Phenothiazine-cyanine-functionalized upconversion nanoparticles for LRET and colorimetric sensing of cyanide ions in water samples

A Review of Nanotechnology-Enabled Fluorescent Chemosensors for Environmental Toxic Ion Detection

This review examines the utilization of nanotechnology-based chemosensors for identifying environmental toxic ions. Over recent decades, the creation of nanoscale materials for applications in chemical sensing, biomedical, and biological analyses has emerged as a promising avenue. Nanomaterials play a vital role in improving the sensitivity and selectivity of chemosensors, thereby making them effective tools for monitoring and evaluating environmental contamination. This is due to their highly adjustable size- and shape-dependent chemical and physical properties. Nanomaterials possess distinct surface chemistry, thermal stability, high surface area, and large pore volume per unit mass, which can be harnessed for sensor development. The discussion encompasses different types of nanomaterials utilized in chemosensor design, LOD, their sensing mechanisms, and their efficacy in detecting specific toxic ions. Furthermore, the review explores the progress made, obstacles faced, and future prospects in this rapidly evolving field, highlighting the potential contributions of nanotechnology to the creation of robust sensing platforms for environmental monitoring.

Nanoparticles Based Sensors for Cyanide Ion Sensing, Basic Principle, Mechanism and Applications

Rapidly detecting potentially toxic ions such as cyanide is paramount to maintaining a sustainable and environmentally friendly ecosystem for living organisms. In recent years, molecular sensors have been developed to detect cyanide ions, which provide a naked-eye or fluorometric response, making them an ideal choice for cyanide sensing. Nanosensors, on the other hand, have become increasingly popular over the last two decades due water solubility, quick reaction times, environmental friendliness, and straightforward synthesis. Researchers have designed many nanosensors and successfully utilized them for the detection of cyanide ions in various environmental samples. The majority of these sensors use gold and silver-based nanosensors because cyanide ions have a high affinity for these metals ions and coordinate through covalent bonds. These metal nanoparticles are typically combined or coated with fluorescent materials, which quench their fluorescence. However, adding cyanide ions etches out the metal nanoparticles, restoring their fluorescence/color. This principle has been followed by most nanosensors used for cyanide ion sensing. In this review, different nanosensors and their sensing mechanisms are discussed in relation to cyanide ions. The primary purpose is to compare the sensing abilities of these sensors, mainly their sensitivity, advantages, application and to find out research gaps for future work. In this review paper, the development made in nanosensors in the last thirteen years (2010-2023) was discussed and the nanosensors for cyanide ions were compared with molecular sensors while the nanosensors with the excellent limit of detection were highlighted.

A new nitrile vinyl linked ultrafast receptor to track cyanide ions: Utilization on realistic samples and HeLa cell imaging

A simple D - A (donor - acceptor) type receptor ((2E, 2'E)-3, 3'-(10-octyl-10H-phenothiazine-3,7-diyl)bis(2-(benzo[d]thiazol-2-yl)acrylonitrile)) (PBTA) containing nitrile-vinyl linkage was designed and completely characterized. The receptor PBTA detects CN^- ions based on "turn-off" effect with admirable spectral properties. It also owns some of the merits like "naked-eye" color change, ultrafast response (90 s), lowest detection limit (1.25 × 10^-10 M) as well as quantitation limit (4.17 × 10^-10 M) with the pH range 4-11 which is more suitable pH to make use of the receptor PBTA in physiological medium. The instant detecting ability of the receptor over CN^- ions was proved using paper test strip and cotton balls. Further, the utilization of the receptor PBTA was also extended to track CN^- ions in realistic samples (water and food samples) and in HeLa cells bioimaging.

Plasmonic surface-enhanced Raman scattering nano-substrates for detection of anionic environmental contaminants: Current progress and future perspectives

Surface-enhanced Raman scattering spectroscopy (SERS) is a powerful technique of vibrational spectroscopy based on the inelastic scattering of incident photons by molecular species. It has unique properties such as ultra-sensitivity, selectivity, non-destructivity, speed, and fingerprinting properties for analytical and sensing applications. This enables SERS to be widely used in real-world sample analysis and basic plasmonic mechanistic studies. However, the desirable properties of SERS are compromised by the high cost and low reproducibility of the signals. The development of multifunctional, stable and reusable nano-engineered SERS substrates is a viable solution to circumvent these drawbacks. Recently, plasmonic SERS active nano-substrates with various morphologies have attracted the attention of researchers due to promising properties such as the formation of dense hot spots, additional stability, tunable and controlled morphology, and surface functionalization. This comprehensive review focused on the current advances in the field of SERS active nanosubstrates suitable for the detection and quantification of anionic environmental pollutants. The common fabrication methods, including the techniques for morphological adjustments and surface modification, substrate categories, and the design of nanotechnologically fabricated plasmonic SERS substrates for anion detection are systematically presented. Here, the need for the design, synthesis, and functionalization of SERS nano-substrates for anions of great environmental importance is explained in detail. In addition, the broad categories of SERS nano-substrates, namely colloid-based SERS substrates and solid-support SERS substrates are discussed. Moreover, a brief discussion of SERS detection of certain anionic pollutants in the environment is presented. Finally, the prospects in the fabrication and commercialization of pilot-scale handheld SERS sensors and the construction of smart nanosubstrates integrated with novel amplifying materials for the detection of anions of environmental and health concern are proposed.

