Optical Carbon Dioxide Sensor Research Articles

Bodipy-based dyes for ionic-liquid-based optical carbon dioxide sensors

When ionic liquids come in contact with CO2 gas, their polarity and viscosity increase. Owing to these properties, ionic liquids containing organic dyes, which can change their optical properties depending on their surrounding polarity and viscosity, have recently been applied in portable CO2 optical sensors. Although ionic–liquid-based CO2 optical sensors have excellent sensing properties, the optimal organic dyes for ionic–liquid-based CO2 optical gas sensors have not been extensively investigated. Hence, we synthesized and characterized four 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY)-based dyes (PTPBDP, MTPBDP, TPABDP, and TPAMBDP) to explore the optimal structure for liquid-based CO2 optical sensors, with intramolecular charge transfer (ICT) and aggregation-induced emission (AIE) investigated. In addition, the synthesized dyes were applied to an ionic liquid, with their optical properties measured to analyze and compare their detection abilities and selectivity toward CO2 gas. As the CO2 concentration increased, all sensors, except TPAMBDP, showed changes in the optical properties in the visual and fluorescence channels. This approach facilitates the development of a portable sensor capable of detecting CO2 across diverse environmental conditions, showcasing its potential for versatile application in monitoring and analysis tasks. We believe these results provide insights into the design of organic dye structures for ionic liquid-based CO2 optical sensors.

Optical Carbon Dioxide Detection in the Visible Down to the Single Digit ppm Range Using Plasmonic Perfect Absorbers.

To tackle climate change and reduce CO2 emissions, it is important to measure CO2 output precisely. Even though there are many different techniques, no simple and cheap optical method in the visible is available. This work studies plasmonically enhanced optical carbon dioxide sensors in the visible wavelength range. The sensor samples are based on an inert plasmonic perfect absorber, which can be easily and cheaply fabricated by colloidal etching lithography. A CO2-sensitive polyethylenimine (PEI) layer is then spin-coated on top to complete the samples. The samples are examined continuously by microspectroscopy during different CO2 exposures to track spectral changes, particularly the position of the resonance centroid wavelength. The samples exhibit a resonance shift of up to 7 nm, depending on the CO2 concentration and the temperature. The temperature influences the rise time as well as the sensitive concentration range. The concentration dependence of the resonance shift overall follows the shape of a Langmuir isotherm, which includes a nearly linear relation at lower concentrations and elevated temperatures and a saturating behavior at higher concentrations and lower temperatures. The results indicate that a sensitivity in the full range from 100 vol % to below 1 ppm can be achieved. The samples degenerate in a dry inert atmosphere in a matter of days but are useable over multiple weeks when exposed to humidity and CO2. The PEI reacts very selectively to CO2, showing no response to CO, NH3, NO2, CH4, H2, and only a very small response to O2. Overall, polyethylenimine is very promising as a CO2-sensitive material for many practical sensing applications over a wide range of concentrations. An adjustment of the temperature is mandatory to control the sensitivity and response time.

Green to red emitting BODIPY dyes for fluorescent sensing and imaging of carbon dioxide

Several new BODIPY pH indicators are prepared and tested as transducers in polymer-based optical carbon dioxide sensors. Apart from classical BODIPY chromophore absorbing at around 505 nm, π-extended analogs showing absorption maxima at around 635 and 665 nm are prepared. All the dyes possess excellent brightness due to combination of high molar absorption coefficients and fluorescence quantum yields. Additionally, the π-extended BODIPYs show unmatched photostability whereas the classical 1,3,5,7-tetramethyl-8-aryl-4,4-difluoroboradiazaindacene is found to be photolabile. The phenol receptors render BODIPY dyes pH sensitive inducing fluorescence quenching in the phenolate form. Carbon dioxide sensors are prepared via immobilization of the dyes into ethyl cellulose along with tetraoctylammonium hydrogencarbonate. The sensitivity of these sensors is mainly guided by the nature of the receptor and to a smaller extent by the nature of the chromophore, and can be tuned over a very wide range covering all important applications. Introduction of the receptor bearing carboxylic group in the o-position towards OH group of the receptor enables highly sensitive sensors resolving ambient CO2 levels (LOD 0.009 hPa). Sensors based on other indicators show optimal response from 0.2 to 60 hPa and from 20 to 400 hPa, making them attractive for medical and food packaging applications, respectively. Materials for referenced sensing with phase fluorometry and ratiometric imaging with RGB cameras have also been prepared.

