Simple smartphone merged rapid colorimetric platform for the environmental monitoring of toxic sulfide ions by cysteine functionalized silver nanoparticles

Designing a Simple Quinoline-Based Chromo-Fluorogenic Receptor for Highly Specific Quantification of Copper (II) Ions: Environmental and Bioimaging Applications

Many industries use copper metal ions (Cu2+ ions), and their salts are utilized as supplemental materials in both agriculture and medicine. Identifying and monitoring these Cu2+ ions in biological and environmental specimens is crucial due to their association with several health issues. In this investigation, we have designed a simple quinoline-based receptor (E)-3-(((2,4-di-tert-butyl-5-hydroxyphenyl)imino)methyl)-6-methoxyquinolin-2(1H)-one (QAP) containing imine functional groups to inspect its capability to identify metal ions in a semi-aqueous medium. The photophysical characteristics and structural confirmation of the receptor QAP were investigated using various spectroscopic techniques. Among various metal ions, the receptor QAP displayed an intense color shift from slightly yellow to strong yellow in the existence of Cu2+ ions, as visualized by the nude eye. Furthermore, the fluorescence spectral maximum wavelength at 485 nm and the strong cyan fluorescence color were quenched upon introducing Cu2+ ions. The alteration in the spectral and colorimetric features of QAP with Cu2+ ions is due to coordination complex formation. The present sensor shows the linear range from 3 to 69 μM, subsequent in a computed limit of detection as 3.16 nM, which is much lower than that of the maximum threshold of Cu2+ ions in drinking water set by WHO. Therefore, the receptor can respond to Cu2+ ions sensing in two ways: by changing color and by quenching fluorescence. The binding mode of the Cu2+ ions to the functional groups of the receptor QAP is a 1:1 stoichiometry, according to ESI-mass, Job's plot analysis, and density functional theory (DFT) computations. The practical utility of the fluorescent receptor QAP was applied for Cu2+ ions determination in environmental samples (drinking, tap, and dam water) and cancer cells (HeLa cells).

Pb-based metal organic framework as substrate: Chemical vapor generation-visual/smartphone colorimetric analytical system for sensitive and selective detection of sulfide ion in water and beers

A visual/smartphone colorimetric system was developed for the sensitive and selective detection of sulfide ion (S2-) using chemical vapor generation (CVG) as a gaseous sampling technique. S2- in samples were converted into H2S after the addition of H2SO4, which separated from the solution during CVG process, ensuring high efficiency of vapor generation (sensitivity) and eliminated interferences (selectivity). The H2S was subsequently reacted with Pb-BTC and PbS was thus formed, causing the test paper turned to black. It was utilized for the detection of S2- by visual/smartphone colorimetric system. Detectable limits of 0.05 μg/mL and 0.2 μg/mL were obtained under smartphone mode and visual mode, respectively. Furthermore, this colorimetric system was successfully used for the analysis of S2- in several beer samples and water samples, with recoveries ranging 97 %-111 %. This system represents a potential miniaturized, easy used and high-effective method for rapid and on-site detection of S2-.

Digitalization of Colorimetric Sensor Technologies for Food Safety

Colorimetric sensors play a crucial role in promoting on-site testing, enabling the detection and/or quantification of various analytes based on changes in color. These sensors offer several advantages, such as simplicity, cost-effectiveness, and visual readouts, making them suitable for a wide range of applications, including food safety and monitoring. A critical component in portable colorimetric sensors involves their integration with color models for effective analysis and interpretation of output signals. The most commonly used models include CIELAB (Commission Internationale de l'Eclairage), RGB (Red, Green, Blue), and HSV (Hue, Saturation, Value). This review outlines the use of color models via digitalization in sensing applications within the food safety and monitoring field. Additionally, challenges, future directions, and considerations are discussed, highlighting a significant gap in integrating a comparative analysis toward determining the color model that results in the highest sensor performance. The aim of this review is to underline the potential of this integration in mitigating the global impact of food spoilage and contamination on health and the economy, proposing a multidisciplinary approach to harness the full capabilities of colorimetric sensors in ensuring food safety.

Critical importance of RGB color space specificity for colorimetric bio/chemical sensing: A comprehensive study

The use of the RGB color model in colorimetric chemical sensing via imaging techniques is widely prevalent in the literature. However, the lack of specificity in the selection of RGB color space during capture and analysis presents a significant challenge in creating standardised methods for this field and possible discrepancies. In this study, we conducted a comprehensive comparison and contrast of a total of 68 RGB color spaces to evaluate their respective impacts on colorimetric bio/chemical sensing. We explore the impact of dynamic range, sensitivity, and limit of detection, and show that the lack of specificity in RGB color space selection can significantly impact colorimetric chemical sensing by 42-77%. We also explore the impact of underlying RGB comparisons and demonstrate a further 18.3% discrepancy between RGB color spaces. By emphasising the importance of proper RGB color space selection and handling, our findings contribute to a better understanding of this critical area and present valuable opportunities for future research. We further provide valuable insights for creating standardised methods in this field, which can be utilised to avoid discrepancies and ensure accurate and reliable analysis in colorimetric bio/chemical sensing.

