Photoelectrochemical sensor for nitrite determination based on the etching of BiOCl/Zn0.5Cd0.5S.

A rapid photoelectrochemical (PEC) sensor was constructed for nitrite detection in food based on the one-step chemical etching strategy of BiOCl/Zn0.5Cd0.5S (BOC/ZCS) nanocomposites by nitrite. BOC/ZCS heterojunction was prepared by a simple coprecipitation method, and it was found that BOC/ZCS showed significant photoelectrochemical (PEC) activity. The results of this study confirmed that the decrease in the photocurrent of the sensor was linked to the etching of ZCS by nitrite under acidic conditions. Under optimized conditions, the BOC/ZCS-based PEC sensor showed good analytical properties for detecting nitrite, with linear ranges of 1-100 µM and 100-600 µM. The detection limit of the sensor was 0.41 µM (S/N = 3). Excellent repeatability, reproducibility, low background noise, and immunity to interference were demonstrated using the proposed system, and satisfactory results were achieved for the nitrite assay using real samples. These results demonstrate a new method for nitrite detection developed using the proposed PEC sensor.

A novel electrochemical sensor with NiSx@MoS2 composite for efficient NO2- sensing.

Excess nitrites are potentially threatening to human health, so it is urgent to develop accurate and sensitive methods. The development of sensors can provide early warning of possible hazards and alert people to protect public health. This work presents an NiSx@MoS2-composite with excellent electrochemical activity, representing a key finding for highly sensitive NO2- detection and sensor development. With the assistance of NiSx@MoS2, this electrochemical sensor has excellent quantitative detection performance. It has a wide detection range (0.0001-0.0020 mg/mL) and a low detection limit (1.863*10-5 mg/mL) for NO2-. This electrochemical sensor maintains excellent specificity among numerous interferences, and it completes the accurate detection of different real food samples. Pleasingly, the electrochemical sensor has satisfactory repeatability stability, and potential for practical applications. It would demonstrate tremendous potential in scientific dietary guidance, food safety detection and other fields.

Multifunctional MOF: Cold/hot adapted sustainable oxidase-like MOF nanozyme with ratiometric and color tonality for nitrite ions detection.

Integrating multiple functionalities into a single entity is highly important, especially when a broad spectrum of application is required. In the present work, we synthesized a novel manganese-based MOF (denoted as UoZ-6) that functions as a cold/hot-adapted and recyclable oxidase nanozyme (Km 0.085 mM) further developed for ratiometric-based colorimetric and color tonality visual-mode detection of nitrite in water and food. Nitrite ions promote the diazotization process of the oxTMB product, resulting in a decay in the absorbance signal at 652 nm and the emergence of a new signal at 461 nm. The dual-absorbance ratiometric platform for nitrite ion detection functions effectively across a wide temperature range (0 °C to 100 °C), offering a linear detection range of 5-45 µM with a detection limit of 0.15 µM using visual-mode. This approach is sensitive, reliable, and selective, making it effective for detecting nitrite ions in processed meat and water.

Recent advances in electrochemical approaches for detection of nitrite in food samples.

Nitrite is a common ingredient in the industry and agriculture; it is everywhere, like water, food, and surroundings. Recently, several approaches have been developed to measure the nitrite levels. So, this review was presented as a summary of many approaches utilized to detect the nitrite. Furthermore, the types of information that may be acquired using these methodologies, including optic and electrical signals, were discussed. In electrical signal methods, electrochemical sensors are usually developed using different materials, including carbon, polymers, oxides, and hydroxides. At the same time, optic signals receiving techniques involve utilizing fluorescence chromatography, absorption, and spectrometry instruments. Furthermore, these methodologies' benefits, drawbacks, and restrictions are examined. Lastly, due to the efficiency and fast means of electrochemical detectors, it was suggested that they can be used for detecting nitrite in food safety. Futuristic advancements in the techniques used for nitrite determination are subsequently outlined.

Multi-deformable interpenetrating network thermosensitive hydrogel fluorescent device for real-time and visual detection of nitrite.

