Carbon dots-MnO2 nanocomposites for As(III) detection in groundwater with high sensitivity and selectivity

Advances in Nanomaterials and Colorimetric Detection of Arsenic in Water: Review and Future Perspectives

Arsenic, existing in various chemical forms such as arsenate (As(V)) and arsenite (As(III)), demands serious attention in water and environmental contexts due to its significant health risks. It is classified as "carcinogenic to humans" by the International Agency for Research on Cancer (IARC) and is listed by the World Health Organization (WHO) as one of the top 10 chemicals posing major public health concerns. This widespread contamination results in millions of people globally being exposed to dangerous levels of arsenic, making it a top priority for the WHO. Chronic arsenic toxicity, known as arsenicosis, presents with specific skin lesions like pigmentation and keratosis, along with systemic manifestations including chronic lung diseases, liver issues, vascular problems, hypertension, diabetes mellitus, and cancer, often leading to fatal outcomes. Therefore, it is crucial to explore novel, cost-effective, and reliable methods with rapid response and improved sensitivities (detection limits). Most of the traditional detection techniques often face limitations in terms of complexity, cost, and the need for sophisticated equipment requiring skilled analysts and procedures, which thereby impedes their practical use, particularly in resource-constrained settings. Colorimetric methods leverage colour changes which are observable and quantifiable using simple instrumentation or even visual inspection. This review explores the colorimetric techniques designed to detect arsenite and arsenate in water. It covers recent developments in colorimetric techniques, and advancements in the role of nanomaterials in colorimetric arsenic detection, followed by discussion on current challenges and future prospects. The review emphasizes efforts to improve sensitivity, selectivity, cost, and portability, as well as the role of advanced materials/nanomaterials to boost the performance of colorimetric assays/sensors towards combatting this pervasive global health concern.

Red emitting carbon dots: surface modifications and bioapplications

Quantum dots (QDs), and carbon quantum dots (CDs) in particular, have received significant attention for their special characteristics. These particles, on the scale of several nanometers, are often produced using simple and green methods, with naturally occurring organic precursors. In addition to facile production methods, CDs present advantageous applications in the field of medicine, primarily for bioimaging, antibacterial and therapeutics. Also, CDs present great potential for surface modification through methods like doping or material mixing during synthesis. However, the bulk of current literature focuses on CDs emitting in the blue wavelengths which are not very suitable for biological applications. Red emitting CDs are therefore of additional interest due to their brightness, photostability, novelty and deeper tissue penetration. In this review article, red CDs, their methods of production, and their biological applications for translational research are explored in depth, with emphasis on the effects of surface modifications and doping.

Decoupling the adsorption mechanisms of arsenate at molecular level on modified cube-shaped sponge loaded superparamagnetic iron oxide nanoparticles

In this study, a commercial cube-shaped open-celled cellulose sponge adsorbent was modified by in-situ co-precipitation of superparamagnetic iron oxide nanoparticles (SPION) and used to remove As(V) from aqueous solutions. Fe K-edge X-ray absorption spectroscopy (XAS) and TEM identified maghemite as the main iron phase of the SPION nanoparticles with an average size 13 nm. Batch adsorption experiments at 800 mg/L showed a 63% increase of adsorption capacity when loading 2.6 wt.% mass fraction of SPION in the cube-sponge. Experimental determination of the adsorption thermodynamic parameters indicated that the As(V) adsorption on the composite material is a spontaneous and exothermic process. As K-edge XAS results confirmed that the adsorption enhancement on the composite can be attributed to the nanoparticles loaded. In addition, adsorbed As(V) did not get reduced to more toxic As(III) and formed a binuclear corner-sharing complex with SPION. The advantageous cube-shape of the sponge-loaded SPION composite together with its high affinity and good adsorption capacity for As(V), good regeneration capability and the enhanced-diffusion attributed to its open-celled structure make this adsorbent a good candidate for industrial applications.

