Recent advances in selective formaldehyde detection in biological and environmental samples by fluorometric and colorimetric chemodosimeters

Research progress of fluorescent composites based on cyclodextrins: Preparation strategies, fluorescence properties and applications in sensing and bioimaging

Fluorescence analysis has been regarded as one of the commonly used analytical methods because of its advantages of simple operation, fast response, low cost and high sensitivity. So far, various fluorescent probes, with noble metal nanoclusters, quantum dots, organic dyes and metal organic frameworks as representatives, have been widely reported. However, single fluorescent probe often suffers from some deficiencies, such as low quantum yield, poor chemical stability, low water solubility and toxicity. To overcome these disadvantages, the introduction of cyclodextrins into fluorescent probes has become a fascinating approach. This review (with 218 references) systematically covers the research progress of fluorescent composites based on cyclodextrins in recent years. Preparation strategies, fluorescence properties, response mechanisms and applications in sensing (ions, organic pollutants, bio-related molecules, temperature, pH) and bioimaging of fluorescent composites based on cyclodextrins are summarized in detail. Finally, the current challenges and future perspectives of these composites in relative research fields are discussed.

The impact of formaldehyde exposure on lung inflammatory disorders: Insights into asthma, bronchitis, and pulmonary fibrosis

Lung inflammatory disorders are a major global health burden, impacting millions of people and raising rates of morbidity and death across many demographic groups. An industrial chemical and common environmental contaminant, formaldehyde (FA) presents serious health concerns to the respiratory system, including the onset and aggravation of lung inflammatory disorders. Epidemiological studies have shown significant associations between FA exposure levels and the incidence and severity of several respiratory diseases. FA causes inflammation in the respiratory tract via immunological activation, oxidative stress, and airway remodelling, aggravating pre-existing pulmonary inflammation and compromising lung function. Additionally, FA functions as a respiratory sensitizer, causing allergic responses and hypersensitivity pneumonitis in sensitive people. Understanding the complicated processes behind formaldehyde-induced lung inflammation is critical for directing targeted strategies aimed at minimizing environmental exposures and alleviating the burden of formaldehyde-related lung illnesses on global respiratory health. This abstract explores the intricate relationship between FA exposure and lung inflammatory diseases, including asthma, bronchitis, allergic inflammation, lung injury and pulmonary fibrosis.

ESIPT-based probes for cations, anions and neutral species: recent progress, multidisciplinary applications and future perspectives

Fluorescent and colourimetric probes for small analytes (cations, anions and neutral molecules) have drawn significant attention in recent years. These probes interact with analytes and induce spectral change due to the variations in the photo-physical properties of the fluorophore/chromophore used. Among several photo-physical mechanisms, ESIPT (excited state intramolecular proton transfer) based probes are more advantageous due to their photo-physical properties viz. solvent polarity effect, large spectral shift with multi-channel fluorescence, high quantum yield etc. In recent years, ESIPT-based probes have shown several promising applications, especially monitoring small analytes in biological samples, smartphone app-assisted heavy metal detection in environmental samples, inkless writing, anti-counterfeiting applications etc. Therefore, this review is dedicated to recently reported ESIPT-based probes for small analytes. We have highlighted the organic units responsible for the ESIPT mechanism, their photo-physical parameters, selectivity and sensitivity properties and recent advances in their applications.