Functionalized thermosensitive hydrogel materials exhibit excellent properties for the fabrication of sensing devices that enable real-time visual detection of food safety duo to their good plasticity and powerful loading capacity. Here, a ratiometric fluorescent device based on an interpenetrating network (IPN) thermosensitive hydrogel was designed to embed functionalized Au nanoclusters (Au NCs) and Blue Carbon dots (BCDs) composites in a multi-network structure to build a sensitive hazardous material nitrite (NO2-) chemsensor. The hydrogel was utilized poloxamer 407 (P407), lignin and cellulose to form stable IPN structure, which resulted in complementation and synergy, thereby strengthening its porous network structure. The combination of fluorescent nanoprobes with the porous network structure has the potential to enhance stable fluorescence signals and improve sensing sensitivity. Moreover, the thermosensitive liquid-solid transition characteristics of the hydrogel facilitate its preparation into diverse sensing devices following curing at room temperature. The hydrogel device, when combined with a smartphone system, converted image information into data information, thereby enabling the accurate quantification of NO2- with a detection limit of 9.38 nM in 2 s. The designed multi-functional hydrogel device is capable of real-time differentiation of NO2- dosage with the naked eye, offering a high-contrast, rapid-response sensing methodology for visual assessment of food freshness. This research contributes to the expansion of hydrogel materials applications and the detection of hazardous materials in food safety.

Conditionally restricted detection of nitrite under acidic conditions by activatable fluorescent probes.

As a commonly used food additive, excessive nitrite intake seriously affects people's health in daily life. As the stomach is the main organ involved in nitrite intake, achieving fast and in situ detection of nitrite in the stomach is of great significance for avoiding the hazards caused by nitrite. However, owing to the poor stability or low sensitivity of existing fluorescent probes under acidic conditions, their application for nitrite detection within the stomach remains challenging. To solve this problem, we developed novel probes specifically designed to maintain stability and demonstrate high sensitivity to nitrite under acidic conditions. Utilizing the optimized probe (DHUROS-11), nitrite levels in environmental and real samples were successfully quantified. Notably, tracing of nitrite within the stomach of mice in real time was realized by using DHUROS-11 as the probe.

An acid-free sensing strategy for detecting nitrite using dihydroquinoline-8-carboxylate as a probe.

Nitrite (NO2-) has been identified as a typical pollutant harmful to the human body and heavily assayed in the fields of food safety and water quality control. The mainstream sensing strategies for detecting NO2- depend on Griess reaction or its improved methods which employ Griess reaction to initiate further inter-or intramolecular interaction to generate readout signals. However, a significant drawback of these methods is the use of strongly acidic media. In this study, we designed and synthesized a new NO2--specific fluorescent probe (ethyl 3-cyano-2-hydroxy-5-imino-8-(3-methoxy-3-oxopropyl)-4-(pyridin-2-yl)-5,8-dihydroquinoline-8-carboxylate, DHQC). DHQC exhibited strong green fluorescence in an acetonitrile-PBS (10 mM) mixed system (pH 7.0). In the neutral medium and at room temperature, the fluorescence of DHQC changed from green to blue with the addition of NO2-. The preliminary mechanistic investigation reveals that NO2- can induce the decarboxylation of the probe DHQC. Based on this finding, a high sensitive and selective method for NO2--detection was established, which showed good linearity in a range of 5∼50 µM with a limit detection of 3.5 nM (3σ). Given the unique properties of DHQC, a DHQC-loaded hydrogel bead device was further developed and employed for rapid monitoring of NO2-, exhibiting the advantages of simple preparation, high sensitivity, and fast response compared with traditional sensing reagents. In addition, DHQC was also used as a fluorescent probe for cell-imaging in live cells, exhibiting good cell permeability and biocompatibility. This study proposes a potential strategy for constructing smart fluorimetric probes used for NO2- detection.

Intrinsic oxidase-mimicking activity of nitrite upon visible light illumination and its colorimetric detection in saliva.

Small molecules with enzyme-like properties have recently attracted considerable attention. Herein, we discovered that nitrite possesses intrinsic oxidase-mimicking activity upon visible light, catalyzing the oxidation of the typical chromogenic substrate in the absence of H2O2. Notably, nitrite exhibited a markedly high value of Kcat, approximately 4, 7, and 4000-fold greater than that of Acr+-Mes, Eosin Y, and Diacetyl, respectively. Comprehensive investigation elucidated that O2•⁻ and •OH are the primary reactive oxygen species (ROS) responsible for the oxidation of 3,3',5,5'-tetramethylbenzidine dihydrochloride hydrate (TMB). Leveraging the linear correlation between the absorbance of oxidized TMB (oxTMB) at 652 nm and nitrite concentration, a simple colorimetric approach for nitrite detection was successfully established in the range of 1-75 µM with a detection limit of 0.14 µM. Moreover, the proposed strategy could be applied to determine the nitrite concentration in saliva, exhibiting a great prospect for clinical diagnosis. This work contributes novel insights into the exploration of small-molecule enzyme mimics.

