On paper synthesis of metal-organic framework as a chemiluminescence enhancer for estimating the total phenolic content of food samples using a smartphone readout

Innovative Fe(IV)-Triggered Chemiluminescence Assay for Rapid and Selective Detection of Total Phenolic Content

Total phenolic content reflecting the overall concentration of phenolics in water is a valuable indicator for evaluating water quality. However, current total phenolic content quantification technologies are unsatisfactory due to their complexity, time-consuming nature, limited reliability, and low selectivity. To overcome these problems, we utilized the high reactivity and selectivity of tetravalent iron (Fe(IV)) toward phenolics to develop a surrogate method for total phenolic content based on the quenching effect of phenolics on the chemiluminescence (CL) produced during the oxidation of naproxen (NAP) by Fe(IV) in the Fe(II)-activated periodate (Fe(II)/PI) process. Experimental results showed a strong linear relationship between the chemiluminescence quenching capacity (CLQC) values and total phenolic content in the Fe(II)/PI-NAP process. The high reactivity and superior selectivity of Fe(IV) toward phenolics enable rapid, highly sensitive, and robust anti-interference quantification of total phenolic content using the developed CL method. The limit of quantitation and limit of detection of the developed CL method for total phenolics determination were 1.34 and 0.40 μM, respectively, expressed as phenol equivalents. Finally, we validated the feasibility of using the CLQC value as a surrogate indicator for total phenolic content in various real water samples. This work introduces a novel method for quantifying total phenolic content by determining the CLQC value of water samples using the Fe(II)/PI-NAP process, offering a promising alternative for controlling the discharge of phenolics.

Advanced electrochemiluminescent approaches for contaminant detection in food matrices using metal-organic framework composites

Metal-organic frameworks (MOFs) are highly valued for their electronic and optical capabilities in food sample analysis. Implementing MOF-based sensors is crucial for public health safety. This review centers on electrochemiluminescence (ECL) MOFs for monitoring food samples, highlighting signal changes from combining MOFs with Ru(bpy)32+, TPrA, nanomaterials, and biomolecules. It systematically reviews the development, mechanisms, signal pathways, and findings related to ECL MOF food sensors. Notably, immobilizing ZIF-8 and various metals with transducers like gold nanoparticles enhances ECL signals, enabling effective monitoring across media types. Moreover, MOFs excel in co-reactant processes, resonance energy transfer, and catalytic redox reactions for detecting analytes in food, presenting opportunities for advanced sensory analysis and the creation of cost-effective, sensitive signal transducers for food safety and quality control.

Present and future of smartphone-coupled chemiluminescence and electrochemiluminescence assays: a mini-review

The convergence of smartphones with chemiluminescence and electrochemiluminescence (CL/ECL) assays marks a transformative leap in the realm of sensing technologies. The traditional CL/ECL assays, known for their high sensitivity and versatility, find extensive applications in medical diagnostics, environmental monitoring, food safety, and forensic sciences. However, these techniques have long been constrained due to the requirement of expensive instrumentation and complex reagent handling and hence their accessibility within certain environments is limited. In an era where rapid, accurate, and routine analysis is critical, smartphone-enabled CL/ECL systems offer substantial advantages over conventional analytical methods. By leveraging the universal accessibility and technological sophistication of smartphones and combining them with CL/ECL-based sensing, the smartphone has evolved into a cost-efficient and accessible analytical platform. The ability of the combined platform to conduct on-site analysis in real-time with minimal effort has emerged as a game-changer, particularly in low-resource settings. This mini-review explores the rapid evolution of smartphone-coupled CL/ECL systems over the last five years. The article covers the areas where the combined platform has been implemented in recent years for various sensing applications. The review further identifies key challenges that are associated with such combined platforms and finally highlights the future perspectives of the present topic.