Naked-Eye Chromogenic Test Strip for Cyanide Sensing Based on Novel Phenothiazine Push-Pull Derivatives

Monitoring and detection of cyanide are of crucial interest as the latter plays versatile roles in many biological events, is ubiquitous in environment, and responsible for several acute poisoning and adverse health effects if ingested. We describe herein the synthesis and characterization of novel phenothiazine-based push-pull chromogenic chemosensors suitable for naked eye cyanide sensing. Indeed, specific detections were achieved for cyanide with a LOD of ca 9.12 to 4.59 µM and, interestingly, one of the new chemosensors has also revealed an unprecedented affinity for acetate with a LOD of ca 2.68 µM. Moreover, as proof of concept for practical applications, a paper test strip was prepared allowing its use for efficient qualitative naked eye cyanide sensing.

Determination of cyanide based on a dual-emission ratiometric nanoprobe using silver sulfide quantum dots and silicon nanoparticles

A novel ratiometric fluorescent nanoprobe was designed for the sensitive determination of cyanide anion (CN^-) by the electrostatic attraction between positively charged silicon nanoparticles (Si NPs) and negatively charged silver sulfide quantum dots (Ag₂S QDs). The nanoprobe exhibited two well-resolved emission peaks at 446 nm and 540 nm under a single excitation wavelength (360 nm). In the presence of CN^-, the fluorescence of Ag₂S QDs at 540 nm was remarkably quenched, while the fluorescence of the Si NPs at 446 nm remained constant, establishing the desired conditions for ratiometric fluorescence detection. Under optimal conditions, the ratiometric fluorescence assay showed good linearity (R² = 0.9921) within the range 0.05-15 μM, and the limit of detection was calculated to be 56 nM (at an S/N ratio of 3). The proposed Ag₂S QD/Si NP nanoprobe has been successfully used to determine CN^- in water and sprouting potato samples with satisfactory recoveries in the range 97-110.5%.

Exploring the use of upconversion nanoparticles in chemical and biological sensors: from surface modifications to point-of-care devices

Upconversion nanoparticles (UCNPs) have emerged as promising luminescent nanomaterials due to their unique features that allow the overcoming of several problems associated with conventional fluorescent probes. Although UCNPs have been used in a broad range of applications, it is probably in the field of sensing where they best evidence their potential. UCNP-based sensors have been designed with high sensitivity and selectivity, for detection and quantification of multiple analytes ranging from metal ions to biomolecules. In this review, we deeply explore the use of UCNPs in sensing systems emphasizing the most relevant and recent studies on the topic and explaining how these platforms are constructed. Before diving into UCNP-based sensing platforms it is important to understand the unique characteristics of these nanoparticles, why they are attracting so much attention, and the most significant interactions occurring between UCNPs and additional probes. These points are covered over the first two sections of the article and then we explore the types of fluorescent responses, the possible analytes, and the UCNPs' integration with various material types such as gold nanostructures, quantum dots and dyes. All the topics are supported by analysis of recently reported sensors, focusing on how they are built, the materials' interactions, the involved synthesis and functionalization mechanisms, and the conjugation strategies. Finally, we explore the use of UCNPs in paper-based sensors and how these platforms are paving the way for the development of new point-of-care devices.

Lanthanide ion (Ln3+ )-based upconversion sensor for quantification of food contaminants: A review

The food safety issue has gradually become the focus of attention in modern society. The presence of food contaminants poses a threat to human health and there are a number of interesting researches on the detection of food contaminants. Upconversion nanoparticles (UCNPs) are superior to other fluorescence materials, considering the benefits of large anti-Stokes shifts, high chemical stability, non-autofluorescence, good light penetration ability, and low toxicity. These properties render UCNPs promising candidates as luminescent labels in biodetection, which provides opportunities as a sensitive, accurate, and rapid detection method. This paper intended to review the research progress of food contaminants detection by UCNPs-based sensors. We have proposed the key criteria for UCNPs in the detection of food contaminants. Additionally, it highlighted the construction process of the UCNPs-based sensors, which includes the synthesis and modification of UCNPs, selection of the recognition elements, and consideration of the detection principle. Moreover, six kinds of food contaminants detected by UCNPs technology in the past 5 years have been summarized and discussed fairly. Last but not least, it is outlined that UCNPs have great potential to be applied in food safety detection and threw new insight into the challenges ahead.