Construction of portable hydrogel kits with self-ratio optical bimodal detection and smartphone imaging for on-site nitrite screening.

Accurate on-site detection of nitrite in complex matrices remains a significant challenge. Herin, we construct a self-ratio optical bimodal portable kit via co-assembling NaErF4:0.5%Tm@NaYF4@NaYbF4:0.5%Tm@NaYF4 (Er:Tm@Yb:Tm) and nitrogen-doped carbon platinum nanomaterials (Pt/CN) in sodium alginate (SA) hydrogel. Pt/CN nanomaterials are synthesized by high-temperature sintering using a zinc-based zeolite imidazolium framework as a sacrificial template. The Pt/CN nanozyme possesses excellent oxidase-like activity to produce the oxidation state 3,3',5,5'-tetramethylbenzidine (oxTMB). Nitrite mediates diazotization of oxTMB to trigger the change of absorption signals, accompanying the ratio fluorescence response of the Er:Tm@Yb:Tm. Crucially, Er:Tm@Yb:Tm and Pt/CN are embedded in SA hydrogel to fabricate a portable kit with efficient and sensitive performance. An image processing algorithm is used to analyze the nitrite-induced signal change of the portable hydrogel kit, resulting in detection limits of 0.63 µM. This method has great potential for point-of-care applications due to its reliability, long-term stability, accuracy, sensitivity, and portability.

Folic acid capping Bi3+-doped Ag quantum dots for enzyme-like dual-mode recognition of toxic S2- and visual sensing of NO2.

BACKGROUND: NO2- and S2- are two kinds of common toxic anions widely distributed in environmental water, soil and food products. Human beings have suffered a lot of diseases from intake of excessive NO2- or S2-, i.e., infantile methemoglobin, cancer and even to death. Although tremendous efforts have been afforded to monitor NO2- and S2-, most were high instrument-depended with complex processing procedures. To keep food safety and to protect human health, it will be a huge challenge to develop a convenient and efficient way to monitor S2- and NO2- in practice. RESULTS: A kind of folic acid capping Bi3+-doped Ag quantum dots (FA@Bi3+-Ag QDs) was developed for the first time by one-pot homogeneous reduced self-assembly. Not only did FA@Bi3+-Ag QDs possess intrinsic fluorescent property, it expressed synergistic peroxidase-like activity to catalyze the redox of 3,3',5,5'-tetramethylbenzidine (TMB) and H2O2 with Km/vmax of 0.087 mM/6.61 × 10-8 M s-1 and 6.42 mM/6.25 × 10-7 M s-1 respectively. Interestingly, trace S2- could exclusively alter its fluorescent property and peroxidase-like activity, exhibiting significant hypochromic and "turn-on" fluorescent effects. While trace NO2- could make FA@Bi3+-Ag QDs-TMB-H2O2 system hyperchromic. Under the optimized conditions, FA@Bi3+-Ag QDs were applied for dual-mode recognition of S2- and visual sensing of NO2- in real food samples with satisfactory recoveries, i.e., 100.7-107.9 %/95.8-104.7 % and 97.2-104.8 % respectively. The synergistic enzyme-mimic mechanism of FA@Bi3+-Ag QDs and its selective response mechanisms to S2- and NO2- were also proposed. SIGNIFICANCE: This represents the first nanozyme-based FA@Bi3+-Ag QDs system for dual-mode recognition of S2- and visual sensing of NO2-, well meeting the basic requirement in drinking water set by WHO. It will offer a promising way for multi-mode monitoring of different pollution using the same nanozyme-based sensor.

A high-performance electrochemical sensor based on dendritic Au/Zn modified carbon cloth for the determination of nitrite in aquaculture.