Smartphones as a platform for molecular analysis: concepts, methods, devices and future potential

Over the past 15 years, smartphones have had a transformative effect on everyday life. These devices also have the potential to transform molecular analysis over the next 15 years. The cameras of a smartphone, and its many additional onboard features, support optical detection and other aspects of engineering an analytical device. This article reviews the development of smartphones as platforms for portable chemical and biological analysis. It is equal parts conceptual overview, technical tutorial, critical summary of the state of the art, and outlook on how to advance smartphones as a tool for analysis. It further discusses the motivations for adopting smartphones as a portable platform, summarizes their enabling features and relevant optical detection methods, then highlights complementary technologies and materials such as 3D printing, microfluidics, optoelectronics, microelectronics, and nanoparticles. The broad scope of research and key advances from the past 7 years are reviewed as a prelude to a perspective on the challenges and opportunities for translating smartphone-based lab-on-a-chip devices from prototypes to authentic applications in health, food and water safety, environmental monitoring, and beyond. The convergence of smartphones with smart assays and smart apps powered by machine learning and artificial intelligence holds immense promise for realizing a future for molecular analysis that is powerful, versatile, democratized, and no longer just the stuff of science fiction.

Hydrogen peroxide stabilization with silica xerogel for paper-based analytical devices and its application to phenolic compounds determination

BACKGROUND

Hydrogen peroxide is a key reagent in many analytical assays. At the same time, it is rather unstable and prone to evaporation. For these reasons, its application in sensors requiring reagents in solid state, for example in paper-based microfluidics, is hindered. Usually in paper-based analytical devices reagents are stored in a dried form within paper matrix until the device is used. This approach is not feasible in case of hydrogen peroxide. Here, hydrogen peroxide stabilization on paper with the aid of silica xerogel was studied and optimized to create long-term stable systems which rapidly deliver hydrogen peroxide.

RESULTS

The variables affecting hydrogen peroxide stability such as gelation time, silica to H2O2 ratio, type of solid support and storage conditions were optimized to find the combination of variables providing stable H2O2 concentration for the longest time possible. Such paper-silica-H2O2 composites allow to maintain steady hydrogen peroxide concentration for at least 27 days in the optimal conditions. Hydrogen peroxide is rapidly released from silica-paper matrix within a few minutes upon contact with water, without any byproducts. The obtained systems were characterized using scanning electron microscopy with energy dispersive spectroscopy and infrared spectroscopy, revealing that silica is present as a thin film covering cellulose fibers. Finally, to test the developed hydrogen peroxide stabilization method in real sensing scenario, a proof-of-concept paper-based sensor was created for phenolic content determination in fruits and wine.

SIGNIFICANCE

The outcome of this research will open new avenues in the development of user-friendly, long-term stable paper-based analytical devices which utilize hydrogen peroxide as one of reagents. Owing to the fact, that silica matrix is insoluble in water, the proposed H2O2 stabilization method is compatible with most detection schemes without the risk of interfering with the assay.

Bifunctional oxidase-peroxidase mimicking Fe-Ce MOF on paper-based analytical devices to intensify luminol chemiluminescence: Application for measuring different sugars with a smartphone readout

This study presents a potent paper-based analytical device (PAD) for quantifying various sugars using an innovative bi-nanozyme made from a 2-dimensional Fe/Ce metal-organic framework (FeCe-BTC). The MOF showed excellent bifunctional peroxidase-oxidase activities, efficiently catalyzing luminol's chemiluminescence (CL) reaction. As a peroxidase-like nanozyme, FeCe-BTC could facilitate the dissociation of hydrogen peroxide (H2O2) into hydroxyl radicals, which then oxidize luminol. Additionally, it was also discovered that when reacting with H2O2, the MOF turns into a mixed-valence MOF, and acts as an oxidase nanozyme. This activity is caused by the generated Ce4+ ions in the structure of MOF that can directly oxidize luminol. The MOF was directly synthesized on the PAD and cascaded with specific natural enzymes to establish simple, rapid, and selective CL sensors for the measurement of different sugars. A cell phone was also used to record light intensities, which were then correlated to the analyte concentration. The designed PAD showed a wide linear range of 0.1-10 mM for glucose, fructose, and sucrose, with detection limits of 0.03, 0.04, and 0.04 mM, respectively. It showed satisfactory results in food and biological samples with recovery values ranging from 95.8 to 102.4 %, which makes it a promising candidate for point-of-care (POC) testing for food control and medicinal purposes.

