Fluorescent and Colorimetric Sensors Based on the Oxidation of o-Phenylenediamine

Multifunctional nanozymatic biosensors: Awareness, regulation and pathogenic bacteria detection

It is estimated that approximately 700,000 fatalities occur annually due to infections attributed to various pathogens, which are capable of dissemination via multiple environmental vectors, including air, water, and soil. Consequently, there is an urgent need to enhance and refine rapid detection technologies for pathogens to prevent and control the spread of associated diseases. This review focuses on applying nanozymes in constructing biosensors, particularly their advancement in detecting pathogenic bacteria. Nanozymes, which are nanomaterials exhibiting enzyme-like activity, combine unique magnetic, optical, and electronic properties with structural diversity. This blend of characteristics makes them highly appealing for use in biocatalytic applications. Moreover, their nanoscale dimensions facilitate effective contact with pathogenic bacteria, leading to efficient detection and antibacterial effects. This article briefly summarizes the development, classification, and strategies for regulating the catalytic activity of nanozymes. It primarily focuses on recent advancements in constructing biosensors that utilize nanozymes as probes for sensitively detecting pathogenic bacteria. The discussion covers the development of various optical and electrochemical biosensors, including colorimetric, fluorescence, surface-enhanced Raman scattering (SERS), and electrochemical methods. These approaches provide a reliable solution for the sensitive detection of pathogenic bacteria. Finally, the challenges and future development directions of nanozymes in pathogen detection are discussed.

Ratiometric fluorescent probes based on fluorogenic reactions of o-phenylenediamine for multiple sensing applications

In recent years, construction of ratiometric fluorescent probes based on the in-situ fluorescence reaction of o-phenylenediamine (OPD) is more convenient, simple and efficient for sensing various targets, which has attracted widespread attention from researchers. However, there is still a lack of systematic summary of its design strategies and applications, which may prevent its further development in this field. In this review, we will focus on the construction and application of ratiometric probes based on the in-situ fluorescence reaction of OPD. In addition, construction strategies of ratiometric fluorescent probes are divided into three main categories according to the different generated fluorescent products via in-situ fluorescence reaction of OPD. The first category of construction ratiometric fluorescent probe is based on the yellow fluorescence product. The second category of construction ratiometric fluorescent probe is based on the blue fluorescence product. The third category of construction ratiometric fluorescent probe is combined blue with yellow fluorescent products mentioned-above. Meanwhile, the multiple applications of the three types ratiometric fluorescent probes are summarized. This will provide us in-depth idea for the multiple-function development of ratiometric fluorescent probes in terms of the in-situ fluorescence reaction of OPD, and promote its research in broader fields in the future.

Polarized Transilluminating Dermoscopy in Diagnosis of Hair Shaft Disorders

BACKGROUND

Polarized transilluminating dermoscopy is a novel technique that can be used to diagnose hair shaft disorders. The technique has been used once to describe the findings of trichothiodystrophy, but its use in other hair shaft disorders has not yet been studied.

OBJECTIVES

To assess the efficacy and utility of polarized transilluminating dermoscopy (PTD) in various hair shaft disorders and describe the observations noted.

METHODS

Six patients with suspected hair shaft disorder were enrolled based on history and clinical examination. Trichogram, trichoscopy, and PTD were performed in all the cases, and the findings were described.

RESULT

PTD enhances the visualization of hair shaft disorders, including pili torti, trichorrhexis nodosa, trichorrhexis invaginata, pili trianguli et canaliculi, and woolly hair. The utilization of the given method in hair analysis represents a significant advancement in the field, offering distinctive insights into the inner structures of hair shafts.

CONCLUSION

In contrast to simple trichoscopy using a polarizing dermatoscope, PTD revealed detailed defects and was confirmatory for the diagnosis of the respective disorder.