Pattern Recognition and Visual Detection of Aldehydes Using a Single ESIPT Dye

The accurate discrimination and quantification of aldehydes is a worthy objective made challenging by their similar chemical reactivities. Considering the nucleophilic reaction mechanism between an aldehyde and a primary amine, it is reasonable to vary the reaction pH to manipulate the reactivity of aldehydes and the stability of the resulting Schiff base for analytical purposes. We have designed and synthesized three benzothiazole-based fluorescent molecules (BS1-BS3) containing an amino group substituted at the ortho-, meta-, and para-positions for aldehyde sensing. It was determined that only BS1 having an amino group at the ortho-position exhibits a significant fluorescence response in the presence of formaldehyde at a particular pH, whereas BS2 and BS3 gave negligible responses, indicating that the ESIPT process in BS1 should be responsible for the changes in its fluorescence. Accordingly, a pH-mediated sensor array BS1SA was constructed by dissolving BS1 in aqueous solvents with different pH values. BS1SA was found to be reliable for the discrimination of seven different aldehydes and identification of unknown aldehyde samples. Moreover, BS1 was successfully applied to prepare a fluorescent test paper for the visual detection of formaldehyde vapor.

Study on the color-changing mechanism and law of visual formaldehyde sensing system based on hyperbranched polyamines

This study focuses on addressing the limitations associated with most chemical derivatization methods commonly used for formaldehyde detection. These methods often suffer from prolonged derivative times (≥30 min) and complex procedures, which hinder their ability to meet the requirements of real-time and accurate sensing. In this research, a novel formaldehyde indicator system based on hyperbranched polyamine molecule was developed, and its mechanism and principles of color change were investigated. The findings revealed that hyperbranched polyamine molecule effectively reacts with formaldehyde, leading to a reduction in electron cloud density in the amine group N and subsequently causing a decrease in pH value. This reaction enables the visualization of formaldehyde detection through changes in the indicator spectrum. Moreover, the spectral variation pattern exhibits a strong linear correlation with the formaldehyde concentration when the PAMAM concentration is optimized. The detection limit of this method was determined to be 1.8 ppm. Notably, the reaction between PAMAM and formaldehyde is almost instantaneous, the color change is insensitive to temperature, and the method demonstrates high selectivity. Overall, this research contributes to the advancement of real-time formaldehyde monitoring technology and provides insights for future developments in this field.

Synthesis and Characterization of Multi-Reducing-End Polysaccharides

Site-specific modification is a great challenge for polysaccharide scientists. Chemo- and regioselective modification of polysaccharide chains can provide many useful natural-based materials and help us illuminate fundamental structure-property relationships of polysaccharide derivatives. The hemiacetal reducing end of a polysaccharide is in equilibrium with its ring-opened aldehyde form, making it the most uniquely reactive site on the polysaccharide molecule, ideal for regioselective decoration such as imine formation. However, all natural polysaccharides, whether they are branched or not, have only one reducing end per chain, which means that only one aldehyde-reactive substituent can be added. We introduce a new approach to selective functionalization of polysaccharides as an entrée to useful materials, appending multiple reducing ends to each polysaccharide molecule. Herein, we reduce the approach to practice using amide formation. Amine groups on monosaccharides such as glucosamine or galactosamine can react with carboxyl groups of polysaccharides, whether natural uronic acids like alginates, or derivatives with carboxyl-containing substituents such as carboxymethyl cellulose (CMC) or carboxymethyl dextran (CMD). Amide formation is assisted using the coupling agent 4-(4,6-dimethoxy-1,3,5-triazin-2-yl)-4-methylmorpholinium chloride (DMTMM). By linking the C2 amines of monosaccharides to polysaccharides in this way, a new class of polysaccharide derivatives possessing many reducing ends can be obtained. We refer to this class of derivatives as multi-reducing-end polysaccharides (MREPs). This new family of derivatives creates the potential for designing polysaccharide-based materials with many potential applications, including in hydrogels, block copolymers, prodrugs, and as reactive intermediates for other derivatives.

