A New Environmentally-Friendly Colorimetric Probe for Formaldehyde Gas Detection under Real Conditions

Research Progress on the Application of Multifunctional Amino Derivative Fluorescent Probes in Food, the Environment, and the Microenvironment

The amino group is regarded as a multifunctional recognition group in fluorescent probes. It is nucleophilic, a strong electron-donating group and is a polar group with active hydrogen. Based on these characteristics, amino-based fluorescent probes combined with various fluorescent precursors have been constructed, with excellent sensing performance and low cytotoxicity. These probes have significant application value in the detection of food, living cells and organisms. Here, the relevant studies on amino fluorescent probes from 2016 to 2024 are systematically reviewed and their molecular design principles, recognition mechanisms and applications are described. These studies included 14 on exogenous and endogenous formaldehyde detection, five that detected polarity changes in the external environment and organelles in vivo, four intracellular mitochondrial and lysosomal viscosity detections, seven physiological environment and intracellular pH detections, seven metal ion detections in biological and environmental systems and four rapid detections of the hypochlorite anion (ClO-) in a variety of physiological processes and cells. The application scope of amino fluorescent probes is constantly expanding at present but, research progress in multiple application fields has not been summarized. This article mainly reviews the latest progress in amino fluorescent probes in the fields of food, the environment and the microenvironment, as well as looking forward to the development prospects of these fluorescent probes. Improving the reactivity of amino recognition groups and visual detection may become hot issues in future research.

Recent Advances in Electrochemical Sensors for Formaldehyde

Formaldehyde, a ubiquitous indoor air pollutant, plays a significant role in various biological processes, posing both environmental and health challenges. This comprehensive review delves into the latest advancements in electrochemical methods for detecting formaldehyde, a compound of growing concern due to its widespread use and potential health hazards. This review underscores the inherent advantages of electrochemical techniques, such as high sensitivity, selectivity, and capability for real-time analysis, making them highly effective for formaldehyde monitoring. We explore the fundamental principles, mechanisms, and diverse methodologies employed in electrochemical formaldehyde detection, highlighting the role of innovative sensing materials and electrodes. Special attention is given to recent developments in nanotechnology and sensor design, which significantly enhance the sensitivity and selectivity of these detection systems. Moreover, this review identifies current challenges and discusses future research directions. Our aim is to encourage ongoing research and innovation in this field, ultimately leading to the development of advanced, practical solutions for formaldehyde detection in various environmental and biological contexts.

Inhalational exposure to formaldehyde, carcinogenic, and non-carcinogenic risk assessment: A systematic review

Formaldehyde is one of the most widely used substances in a variety of industries, although it was classified as a human carcinogen by the International Agency for Research on Cancer (IARC). The present systematic review was conducted to retrieve studies related to occupational exposure to formaldehyde until November 2, 2022. Aims of the study were to identify workplaces exposed to formaldehyde, to investigate the formaldehyde concentrations in various occupations and to evaluate carcinogenic and non-carcinogenic risks caused by respiratory exposure to this chemical among workers. A systematic search was done in Scopus, PubMed and Web of Science databases to find the studies done in this field. In this review, studies that did not meet the criteria specified by Population, Exposure, Comparator, and Outcomes (PECO) approach were excluded. In addition, the inclusion of studies dealing with the biological monitoring of FA in the body and review studies, conference articles, books, and letters to the editors were avoided. The quality of the selected studies was also evaluated using the Joanna Briggs Institute (JBI) checklist for analytic-cross-sectional studies. Finally, 828 studies were found, and after the investigations, 35 articles were included in this study. The results revealed that the highest formaldehyde concentrations were observed in waterpipe cafes (1,620,000 μg/m³) and anatomy and pathology laboratories (4237.5 μg/m³). Carcinogenic and non-carcinogenic risk indicated the potential health effects for employees due to respiratory exposure as acceptable levels of CR = 1.00 × 10^-4 and HQ = 1, respectively were reported to be exceeded in more than 71% and 28.57% of the investigated studies. Therefore, according to the confirmation of formaldehyde's adverse health effects, it is necessary to adopt targeted strategies to reduce or eliminate exposure to this compound from the occupational usage.