Fluorescent polymers for environmental monitoring: Targeting pathogens and metal contaminants with naphthalimide derivatives

Monitoring Hg2+ levels in aqueous environments is crucial to assess the potential methylmercury contamination via bacterial conversion, however, existing methods often require extensive sample treatment and expensive equipment. To mitigate this issue, this study examines the synthesis and application of three naphthalimide-based compounds, with significant fluorescent and solvatochromic behavior (C1, C2, and C3). Compounds C1 and C2 demonstrated a strong affinity for Hg2+ metal ions, with C2 showing selectivity and a strong antibacterial profile, particularly against S. aureus (MIC50 (C2) = 0.01 µg/mL). Moreover, these compounds were incorporated into three polymeric matrices, namely polyvinyl chloride (PVC), poly (methyl methacrylate-co-methacrylic acid) (PMMMA), and Starch, allowing for the development of solid-support sensors/surfaces with a strong antibacterial profile, highlighting the inherent dual-functionality of the compounds. Interestingly, the C2-doped Starch biopolymer detected low concentrations of Hg2+ ions, such as 23 nM in tap water (value within the WHO standards for drinking water), through a rapid spectroscopic evaluation without sample treatment. This biopolymer was generated via a sustainable, green-chemistry-oriented, temperature-dependent water/Starch synthetic route, without the addition of plasticizers and any associated ecotoxicity. The study used sustainable methods for environmental monitoring and antibacterial applications, advancing material science to offer effective, accessible, and eco-friendly solutions for detecting and mitigating mercury pollution and bacterial contaminations, enhancing environmental and health safety.

Reductive carbon dots for reduction, ratiometric fluorescence determination, and intracellular imaging of Au3

Many studies show that ortho-phenylenediamine (OPD) produces an oxidized fluorescent product when exposed to an oxidizing agent that enables the direct or indirect fluorescence detection of a range chemical and biochemical analytes. However, there is no report on this unique optical behavior for other two isomers of phenylenediamine. This study demonstrates that a simple hydrothermal treatment of para-phenylenediamine (PPD) in the presence of sulfuric acid results in the formation of fluorescent N, S-doped carbon dots (CDs) with triple functionalities including the reduction of Au3+ into gold nanoparticles (AuNPs), the stabilization of the produced AuNPs, and the determination of Au3+ concentration through an intrinsic ratiometric fluorescence signal. In the presence of Au3+, the blue emission of CDs at 437 nm quenched, and a green emission at 540 nm emerged. The linear concentration range for the determination of Au3+ was 20 nM-16 µM with a detection limit of 16 nM. Additionally, the dual emissive CDs-AuNPs hybrid probe showed potential for the indirect fluorescence ratiometric determination of cysteine and sulfide ions. The linear concentration range for cysteine and sulfide ions were 0.25-8 μM and 0.1-6 μΜ, with detection limits of 0.095 μM and 0.041 μM, respectively. Accordingly, CDs were applied to detect Au3+ and S2- in real water samples. Moreover, the synthesized CDs showed no cytotoxicity for HeLa cells up to 300 µg mL-1, as determined by the MTT assay. Therefore, their potential for intracellular imaging of Au3+ in living cells was also investigated.

A novel strategy for ratiometric determination of o-phenylenediamine via in-situ fluorogenic reaction and generation of metal nanoparticles

Herein, a novel ratiometric strategy for ultra-sensitive detection of o-phenylenediamine (OPD) was proposed based on combinatorial reactions of in-situ fluorogenic reaction and in-situ formation of red fluorescent dithiothreitol-copper nanoparticles (DTT-CuNPs). Here, Cu2+ is used both as an oxidant and as a precursor. Dehydroascorbic acid (DHAA) is formed via redox reaction of AA and Cu2+. Then, DHAA reacts with OPD to yield blue fluorescent quinoxaline (OXD) with emission peak at 434 nm through in-situ fluorogenic reaction. Red emitting DTT-CuNPs with emission peak at 666 nm is instantly generated due to the coordination reaction between DTT and the residual Cu2+ which is not consumed by AA. The fluorescence intensity (FI) of OXD at 434 nm is closely relied on the concentration of OPD, which can be used as a response signal for OPD detection. Meanwhile, FI of DTT-CuNPs at 666 nm has no significant change, which can be used as a reference signal for OPD detection. Thus, the ratio (F434/F666) of the Cu2+/AA/DTT sensing system is successfully employed to quantify OPD, exhibiting a wide linear range from 0.2 µM to 60 µM, with LOD of 0.09 µM.

