Sensitive Fluorescent Sensor Research Articles

Study of the pH effect on the optical and morphological properties of S, N self-doped carbon dots applied as fluorescent anti-counterfeiting ink and pH sensor

The pH value is an important parameter as it is part of several processes, whether environmental or biological. In this report, S, N self-doped carbon dots (CDs) were synthesized by a simple hydrothermal method using cysteine (cys) and citric acid as precursors for a detailed investigation of size, morphological, photoluminescent, and structural changes at different pH values and its use as pH sensor and fluorescent ink. The fluorescence intensity of cys-CDs was dependent on the pH, presenting a linear relationship with pH values in the range of 2.0–9.0. Using spectroscopic techniques, a mechanism for the pH-dependent fluorescence is proposed, based on the aggregation of cys-CDs and also protonation/deprotonation of surface functional groups that change the excited state. The cys-CDs were found to be efficient as fluorescent pH sensors using real samples (distilled water and tap water). Furthermore, the pH changes in cys-CDs can be used for the visual enhancement of anti-counterfeiting technologies. Thus, the results of this study show that cys-CDs can act as an efficient and pH sensitive fluorescent sensor, which can be used to measure the pH value of water samples, due to its high fluorescence intensity, and can be applied successfully as a fluorescent ink.

Stable Co(II)-based coordination polymer as fluorescence sensor for the discriminative sensing of biomarker methylmalonic acid

Three novel Co-based coordination polymers including {[Co(L)(μ3-O)1/3]2}n (1), {[Co(L)(bimb)]}n (2) and {[Co(L)(bimmb)1/2]}n (3) (H2L = 2,6-di(4-carboxylphenyl)-4-(4-(triazol-1-ylphenyl))pyridine), bimb = 1,4-bis(lmidazol) butane, bimmb = 1,4-bis(imidazole-1-ylmethyl)benzene) were successfully prepared under solvothermal conditions and characterized. Single-crystal X-ray diffraction analyses revealed that 1 possesses a 3D architecture composed of a trinuclear cluster [Co3N3(CO2)6(μ3-O)], 2 exhibits a 2D new topological framework with the point symbol (84·122)(8)2, whereas 3 shows a unique six-fold interpenetrated 3D framework with a (63·82·10)2(63)2(8) topology. Impressively, all of them can function as a highly selective and sensitive fluorescent sensor for the biomarker methylmalonic acid (MMA) via fluorescence quenching. The low detection limit, reusability and high anti-interference performance together make 1–3 become promising sensors for the practical detection of MMA. Furthermore, the successful application of MMA detection in urine sample was demonstrated, which may be a potential candidate for the further development of clinical diagnostic tools.

Development of a Low-Cost, Sensitivity-Optimized Fluorescence Sensor for Visible Spectrum Analysis

This paper presents an economically viable, sensitivity-optimized fluorescence sensor for detecting low concentrations of fluorophores in the visible spectrum range. The sensor employs a deep ultraviolet (DUV) 275-nm LED and a dichroic mirror to establish a co-axial optical path for excitation and emission. Instead of utilizing a general-purposed spectrometer optimized for high spectral resolution, the sensor strikes a balance between resolution and sensitivity by using an appropriate aperture size and optimized optical design tailored for the spectral characteristics of fluorophores. The manuscript demonstrates measurements of ppb-level rare earth element (REE) samples containing terbium (Tb), europium (Eu), dysprosium (Dy), and samarium (Sm) in aqueous solutions. Through balanced design that optimizes collection of fluorescence emission without losing spectral information, this work shows the feasibility of developing a low-cost, compact, and highly sensitive fluorescence sensors with improved detection sensitivity when compared to bench-top commercial spectrofluorometers at far higher costs.

A sensitive fluorescence sensor based on a glutathione modified quantum dot for visual detection of copper ions in real samples.