Progress in the design of portable colorimetric chemical sensing devices

The need for precise determination of heavy metals, anions, biomolecules, pesticides, drugs, and other substances is vital across clinical, environmental, and food safety domains. Recent years have seen significant progress in portable colorimetric chemical sensing devices, revolutionizing on-the-spot analysis. This review offers a comprehensive overview of these advancements, covering handheld colorimetry, RGB-based colorimetry, paper-based colorimetry, and wearable colorimetry devices. It explores the underlying principles, functional materials (chromophoric reagents/dyes and nanoparticles), detection mechanisms, and their applications in environmental monitoring, clinical care, and food safety. Noble metal nanoparticles (NPs) have arisen as promising substitutes in the realm of sensing materials. They display notable advantages, including heightened sensitivity, the ability to fine-tune their plasmonic characteristics for improved selectivity, and the capacity to induce visible color changes, and simplifying detection. Integration of NPs fabricated paper device with smartphones and wearables facilitates reagent-free, cost-effective, and portable colorimetric sensing, enabling real-time analysis and remote monitoring.

Smartphone-enabled colorimetric visual quantification of highly hazardous trivalent chromium ions in environmental waters and catalytic reduction of p-nitroaniline by thiol-functionalized gold nanoparticles

High-efficiency sensing systems for extremely hazardous chromium (Cr(III)) ions are important due to their detrimental effects on human health and the environment. We employed a spectrophotometric method combined with a smartphone (red, green, and blue (RGB) color ratio)-based detection platform to realize the quick, visually quantifiable in situ detection of Cr(III) ions using surface plasmon resonance (SPR)-aided colorimetry. For optical sensing nanoprobes, we synthesized the 2-Mercapto-5-methyl-1,3,4-thiadiazole (MMT)-modified gold nanoparticles (MMT-AuNPs) using a wet chemical method. By way of a coordination reaction, the Cr(III) ions induce the as-prepared MMT-AuNPs to aggregate and subsequently change the SPR wavelength band. The freshly synthesized MMT-AuNPs exhibited a wine-red color. While Cr(III) ions interact with the MMT-AuNPs, the color of the latter evolved from wine red to purple, thus facilitating visual monitoring. The SPR-relevant color change allowed the quantitative sensing of Cr(III) ions in the range of 40-128 nM, with the limit of detection of 6.93 nM when employing the spectrophotometric method and 12.4 nM when using the smartphone RGB color ratio. Furthermore, we developed the spectrophotometric technique that used the smartphone RGB color ratio for on-site analysis of Cr(III) ions in environmental water samples, indicating the possibility of its chemo-sensing applications for portable quantitative detection devices. Additionally, the catalytic performance of the MMT-AuNPs was demonstrated by the reduction of p-nitroaniline in the presence of sodium borohydride. It was interestingly unveiled that the MMT-AuNPs showed outstanding catalytic performance with a catalytic rate constant of 6.31 × 10-3 s-1.

Cysteamine-decorated gold nanoparticles for plasmon-based colorimetric on-site sensors for detecting cyanide ions using the smart-phone color ratio and for catalytic reduction of 4-nitrophenol

In this paper, we have reported the cyanide ions (CN^-) sensing in environmental water samples using cysteamine-capped gold nanoparticles (Cyst-AuNPs) by spectrophotometric, colorimetric, and smartphone-based RGB color detection. The surface plasmon resonance shift at around 525 nm for the Cyst-AuNPs could be used to detect quantitatively the amounts of CN^- with concomitant alteration of their color from wine red to purple visualized by the naked eye. For the first time, the Cyst-AuNPs-based visual sensing of CN^- was performed using smartphone-based detection with its detection limit of 159 × 10^-9 M, ten times lower than that of the highest tolerance level (2 × 10^-6 M) permitted by the world health organization. The Cyst-AuNPs displayed excellent specificity for detecting the concentration of 30 × 10^-6 M even amid the presence of other interfering inorganic anions with their concentrations about five times higher than it. Environmental real water samples were used to arrange the three different CN^- concentrations for plasmon-based colorimetric detection and smartphone-based method. Additionally, the catalytic performance of Cyst-AuNPs was demonstrated for the fast catalytic conversion of hazardous 4-nitrophenol (selected environmental contaminant) to the analogous amino aromatic compounds. A chemical kinetic study showed the conversion rate to be estimated as 1.65 × 10^-2 s^-1. Cyst-AuNPs can find an application in colorimetric sensing of CN^- while being able to be utilized as a catalytic nanomaterial for ecological remedies associated with health care.