A fluorescence-enhanced method specific for furfural determination in Chinese Baijiu based on luminescent carbon dots and direct surface reaction

Detecting the furfural concentration in Baijiu can be used to assess the quality of Baijiu, allowing for the optimization of processing techniques and the enhancement of overall quality. In this paper, a fluorescence-enhanced method based on carbon dots (o-CDs) is developed for the furfural determination in Chinese Baijiu. In an environment full-filled with ·SO4- and ·OH, furfural undergone a direct surface reaction with the ortho-diamino groups at o-CDs. The created furan-based imidazole increased the surface electron density, leading an emission enhancement and color changes from orange to green. Thereby, a linear fluorescence response of o-CDs-TA to furfural is established in water with a detection limit of 30.5 nM. Finally, after ethanol correction it is used to determine furfural in Chinese Baijiu with high precision and reproducibility, providing a new strategy with low-cost and high sensitivity. In particular, the idea of covalently connecting target molecule to the CDs surface via the assistance of free radical opens a new avenue to merge the nanoscale and molecular realms through implementing chemical role into carbon nanostructures.

Overview of the Design and Application of Dual-Signal Immunoassays

Immunoassays have been widely used for the determination of various analytes in the fields of disease diagnosis, food safety, and environmental monitoring. Dual-signal immunoassays are now advanced and integrated detection technologies with excellent self-correction and self-validation capabilities. In this work, we summarize the recent advances in the development of optical and electrochemical dual-signal immunoassays, including colorimetric, fluorescence, surface-enhanced Raman spectroscopy (SERS), electrochemical, electrochemiluminescence, and photoelectrochemical methods. This review particularly emphasizes the working principle of diverse dual-signal immunoassays and the utilization of dual-functional molecules and nanomaterials. It also outlines the challenges and prospects of future research on dual-signal immunoassays.

The Accurate and Exclusive Quantification of Somatic Cells in Raw Milk with an OPD-Cu2+ System-Based Colorimetric Method

The somatic cell count (SCC) refers to the number of somatic cells present in each milliliter of raw milk and serves as a crucial indicator of dairy cow udder health and raw milk quality. Traditional SCC detection methods are often time-consuming, expensive, and susceptible to bacterial interference, rendering them unsuitable for the rapid and unbiased assessment of raw milk quality. Consequently, there is an urgent need for a low-cost, accurate, and user-friendly SCC quantification method. Here, a method based on an OPD-Cu2+ system for SCC quantification was developed. It was found that OPD oxidation signals exhibited a linear correlation with SCC. Following optimization, the detection system was established with a Cu2+ concentration of 25 μM, an OPD concentration of 2 mM, and an incubation time of 15 min. Furthermore, the method demonstrated significant resistance to bacterial interference, though it produced weaker signals in response to bacteria. The somatic cell recovery rate in milk after pretreatment was 88.9%, and SCC was quantified accurately within 45 min, with a linear range of 104-106 cells/mL. In summary, the method developed is cost-effective, straightforward, and facilitates precise somatic cell quantification, offering significant practical value and a new approach for SCC detection in raw milk.

Comprehensive insights into fluorescent probes for the determination nitric oxide for diseases diagnosis

Nitric oxide (NO) plays an important role in multiple physiological processes of the body involved in regulation, such as cardiovascular relaxation, neural homeostasis, and immune regulation, etc. The real-time monitoring of NO is of great significance in the investigation of related disease mechanisms and the evaluation of pharmacodynamics. Fluorescent probes are considered as a highly promising approach for pharmaceutical analysis and bioimaging due to their non-invasive character, real-time detection, and high sensitivity. However, there are still some challenges in the determination of biological nitric oxide with fluorescent probes, such as low anti-interference ability, poor function modifiability, and low organ specificity. Therefore, it would be beneficial to develop a new generation of fluorescent probes for real-time bioimaging of NO in vivo after this systematic summary.