Recent Progress in the Development of Organic Chemosensors for Formaldehyde Detection

Formaldehyde has become a prominent topic of interest because of its simple molecular structure, release from various compounds in the near vicinity of humans, and associated hazards. Thus, several researchers designed sophisticated instrumentations for formaldehyde detection that exhibit real-time sensing properties and are cost-effective and portable with high detection limits. On these grounds, this review is centered on an analysis of optical chemosensors for formaldehyde that specifically fall under the broad spectrum of organic probes. In this case, this review discusses different organic functionalities, including amines, imines, aromatic pillar arenes, β-ketoesters, and β-diketones, taking part in various reaction mechanisms ranging from aza-Cope rearrangement and Schiff base and Hanztch reactions to aldimine condensation. In addition, this review distinguishes reaction mechanisms according to photophysical phenomena, that is, aggregation-induced emission, photoinduced electron transfer, and intramolecular charge transfer. Furthermore, it addresses the instrumentation involved in gas-based and liquid formaldehyde detection. Finally, it discusses the gaps in existing technologies followed by a succinct set of recommendations for future research.

Quantum dot assisted precise and sensitive fluorescence-based formaldehyde detection in food samples

Formaldehyde has an extremely reactive carbonyl group, commonly used as an antibacterial agent to sterilize and prevent food to spoil. This article describes an efficient and rapid detection method of formaldehyde from an aqueous solution by synthesizing 3-Aminopropyltriethoxysilane (APTES) quantum dots (Nano A) which react with formaldehyde to generate a Schiff base reaction. The photoinduced electron transfer produced by the quantum dots themselves results in fluorescence quenching to detect formaldehyde. The detection limit can reach 10^-9 M, and it can further be used to detect formaldehyde content in foods, such as baby vegetables, mushrooms, and vermicelli among other daily foods.

Development of a Rapid and Sensitive Fluorescence Sensing Method for the Detection of Acetaldehyde in Alcoholic Beverages

Acetaldehyde is regarded as an important flavor compound in alcoholic beverages. With the advantages of rapidity, low cost and high sensitivity, fluorescent probe could be used as a new tool for the detection of acetaldehyde. Here, an effective fluorescence sensing method based on fluorescent probe N1 (FPN1) was established in this study. The function of FPN1 relies on the nucleophile substitution reaction and photoinduced electron transfer (PET), resulting in a fluorescence increase. Remarkably, the pretreatment background removal method (BRM) was successfully applied for removal of the interference of pyruvate and acetal. The linearity range (LR), limit of detection (LOD) and recovery of the fluorescence sensing method with BRM were 0.0053–200 mg/L, 0.0016 mg/L and 94.02–108.12%, respectively, which showed a broader detection range and better performance on sensitivity compared with the traditional quantitation using gas chromatography (GC). Furthermore, successful application of the method in real samples indicated the advantages of low-cost and rapidity for small-scale detection while assuring the accuracy, which provides a new strategy for the detection of acetaldehyde concentration in alcoholic beverages.

Novel Method of Analysis for the Determination of Residual Formaldehyde by High-Performance Liquid Chromatography

Formaldehyde is commonly used as an alkylating agent in the pharmaceutical industry. Consequently, its residual level in drug substances and/or their intermediates needs to be accurately quantified. Formaldehyde is a small, volatile molecule with a weak chromophore (the carbonyl group), and its direct analysis by GC-FID and HPLC-UV is difficult. For these reasons, the majority of papers found in the literature are based upon a derivatisation process (most commonly using the desensitised explosive 2,4-dinitrophenylhydrazine) prior to the analysis of formaldehyde. A novel high-performance liquid chromatography (HPLC) method with UV detection for its quantification in a pharmaceutical is described in this paper. The method proposed herein is based upon a derivatisation reaction between formaldehyde and 4-methylbenzenesulfonohydrazide (MBSH) before analysis by HPLC-UV. Selectivity, linearity, limit of quantification, accuracy, repeatability, intermediate precision, and solution stability were successfully assessed as per ICH guideline Q2(R1), and the method has also been validated in a good manufacturing practice (GMP) laboratory in the UK.

