Experimental and theoretical investigations for selective colorimetric recognition and determination of arginine and histidine in vegetable and fruit samples using bare-AgNPs

Selective colorimetric sensing of histidine in aqueous media via Ag nanotriangles in the presence of HgCl2

Silver nanotriangles (AgNTs) were successfully synthesized as a colorimetric probe for selective and sensitive histidine detection in aqueous media within a 15-100 µM range and a detection limit of 330 nM using UV-Vis spectroscopy. The interaction of HgCl2 with AgNTs would lead to the formation of disk-shaped Ag/Hg amalgam as observed from the transmission electron images and X-ray diffraction patterns. Histidine prevents these structural and morphological changes and accordingly, the detection approach was developed based on the correlation between the histidine concentration and the in-plane dipole plasmon resonance (DPR) intensity.

A highly selective solution and film based sensor for colorimetric sensing of arginine in aqueous and blood samples

A benzothiazole-azo based sensor (BTAN) was developed for rapid and on-site detection of arginine. The sensor's selectivity in a semi-aqueous medium was thoroughly investigated, focusing on the colorimetric response to arginine in the presence of 11 different amino acids. Notably, the limit of detection (LOD) for arginine was determined to be 0.7 μM. The underlying sensing mechanism was addressed using 1H-NMR and UV-vis spectroscopy. BTAN exhibited significant changes in both absorption as well as emission spectra exclusively in the presence of arginine. Furthermore, the arginine sensing capability was extended to the solid state by immobilizing BTAN into a starch-PVA hydrogel matrix as well as paper strips. The hydrogel film of BTAN enabled effective on-site sensing of arginine in a 100% aqueous medium. Moreover, the practicability of the sensor was demonstrated by detecting arginine in human blood samples.

A DMSO-assisted iridium(III) complex as a luminescent "turn-on" sensor for selective detection of L-histidine and bacterial imaging

Histidine (His) is a semi-essential amino acid and a unique key neurotransmitter involved in numerous physiological processes. An excessive or deficient amount of His in the body can lead to various related diseases. However, since the chemical structures of L-His and its metabolites (such as histamine (Ha), imidazole-4-acetate (ImA), etc.) are very similar, simple and efficient selective detection of L-His and its related metabolites is of great importance but remains a great challenge. Herein, we successfully designed and synthesized a DMSO-assisted iridium(III) complex (Ir1-DMSO), which can be applied as a "turn-on" photoluminescence (PL) probe for the selective detection and quantification of L-His/Ha. More importantly, Ir1-DMSO exhibited good sensitivity, high selectivity, and anti-interference capability for L-His/Ha/His-containing proteins, which is advantageous due to its simple fabrication and low technical demands. This was attributed to the reaction of Ir1-DMSO with imidazole and amino groups of L-His/Ha. Furthermore, we show the utility of Ir1-DMSO as a PL imaging agent in cultures of E. coli and S. aureus. Considering its diversity of composition and structural flexibility, it can be extended to other solvents and Ir-ligand complexes for various analyses based on specific molecular recognition sensing platforms.

Environmental behavior of silver nanomaterials in aquatic environments: An updated review

The increasing applications of silver nanomaterials (nano-Ag) and their inevitable release posed great potential risks to aquatic organisms and ecosystems. Considerable attention has been attracted on their behaviors and transformations, which were critically important for their subsequent biological toxicities and ecological effects. Therefore, the summary of the recent efforts on the environmental behavior of nano-Ag would be beneficial for understanding the environmental fate and accurate risk assessment. This review summarized the studies on various physical, chemical and biological transformations of nano-Ag, meanwhile, the influencing factors (including the intrinsic properties and environmental conditions) and related mechanisms were highlighted. Surface structure and facets of nano-Ag, abiotic conditions and natural freeze-thaw cycle processes could affect the transformations of nano-Ag under different environmental scenarios (including freshwater, seawater and wastewater). The interactions with co-present components, such as chemicals and other particles, impacted the multiple processes of nano-Ag. Besides, the contradictory effects and mechanisms by several environmental factors were summarized. Lastly, the key knowledge gaps and some aspects that deserve further investigation were also addressed. Therefore, the current review aimed to provide an overall analysis of transformation processes of nano-Ag, which will provide more available information and pave the way for the future research areas.

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.

Parallel Monitoring of Glucose, Free Amino Acids, and Vitamin C in Fruits Using a High-Throughput Paper-Based Sensor Modified with Poly(carboxybetaine acrylamide)

Herein, a cost-effective and portable microfluidic paper-based sensor is proposed for the simultaneous and rapid detection of glucose, free amino acids, and vitamin C in fruit. The device was constructed by embedding a poly(carboxybetaine acrylamide) (pCBAA)-modified cellulose paper chip within a hydrophobic acrylic plate. We successfully showcased the capabilities of a filter paper-based microfluidic sensor for the detection of fruit nutrients using three distinct colorimetric analyses. Within a single paper chip, we simultaneously detected glucose, free amino acids, and vitamin C in the vivid hues of cyan blue, purple, and Turnbull's blue, respectively, in three distinctive detection zones. Notably, we employed more stable silver nanoparticles for glucose detection, replacing the traditional peroxidase approach. The detection limits for glucose reached a low level of 0.049 mmol/L. Meanwhile, the detection limits for free amino acids and vitamin C were found to be 0.236 mmol/L and 0.125 mmol/L, respectively. The feasibility of the proposed sensor was validated in 13 different practical fruit samples using spectrophotometry. Cellulose paper utilizes capillary action to process trace fluids in tiny channels, and combined with pCBAA, which has superior hydrophilicity and anti-pollution properties, it greatly improves the sensitivity and practicality of paper-based sensors. Therefore, the paper-based colorimetric device is expected to provide technical support for the nutritional value assessment of fruits in the field of rapid detection.

Smartphone-Based High-Throughput Fluorimetric Assay for Histidine Quantification in Human Urine Using 96-Well Plates

A high-throughput fluorimetric assay for histidine was developed, using a 96-well plates platform. The analyte reacts selectively with o-phthalaldehyde under mild alkaline conditions to form a stable derivative. Instrumental-free detection was carried out using a smartphone after illumination under UV light (365 nm). The method was proved to be linear up to 100 μM histidine, with an LLOQ (lower limit of quantification) of 10 μM. The assay was only prone to interference from glutathione and histamine that exist in the urine samples at levels that are orders of magnitude lower compared to histidine. Human urine samples were analyzed following minimum treatment and were found to contain histidine in the range of 280 to 1540 μM. The results were in good agreement with an HPLC corroborative method.