Monolithic integrated light-emitting-diode/photodetector sensor for photoactive analyte monitoring: design and simulation

: We present the simulation and design optimization of an integrated light-emitting-diode/photodetector (LED-PD) sensor system for monitoring of light absorbance changes developing in analyte-sensitive compounds. The sensor integrates monolithically both components in a single chip, offering advantages such as downsizing, reduced assembly complexity, and lower power consumption. The changes in the optical parameters of the analyte-sensitive ink are detected by monitoring the power transmission from the LED to the PD. Ray tracing and coupled modeling approach (CMA) simulations are employed to investigate the interaction of the emitted light with the ink. In highly absorbing media, CMA predicts more accurate results by considering evanescent waves. Simulations also suggest that an approximately 39% change in optical transmission can be achieved by adjusting the ink-deposited layer thickness and varying the extinction coefficient from 10-4 to 3×10-4

Colorimetric detection of hydrogen sulfide in ambient air

We present a fast method to monitor hydrogen sulfide (H2S) in ambient air based on a visible color change. Therefore, an immobilized copper(II) complex of the azo dye 1-(2-pyridylazo)-2-naphtol (H-PAN) was synthesized and prepared in a matrix for screen printing. Different materials, reaching from opaque paper to transparent foils served as substrate. The reaction of the copper(II) complex (Cu-PAN) to the target gas H2S was measured in reflection via UV/VIS spectroscopy

Screen-Printed Sensors for Colorimetric Detection of Hydrogen Sulfide in Ambient Air

A fast and sensitive method to monitor hydrogen sulfide (H2S) in ambient air based on a visible color change of a printed disposable sensor has been developed. As gas-sensitive material, an immobilized copper(II) complex of the azo dye 1-(2-pyridylazo)-2-naphtol (H-PAN) was synthesized and prepared in an ethyl cellulose matrix for screen printing. If H2S is present in ambient air, the gas sensitive layer changes its color from purple to yellow. A pre-primed polyethylene (PE) foil and a coated offset paper served as the printing substrate. The colorimetric response to the target gas was measured by UV/Vis spectroscopy in reflection at H2S concentrations between 1 to 20 ppm. Possible cross-sensitivities of the printed sensors towards methane (CH4), formaldehyde (CH2O), carbon monoxide (CO), ammonia (NH3), and nitrogen dioxide (NO2), as well as the long-term stability was investigated. Furthermore, reflection measurements of the Cu-PAN complex on an amorphous silica powder under gas admission served as preliminary test for the subsequent paste development

Colorimetric Materials for Fire Gas Detection—A Review

The damage caused by outbreaks of fire continues to be enormous despite ongoing improvements in fire detection and fighting. Therefore, the detection of fires at the earliest possible stage is essential. The latest developments in fire detection devices include the addition of carbon monoxide (CO) or temperature sensors into the widespread smoke detectors, but also alternative solutions are searched for. Advantageous is the direct detection of the most relevant fire gases CO and nitrogen dioxide (NO2), because they are produced very early in a developing fire. A sensitive, selective, and low-cost method to detect these gases is the use of colorimetric materials combined with a compact optical readout. In this review, we take account of recent developments in this research field and provide a comprehensive overview on suitable materials for CO and NO2 detection in fire gas sensing and first steps towards novel fire gas detectors

Gasochromic detection of NO2 on the example of the food additive E141 (ii)

We present our investigation on the gasochromic reaction of E141 (ii) towards the toxic gas nitrogen dioxide (NO2). E141 (ii) is a chlorophyllin-based food additive, typically used as green coloring for nearly all kinds of sweets. In this presentation we show an alternative approach for using E141 (ii) as optical gas indicator. All solid samples are prepared by multi-layer screen printing on different substrates like paper and PE-foil. Gas measurements are performed using an UV/Vis spectrometer. The influence of the substrate and according layer thickness is shown

Investigation of gasochromic rhodium complexes regarding their reactivity towards CO

The detection of the toxic gas carbon monoxide (CO) in the low ppm range is required in different applications. We present a study of the reactivity of different gasochromic rhodium complexes towards the toxic gas carbon monoxide (CO). Therefore, the binuclear rhodium complexes with different ligands were prepared and their influence regarding reaction velocity and sensitivity towards CO was investigated. The most promising rhodium complex was embedded into a polymer with which glass substrates were coated. The reactivity towards CO of these layers was also investigated

Does `Aggregation Bias' Explain the PPP Puzzle?

We present a fast and simple method to monitor toxic gases in ambient air based on a visible color change of a printed paper sensor, which can be evaluated using a camera (e.g. smartphone) or naked eye. This study focuses on the development of gas-sensitive pastes for the processing of the colorimetic material by screen printing. Indicators for the detection of ammonia (NH3 ), hydrogen sulfide (H2S) and formaldehyde (CH2O) were examined in closer detail. The sensing properties of the respective indicator towards the target gas was characterized via UV/Vis spectroscopy in reflection