A Simple Probe for the Colorimetric Detection of Carbon Dioxide

Metallic-Nanoparticle-Based Sensing: Utilization of Mixed-Ligand Monolayers

The last two decades have seen great advancements in fundamental understanding and applications of metallic nanoparticles stabilized by mixed-ligand monolayers. Identifying and controlling the organization of multiple ligands in the nanoparticle monolayer has been studied, and its effect on particle properties has been examined. Mixed-ligand protected particles have shown advantages over monoligand protected particles in fields such as catalysis, self-assembly, imaging, and drug delivery. In this Review, the use of mixed-ligand monolayer protected nanoparticles for sensing applications will be examined. This is the first time this subject is examined as a whole. Mixed-ligand nanoparticle-based sensors are revealed to be divided into four groups, each of which will be discussed. The first group consists of ligands that work cooperatively to improve the sensors' properties. In the second group, multiple ligands are utilized for sensing multiple analytes. The third group combines ligands used for analyte recognition and signal production. In the final group, a sensitive, but unstable, functional ligand is combined with a stabilizing ligand. The Review will conclude by discussing future challenges and potential research directions for this promising subject.

Facile conversion of zinc hydroxide carbonate to CaO-ZnO for selective CO2 gas detection

Tailored synthesis of heterostructures for low temperature (sub 200 °C) CO₂ sensing continues to be a challenging task. The present study demonstrates CO₂ sensing characteristics of CaO-ZnO heterostructures achieved by zinc hydroxide carbonate (Zn₅(CO₃)₂(OH)₆) conversion to ZnO using Ca(OH)₂ at 50 °C. Control samples namely, Zn₅(CO₃)₂(OH)₆, Ca(OH)₂, ZnO, and CaO integrated microsensors exhibited low sensitivity towards CO₂ gas. However, CaO-ZnO heterostructures demonstrated significant sensitivity (26 to 91%) at 150 °C for gas concentration ranging from 100 to 10000 ppm, respectively. In this study, zinc hydroxide carbonate sensitized with 25 wt% Ca(OH)₂ to form CaO-ZnO heterostructures (25CaZMS) displayed a promising sensitivity (77%) and selectivity (98%) towards 500 ppm CO₂ gas. Moreover, the selectivity studies were conducted in the presence of 10 commonly found gases and their sensing performance was compared against CO₂ gas in dry and humid conditions. The developed CaO-ZnO sensor exhibited faster kinetics in comparison to the control samples. Improved sensing performance observed here is attributed to the low-temperature synthesis route which resulted in a large number of active pores and high surface area morphology. Additionally, the high CO₂ adsorption capacity of CaO combined with compatible n-type semiconductors in forming highly dynamic nano-interfaced heterostructure is a promising step towards developing a precise CO₂ gas microsensor.

Overview of the Evolution of Silica-Based Chromo-Fluorogenic Nanosensors

This review includes examples of silica-based, chromo-fluorogenic nanosensors with the aim of illustrating the evolution of the discipline in recent decades through relevant research developed in our group. Examples have been grouped according to the sensing strategies. A clear evolution from simply functionalized materials to new protocols involving molecular gates and the use of highly selective biomolecules such as antibodies and oligonucleotides is reported. Some final examples related to the evolution of chromogenic arrays and the possible use of nanoparticles to communicate with other nanoparticles or cells are also included. A total of 64 articles have been summarized, highlighting different sensing mechanisms.

Highly Sensitive Squaraine-Based Water-Soluble Far-Red/Near-Infrared Chromofluorogenic Thiophenol Probe

A squaraine-based far-red/near-infrared fluorescent probe (SQ-DNBS) was exploited for thiophenol detection. SQ-DNBS is a colorimetric and "off-on" fluorometric dual-channel "naked-eye" chemosensor showing high selectivity, high sensitivity (detection limit: 9.9 nM), and rapid response to thiophenol in aqueous solution. SQ-DNBS also can be used in practical applications for the detection of thiophenol in water samples. Photophysical and spectral characterization results revealed that the probing mechanism of SQ-DNBS toward thiophenol lies in the thiolate-mediated cleavage reaction. Our discovery demonstrates the potential of the arylmethylene-squaraine skeleton as a promising fluorophore unit to construct high-performance far-red/near-infrared chemosensors.

CO2-Responsive fluorescent hyperbranched poly(ether amine)s

Hyperbranched polymers bearing a fluorophore display gas-controlled fluorescence switching as a result of reversible protonation/deprotonation of amino groups in their structure.

Chromogenic Detection of Aqueous Formaldehyde Using Functionalized Silica Nanoparticles

Silica nanoparticles functionalized with thiol reactive units and bulky polar polyamines were used for the selective colorimetric detection of formaldehyde. The reaction of thiols groups in the nanoparticles surface with a squaraine dye resulted in loss of the π-conjugation of the chromophores, and the subsequent bleaching of the solution. However, when formaldehyde was present in the suspension, the thiol-squaraine reaction was inhibited and a chromogenic response was observed. A selective response to formaldehyde was observed only when the thiol and polyamine groups were anchored to the silica surface. The observed selective response was ascribed to the fact that bulky polyamines generate a highly polar environment around thiols, which were only able to react with the small and polar formaldehyde, but not with other aldehydes. The sensing nanoparticles showed a limit of detection (LOD) for formaldehyde of 36 ppb in water.

A recyclable polyoxometalate-based supramolecular chemosensor for efficient detection of carbon dioxide

A new type of supramolecular chemosensor based on the polyoxometalate (POM) Na9DyW10O36 (DyW10) and the block copolymer poly(ethylene oxide-b-N,N-dimethylaminoethyl methacrylate) (PEO114-b-PDMAEMA16) is reported. By taking advantage of the CO2 sensitivity of PDMAEMA blocks to protonate the neutral tertiary amino groups, CO2 can induce the electrostatic coassembly of anionic DyW10 with protonated PDMAEMA blocks, and consequently trigger the luminescence chromism of DyW10 due to the change in the microenvironment of Dy3+. The hybrid complex in dilute aqueous solution is very sensitive to CO2 content and shows rapid responsiveness in luminescence. The luminescence intensity of the DyW10/PEO-b-PDMAEMA complex increases linearly with an increasing amount of dissolved CO2, which permits the qualitative and quantitative detection of CO2. The complex solution also shows good selectivity for CO2, with good interference tolerance of CO, N2, HCl, H2O and SO2. The supramolecular chemosensor can be recycled through disassembly of the hybrid complex by simply purging with inert gases to remove CO2.

A squaraine-based colorimetric and F− dependent chemosensor for recyclable CO2 gas detection: highly sensitive off–on–off response

An unsymmetrical squaraine-based chemosensor SH₂ has been synthesized, and its sensing behavior towards CO₂ gas was described in detail by UV-vis and ¹H NMR spectroscopies in DMSO.