Highly sensitive poisoning-resistant optical carbon dioxide sensors for environmental monitoring

Resistivity of optical carbon dioxide chemosensors towards poisoning by acidic gases is significantly improved by using an additional perfluorinated polymer coating making the sensors suitable for long-term measurements.

Optical carbon dioxide sensor based on fluorescent capillary array

A novel carbon dioxide (CO2) gas sensor based on capillary array is presented. The capillary array is composed of 51 capillaries and modified by fluorescent dye 8-hydroxy-1,3,6-pyrenetrisulfonic acid trisodium salt (HPTS, PTS−) and tetraoctylammonium cation (TOA+) doped porous ethyl cellulose. A Y-fiber is used to transmit exciting light and fluorescence. A fiber optic pigtail-contained spectrophotometer is used to collect and deal with optical signals. Due to its structural features, each capillary has the two rolling-up layers of inner and outer sensing films, which make the 2cm long capillary array has large sensing area about 12.81cm2 and the fluorescence signal easily be collected. The sensing probe has advantages such as small volume, compact structure and large sensing area. The results demonstrate that the sensor has a linear response in the CO2 volume ratio range from 0 to 10%.

Carbon dioxide gas sensor based on optical control of color in liquid indicator

A new optical carbon dioxide sensor based on the change in glow intensity of the Europium-III complex, caused by CO2 absorption to various pH-indicators (thymol blue, phenol red and cresol red) of carbon dioxide was developed, and its sensitive properties were studied.

NIR optical carbon dioxide sensors based on highly photostable dihydroxy-aza-BODIPY dyes

Optical carbon dioxide sensors based on novel self-referenced NIR colorimetric dihydroxy-aza-BODIPY dyes are presented. They possess tunable dynamic ranges and unmatched photostability.

Carbon dioxide luminescent sensor based on a CMOS image array

In this work, we describe an optical carbon dioxide (CO2) sensor based on luminescent quenching of hydroxy-pyrenetrisulfonic acid (HPTS). A low-cost CMOS image array was used as detector, while cross-polarization was used to filter the excitation light and reduce background interference. The sensor exhibited excellent performance, with high sensitivity over a wide dynamic range of 0–100% CO2. As proof-of-concept demonstration, the sensor was field-tested with automobile exhaust and benchmarked with a commercial sensor as a reference. By using an image sensor typically found in consumer products, a compact, low-cost luminescence-based CO2 sensor was successfully demonstrated with performance comparable to that of the commercial sensors.

Diketo-Pyrrolo-Pyrrole Dyes as New Colorimetric and Fluorescent pH Indicators for Optical Carbon Dioxide Sensors

New indicators for optical CO2 sensors are synthesized in two steps from the commercially available diketo-pyrrolo-pyrrole (DPP) pigments Irgazin Ruby and Irgazin Scarlet. After introduction of bis(2-ethylhexyl) sulfonamide groups via a simple two-step synthesis, the pigments are rendered highly soluble in organic solvents and in polymers and show pH-dependent absorption and emission spectra. The new indicators have molar absorption coefficients in a 20 000-50 000 M(-1) cm(-1) range, possess quantum yields close to unity, and feature good photostability. The indicators along with a quaternary ammonium base are embedded into ethyl cellulose to give optical carbon dioxide sensors. The absorption and emission spectra of the deprotonated form are bathochromically shifted by more than 100 nm compared to the neutral form (λmax absorption 496-550 nm; λmax emission 564-587 nm). This enables colorimetric read-out and self-referenced ratiometric fluorescence intensity measurements. Importantly, the dynamic range of the sensors based on the new indicators is significantly different (0-10 kPa and 1-100 kPa CO2) that enables a broad variety of applications. New DPP dyes are conveniently prepared from commercially available pigments and represent a new class of colorimetric and fluorescent pH indicators for optical carbon dioxide sensors.