Nitrite is a common nitrogen-containing compound that possesses high biological toxicity, thereby posing a serious threat to aquatic organisms. Therefore, it is imperative to develop a rapid and quantitative determination approach for nitrite. In this study, the aim was to prepare a novel electrochemical sensor to determine nitrite. This was achieved by synthesizing Au/Zn dendritic complexes on a carbon cloth self-supported electrode after plasma treated by a stepwise strategy of electrodeposition and in-situ corrosion. In accordance with the optimal experimental conditions, the electrode exhibited remarkable catalytic activity for the electrooxidation of nitrite ions (pH = 8.0), accompanied by a considerable enhancement in peak anodic current in comparison to the unmodified electrode. The sensor exhibited a wide linear range (1-833 µM, 833-8330 µM), high sensitivity (3506 µA mM-1 cm-2, 538 µA mM-1 cm-2), a low detection limit (0.43 µM), and excellent selectivity, reproducibility, and stability for the determination of nitrite. Furthermore, the prepared sensor was successfully applied to the detection of nitrite in tap water, fish holding pond water and duck pond water, demonstrating good recovery and no significant difference from the spectrophotometric results. The results suggest that the electrochemical sensor developed in this study represents a straightforward yet efficacious approach to the development of advanced portable sensors for aquaculture applications.

Development of a simple and rapid dipstick paper-based test strip for colorimetric determination of nitrate and nitrite in water and foodstuffs.

A rapid user-friendly paper-based test strip using zinc microparticles in conjugation with Griess reagent was developed for nitrite and nitrate detection. Test strips were fabricated using a simple and fast method of step-by-step immersion into reagents so that each strip contained a single detection pad for nitrite detection and another separate pad for nitrate detection. To reduce nitrate to nitrite, zinc microparticles suspended in ethanolic solution of polyvinylpyrrolidone (PVP) were uniformly immobilized on the paper strips that were previously impregnated in the Griess reagent and dried. The Griess reagent components were optimized to reach the highest color intensity. The optimized test strip was able to determine both nitrite and nitrate with respective detection limits of 0.43 and 9.43 mg/kg and a detection time of 60 s. The performance of the new test strips was evaluated for the simultaneous colorimetric detection of nitrite and nitrate in water and different food samples.

Skeletal Muscle, Skin, and Bone as Three Major Nitrate Reservoirs in Mammals: Chemiluminescence and 15N-Tracer Studies in Yorkshire Pigs.

In mammals, nitric oxide (NO) is generated either by the nitric oxide synthase (NOS) enzymes from arginine or by the reduction of nitrate to nitrite by tissue xanthine oxidoreductase (XOR) and the microbiome and further reducing nitrite to NO by XOR or several heme proteins. Previously, we reported that skeletal muscle acts as a large nitrate reservoir in mammals, and this nitrate reservoir is systemically, as well as locally, used to generate nitrite and NO. Here, we report identifying two additional nitrate storage organs-bone and skin. We used bolus of ingested 15N-labeled nitrate to trace its short-term fluxes and distribution among organs. At baseline conditions, the nitrate concentration in femur bone samples was 96 ± 63 nmol/g, scalp skin 56 ± 22 nmol/g, with gluteus muscle at 57 ± 39 nmol/g. In comparison, plasma and liver contained 34 ± 19 nmol/g and 15 ± 5 nmol/g of nitrate, respectively. Three hours after 15N-nitrate ingestion, its concentration significantly increased in all organs, exceeding the baseline levels in plasma, skin, bone, skeletal muscle, and in liver 5-, 2.4-, 2.4-, 2.1-, and 2-fold, respectively. As expected, nitrate reduction into nitrite was highest in liver but also substantial in skin and skeletal muscle, followed by the distribution of 15N-labeled nitrite. We believe that these results underline the major roles played by skeletal muscle, skin, and bone, the three largest organs in mammals, in maintaining NO homeostasis, especially via the nitrate-nitrite-NO pathway.

In Situ Collection and SERS Detection of Nitrite in Exhalations on Facemasks Based on Wettability Differences.