Enhanced detection of ascorbic acid with cascaded fluorescence recovery of a dual-nanoquencher system

An innovative strategy with target-triggered cascade fluorescence recovery of a dual-nanoquencher system was developed to detect ascorbic acid (AA). Herein, manganese dioxide (MnO₂) nanosheets and gold nanoparticles (AuNPs) were used as nanoquenchers simultaneously. Owing to their synergistic effects, the fluorescence of 2,3-diaminophenazine (DAP) was decreased efficiently, thus minimizing the background fluorescence. The introduction of AA triggered the decomposition of MnO₂ into Mn²⁺, which induced the aggregation of AuNPs. Both the decomposed MnO₂ and aggregated AuNPs possess weak quenching abilities towards DAP. Such a cascade amplification strategy enhanced the detection sensitivity for AA with a LOD as low as 6.7 nM, which was two orders of magnitude lower than that of MnO₂-based fluorescence assay. Furthermore, this amplification strategy was successfully applied to detect AA in food samples.

A blue arsenomolybdic acid-crystal violet ion-associate pair paving the way for the field detection of arsenic in groundwater

A simple visual colorimetric method based on arsenomolybdic acid-crystal violet ion-associate pair formation is described for the detection of As in groundwater at about 10, 25 and 50 μg L^-1 levels. The pair exhibits light green coloration at ≤5 μg L^-1 and blue colorations of distinctly different intensities at about 10, 25 and 50 μg L^-1 concentrations of arsenic. High sensitivity is achieved by the preconcentration of As that entails simultaneous sorption of both As(III) and As(V) from groundwater on covellite (CuS) and, later, their elution as As(V), which subsequently participates in the formation of arsenomolybdic acid. The interference in the color development from PO₄^3-ions that are as efficiently sorbed on CuS and eluted as the oxyanions of As is eliminated by their selective removal by Ce⁴⁺ ions under basic (pH ∼ 8.5) conditions. The removal is caused by the formation of cerium phosphate and its co-precipitation with calcium hydroxide. SiO₄^2- ions do not interfere in the process as they are not sorbed by CuS. Groundwater containing ≤0.5 mg L^-1 P and ≥200 mg L^-1 total dissolved solid can be conveniently analysed by the method. The direct sensing of As(III) as well as As(V), the use of benign and easily available chemicals, the absence of any hazardous by-product, undiminished applicability in sunlight, the testing procedure lasting only for about 30 min, and rapidity are the major advantages of the method. Thus, the method is potentially well-suited for the on-site testing of groundwater potability under different regulations.

A Review on Carbon Dots: Synthesis, Characterization and Its Application in Optical Sensor for Environmental Monitoring

The development of carbon dots (CDs), either using green or chemical precursors, has inevitably led to their wide range application, from bioimaging to optoelectronic devices. The reported precursors and properties of these CDs have opened new opportunities for the future development of high-quality CDs and applications. Green precursors were classified into fruits, vegetables, flowers, leaves, seeds, stem, crop residues, fungi/bacteria species, and waste products, while the chemical precursors were classified into acid reagents and non-acid reagents. This paper quickly reviews ten years of the synthesis of CDs using green and chemical precursors. The application of CDs as sensing materials in optical sensor techniques for environmental monitoring, including the detection of heavy metal ions, phenol, pesticides, and nitroaromatic explosives, was also discussed in this review. This profound review will offer knowledge for the upcoming community of researchers interested in synthesizing high-quality CDs for various applications.

Glutathione-functionalized long-period fiber gratings sensor based on surface plasmon resonance for detection of As3+ ions

Development of simple and accurate methods for the detection of As³⁺is highly desirable and technically important. In this work, a highly sensitive and selective long-period fiber gratings sensor based on surface plasmon resonance was developed for As³⁺detection by designing glutathione-functionalized Au nanoparticles as a signal amplification tag. Based on the chemical interaction between As³⁺and glutathione, the self-assembling glutathione on the surface of the gold film combines selectively with As³⁺, and then anchors the glutathione-functionalized Au nanoparticles, which changes the refractive index of the surrounding environment, resulting in a shift of the transmission spectrum. Results show that the sensor could detect As³⁺with concentrations ranging from 0.02 to 2 ppb. The sensor exhibited excellent specificity for As³⁺against other metal ions, such as Na⁺, Fe³⁺, Mg²⁺, Cu²⁺, Pb²⁺, Ni²⁺, Ba²⁺, and Co³⁺. The fiber sensor was successfully employed to detect As³⁺in pond water samples, demonstrating that it has the potential for As³⁺detection with the advantages of low cost, high sensitivity, and a simple structure.