Approaches to Formaldehyde Measurement: From Liquid Biological Samples to Cells and Organisms

Formaldehyde (FA) is the simplest aldehyde present both in the environment and in living organisms. FA is an extremely reactive compound capable of protein crosslinking and DNA damage. For a long time, FA was considered a "biochemical waste" and a by-product of normal cellular metabolism, but in recent decades the picture has changed. As a result, the need arose for novel instruments and approaches to monitor and measure not only environmental FA in water, cosmetics, and household products, but also in food, beverages and biological samples including cells and even organisms. Despite numerous protocols being developed for in vitro and in cellulo FA assessment, many of them have remained at the "proof-of-concept" stage. We analyze the suitability of different methods developed for non-biological objects, and present an overview of the recently developed approaches, including chemically-synthesized probes and genetically encoded FA-sensors for in cellulo and in vivo FA monitoring. We also discuss the prospects of classical methods such as chromatography and spectrophotometry, and how they have been adapted in response to the demand for precise, selective and highly sensitive evaluation of FA concentration fluctuations in biological samples. The main objectives of this review is to summarize data on the main approaches for FA content measurement in liquid biological samples, pointing out the advantages and disadvantages of each method; to report the progress in development of novel molecules suitable for application in living systems; and, finally, to discuss genetically encoded FA-sensors based on existing natural biological FA-responsive elements.

Quinolizinium-based fluorescent probes for formaldehyde detection in aqueous solution, serum, and test strip via 2-aza-Cope rearrangement

Formaldehyde is an abundant contaminant in food and environments causing various diseases. Thus, the development of fast, simple, and selective formaldehyde detection is of great interest. Herein, novel quinolizinium-based fluorescent probes were designed based on a 2-aza-Cope rearrangement reaction and showed high selectivity to formaldehyde by fluorescence emission shift. We successfully reduced the detection time by increasing the bulkiness of the homoallylic moiety. The probes were applied to detect formaldehyde in aqueous solution, serum, and paper format.

Activity-based fluorescent probes for sensing and imaging of Reactive Carbonyl species (RCSs)

This review explains various strategies for developing fluorescent probes to detect reactive carbonyl species (RCS). There are sevaral number of mono and diacarbonyls among 30 varieties of reactive carbonyl species (RCSs) so far discovered, which play pivotal roles in pathological processes such as cancer, neurodegenerative diseases, cardiovascular disease, renal failure, and diabetes mellitus. These RCSs play essential roles in maintaining ion channels regulation, cellular signaling pathways, and metabolisms. Among RCSs, Carbon moxide (CO) is also utilized for its cardioprotective, anti-inflammatory, and anti-apoptotic effects. Fluorescence-based non-invasive optical tools have come out as one of the promising methods for analyzing the concentrations and co-localizations of these small metabolites. There has been a tremendous eruption in developing fluorescent probes for selective detection of specific RCSs within cellular and aqueous environments due to its high sensitivity, high spatial and temporal resolution of fluorescence imaging. Fluorescence-based sensing mechanisms such as intramolecular charge transfer (ICT), photoinduced electron transfer (PeT), excited-state intramolecular proton transfer (ESIPT), and fluorescence resonance energy transfer (FRET) are described. In particular, probes for dicarbonyls such as methylglyoxal (MGO), malondialdehyde (MDA), along with monocarbonyls that include formaldehyde (FA), carbon monoxide (CO) and phosgene are discussed. One of the most exciting advances in this review is the summary of fluorescent probes of dicarbonyl compounds.

From small molecules to polymeric probes: recent advancements of formaldehyde sensors

Formaldehyde is a well-known industrial material regularly used in fishery, vegetable markets, and fruit shops for maintaining their freshness. But due to its carcinogenic nature and other toxic effects, it is very important to detect it in very low concentrations. In recent years, amine-containing fluorescent probes have gained significant attention for designing formaldehyde sensors. However, the major drawbacks of these small molecular probes are low sensitivity and long exposure time, which limits their real-life applications. In this regard, polymeric probes have gained significant attention to overcome the aforementioned problems. Several polymeric probes have been utilized as a coating material, nanoparticle, quartz crystal microbalance (QCM), etc., for the selective and sensitive detection of formaldehyde. The main objective of this review article is to comprehensively describe the recent advancements in formaldehyde sensors based on small molecules and polymers, and their successful applications in various fields, especially in situ formaldehyde sensing in biological systems.