VS4 Nanodendrites with Narrow Bandgaps in Activating Dissolved Oxygen for Boosted Chemiluminescence and Hemin Detection by Unexpected Quenching

Chemiluminescence (CL)-based analytical methods utilize luminophores that need to be activated with an oxidizing agent to trigger CL emission. Despite its susceptibility to decomposition when exposed to external light or trace metals, hydrogen peroxide (H2O2) has been widely used to develop chemiluminescent methods due to the limited number of suitable alternatives for activating chemiluminescent luminophores. Also, analytical methods based on the well-known luminol/H2O2 CL system have low sensitivity. Dissolved oxygen (DO) is a naturally abundant and environmentally benign alternative oxidant for luminol and other CL luminophores. However, DO alone is inactive and needs an efficient catalyst or a coreaction accelerator for its activation. Because of the narrow bandgap of VS4 (ca. 1.12 eV), it can facilitate fast electron-transfer kinetics with an acceptor molecule such as DO. Here, we introduce vanadium tetrasulfide (VS4) to boost CL for the first time. Under the optimized conditions, VS4 nanodendrite catalyzes the generation of reactive oxygen species by activating DO which subsequently reacts with luminol to generate intense CL. It enhances the CL intensity of luminol/DO by about 10,000 times. Surprisingly, hemin remarkably quenches the generated CL of luminol/DO/VS4 nanodendrites, which is completely opposite to its typical enhancement of luminol CL. Based on the remarkable concentration-dependent quenching of the luminol/DO/VS4 nanodendrite CL by hemin, we have developed a sensitive CL method that can selectively detect hemin in the linear concentration range of 1-250 nM and achieved a limit of detection of 0.11 nM. The practical utility of the developed method was demonstrated by the determination of hemin in a pharmaceutical drug for the treatment of acute intermittent porphyria and in human serum. This study demonstrates that VS4 holds great promise in analytical method development.

An Automated Microfluidic Paper-Based Analytical Device for Chemiluminescence Immunoassay

This paper introduces a high-integrated microfluidic paper-based analytical device (μPAD) that has a reliable and programmable rotary valve and automated injection device. By controlling the rotation of valves, different regions on the μPAD can be connected or disconnected, allowing reagents to be effectively transported to the test zone. In order to address the limitations of traditional chemiluminescent immunoassays (CLIA), which involve expensive equipment and extensive manual operations, we utilize a smartphone to read the results and program each component of the device to automate the detection process. As a proof-of-concept, we conducted the detection of rabbit IgG under optimized experimental conditions (H2O2 concentration at 0.1 M, HRP-conjugated antibody concentration at 150 μg/mL, and plasma treatment time of 4 minutes), achieving a limit of detection of 3.58 pM. Our device combines the multifunctionality of μPAD with the sensitivity and specificity of CLIA, which potentially advances the development of point-of-care testing.

A portable fluorescence detection device based on a smartphone employing carbon nanodots for Mn2+ sensing

The measurement of fluorescence emission for quantitative analysis is typically based on a traditional spectrofluorometer, which limits an onsite detection approach. Thus, an alternative device should be developed for fulfilling this analysis outside of the laboratory. Therefore, a low-cost, portable, and low-energy consumption fluorescence reader-based smartphone device was developed. An ultraviolet light-emitting diodes (UV-LED) was used to construct the fluorescence device-based smartphone as a low-power excitation light source. The smartphone camera was used as a detector for detecting photons from the fluorescence emission process of the fluorescence probe and was connected to a digital image platform. Transparent acrylic with orange and yellow colors was employed as a filter for reducing the interference from light source intensity. The obtained digital image was converted to red, green and blue (RGB) intensity using a custom-designed smartphone application. N,S-doped carbon nanodots (N,S-CDs) were demonstrated to be a good fluorescence indicator for determining trace quantities of Mn2+ in cosmetics. The approach exhibited high selectivity and sensitivity, detecting and quantifying analytes at 1-5 μM concentrations. Furthermore, the method's detection limit of 0.5 μM reflects its capacity to detect trace amounts of a target analyte. Mn2+ in cosmetic products was successfully analyzed using this device with high accuracy comparable with the results from inductively coupled plasma-optical emission spectroscopy (ICP-OES).

BODIPY-labeled aptasensor based on multi-walled carbon nanotubes as the quencher for "off-on" detection of catechin

A low-cost and simple boron-dipyrromethene (BODIPY)-labeled aptasensor (B-aptamer) was designed for rapid, sensitive and turn-on catechin detection. B-aptamer as signal indicator and recognition element initially stacked on the surface of multi-walled carbon nanotubes (MWCNTs) via π-π conjugation, resulting in efficient quenching of the fluorescence of the aptasensor. Upon addition of catechin, catechin was adsorbed to B-aptamer, thereby undergoing a conformational change to form B-aptamer/catechin complex, which prompted the release of the signaling probe from the surface of MWCNTs. Hence, the fluorescence intensity (FL) of the B-aptamer was increasing with the increase of catechin concentrations with the limit of detection (LOD) of 5 ng/mL. Furthermore, the method was used to analyze catechin in food samples with the recovery rate of 92.7-107.1 %. This method provided a proper analysis method for clinical analysis and pharmaceutical quality control.