As one of the common carriers of biological information, along with human urine specimens and blood, exhaled breath condensate (EBC) carries reliable and rich information about the body's metabolism to track human physiological normal/abnormal states and environmental exposures. What is more, EBC has gained extensive attention because of the convenient and nondestructive sampling. Facemasks, which act as a physical filter barrier between human exhaled breath and inhaled substances from the external environment, are safe, noninvasive, and economic devices for direct sampling of human exhaled breath and inhaled substances. Inspired by the ability of fog collection of Namib desert beetle, a strategy for in situ collecting and detecting EBC with surface-enhanced Raman scattering is illustrated. Based on the intrinsic and unique wettability differences between the squares and the surrounding area of the pattern on facemasks, the hydrophilic squares can capture exhaled droplets and spontaneously enrich the analytes and silver nanocubes (AgNCs), resulting in good repeatability in situ detection. Using R6G as the probe molecule, the minimal detectable concentration can reach as low as 10-16 M, and the relative standard deviation is less than 7%. This proves that this strategy can achieve high detection sensitivity and high detection repeatability. Meanwhile, this strategy is applicable for portable nitrite analysis in EBC and may provide an inspiration for monitoring other biomarkers in EBC.

Development of an accurate hand-held sensing platform for nitrite detection based on nitrogen-doped carbon dots.

As is well known, excessive nitrite can seriously pollute the environment and can harm human health. Although existing methods can be used to determine nitrite content, they still have some drawbacks, such as relatively complicated operation and expensive equipment. Herein, a hand-held sensing platform (HSP) for NO2- determination was developed. First, ammonia-rich nitrogen-doped carbon dots with orange-yellow emission were designed and synthesised, which were suitable as fluorescent probes because of their good optical properties and stability. Then, the HSP based on fluorescence using photoelectric conversion technology was designed and manufactured using three-dimensional printing technology. Under optimum conditions, the voltage (V/V0) of the proposed HSP showed good linearity for NO2- detection in the range of 10-500 µM, with a detection limit of 1.95 µM. This portable sensor showed good stability, accuracy and reliability in detecting actual water and meat samples, which may ensure food safety in practical applications. Moreover, the HSP is compact, portable and easily assembled and is suitable for on-site real-time detection, which shows great application potential and prospects.

A nanosilica-coated thread-based analytical device for nitrate and nitrite detection in food samples.

A new microfluidic thread-based analytical device (µTAD) for nitrate and nitrite determination in food samples was developed. The cotton thread substrate was coated with nanosilica to increase its hydrophilicity and stability, and polylactic acid was applied to one end of the nanosilica-coated thread to constrain the fluid flow along the thread in one direction. Quantification of nitrate and nitrite was based on the modified Griess reaction, using sulfanilamide and N-(1-naphthyl) ethylenediamine as chromogenic reagents, and utilizing a distance-based detection technique. Linear responses were observed in a range of 4-25 mg L-1 (R2 = 0.9991) for nitrite and a range of 8-50 mg L-1 (R2 = 0.9989) for nitrate. The limits of detection for nitrite and nitrate were 1.5 and 3.1 mg L-1, respectively. The detection time was 5 min for nitrite analysis, and 7 min for nitrate analysis. The new method demonstrated good precision, accuracy, selectivity, and stability. The performance of the proposed µTAD for nitrite and nitrate determination in real food samples was comparable to that of the conventional UV-Vis spectrophotometric method. The proposed µTAD could serve as a simple, low-cost, and portable method for nitrite and nitrate detection in food samples.

Ag nanoisland functionalized hollow carbon nanofibers as a non-invasive, label-free SERS salivary biosensor platform for salivary nitrite detection for pre-diagnosis of oral cancer.

A highly selective, label-free, surface-enhanced Raman spectroscopy (SERS) based sensor platform employing hollow carbon nanofibers functionalized with silver nanoparticles (Ag@HCNFs) has been developed to monitor anomalous concentrations of potential biomarkers, such as salivary nitrite facilitating pre-diagnosis of oral cancer. Co-axial electrospinning was used for the fabrication of the nanofibrous Ag@HCNFs followed by thermal treatment of PAN/PVP core-shell nanofibers and chemical reduction of silver nanoislands. The developed plasmonic Ag@HCNFs was structurally and morphologically characterized using X-Ray diffraction, Raman spectroscopy, scanning electron microscopy, and transmission electron microscopy, which clearly demonstrated the successful anchoring of silver nanoparticles on hollow carbon nanofibers. The properties of Ag@HCNFs showed significant SERS enhancement of the order of 107 with a detection limit of 10-11 M with R6G, demonstrating its efficacy to investigate real-time salivary samples, particularly towards the detection of salivary nitrite within the clinically relevant range (50 µM-300 µM) towards the pre-diagnosis of oral cancer. The proposed SERS-based salivary platform has the potential to be used as a low-cost, non-invasive pre-diagnostic tool for early diagnosis and mass screening of oral cancer.

