Piezoresistive pH Microsensors Based on Stimuli-Sensitive Polyelectrolyte HydrogelsPiezoresistive pH-Mikrosensoren auf der Basis stimuli-sensitiver polyelektrolytischer Hydrogele

Gerlach

2019

Sensors

Self Cite

Ammonia is an essential key compound in the chemical industry. However, excessively high ammonia concentrations can be harmful to the environment. Sensors for the detection of ammonia are therefore particularly important for environmental analysis. In this article, a novel hydrogel-based piezoresistive ammonia sensor is presented. In aqueous solution, ammonia reacts as a base. This alkaline pH change can be detected with stimuli-sensitive hydrogels. For such an application, highly sensitive hydrogels in the alkaline range with sufficient mechanical stability for the sensor application has to be developed. These conditions are fulfilled by the presented hydrogel system based on acrylic acid (AAc) and 2-(dimethylamino)ethyl methacrylate (DMAEMA). The hydrogel composition has a significant influence on the swelling behavior of the gel. Furthermore, the hydrogel swelling in ammonia solutions was tested and a detection limit in the range of 1 mmol/L ammonia depending on the buffer solution was determined. Ammonia-sensitive hydrogels can be used multiple times due to the repeatable swelling of the gel over several swelling cycles. To generate a measurable output voltage, the swelling pressure of ammonia-sensitive hydrogels were detected by using piezoresistive pressure sensors. All results of the free hydrogel swelling were verified in the sensor application. This low-cost ammonia sensor with a high sensitivity could be interesting for industrial chemical and biotechnological applications.

Section: Prospects For Commercial Sensing Applicationssupporting

confidence: 64%

Section: Prospects For Commercial Sensing Applicationsmentioning

confidence: 99%

Piezoresistive Hydrogel-Based Sensors for the Detection of Ammonia

Erfkamp

Gerlach

2019

Sensors

Self Cite

“…After 15 min, 90 % of the final steady-state value is reached, which shows an improvement of the response time by a factor of 2 in comparison to other systems exploiting this kind of hydrogel (Schmidt et al, 2016;Schulz et al, 2010). This improvement is caused by using a much thinner hydrogel layer (30 µm instead of > 100 µm), which, in turn, leads to lower diffusion times of the surrounding liquid into the gel and, hence, to a faster response to changing pH.…”

Section: Resultsmentioning

confidence: 76%

“…As the first step, we report here on initial results on the optical detection of different swelling states of our pH-sensitive hydrogel on a nanostructured gold surface. As we also envision implantable sensors for biomedical applications, a hydrogel composition is investigated, which can be used in the physiological pH range (Schulz et al, 2010). The combination of this specific hydrogel and a nanostructured plasmonic sensor substrate is studied for the first time, which provides data on the interrogation of physiologically applicable gels with optical methods.…”

Section: Introductionmentioning

confidence: 99%

Evaluation of the pH-sensitive swelling of a hydrogel by means of a plasmonic sensor substrate

Kroh

Wuchrer

et al. 2018

J. Sens. Sens. Syst.

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Abstract. The inline monitoring of parameters in aqueous liquids is facing an increasing demand in many different application areas. Hydrogels with pH-induced swelling and deswelling behavior offer a means to measure pH in such liquids. Here we investigate the optical interrogation of a pH-sensitive hydrogel which can be applied in the physiological pH range. For this, a nanostructured gold substrate supporting surface plasmon oscillations is coated with a HPMA/DMAEMA/TEGDMA/EG hydrogel. The gel swells in the pH range under investigation (here 4.5 to 6.5), and the resulting refractive index changes subsequently lead to a spectral shift of the plasmon resonance of the gold nanostructure. The spectral resonance position is determined from optical transmittance spectra of the sensor substrates, and the initial results for our hydrogel reported here indicate a nearly linear dependence between the swelling state and the plasmon resonance wavelength.

“…Sweet liquors have a pH value in a range from pH 3.3 to 3.9, and strong alcoholic drinks in a range from pH 6.5 to 6.9 [27]. However, most hydrogel systems show an influence of the pH value on the swelling behavior [28,29,30]. Therefore, the pH sensitivity of hydrogel-based ethanol sensors was tested in an acidic pH range from pH 7.4 to 4.01 (Figure 6).…”

Section: Resultsmentioning

confidence: 99%

Hydrogel-Based Sensors for Ethanol Detection in Alcoholic Beverages

Erfkamp

Gerlach

2019

Sensors

Self Cite

A fast and reliable determination of the ethanol concentration is essential in the analysis of alcoholic beverages. However, different factors like pH value or salt concentration can influence the ethanol measurement. Furthermore, analytical figures of merit for the alcohol sensor, such as limit of detection, sensitivity and measurement uncertainty, are necessary for the application. In this paper, a detailed sensor characterization of a novel sensor based on ethanol-sensitive poly acrylamide hydrogels will be presented. The resulting swelling pressure of the hydrogel was transformed via a piezoresistive pressure sensor into a measurable output voltage. These kinds of sensors can be used over a large measuring range, up to 50 vol% ethanol and more, with a high sensitivity. In the range from pH 7.4 to 4, the pH value had no influence on the sensor signal. Higher salt concentrations can slightly influence the measurement. The detection limit amounts to 0.06–0.65 vol% ethanol. The concentration of a vodka sample was determined with a sufficient measuring uncertainty.