analysis time (8 min per sample)
among all voltammetric methods that detect SO2(g) via membrane
gas diffusion.
This work presents the first planar three-electrode electrochemical sensor comprising local gold leaf as the working electrode and printed, or hand-drawn, counter and reference electrodes, respectively. The gold leaf was...
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