Cerium vanadate/functionalized carbon nanofiber composite for the electrochemical detection of nitrite.

This study presents a facial and quick electrochemical sensor platform that offers remarkable water and food safety applications. The present work represents a study of the synthesis and characterization for efficient cerium vanadate (CeVO4) with a functionalized carbon nanofiber (f-CNF) decorated electrode, which is a highly effective electrode modifier for sensitive nitrite detection. The CeVO4 nanoparticles were synthesized using the facial hydrothermal technique, and a composite (CeVO4@f-CNF) was prepared using the sonication method. Afterward, the produced materials were confirmed with spectroscopic and microscopic analysis. The electrochemical behavior of nitrite was studied through cyclic voltammetry (CV) and differential pulse voltammetry (DPV). The DPV analysis depicts an excellent linear range of 0.1-1033 µM and a promising detection limit of 0.004 µM for the proposed electrode. The CeVO4@f-CNF electrode was applied to detect nitrite in water and meat samples. The proposed electrochemical sensor attributes the significant results towards the detection of nitrite.

Exploration and detection of nitrosamine impurity nitroso-STG-19 in sitagliptin tablets and API as well as nitrites in excipients by LC-MS/MS methods.

The Food and Drug Administration (FDA) recently reported a new nitrosamine impurity in sitagliptin that was named nitroso-STG-19 (NTTP), whose acceptable intake limit was extremely low at 37 ng per day. In addition, NTTP was found to be a degradation impurity in sitagliptin tablets, which was formed by the reaction of 3-(trifluoromethyl)-5,6,7,8-tetrahydro-[1,2,4]triazolo[4,3-a]pyrazine hydrochloride and nitrite salts introduced via excipients. Consequently, the NTTP content in tablets was larger than that in active pharmaceutical ingredients (APIs). To control the impurity, an ultra-performance liquid chromatography coupled with tandem mass spectrometry (UPLC-MS/MS) procedure for the detection of NTTP in sitagliptin phosphate tablets and APIs was developed and validated. Furthermore, a derivatization method for the detection of nitrite salts at lower concentration was developed to select applicable excipients to decelerate the generation of NTTP. During validation of the analytical procedure for NTTP, the quantitation limit (LOQ) of NTTP was 56 ppb (0.056 ng mL-1), the linear correlation coefficient was 0.9998, and recoveries of NTTP in spiked samples ranged from 95.5% to 105.2%, indicating that the method is rapid, sensitive and accurate for an NTTP test. In the nitrite salt detection method, the LOQ was 0.21 ng mL-1, and recoveries of NTTP in spiked samples ranged from 87.6% to 107.8%, indicating a sensitive and accurate method, suitable for screening appropriate pharmaceutical excipients.

Machine learning trained poly (3,4-ethylenedioxythiophene) functionalized carbon matrix suspended Cu nanoparticles for precise monitoring of nitrite from pickled vegetables.

Precise monitoring of nitrite from real samples has gained significant attention due to its detrimental impact on human health. Herein, we have fabricated poly(3,4-ethylenedioxythiophene) functionalized carbon matrix suspended Cu nanoparticles (PEDOT-C@Cu-NPs) through a facile green synthesis approach. Additionally, we have used machine learning (ML) to optimize experimental parameters such as pH, drying time, and concentrations to predict current of the designed electrochemical sensor. The ML optimized concentration of fabricated C@Cu-NPs was further functionalized by PEDOT (π-electron mediator). The designed PEDOT functionalized C@Cu-NPs (PEDOT-C@Cu-NPs) electrode has shown excellent electro-oxidation capability towards NO2- ions due to highly exposed Cu facets, defects rich graphitic C and high π-electron density. Additionally, the designed material has shown low detection limit (3.91 µM), high sensitivity (0.6372 µA/µM/cm2), and wide linear range (5-580 µM). Additionally, the designed electrode has shown higher electrochemical sensing efficacy against real time monitoring from pickled vegetables extract.