Strontium cobaltite coated optical sensors for high temperature carbon dioxide detection

Carbon dioxide sorption on perovskite type metal oxide, Ba 0.5Sr 0.5Co 0.8Fe 0.2O 3− δ , was studied at high temperatures for the development of a high temperature optical carbon dioxide sensor. When exposed to carbon dioxide in 600–700 °C Ba 0.5Sr 0.5Co 0.8Fe 0.2O 3− δ reacts with carbon dioxide to form Sr 0.6Ba 0.4CO 3. The sorption capacity increases with carbon dioxide pressures. The perovskite structure of the metal oxide after carbon dioxide sorption can be recovered by exposing the material to air at a temperature higher than 680 °C. The sorption rate with temperature and the high temperature sorption mechanism can be described by the homogeneous model. The optical sensor uses Ba 0.5Sr 0.5Co 0.8Fe 0.2O 3− δ as the sensing material and long period fiber gratings as the optical component. The Ba 0.5Sr 0.5Co 0.8Fe 0.2O 3− δ coated long period fiber grating (LPFG) can measure carbon dioxide in the concentration range of 1–30% in air (1 atm total pressure) at 600 and 700 °C. The sensor maintains its functionality after several repeated cycles of carbon dioxide detection at 700 °C.

Optical Carbon Dioxide Sensors Based on Silicone-Encapsulated Room-Temperature Ionic Liquids

Novel optical carbon dioxide sensors are based on emulsion of room-temperature ionic liquids (RTILs)–1-butyl-3-methylimidazolium salts in a silicone matrix. Semiquantitative determination of CO2 is achieved by dissolving an absorption-based pH indicator (thymol blue, TB, or bromthymol blue, BTB) in the RTIL. A quantitative fluorimetric sensor makes use of 8-hydroxypyrene-1,3,6-trisulfonate (HPTS). The response of the fluorimetric sensors to CO2 can easily be linearized which makes (re)calibration of the sensor very simple. It is demonstrated that a reference inert fluorescent dye (4-dicyanomethylene-2-methyl-6-(4-(dimethylamino)styryl)-4H-pyrane) can be added for ratiometric measurements. It is also shown that stable inorganic salts such as sodium phosphate can be used instead of quaternary ammonium hydroxides. Sensitivity of the material can be tuned by varying the pKa of an indicator. The sensors can find application in biotechnology, environmental monitoring, and food-packaging technology.

Sol-gel based optical carbon dioxide sensor employing dual luminophore referencing for application in food packaging technology.

An optical sensor for the measurement of carbon dioxide in Modified Atmosphere Packaging (MAP) applications has been developed. It is based on the fluorescent pH indicator 1-hydroxypyrene-3,6,8-trisulfonate (HPTS) immobilised in a hydrophobic organically modified silica (ormosil) matrix. Cetyltrimethylammonium hydroxide was used as an internal buffer system. Fluorescence is measured in the phase domain by means of the Dual Luminophore Referencing (DLR) sensing scheme which provides many of the advantages of lifetime-based fluorometric sensors and makes it compatible with established optical oxygen sensor technology. The long-term stability of the sensor membranes has been investigated. The sensor displays 13.5 degrees phase shift between 0 and 100% CO2 with a resolution of better than 1% and a limit of detection of 0.08%. Oxygen cross-sensitivity is minimised (0.6% quenching in air) by immobilising the reference luminophore in polymer nano-beads. Cross-sensitivity towards chloride and pH was found to be negligible. Temperature effects were studied, and a linear Arrhenius correlation between ln k and 1/T was found. The sensor is stable over a period of at least seven months and its output is in excellent agreement with a standard reference method for carbon dioxide analysis.

Microsecond lifetime-based optical carbon dioxide sensor using luminescence resonance energy transfer

A lifetime-based optical sensor for the measurement of dissolved and gaseous carbon dioxide has been developed. The basic principle is radiationless energy transfer from ruthenium(II)-4,4′-diphenyl-2,2′-bipyridyl as luminescent donor to thymol blue (a common pH indicator) as acceptor, both embedded in a hydrophobic matrix. In the presence of carbon dioxide thymol blue is protonated and changes its color from blue to yellow resulting in a decrease in the rate of energy transfer and consequently an increase in decay time. The decay time as a pCO 2-dependent parameter was measured in the frequency domain with a blue light emitting diode as a light source modulated at 75 kHz. The present sensor displays a phase shift up to 16° in the range 0–30 hPa of pCO 2 corresponding to a change in decay time from 0.38 to 1.05 μs. The detection limit was found to be 0.5 μM (22 ppb) of dissolved carbon dioxide and the response times are of the order of 15 s when going from 0 to 30 hPa pCO 2. The temperature behavior of the sensor has been studied in detail and a linear relationship Arrhenius plot has been found. The effect of molecular oxygen as a potential quencher of the luminescence was investigated in detail. The carbon dioxide sensor is stable over weeks, and is robust.

