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.

Inkjet-printed flexible graphene paper electrode for the electrochemical determination of mercury.

Here, we report an inkjet-printed graphene paper electrode (IP-GPE) for the electrochemical analysis of mercuric ions (Hg(ii)) in industrial wastewater samples. Graphene (Gr) fabricated on a paper substrate was prepared by a facile solution-phase exfoliation method in which ethyl cellulose (EC) behaves as a stabilizing agent. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were utilized to determine the shape and multiple layers of Gr. The crystalline structure and ordered lattice carbon of Gr were confirmed by X-ray diffraction (XRD) and Raman spectroscopy. The nano-ink of Gr-EC was fabricated on the paper substance via an inkjet printer (HP-1112) and IP-GPE was exploited as a working electrode in linear sweep voltammetry (LSV) and cyclic voltammetry (CV) for the electrochemical detection of Hg(ii). The electrochemical detection is found to be diffusion-controlled illustrated by obtaining a correlation coefficient of 0.95 in CV. The present method exhibits a better linear range of 2-100 µM with a limit of detection (LOD) of 0.862 µM for the determination of Hg(ii). The application of IP-GPE in electrochemical analysis shows a user-friendly, facile, and economical method for the quantitative determination of Hg(ii) in municipal wastewater samples.

Inkjet-printed paper-based colorimetric sensor coupled with smartphone for determination of mercury (Hg2+).

We report an inkjet-printed paper based colorimetric sensor with silver nanoparticles (AgNPs) using smartphone and color detector App for on-site determination of mercuric ion (Hg2+) from environmental water samples. The AgNPs printed on Whatman filter paper (No. 1) is employed for detection of Hg2+ which is reliant on the color change of NPs from yellow to discoloration depending on the concentration of target analyte in sample solution. The quantitative determination was performed by calculating the signal intensity of AgNPs on printed paper substrate after the introduction of Hg2+ using smartphone and RGB color detector. The mechanism for detection of Hg2+ on paper substrate is verified using UV-Vis spectrophotometry (UV-Vis), transmission electron microscope (TEM), X-ray photoelectron spectroscopy (XPS), dynamic light scattering (DLS) and basic chemical assays. The linear range acquired for paper based colorimetric detection in the range of 40-1200 µgL-1 with limit of detection of 10 µgL-1. The results obtained using an inkjet-printed paper-based chemical sensor combined with a smartphone is validated with data of inductively coupled plasma-atomic emission spectroscopy (ICP-AES) measurement. The advantages of paper based detection are simple, rapid, economic and can be applied at the sample sources for determination of Hg2+.

Colorimetric determination of L-cysteine in milk samples with surface functionalized silver nanoparticles.

A simple, selective and sensitive method is proposed for determination of cysteine (Cys) in milk samples using ionic liquid functionalized silver nanoparticles (ILs-AgNPs) as a colorimetric probe. ILs-AgNPs was synthesized by simple reduction method using silver nitrate as a precursor and sodium borohydride as a reducing agent and functionalized with ILs to prevent particles from self-aggregation. The sensing mechanism has been dependent on the color change of ILs-AgNPs and red shift of absorption band from 395 nm to 560 nm in the visible region, which is found proportional to the concentration of target analyte in sample. ILs-AgNPs was characterized in absence and presence of Cys by UV-vis, Fourier transform-infrared (FTIR) spectroscopy, transmission electron microscope (TEM) and dynamic light scattering (DLS). The linear range was acquired in the range of 0-100 ng mL-1, with correlation coefficient (R2) of 0.996 and limit of detection (LOD) of 4.0 nM. The binding mechanism and interactions between Cys and ILs-AgNPs was confirmed by calculating the binding constant and thermodynamic parameters such as enthalpy (∆H), entropy (∆S) and Gibb's free energy (∆G). The use of ILs-AgNPs exhibited high colorimetric selectivity for Cys in milk samples in presence of other amino acids. This proposed strategy possessed the advantages of simplicity and selectivity, hence is applied for analysis of Cys in milk samples.

Colorimetric and smartphone-integrated paper device for on-site determination of arsenic (III) using sucrose modified gold nanoparticles as a nanoprobe.