A Recent Advancement in Food Quality Assessment: Using MOF-Based Sensors: Challenges and Future Aspects

Monitoring food safety is crucial and significantly impacts the ecosystem and human health. To adequately address food safety problems, a collaborative effort needed from government, industry, and consumers. Modern sensing technologies with outstanding performance are needed to meet the growing demands for quick and accurate food safety monitoring. Recently, emerging sensors for regulating food safety have been extensively explored. Along with the development in sensing technology, the metal-organic frameworks (MOF)-based sensors gained more attention due to their excellent sensing, catalytic, and adsorption properties. This review summarizes the current advancements and applications of MOFs-based sensors, including colorimetric, electrochemical, luminescent, surface-enhanced Raman scattering, and electrochemiluminescent sensors. and also focused on the applications of MOF-based sensors for the monitoring of toxins such as heavy metals, pesticide residues, mycotoxins, pathogens, and illegal food additives from food samples. Future trends, as well as current developments in MOF-based materials.

Hg2+ detection and information encryption of new [1+1] lanthanide cluster

The sensing of heavy metal ion and information encryption are two very important research areas. Therefore, developing multi-functional materials capable of sensing heavy metal ions and encrypting information is highly important. In this work, three [1 + 1] lanthanide clusters [Ln(TFBA)3(dmp) (H2O)2]2 (Ln = Tb3+Tb1+1, Eu3+Eu1+1, Gd3+Gd1+1, HTFBA = 2,3,4,5-tetrafluorobenzoic acid, dmp = 4,7-dimethyl-1,10-phenanthroline) were designed and synthesized. Among them, Tb1+1 shows excellent luminescence sensing towards Hg2+ (Ex = 350 nm, Em = 545 nm). Results demonstrates the sensing with high selectivity, strong anti-interference, 20-s response time, high accuracy, excellent linear relationship in 0-20.0 μM, and a very low limit of detection (0.02 ppb). Furthermore, paper strips based on Tb1+1 is fabricated for visual detection of Hg2+ in real samples of tap water, lake water, human urine, and human serum. More interestingly, a new method for confidentiality of information is realized through multi-color anti-counterfeiting patterns with the [1 + 1] lanthanide cluster ink, based on the luminescence "on-off" sensing towards Hg2+.

Combining microfluidic paper-based platform and metal-organic frameworks in a single device for phenolic content assessment in fruits

A microfluidic paper-based device (µPAD) has been combined with metal-organic frameworks (MOFs) for total phenolic compounds (TPC) quantification in fruit samples for the first time. The performance of the µPAD, based upon the vertical flow approach, was enhanced in order to determine the TPC content with high accuracy in fruit samples. The method was based on the traditional Folin-Ciocalteu Index using gallic acid or oenotannin as reference phenolic compounds. This novel design and construction of the device are in agreement with the principles of Green Chemistry avoiding wax technology (lower toxicity). The analytical parameters that affect the colorimetric method (using digital imaging of the colored zone) performance were optimized including design, sample volume, and MOF amount. Then, the analytical features of the developed method were investigated such as dynamic range (1.6-30 mg L^-1), limit of detection (0.5 mg L^-1), and precision (RSD < 9%). Besides, the in-field analysis is achievable with a color stability up to 6 h after the loading process of the sample and storage stability for at least 15 days without performance losses (under vacuum at - 20 °C). Furthermore, the MOF ZIF-8@paper was characterized to study its composition and the successful combination. The feasibility of the proposed method was demonstrated by determining the TPC in 5 fruit samples using oenotannin as reference solute. The accuracy was validated by comparison of the data with the results obtained with the recommended protocol proposed by the International Organisation of Vine and Wine (OIV).