The impact of operational factors on degradation of formaldehyde as a human carcinogen using Ag3 PO4 /TiO2 photocatalyst

Background: The International Agency for Research on Cancer (IARC) identified formaldehyde as a carcinogen in 2004, yet formaldehyde is widely used in health care settings and various industries. In recent years, photocatalytic oxidation has been developed as a potential technique for removing pollutants arising from organic chemical agents and consequently promoting the health indices. This study investigated the effect of operational factors in optimizing formaldehyde removal from the air using Ag₃ PO₄ /TiO₂ photocatalyst. Methods: An experimental study was designed to investigate the effect of operational factors on the efficiency of formaldehyde degradation. The variables investigated in this study include pollutant retention time, initial pollutant concentration and relative humidity. Sol-gel method was used to synthesize the nano-composite photocatalyst. An ideal experimental design was carried out based on Box-Behnken design (BBD) with response surface methodology (RSM). The sample size in this study includes all the glasses coated with Ag₃ PO₄ /TiO₂ photocatalyst. Results: The maximum formaldehyde degradation of 32% was obtained at the initial concentration of 2 ppm, 20% relative humidity, and 90 minutes of retention time. Based on the statistical results, the correlation coefficient of the present study for the impact of operational factors on formaldehyde degradation was 0.9635, which means that there is only 3.65% probability of error in the model. Conclusion: The operational factors examined in this study (retention time, relative humidity, and initial formaldehyde concentration) were significantly influential in the degradation efficiency of formaldehyde by the photocatalyst. Due to the high exposure of employees and clients of health and treatment centers to formaldehyde as a carcinogenic substance, the results of this study can be used in ventilation systems to remove environmental pollutants in health care centers and other occupational settings.

Progress in the Study of Optical Probes for the Detection of Formaldehyde

Formaldehyde, one of the simplest reactive carbonyl substances, is involved in many physiological and pathological processes in living organisms. There is a large amount of data showing that abnormal elevation of formaldehyde is associated with a variety of diseases in the body, such as neurodegenerative diseases, Alzheimer's disease, cardiovascular diseases and cancer, and is also a representative carcinogen, so monitoring formaldehyde is of great importance for disease diagnosis and treatment. In this review, In this paper, we summarize and classify the last ten years of probes for the detection of formaldehyde according to different reaction mechanisms and discuss the structures and applications of the probes. Finally, we briefly describe the challenges and possible solutions in this field. We believe that more new probes provide powerful tools to study the function of formaldehyde in living systems.

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.

The exposure to formaldehyde in industries and health care centers: A systematic review and probabilistic health risk assessment

Formaldehyde is classified as a definitive human carcinogen by the International Agency for Research on Cancer (IARC). The workers in several industries such as foundry, melamine, resin, and health care centers (pathology and anatomy laboratories and operating rooms) are exposed to airborne formaldehyde. In this systematic review, studies conducted from 2000 to 2020 on occupational exposure to airborne formaldehyde in Iran were collected and analyzed. The carcinogenic and non-carcinogenic risk assessments of exposure to airborne formaldehyde were estimated using the recommended United State Environmental Protection Agency (USEPA) method by Monte-Carlo simulation. Results demonstrated that in both health care centers and industrial settings, mean concentrations of airborne formaldehyde were higher than that 8- hour time-weighted average threshold limit value (TWA-TLV) recommended by the American Conference of Governmental Industrial Hygienists (ACGIH). Also, results showed that cancer and non-cancer risks due to exposure to airborne formaldehyde (Neurological, dermal, respiratory effects and so on) were considerable in both industrial settings and health care settings. The results of this study could be used by health policy makers to eliminate or reduce exposure to airborne formaldehyde in workplaces.

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.