Fluorescence sensing of cyanide anions based on Au-modified upconversion nanoassemblies

Cyanides have been recognized as one of the most toxic chemicals and are harmful to the environment and human beings. Herein, fluorescence resonance energy transfer (FRET)-based upconversion nanoprobes for cyanide anions have been designed and prepared by assembling Au nanoparticles (NPs) on core-shell-structured NaYF₄:Yb,Er@NaYF₄:Yb upconversion NPs (csUCNPs), where csUCNPs act as the energy donor and Au NPs act as the energy acceptor. The Au content was optimized in order to have a large quenching efficiency in upconversion luminescence (UCL). The cyanide-mediated redox reaction leads to the consumption of Au NPs, resulting in UCL recovery by the inhibition of the FRET process. On the basis of these features, csUCNP/Au nanoassemblies can serve as sensitive nanoprobes for cyanide ions with a detection limit of 1.53 μM. Moreover, no significant UCL variation was observed upon the addition of other interfering ions, showing the excellent selectivity of nanoprobes toward cyanide ion sensing. The easy preparation of such upconversion-based nanoprobes provides a promising platform for sensitive and selective sensing of other hazardous species.

Synthesis of Tris-pillar[5]arene and Its Association with Phenothiazine Dye: Colorimetric Recognition of Anions

A multicyclophane with a core based on tris(2-aminoethyl)amine (TREN) linked by amide spacers to three fragments of pillar[5]arene was synthesized. The choice of the tris-amide core allowed the multicyclophane to bind to anion guests. The presence of three terminal pillar[5]arene units provides the possibility of effectively binding the colorimetric probe N-phenyl-3-(phenylimino)-3H-phenothiazin-7-amine (PhTz). It was established that the multicyclophane complexed PhTz in chloroform with a 1:1 stoichiometry (lgK_a = 5.2 ± 0.1), absorbing at 650 nm. The proposed structure of the complex was confirmed by ¹H-NMR spectroscopy: the amide group linking the pillar[5]arene to the TREN core forms a hydrogen bond with the PhTz imino-group while the pillararenes surround PhTz. It was established that the PhTz:tris-pillar[5]arene complex could be used as a colorimetric probe for fluoride, acetate, and dihydrogen phosphate anions due to the anion binding with proton donating amide groups which displaced the PhTz probe. Dye displacement resulted in a color change from blue to pink, lowering the absorption band at 650 nm and increasing that at 533 nm.

Surface Modifications for Photon-Upconversion-Based Energy-Transfer Nanoprobes

An emerging class of inorganic optical reporters are near-infrared (NIR) excitable lanthanide-based upconversion nanoparticles (UCNPs) with multicolor emission and long luminescence lifetimes in the range of several hundred microseconds. For the design of chemical sensors and optical probes that reveal analyte-specific changes in their spectroscopic properties, these nanomaterials must be combined with sensitive indicator dyes that change their absorption and/or fluorescence properties selectively upon interaction with their target analyte, utilizing either resonance energy transfer (RET) processes or reabsorption-related inner filter effects. The rational development of UCNP-based nanoprobes for chemical sensing and imaging in a biological environment requires reliable methods for the surface functionalization of UCNPs, the analysis and quantification of surface groups, a high colloidal stability of UCNPs in aqueous media as well as the chemically stable attachment of the indicator molecules, and suitable instrumentation for the spectroscopic characterization of the energy-transfer systems and the derived nanosensors. These topics are highlighted in the following feature article, and examples of functionalized core-shell nanoprobes for the sensing of different biologically relevant analytes in aqueous environments will be presented. Special emphasis is placed on the intracellular sensing of pH.

Recent Advances on Functionalized Upconversion Nanoparticles for Detection of Small Molecules and Ions in Biosystems

Significant progress on upconversion-nanoparticle (UCNP)-based probes is witnessed in recent years. Compared with traditional fluorescent probes (e.g., organic dyes, metal complexes, or inorganic quantum dots), UCNPs have many advantages such as non-autofluorescence, high chemical stability, large light-penetration depth, long lifetime, and less damage to samples. This article focuses on recent achievements in the usage of lanthanide-doped UCNPs as efficient probes for biodetection since 2014. The mechanisms of upconversion as well as the luminescence resonance energy transfer process is introduced first, followed by a detailed summary on the recent researches of UCNP-based biodetections including the detection of inorganic ions, gas molecules, reactive oxygen species, and thiols and hydrogen sulfide.