A sensitive colori/fluorimetric nanoprobe for detection of polyphenols using peroxidase-mimic plasma-modified MoO3 nanoparticles

Herein, MoO₃ nanoparticles were synthesized and modified using Argon cold plasma treatment (Ar-MoO₃NPs) for the first time. Various characterization studies were performed using various methods, including SEM, XRD, and FTIR techniques. The catalytic activity of MoO₃NPs before and after modification was investigated using fluorometric and colorimetric experiments. The results indicated that the enzyme-mimic activity of MoO₃NPs increased after plasma-surface modification (1.5 fold). Also, a fluorometric method based on the oxidation of a non-fluorescent terephthalic acid by Ar-MoO₃NPs in the presence of H₂O₂ and the production of a compound with a high emission was designed for polyphenols detection. Quercetin was used as a polyphenol standard for the optimization of the proposed system. Under the optimum conditions, the dynamic ranges of the calibration graphs and the detection limits were calculated for different polyphenols (μmol/L): quercetin (2-232, 12.22), resveratrol (2-270, 61.89), curcumin (39-400, 38.89), gallic acid (2-309, 21.5) and ellagic acid (39-309, 16.25). Also, the precision of the method, which was expressed as RSD%, was in the range of 0.286-1.19%. The proposed system could detect individual polyphenols and total polyphenols in three different fruit extracts (apple, orange, and grapes) with high sensitivity. The obtained total concentrations of polyphenols in real samples were comparable to those calculated by the spectrophotometric method. So, a novel and sensitive optical nanosensor for the detection of polyphenols was reported as an alternative to the routine Folin-Ciocalteu spectrophotometric technique.

Carbon dots-modified paper-based chemiluminescence device for rapid determination of mercury (II) in cosmetics

Herein, a simple and portable paper-based analytical device (PAD) based on the inherent capability of carbon quantum dots (CQDs) to serve as a great emitter for the bis(2,4,6-trichlorophenyl) oxalate (TCPO)-hydrogen peroxide (H₂O₂) chemiluminescence (CL) reaction is introduced for the detection of harmful mercury ions (Hg²⁺ ). The energy is transferred from the unstable reaction intermediate (1,2-dioxetanedione) to CQDs, as acceptors, and an intensive orange-red CL emission is generated at about 600 nm, which is equal to the fluorescence emission wavelength of CQDs. The analytical applicability of this system was examined for the determination of Hg²⁺ . It was observed that Hg²⁺ could significantly quench the produced emission, which can be attributed to the formation of a stable and non-luminescent Hg²⁺ -CQDs complex. Accordingly, a simple and rapid PAD was established for monitoring Hg²⁺ , with a limit of detection (LOD) of 0.04 μg mL^-1 . No interfering effect on the signal was found from other examined cations, indicating the acceptable specificity of the method. The designed assay was appropriately utilized to detect the Hg²⁺ in cosmetic samples with high efficiency. It is characterized by its low-cost, easy-to-use, facile but, accurate, and high selective for the detection of Hg²⁺ ions. Besides, the portability of this probe makes it suitable for on-site screening purposes.

A Three-Reagent “Green” Paper-Based Analytical Device for Solid-Phase Spectrometric and Colorimetric Determination of Dihydroquercetin

Microfluidic paper-based analytical devices (µPADs) represent one of the promising green analytical strategies for low-cost and simple determination of various analytes. The actual task is the development of such devices for quantitation of antioxidants, e.g., flavonoids. In this paper, possibilities of a novel three-reagent µPAD including silver nitrate, 4-nitrophenyldiazonium tetrafluoroborate, and iron(III) chloride as reagents are assessed with respect to the determination of dihydroquercetin. It is shown that all the three reagents produce different colorimetric responses that can be detected by a mini-spectrophotometer–monitor calibrator or by a smartphone. The method is applicable to direct measuring high contents of dihydroquercetin (the linearity range is 0.026–1 mg mL⁻¹, and the limit of detection is 7.7 µg mL⁻¹), which is favorable for many dietary supplements. The analysis of a food supplement was possible with the relative standard deviations of 9–26%, which is satisfactory for quantitative and semiquantitative determinations. It was found that plotting a calibration graph in 3D space of the three reagents’ responses allows us to distinguish dihydroquercetin from its close structural analogue, quercetin.

A red luminescent europium metal organic framework (Eu-MOF) integrated with a paper strip using smartphone visual detection for determination of folic acid in pharmaceutical formulations

Integration of smartphone with visual-based paper strip as a low-cost, fast, and reliable probe for semi-quantitative analysis of folic acid.