Effect of precipitant on pro-oxidative and antibacterial properties of CeO2 nanoparticles - an experimental study

In this study, the synthesis of pro-oxidative cerium-oxide nanozymes (CeO2 NZs) is reliably performed via the co-precipitation method using ceric ammonium nitrate as a precursor and ammonium carbonate as a precipitating agent. Different samples of CeO2 NZs were prepared by varying the amount of the precipitant. The synthesized NZs were characterized by ultraviolet-visible (UV-vis) spectroscopy, particle size analysis, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and high-resolution transmission electron microscopy (HRTEM) and then checked for their pro-oxidative (peroxidase and oxidase) activity. Furthermore, we studied the NZ kinetics and antibacterial properties of synthesized samples.

High-sensitivity piezoresistive sensors based on cellulose handsheets using origami-inspired corrugated structures

Cellulose-based composites have attracted significant attention in the fabrication and advancement of wearable devices due to their sustainable, degradable, and cost-effective properties. However, achieving a cellulosic sensor with reliable sensory feedback remains challenging owing to the deficiency in reversible microstructures during response processes. In this study, we developed a piezoresistive sensor consisting of nearly pure cellulose handsheets using origami-inspired corrugated structures to achieve durable and sensitive piezoresistive responses. Multi-walled carbon nanotubes (MWCNTs) were used as conducting agents. With the addition of 7 wt% MWCNTs, 36.27 % of the cellulose fiber surface was covered and the conductivity of cellulose handsheets was increased to 8.7 S/m. The obtained conductive cellulose handsheets were transformed into corrugated structures and integrated orthogonally to construct the piezoresistive sensors with reversible electrical paths for electrons. The restorable corrugated structure endowed the sensors with a wide workable pressure range (0-10 kPa), high sensitivity (6.09 kPa-1 in a range of 0-0.92 kPa), fast response time (<280 ms), and good durability (>1000 cycles). Furthermore, the practical applications of the proposed sensors as wearable devices were demonstrated through phonation, real-time sports monitoring, and step pressure tests.

Ce4+/Ce3+ as the switch of AIE-copper nanoclusters for highly selective detection of ascorbic acid in soft drinks

An ultrasimple "turn-on" sensor for indirectly detecting ascorbic acid (AA) was prepared using N-acetyl-L-cysteine stabilized copper nanoclusters (NAC-CuNCs) via the AIE (aggregation-induced emission) effect controlled by Ce4+/Ce3+ redox reaction. This sensor fully utilizes the different properties of Ce4+ and Ce3+. Non-emissive NAC-CuNCs were synthesized by a facile reduction method. NAC-CuNCs easily aggregate in the presence of Ce3+ due to AIE, resulting in fluorescence enhancement. However, this phenomenon cannot be observed in the presence of Ce4+. Ce4+ possesses strong oxidizing ability and produces Ce3+ by reacting with AA via a redox reaction, followed by switching on the luminescence of NAC-CuNCs. Moreover, the fluorescence intensity (FI) of NAC-CuNCs increases with the concentration of AA in the range of 4-60 µM, with the limit of detection (LOD) as low as 0.26 µM. This probe with excellent sensitivity and selectivity was successfully used in the determination of AA in soft drinks.

Functional fluorescent nanomaterials for the detection, diagnosis and control of bacterial infection and biofilm formation: Insight towards mechanistic aspects and advanced applications