Old silver mirror in qualitative analysis with new shoots in quantification: Nitrogen-doped carbon dots (N-CDs) as fluorescent probes for "off-on" sensing of formalin in food samples

A novel fluorometric assay for selective and sensitive determination of formalin (FA) was developed based on nitrogen-doped carbon dots (N-CDs) coupled with silver mirror reaction. N-CDs was synthesized using the hydrothermal method with the ethylene glycol and ammonia solution as carbon and nitrogen precursors, respectively. The detection principle was based on "off-on" fluorescence switching. Specifically, the fluorescence signal of N-CDs was first turned off after incorporating the Ag⁺ and Tollens' reagents. Then, in the presence of FA, the Ag⁺ species on the N-CDs surface were reduced to Ag⁰ species and the fluorescence signal of N-CDs was switched back on. The fluorescence intensity due to the N-CDs signal linearly increased with the increasing FA concentrations in the range of 5-100 mg L^-1, with the detection limit of 1.5 mg L^-1. The proposed approach provides rapid, simple, sensitive, and selective detection of FA in various food samples.

PVA-SM microstructure enhanced ratiometric fluorescence probe for formaldehyde detection in solution and gas

Formaldehyde (FA) is one of the most common pollutants, which has tremendous harm to humans and environment. In this work, 4-amino-3-pentene-2-one (Fluoral-p) and SiO₂ coated quantum dot (QD@SiO₂) were combined to implement a new ratiometric fluorescence probe QD@SiO₂-Fluoral-p for FA detection. In addition, by utilization of polyvinyl alcohol (PVA) and SiO₂ microsphere (SM), a kind of PVA-SM microstructure was assembled with QD@SiO₂-Fluoral-p to composite a signal enhanced sensing film. The QD@SiO₂-Fluoral-p exhibited good response to 0-400 mg/L FA solution and an enhancement around 15 folds was realized after introducing PVA-SM. In both situations, the probe showed linear relationship to FA concentration (C_FA), with detection limits of 14 and 0.5 mg/L, respectively. Also, the sensing film showed a good linear response to FA gas in the range of 0 to 2 ppm, with a detection limit 0.03 ppm. As a result, the PVA-SM enhanced ratiometric fluorescence probe features high sensitivity, low detection limit, good selectivity, as well as portable, which can serve as a useful tool for investigating FA in solution and gas at room temperature.

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

Formaldehyde, a highly reactive carbonyl species, has been widely used in day-to-day life owing to its numerous applications in essential commodities, etc.; the extrusion of formaldehyde from these sources basically leads to increased formaldehyde levels in the environment. Additionally, formaldehyde is endogenously produced in the human body via several biological processes. Considering the adverse effects of formaldehyde, it is highly important to develop an efficient and reliable method for monitoring formaldehyde in environmental and biological samples. Several chemodosimeters (reaction-based sensing probes) have been designed and synthesized to selectively detect the presence of formaldehyde utilizing the photophysical properties of molecules. In this review, we have comprehensively discussed the recent advances in the design principles and sensing mechanisms of developed probes and their biological/environmental applications in selective formaldehyde detection and imaging endogenous formaldehyde in cells. We have summarized the literature based on three different categories: (i) the Schiff base reaction, (ii) the 2-aza-Cope sigmatropic rearrangement reaction and (iii) miscellaneous approaches. In all cases, reactions are accompanied by changes in color and/or emission that can be detected by the naked eye.

A non-enzymatic electrochemical biosensor for the detection of formalin levels in fishes: Realization of a novel comparator effect based on electrolyte

