Development of a Gas-Diffusion Microfluidic Paper-Based Analytical Device (μPAD) for the Determination of Ammonia in Wastewater Samples

Abstract

An inexpensive, disposable and highly selective microfluidic paper-based analytical device (μPAD) is described for the determination of ammonia (molecular ammonia and ammonium cation) in wastewaters which implements for the first time a gas-diffusion separation step on a paper-based platform. Its hydrophilic reagent zones were defined by printing filter paper with a hydrophobic paper sizing agent using a conventional inkjet printer. The sample was introduced into the sodium hydroxide impregnated sample zone of the μPAD. This allowed the quantitative conversion of the ammonium ion to molecular ammonia which diffused across the hydrophobic microporous Teflon membrane of the device into an adjacent hydrophilic reagent zone containing the acid-base indicator 3-nitrophenol or bromothymol blue. The change in indicator color was measured using a desktop scanner for ammonia quantification. Under optimal conditions, the μPAD is characterized by a limit of detection of 0.8 and 1.8 mg N L(-1) and repeatability of 3.1 and 3.7% (n ≥ 10, 20 mg N L(-1)), expressed as relative standard deviation, in the case of 3-nitrophenol or bromothymol blue, respectively. This μPAD was used successfully for the determination of ammonia in sewage and soil water samples. The small dimensions, minimal reagent consumption, low cost, simplicity of operation, and possibility of using a portable scanner make the proposed μPAD suitable for on-site ammonia monitoring in contaminated environmental waters and domestic, agricultural and industrial wastewaters. The successful implementation of the gas-diffusion approach on a paper-based platform is expected to result in the development of other μPADs for volatile analytes.

A Portable, Single-Use, Paper-Based Microbial Fuel Cell Sensor for Rapid, On-Site Water Quality Monitoring

“…Microfluidic paper-based analytical devices (µPADs) have attracted a lot of attention as water quality sensors due to the easy fabrication and cost-effective nature of paper. The most commonly used method for µPAD-based water analysis is the colorimetric detection method [20][21][22]. However, colorimetric techniques can only provide qualitative or semi-quantitative analysis given that a calibration chart and external digital scanners or cameras are provided [23].…”

A Fully Integrated Paper-Microfluidic Electrochemical Device for Simultaneous Analysis of Physiologic Blood Ions

“…. (6) In this case, the zero current potential E is a function of the sodium ion concentration only. Potentiometric measurement of calcium ion concentration is the same as described above, except the calcium permeable film and CaCl2 electrolyte should be used.…”

“…Paper microfluidic electrochemical devices almost perfectly meet this need, while allowing an external power-free separation of a sample solution, and selective detection of target materials through the microfluidic channel at one time. Due to their low cost, effectiveness, and convenience for field-based point-of-care detection, the paper microfluidic devices are excellent analytical tools, especially in electrical power-deficient underdeveloped countries [3][4][5][6]. Recently, even more advanced versions of the paper devices have been introduced by combination with surface-enhanced Raman spectroscopic substrates, or with enzyme-linked immunosorbent assay [7,8].…”

Paper-based microfluidic devices by asymmetric calendaring

“…To validate the capability of fabricated channels as microfluidic devices, a "Y" design was used for fluid flow and theoretically compared with the literature (Figures 3(a)-3(c)). 5,8,10,11,14,16,18,20,[37][38][39][40][41][42][43] Other geometries were also fabricated (Figures 3(d) and 3(e)) to show the versatility of the targeted asymmetric calendaring and hydrophobization (TACH) method. The microfluidic devices were manufactured using paper and tested with dyed water (food color) for visualization.…”