Infectious diseases resulting from the high pathogenic potential of several bacteria possesses a major threat to human health and safety. Traditional methods used for screening of these microorganisms face major issues with respect to detection time, selectivity and specificity which may delay treatment for critically ill patients past the optimal time. Thus, a convincing and essential need exists to upgrade the existing methodologies for the fast detection of bacteria. In this context, increasing number of newly emerging nanomaterials (NMs) have been discovered for their effective use and applications in the area of diagnosis in bacterial infections. Recently, functional fluorescent nanomaterials (FNMs) are extensively explored in the field of biomedical research, particularly in developing new diagnostic tools, nanosensors, specific imaging modalities and targeted drug delivery systems for bacterial infection. It is interesting to note that organic fluorophores and fluorescent proteins have played vital role for imaging and sensing technologies for long, however, off lately fluorescent nanomaterials are increasingly replacing these due to the latter's unprecedented fluorescence brightness, stability in the biological environment, high quantum yield along with high sensitivity due to enhanced surface property etc. Again, taking advantage of their photo-excitation property, these can also be used for either photothermal and photodynamic therapy to eradicate bacterial infection and biofilm formation. Here, in this review, we have paid particular attention on summarizing literature reports on FNMs which includes studies detailing fluorescence-based bacterial detection methodologies, antibacterial and antibiofilm applications of the same. It is expected that the present review will attract the attention of the researchers working in this field to develop new engineered FNMs for the comprehensive diagnosis and treatment of bacterial infection and biofilm formation.

Time-resolved fluorescence nanoprobe of acetylcholinesterase based on ZnGeO:Mn luminescence nanorod modified with metal ions

A novel time-resolved fluorescence nanoprobe (PBMO, PLNR-BSA-Mn2+-OPD) is fabricated for the label-free determination of acetylcholinesterase (AChE). The ZnGeO:Mn persistent luminescence nanorod (PLNR) and Mn(II) are, respectively, exploited as the signal molecule and quencher to construct the PBMO nanopobe using bovine serum albumin (BSA) as the surface-modified shell and o-phenylenediamine (OPD) as the reducing agent. In the presence of H2O2, the persistent luminescence of PBMO at 530 nm is enhanced remarkably within 30 s due to the oxidation of Mn(II). H2O2 can react with thiocholine (TCh), which is produced through the enzymatic degradation of acetylcholine (ATCh) by AChE. The PBMO nanoprobe is successfully applied to the determination of AChE in the linear range of 0.08-10 U L-1, with a detection limit of 0.03 U L-1 (3σ/s). The practicability of this PBMO nanoprobe is confirmed by accurately monitoring AChE contents in human serum samples, giving rise to satisfactory spiking recoveries of 96.2-103.6%.

Fluorescent/Colorimetric Dual-Mode Discriminating Gln and Val Enantiomers Based on Carbon Dots

Discrimination and quantification of amino acid (AA) enantiomers are particularly important for diagnosing and treating diseases. Recently, dual-mode probes have gained a lot of research interest because they can catch more detecting information compared with the single-mode probes. Thus, it is of great significance to develop a dual-mode sensor realizing AA enantiomer discrimination conveniently and efficiently. In this work, carbon dot L-TCDs were prepared by N-methyl-1,2-benzenediamine dihydrochloride (OTD) and l-tryptophan. With the assistance of H2O2, L-TCDs show an excellent discrimination performance for enantiomers of glutamine (Gln) and valine (Val) in both fluorescent and colorimetric modes. The fluorescence enantioselectivity of Gln (FD/FL) and Val (FL/FD) is 5.29 and 4.13, respectively, and the colorimetric enantioselectivity of Gln (ID/IL) and Val (IL/ID) is 13.26 and 3.42, individually. The chiral recognition mechanism of L-TCDs was systematically studied. L-TCDs can be etched by H2O2, and the participation of AA enantiomers results in different amounts of the released OTD, which provides fluorescent and colorimetric signals for identifying and quantifying the enantiomers of Gln and Val. This work provides a more convenient and flexible dual-mode sensing strategy for discriminating AA enantiomers, which is expected to be of great value in facile and high-throughput chiral recognition.