Formalin has been used as the preservative of fishes in the concentration range of 15-25 mgL^-1. However, there have been a high frequency of violations in the optimum use of formalin levels. The consumption of fishes treated with excessive formalin levels leads to nasopharynx, leukaemia and sinonasal cancer and there is a huge demand for the development of formalin sensor. Conventional formalin sensors such as chromogenic and mass balance sensors fall short in real-time analysis due to the lack of specificity and sensitivity in the interference medium. In this context, it has been emphasized to develop a non-enzymatic electrochemical biosensor with microwave synthesized CdS nanoparticles as a nanointerface owing to its surface limited kinetics. NaCl of 1 mM was considered as an electrolyte solution in the present study. Dynamic sensing characteristics with varying formalin levels of 5-50 mgL^-1 was studied in three different concentration ranges as 5-15 mgL^-1 (concentration of formalin < NaCl; conversion of formalin to formic acid), 20-30 mgL^-1 (concentration of formalin ∼ NaCl; equilibrium between the oxidative and reductive product), 35-50 mgL^-1 (concentration of formalin > NaCl; complete oxidation of formic acid to CO₂). Hence, with the exhibition of such a dynamic sensitivity based on electrolyte, the developed biosensor acts as an electrochemical comparator showcasing a switch-like behaviour in detecting formalin levels. The threshold concentration of formalin required for the comparator effect was found to be 14.845 mgL^-1. The developed biosensor, most essentially, exhibited a versatility in quantifying formalin levels in real-time fish samples.

Surface Plasmon-Enhanced Optical Formaldehyde Sensor Based on CdSe@ZnS Quantum Dots

For the first time, a reproducible surface plasmon-enhanced optical sensor for the detection of gaseous formaldehyde was proposed, which was fabricated by depositing a mixture of CdSe@ZnS quantum dots (QDs), fumed silica (FS), and gold nanoparticles (GNs) on the surface of a silica sphere array to meet the urgent requirement of a rapid, sensitive, and highly convenient formaldehyde detection method. Because of the spectral overlap between QDs and GNs, plasmon-enhanced fluorescence was observed in the film of QDs/FS/GNs. When exposed to formaldehyde molecules, the enhanced fluorescence was quenched linearly with the increase of formaldehyde concentration in the range of 0.5-2.0 ppm. The reason is attributed to the nonradiative electron transfer from QDs to the carbonyl of formaldehyde molecules with the assistance of amino groups. Our results demonstrate that the designed sensors are capable of detecting ultralow concentration gaseous formaldehyde at room temperature with a fast response-recovery time and excellent selectivity, stability, and reproducibility. This work provides a simple and low-cost approach for optical formaldehyde sensor fabrication and shows promising applications in environmental detection.

Synthesis of Nano-Praseodymium Oxide for Cataluminescence Sensing of Acetophenone in Exhaled Breath

In this work, we successfully developed a novel and sensitive gas sensor for the determination of trace acetophenone based on its cataluminescence (CTL) emission on the surface of nano-praseodymium oxide (nano-Pr₆O₁₁). The effects of working conditions such as temperature, flow rate, and detecting wavelength on the CTL sensing were investigated in detail. Under the optimized conditions, the sensor exhibited linear response to the acetophenone in the range of 15-280 mg/m³ (2.8-52 ppm), with a correlation coefficient (R²) of 0.9968 and a limit of detection (S/N = 3) of 4 mg/m³ (0.7 ppm). The selectivity of the sensor was also investigated, no or weak response to other compounds, such as alcohols (methanol, ethanol, n-propanol, iso-propanol, n-butanol), aldehyde (formaldehyde and acetaldehyde), benzenes (toluene, o-xylene, m-xylene, p-xylene), n-pentane, ethyl acetate, ammonia, carbon monoxide, carbon dioxide. Finally, the present sensor was applied to the determination of acetophenone in human exhaled breath samples. The results showed that the sensor has promising application in clinical breath analysis.

Resorcinol Functionalized Gold Nanoparticles for Formaldehyde Colorimetric Detection

Gold nanoparticles functionalized with resorcinol moieties have been prepared and used for detecting formaldehyde both in solution and gas phases. The detection mechanism is based on the color change of the probe upon the aggregation of the nanoparticles induced by the polymerization of the resorcinol moieties in the presence of formaldehyde. A limit of detection of 0.5 ppm in solution has been determined. The probe can be deployed for the detection of formaldehyde emissions from composite wood boards.