An optical colorimetric and smartphone-integrated paper device (SIPD) is demonstrated for determination of As (III) in water and soil samples using sucrose modified gold nanoparticles (AuNPs/Suc) as a nanoprobe. The mechanism for determination of As(III) is experimentally validated by performing UV-Vis, transmission electron microscope (TEM), Fourier transforms infra-red spectroscopy (FTIR) and dynamic light scattering (DLS) measurements. The density function theory (DFT) calculations using B3LYP with 6-311G (2d,2p) and LANL2DZ basis sets is used to theoretically prove the mechanism for determination of As(III). In addition, the paper fabricated with AuNPs/SuC was used as a nanoprobe for quantitative determination of As(III) using smartphone and ImageJ software. Calibration plot was linear over 10-800 µgL-1 for colorimetric determination of As(III) with limit of detection (LOD) of 4 µgL-1 acquired when the absorbance ratio obtained at 594 nm/515 nm. The linearity range of 50-3000 µgL-1 with LOD of 20 µgL-1 was determined using smartphone-integrated paper device. AuNPs/Suc is successfully employed for determination of As (III) from contaminated water and soil samples in colorimetry and SIPD. Graphical abstractColorimetric and Smartphone-integrated paper device used for selective detection of arsenic from contaminated water samples using sucrose modified gold nanoparticles (AuNPs/Suc) as a sensing probe.

Smartphone coupled with paper-based chemical sensor for on-site determination of iron(III) in environmental and biological samples.

We report a smartphone-paper-based sensor impregnated with cetyltrimethylammonium bromide modified silver nanoparticles (AgNPs/CTAB) for determination of Fe3+ in water and blood plasma samples. The methodology for determination of Fe3+ is based on the change in signal intensity of AgNPs/CTAB fabricated on a paper substrate after the deposition of analyte, using a smartphone followed by processing with ImageJ software. The mechanism of sensing for detection and determination of Fe3+ is based on the discoloration of AgNPs which impregnated the paper substrate. The discoloration is attributed to the electron transfer reaction taking place on the surface of NPs in the presence of CTAB. Fe3+ was determined when the paper was impregnated with 1 mM AgNPs for 5 min of reaction time and the substrate was kept under acidic conditions. The linear range for determination of total iron in terms of Fe3+ was 50-900 µg L-1 with a limit of determination (LOD) of 20 µg L-1 and coefficient of variation (CV) of 3.2%. The good relative recovery of 91.3-95.0% and interference studies showed the selectivity of the method for determination of total iron in water and blood plasma samples. Smartphone-paper-based sensors have advantages of simplicity, rapidity, user-friendliness, low cost, and miniaturization of the method for on-site determination of total iron compared to methods that require sophisticated analytical instruments. Graphical abstract Smartphone-paper-based sensor with cetyltrimethylammonium bromide modified silver nanoparticles for determination of Fe3+ in water and blood plasma samples.

The direct-writing of low cost paper based flexible electrodes and touch pad devices using silver nano-ink and ZnO nanoparticles.

We report a novel and simple approach for the synthesis of silver nanoparticles capped with inositol (Ag NPs/Ino) by the reduction of silver salt with ascorbic acid under basic conditions. UV-vis, TEM, FTIR and TGA techniques were used to characterize the Ag NPs/Ino to determine the size, shape and surface modification of the NPs. Stable silver nano-ink was prepared in aqueous solution containing 1% PVP (stabilizer) and glycerol (cosolvent) and was used for the direct-writing of a paper electrode with a roller ball-point pen for electrochemical applications. The solvent, stabilizing agents, concentration of NPs (10%), paper substrate, sintering temperature (40 °C) and sintering time (15 min) were optimized to obtain a uniform coating of Ag NPs on the paper substrate. Further, the synthesis and fabrication of ZnO NPs on a paper substrate was put forward to design a touch pad device based on the piezoelectric effect. The preparation of paper based devices suggests a direction for the development of a simple, low cost and compatible approach for the direct-writing of paper based flexible electrodes and electronics for future applications.

The International Commission on Occupational Health (ICOH) and its influence on international organizations.

The ICOH has played a key role in the development of some scientific documents and policy recommendations, but it has not always been scientifically objective, particularly in regard to asbestos and other fibers and some chemicals and pesticides. Many ICOH members are employees of corporations or consultants to industry, serving multinational corporate interests to influence public health policy in the guise of a professional scientific organization. ICOH members' conflicts of interest with the public health dominate the organization and damage the standing of the ICOH. Official recognition of the ICOH compromises the credibility of the WHO and the ILO. It is inappropriate for the ICOH to continue to receive WHO and ILO recognition unless the ICOH is recognized as an industry organization.