Progress in optical sensors-based uric acid detection

The escalating number of patients affected by various diseases, such as gout, attributed to abnormal uric acid (UA) concentrations in body fluids, has underscored the need for rapid, efficient, highly sensitive, and stable UA detection methods and sensors. Optical sensors have garnered significant attention due to their simplicity, cost-effectiveness, and resistance to electromagnetic interference. Notably, research efforts have been directed towards UA on-site detection, enabling daily monitoring at home and facilitating rapid disease screening in the community. This review aims to systematically categorize and provide detailed descriptions of the notable achievements and emerging technologies in UA optical sensors over the past five years. The review highlights the advantages of each sensor while also identifying their limitations in on-site applications. Furthermore, recent progress in instrumentation and the application of UA on-site detection in body fluids is discussed, along with the existing challenges and prospects for future development. The review serves as an informative resource, offering technical insights and promising directions for future research in the design and application of on-site optical sensors for UA detection.

Rhodamine-Anchored Polyacrylamide Hydrogel for Fluorescent Naked-Eye Sensing of Fe3

A fluorescent and colorimetric poly (acrylamide)-based copolymer probe P(AAm-co-RBNCH) has been designed via free radical polymerization of a commercial acrylamide monomer with a rhodamine-functionalized monomer RBNCH. Metal ion selectivity of RBNCH was investigated by fluorescence and colorimetric spectrophotometry. Upon addition of Fe3+, a visual color change from colorless to red and a large fluorescence enhancement were observed for the ring-opening of the rhodamine spirolactam mechanism. The monomer gives a sensitive method for quantitatively detecting Fe3+ in the linear range of 100-200 μM, with a limit of detection as low as 27 nM and exhibiting high selectivity for Fe3+ over 12 other metal ions. The hydrogel sensor was characterized by FTIR, and the effects of RBNCH amount on gel content and swelling properties were explored. According to the recipe of 1.0 mol% RBNCH to the total monomers, the fabricated hydrogel sensor displayed a good swelling property and reversibility performance and has potential for application in the imaging of Fe3+ level in industrial wastewater.

A novel HBI-based ratiometric fluorescent probe for rapid detection of trifluoroborate

A 2-(2'-hydroxyphenyl)benzimidazole (HBI)-based ratiometric fluorescent probe, known as BTEP, was synthesized using 5-bromosalicylaldehyde as the raw material via Sonogashira coupling and condensation reaction. This probe was designed for rapid detection of boron trifluoride solutions and gases. The N and O coordination atoms in the probe undergo a boron difluoride addition with BF3, which affects the process of excited state intramolecular proton transfer (ESIPT) leading to a blue shift of fluorescence emission. Obvious changes in the fluorescence signal can be observed within 60 seconds. The introduction of an acetylene trimethylsilane fragment increases the conjugate plane and is beneficial to improving the selectivity of the probe. The I408/I479 fluorescence ratio of the probe displays a linear relationship with the concentration of BF3 in the range of 5-50 μM, with a detection of limit as low as 69.5 nM. Furthermore, the probe demonstrates specific and selective recognition of BF3 among eight common interference substances. Test strips prepared using BTEP have the capability of real-time naked-eye detection of trace BF3 gas.

Nitrogen-doped Ti3C2 MXene quantum dots as an effective FRET ratio fluorometric probe for sensitive detection of Cu2+ and D-PA

In this work, a ratiometric fluorescence sensing platform was established to detect Cu²⁺ and D-PA (d-penicillamine) based on nitrogen-doped Ti₃C₂ MXene quantum dots (N-MODs) that was prepared via a simple hydrothermal method and exhibited strong fluorescent and photoluminescence performance as well as excellent stability. Since the oxidation reaction between o-phenylenediamine (OPD) and Cu²⁺ induced the formation of 2,3-diaminophenazine (ox-OPD) which not only can emerge an emission peak at 570 nm, but also inhibit the fluorescence intensity of N-MQDs at 450 nm, a ratiometric reverse fluorescence sensor via fluorescence resonance energy transfer (FRET) was designed to sensitively detect Cu²⁺, where N-MQDs acted as energy donor and ox-OPD as energy acceptor. More importantly, another considerably interesting phenomenon was that their catalytic oxidation reaction can be restrained in the presence of D-PA because of the coordination of Cu²⁺ with D-PA, further triggering the obvious changes in ratio fluorescent signal and color, thus a ratiometric fluorescent sensor of determining D-PA was proposed also in this work. After optimizing various conditions, the ratiometric sensing platform showed rather low detection limits for Cu²⁺ (3.0 nM) and D-PA (0.115 μM), coupled with excellent sensitivity and stability.