CARBOCAP® ‐ new carbon dioxide sensor ‐ electrically tuneable interferometer for infrared gas analysis

Reports on CARBOCAP®, a new type of optical carbon dioxide sensor, which guarantees high accuracy. States that CARBOCAP® uses a micromachine electrically tuneable Fabry‐Perot interferometer (FPI) as a filter, which guarantees the high accuracy and stability of a dual‐wavelength instrument, without the problems of mismated filters and detectors, or the wear and tear of a rotating filter.

Sensitivity studies on optical carbon dioxide sensors based on ion pairing

A recent approach to optical carbon dioxide sensing makes use of ion pairs consisting of a pH indicator dye anion (D −) and an organic quaternary cation (Q +). The resulting ‘dry’ (as opposed to the better-known buffer-based ‘wet’ sensor chemistry) or ‘plastic’ sensor membranes comprise a pH indicator dye immobilized along with a quaternary cation, and an additional amount of quaternary hydroxide (Q +OH −) within a polymer layer on a polyester support. Such sensors are applicable to optical sensing of carbon dioxide both in dry gases, where they have an extremely short response time, and in liquid samples. The sensitivity, or degree of response of a sensor to a given analyte concentration, is a vital parameter for describing its performance. In this work, it is shown that the sensitivity of carbon dioxide sensors, based on the ion-pairing method, is largely governed by the molar concentration ratio between the ion pair and the free quaternary hydroxide. We have found that the sensitivity of such optrodes, as well as their degree of linearity, can be adjusted by varying the (Q +D −)/(Q +OH −) ratio. Certain environmental conditions, such as high temperature and the presence of acidic vapours, and also changes due to membrane aging, can shift the dynamic range to lower pCO 2, too. We discuss probable causes for the sensitivity shift.

New hydrophobic materials for optical carbon dioxide sensors based on ion pairing

A hydrophobic polymer material is presented which is optically sensitive to carbon dioxide. It is based on ion pairing between an indicator anion and a quaternary ammonium cation. The ion pair is dissolved in various kinds of silicone rubbers, and the resulting materials are shown to be useful for optically sensing carbon dioxide over the 0–100 hPa (0–76 Torr, 0–100 mbar) partial pressure range. The detection limit is approximately 0.3 hPa. The material can be immobilized on glass or plastic supports, on optical fibers, or in capillaries. A new method for making ion pairs is described which yields sensor materials containing no inorganic ions. This makes the ion pairs soluble even in highly apolar silicones. The silicone rubber based sensors are capable of measuring carbon dioxide both in gases (to which they respond with a τ 90 of 1 s) and in aqueous sample solutions (with response times ranging from 2 to 8 min); there is no need for an additional (proton-impermeable) coating. Due to the use of silicone rubber as the polymer support, there is no cross-sensitivity to pH within the pH 5–9 range. Shelf lifetimes of more than 5 months are found when membranes are stored in sealed plastic bags, but sensors need to be recalibrated. The operational lifetime is in the order of 2 months when used for sensing carbon dioxide in potable water, provided the sensor is not in contact with acidic vapors such as sulfur dioxide or gaseous hydrogen chloride which can be present in many laboratories.

A carbon dioxide sensor based on fluorescence

The optical carbon dioxide sensor is prepared by covering a pH sensor based on fluorescence with a CO 2-permeable membrane and contacting the pH-sensitive membrane with a reservoir of hydrogen carbonate. As carbon dioxide diffuses across the membrane it causes a chnage in pH which is detected by measuring the change in fluorescence from the base form of the pH-sensitive fluorescentdye. The usable range of response depends on the concentration of hydrogen carbonate in contact with the membrane. The sensor also responds to sulfide and sulfite.