Silver-Based Surface Plasmon Sensors: Fabrication and Applications

A series of novel phenomena such as optical nonlinear enhancement effect, transmission enhancement, orientation effect, high sensitivity to refractive index, negative refraction and dynamic regulation of low threshold can be generated by the control of surface plasmon (SP) with metal micro-nano structure and metal/material composite structure. The application of SP in nano-photonics, super-resolution imaging, energy, sensor detection, life science, and other fields shows an important prospect. Silver nanoparticles are one of the commonly used metal materials for SP because of their high sensitivity to refractive index change, convenient synthesis, and high controllable degree of shape and size. In this review, the basic concept, fabrication, and applications of silver-based surface plasmon sensors are summarized.

Optical Sensing of Toxic Cyanide Anions Using Noble Metal Nanomaterials

Water toxicity, one of the major concerns for ecosystems and the health of humanity, is usually attributed to inorganic anions-induced contamination. Particularly, cyanide ions are considered one of the most harmful elements required to be monitored in water. The need for cyanide sensing and monitoring has tempted the development of sensing technologies without highly sophisticated instruments or highly skilled operations for the objective of in-situ monitoring. Recent decades have witnessed the growth of noble metal nanomaterials-based sensors for detecting cyanide ions quantitatively as nanoscience and nanotechnologies advance to allow nanoscale-inherent physicochemical properties to be exploited for sensing performance. Particularly, noble metal nanostructure e-based optical sensors have permitted cyanide ions of nanomolar levels, or even lower, to be detectable. This capability lends itself to analytical application in the quantitative detection of harmful elements in environmental water samples. This review covers the noble metal nanomaterials-based sensors for cyanide ions detection developed in a variety of approaches, such as those based on colorimetry, fluorescence, Rayleigh scattering (RS), and surface-enhanced Raman scattering (SERS). Additionally, major challenges associated with these nano-platforms are also addressed, while future perspectives are given with directions towards resolving these issues.

Polydopamine-Coated Co3O4 Nanoparticles as an Efficient Catalase Mimic for Fluorescent Detection of Sulfide Ion

Surface engineering of nanozymes has been recognized as a potent strategy to improve their catalytic activity and specificity. We synthesized polydopamine-coated Co₃O₄ nanoparticles (PDA@Co₃O₄ NPs) through simple dopamine-induced self-assembly and demonstrated that these NPs exhibit catalase-like activity by decomposing H₂O₂ into oxygen and water. The activity of PDA@Co₃O₄ NPs was approximately fourfold higher than that of Co₃O₄ NPs without PDA, possibly due to the additional radical scavenging activity of the PDA shell. In addition, PDA@Co₃O₄ NPs were more stable than natural catalase under a wide range of pH, temperature, and storage time conditions. Upon the addition of a sample containing sulfide ion, the activity of PDA@Co₃O₄ NPs was significantly inhibited, possibly because of increased mass transfer limitations via the absorption of the sulfide ion on the PDA@Co₃O₄ NP surface, along with NP aggregation which reduced their surface area. The reduced catalase-like activity was used to determine the levels of sulfide ion by measuring the increased fluorescence of the oxidized terephthalic acid, generated from the added H₂O₂. Using this strategy, the target sulfide ion was sensitively determined to a lower limit of 4.3 µM and dynamic linear range of up to 200 µM. The fluorescence-based sulfide ion assay based on PDA@Co₃O₄ NPs was highly precise when applied to real tap water samples, validating its potential for conveniently monitoring toxic elements in the environment.

Smartphone-Based Multiplexed Biosensing Tools for Health Monitoring

Many emerging technologies have the potential to improve health care by providing more personalized approaches or early diagnostic methods. In this review, we cover smartphone-based multiplexed sensors as affordable and portable sensing platforms for point-of-care devices. Multiplexing has been gaining attention recently for clinical diagnosis considering certain diseases require analysis of complex biological networks instead of single-marker analysis. Smartphones offer tremendous possibilities for on-site detection analysis due to their portability, high accessibility, fast sample processing, and robust imaging capabilities. Straightforward digital analysis and convenient user interfaces support networked health care systems and individualized health monitoring. Detailed biomarker profiling provides fast and accurate analysis for disease diagnosis for limited sample volume collection. Here, multiplexed smartphone-based assays with optical and electrochemical components are covered. Possible wireless or wired communication actuators and portable and wearable sensing integration for various sensing applications are discussed. The crucial features and the weaknesses of these devices are critically evaluated.