Colorimetric and Fluorescent Sensing of Copper Ions in Water through o-Phenylenediamine-Derived Carbon Dots

Fluorescent nitrogen and sulfur co-doped carbon dots (NSCDs) were synthesized using a simple one-step hydrothermal method starting from o-phenylenediamine (OPD) and ammonium sulfide. The prepared NSCDs presented a selective dual optical response to Cu(II) in water through the arising of an absorption band at 660 nm and simultaneous fluorescence enhancement at 564 nm. The first effect was attributed to formation of cuprammonium complexes through coordination with amino functional groups of NSCDs. Alternatively, fluorescence enhancement can be explained by the oxidation of residual OPD bound to NSCDs. Both absorbance and fluorescence showed a linear increase with an increase of Cu(II) concentration in the range 1-100 µM, with the lowest detection limit of 100 nM and 1 µM, respectively. NSCDs were successfully incorporated in a hydrogel agarose matrix for easier handling and application to sensing. The formation of cuprammonium complexes was strongly hampered in an agarose matrix while oxidation of OPD was still effective. As a result, color variations could be perceived both under white light and UV light for concentrations as low as 10 µM. Since these color changes were similarly perceived in tap and lake water samples, the present method could be a promising candidate for simple, cost-effective visual monitoring of copper onsite.

Iodine-mediated photoinduced autoinductive tandem chromogenic system for visual colorimetric detection of triacetone triperoxide explosive

A long-standing challenge in colorimetric detection of triacetone triperoxide (TATP) explosive is low sensitivity. We herein developed an iodine-mediated photoinduced auto-inductive tandem chromogenic system to achieve exponential signal amplification. The strategy employs the KI-TATP reaction and photo-induced autocatalytical oxidation of o-phenylenediamine (OPD) that work in tandem. The resulting I₃^- from the KI-TATP reaction oxidizes OPD to yellow 2,3-diaminophenazine (DAP) that is further excited by blue light illumination to produce reactive oxygen species (ROS). The obtained ROS, in turn, promotes the oxidation of OPD to gain more DAP, causing the auto-inductive chromogenic reaction processes. This tandem chromogenic system is applied for visual colorimetric detection of TATP, allowing the selective and sensitive detection of TATP down to 42.8 μM. Moreover, analyses of TATP in real samples are performed, and the satisfactory recovery results are achieved. Furthermore, a field detection kit is also developed.

Facile synthesis of single-crystalline MnO2 nanowire arrays with high photothermal catalytic activity

A simple process has been developed to form single-crystalline β-MnO₂ nanowire arrays (NWAs) with a large surface area of 125 m² g^-1 on a glass plate working as a highly active three dimensional (3D) photothermal catalyst under the illumination of near infrared light due to the efficient light harvesting and heat confinement near the reaction field in addition to the large surface area.

In situ reaction-based ratiometric fluorescent assay for alkaline phosphatase activity and bioimaging

Alkaline phosphatase (ALP) is an important biomarker, it is of great significance to develop a sensitive and efficient analytical method for ALP. In this study, an in situ reaction based ratiometric fluorescence assay for ALP was proposed. l-ascorbic acid-2-phosphate (AA2P) was used as a substrate for ALP, and Cu²⁺/o-phenylenediamine (OPD) were involved in this system. Cu²⁺ can oxidize OPD to 2,3-diaminophenazine (OPDox) with an emission centered at 566 nm. The presence of ALP can catalyze the hydrolysis of AA2P to ascorbic acid (AA), which will inhibit the production of OPDox and reduce the corresponding fluorescence intensity, and AA will react with OPD to generate 3-(dihydroxyethyl)furan[3,4-b]quinoxalin-1-one (DFQ) with an emission peak at 447 nm. The fluorescence ratio of F447/F566 has a linear relationship with ALP activity. The proposed method is highly sensitive, finely selective, cost efficiency and easy to operate, it exhibits good linearity in the range of 0.5-22 and 22-40 mU·mL^-1, with a detection limit as low as 0.06 mU·mL^-1. The excellent applicability of this strategy in human serum samples and MCF-7 cells imaging suggests that this method has promising prospects for biomedical research.