Reaction-based fluorescent and chemiluminescent probes for formaldehyde detection and imaging

Formaldehyde (FA), a reactive carbonyl species, is classified as Group 1 carcinogen by International Agency for Research on Cancer (IARC) in 2004. In addition, clinical studies have implicated that elevated levels of FA have been associated with different kinds of diseases, such as neurodegenerative diseases, diabetes, and chronic liver and heart disorders. However, in addition to the direct inhalation of FA in the environment, most organisms can also produce FA endogenously by demethylases and oxidases during the metabolism of amino acids and xenobiotics. Since FA plays an important role in physiological and pathological processes, developing reliable and efficient methods to monitor FA levels in biological samples is crucial. Reaction-based fluorescent/chemiluminescent probes have provided robust methods for FA detection and real-time visualization in living organisms. In this highlight, we will summarize the major developments in the structure design and applications of FA probes in recent years. Three main strategies for designing FA probes have been discussed and grouped by different reaction mechanisms. In addition, some miscellaneous reaction mechanisms have also been discussed. We also highlight novel applications of these probes in biological systems, which offer powerful tools to discover the diverse functions of FA in physiology and pathology processes.

Recent advances in tin ion detection using fluorometric and colorimetric chemosensors

The innovation of chemosensors for tin ions (Sn4+/Sn2+) has evolved as a key research topic in recent decades, garnering a lot of attention due to their environmental, industrial and biological importance.

Qualitative and quantitative determination of trace aldehydes and ketones in food preservative propionic acid for quality improvement

Aiming at the difficulty in qualitative and quantitative analysis of trace compositions in food preservative propionic acid, the trace compositions and the key components influencing the total aldehyde content in propionic acid were analyzed by gas chromatography-mass spectrometry (GC-MS), high performance liquid chromatography (HPLC) and gas chromatography (GC) in this paper. The results show that the food preservative propionic acid contains 18 trace compositions. The main compositions affecting the total aldehyde content in propionic acid are acetaldehyde, propionaldehyde, 1-cyclopropyl-1-propanone and 2-methyl-2-pentenal, which account for ∼90% of the total aldehyde content in propionic acid. The total aldehyde content in propionic acid can be quickly determined by iodometric titration. However, the impurity compositions, solution oxygen content and pH value of propionic acid may affect the stability of NaHSO3, which lead to a higher titration value of the aldehyde content. The total aldehyde contents in propionic acid determined by GC (148.535-337.890 mg L-1) and HPLC (157.730-335.780 mg L-1) are close and reliable with a relative deviation of 0.31-3.00%. The volatile low-carbon aldehydes and ketones including formaldehyde, acetaldehyde and acetone have a weak response and a high detection limit in GC. The derivation conditions of all aldehydes and ketones in propionic acid should affect the determination results of HPLC. It provides the basic data for quality improvement and ultra-deep purification of food-grade propionic acid.

ICT based water-soluble fluorescent probe for discriminating mono and dicarbonyl species and analysis in foods

A unique and highly water-soluble ICT-based fluorescent probe is developed for efficient detection and discrimination of reactive monocarbonyl formaldehyde (FA) from dicarbonyl methylglyoxal (MGO)/glyoxal (GO) by modulating the ICT process, which was confirmed by photophysical and TD-DFT analysis. The probe is applied in cellular imaging and quantifying FA in preserved food and MGO in manuka honey.

Name reactions: strategies in the design of chemodosimeters for analyte detection

The design and synthesis of suitable chemodosimeters for the detection of toxic analytes has become challenging for new researchers nowadays in the molecular recognition field.