A "turn-on" ESIPT fluorescence probe of 2-(aminocarbonyl)phenylboronic acid for the selective detection of Cu(ii)

Herein, we report a highly selective fluorescent probe for the detection of Cu(ii). The detection mechanism relies on the Cu(ii)-catalyzed oxidative hydroxylation of 2-(aminocarbonyl)phenylboronic acid into salicylamide, thus recovering the excited-state intramolecular proton transfer (ESIPT) effect and inducing more than 35-fold fluorescence enhancement. The simple structure and readily available fluorescent probe give a novel method for quantitatively detecting Cu(ii) in the linear range of 0-22 μM, with a limit of detection down to 68 nM, and exhibiting high selectivity for Cu(ii) over 16 other metal ions.

Fluorescence "Turn-Off" and Colorimetric Sensor for Fe2+, Fe3+, and Cu2+ Ions Based on a 2,5,7-Triarylimidazopyridine Scaffold

Two cyanoimidazopyridine-based sensors (SS1 and SS2) were explored for the colorimetric and fluorometric detection of Fe2+, Fe3+, and Cu2+ ions in the semi-aqueous medium. The "turn-off" fluorescence response of both sensors to these ions was due to the restriction in internal charge transfer. Job's plot and semi-empirical calculations revealed that SS1 and SS2 complexed with Cu2+ ions in a 1:1 ratio and Fe2+/3+ ions in a 2:1 ratio, respectively. The sensors were found to have high binding constant (K a) values and low detection limit values. FMO analysis using the semi-empirical quantum mechanics method revealed the decrease in energy gap after complexation with metal ions. Sensor-coated filter paper strips were prepared and analyzed, where the color changes in the strips could be utilized for the real-time detection of Fe2+, Fe3+, and Cu2+ ions.

Tuning the Sensing Properties of N and S Co-Doped Carbon Dots for Colorimetric Detection of Copper and Cobalt in Water

In this study, nitrogen and sulfur co-doped carbon dots (NS-CDs) were investigated for the detection of heavy metals in water through absorption-based colorimetric response. NS-CDs were synthesized by a simple one-pot hydrothermal method and characterized by TEM, STEM-coupled with energy dispersive X-ray analysis, NMR, and IR spectroscopy. Addition of Cu(II) ions to NS-CD aqueous solutions gave origin to a distinct absorption band at 660 nm which was attributed to the formation of cuprammonium complexes through coordination with amino functional groups of NS-CDs. Absorbance increased linearly with Cu(II) concentration in the range 1–100 µM and enabled a limit of detection of 200 nM. No response was observed with the other tested metals, including Fe(III) which, however, appreciably decreased sensitivity to copper. Increase of pH of the NS-CD solution up to 9.5 greatly reduced this interference effect and enhanced the response to Cu(II), thus confirming the different nature of the two interactions. In addition, a concurrent response to Co(II) appeared in a different spectral region, thus suggesting the possibility of dual-species multiple sensitivity. The present method neither requires any other reagents nor any previous assay treatment and thus can be a promising candidate for low-cost monitoring of copper onsite and by unskilled personnel.

Label-free colorimetric detection of glutathione by autocatalytic oxidation of o-phenylenediamine based on Au3+ regulation and its application

A label-free, rapid, and highly sensitive colorimetric assay for the detection of glutathione (GSH) was developed.

B(C6F5)3-catalyzed three-component tandem reaction to construct novel polycyclic quinone derivatives: synthesis of a carbonate salt chromogenic chemosensor

A series novel polycyclic quinone derivatives were constructed providing a carbonate salt chromogenic chemosensor.