Copper (Cu2+), as a heavy metal, accumulates in the human body to a certain extent, which can induce various diseases and endanger human health. Rapid and sensitive detection of Cu2+ is highly desired. In present work, a glutathione modified quantum dot (GSH-CdTe QDs) was synthesized and applied in a "turn-off" fluorescence probe to detect Cu2+. The fluorescence of GSH-CdTe QDs could be rapidly quenched in the presence of Cu2+ through aggregation-caused quenching (ACQ), resulting from the interaction between the surface functional groups of GSH-CdTe QDs and Cu2+ and the electrostatic attraction. In the range of 20-1100nM, the Cu2+ concentration showed a good linear relationship with the fluorescence decline of the sensor, and the LOD is 10.12nM, which was lower than the U.S. Environmental Protection Agency (EPA) defined limit (20μM). Moreover, aiming to attain visual analysis, colorimetric method was also used for rapidly detecting Cu2+ by capturing the change in fluorescence color. Interestingly, the proposed approach has successfully been applied for the detection of Cu2+ in real samples (i.e., environment water, food and traditional Chinese medicine) with satisfactory results, which provides a promising strategy for the detection of Cu2+ in practical application with the merits of being rapid, simple and sensitive.

Room-temperature synthesis of a covalent organic framework with hydrazine linkages for sensitive fluorescent detecting and renewable removing of copper ions

A hydrazone bonded covalent organic framework (TFPB-DHzDs) was successfully synthesized with acetic acid as the catalyst and acetonitrile as the solvent at room temperature. It was proved that TFPB-DHzDs has good crystallinity and stability, as well as excellent luminescence properties. The solid-state absolute fluorescence quantum yield of TFPB-DHzDs was 6.19%. It is found that copper ions have a specific strong fluorescent quenching effect and can be absorbed by TFPB-DHzDs, which makes it possible for the selective sensing of copper ions. The TFPB-DHzDs COF exhibited excellent ability to determine Cu2+ in aqueous solution ranging from 0.1 to 5 μM with the detection limit of 47.8 nM. Furthermore, TFPB-DHzDs was also proved to be an excellent porous adsorbent for Cu2+ in water matrix and the maximum adsorption capacity is 203 mg g−1. The recycling use of TFPB-DHzDs for detecting and removing of Cu2+ can be easily realized by adding a chelating agent. And it can be recovered and recycled at least six times. This work explores the attractive potential of COF TFPB-DHzDs simultaneously as a sensitive fluorescent sensor and an efficient sorbent material, which broadens the application of COFs in fluorescence sensing, metal removal, and environmental analysis.

Modification of Carbon Dots for Metal‐Ions Detection

AbstractIt is very appealing to develop cheap, highly sensitive and efficient metal ion fluorescence sensors as traditional instrument methods are inherently costly and time‐consuming. Carbon dots (CDs) are widely used for sensing metal ions, attributing to their merits of good biocompatibility, low toxicity, easy surface modification and excellent photostability. This article reviewed the research progress of CDs as metal ion sensors in recent years, and studied their modification methods and detection performances. Finally, the challenges and opportunities of CDs as metal ion sensors were also analyzed. This article is expected to provide inspiration and help for researchers focusing on CDs as metal ion sensors.

Multifunctional Zn(II) Coordination Polymer as Highly Selective Fluorescent Sensor and Adsorbent for Dyes.

A new Zn(II)-based coordination polymer (1) comprising the Schiff base ligand obtained by the condensation of 5-aminosalicylic acid and salicylaldehyde has been synthesized. This newly synthesized compound has been characterized by analytical and spectroscopic methods, and finally, by single-crystal X-ray diffraction technique in this study. The X-ray analysis reveals a distorted tetrahedral environment around the central Zn(II) center. This compound has been used as a sensitive and selective fluorescent sensor for acetone and Ag+ cations. The photoluminescence measurements indicate that in the presence of acetone, the emission intensity of 1 displays quenching at room temperature. However, other organic solvents caused meagre changes in the emission intensity of 1. Additionally, the fluorescence intensity of 1 has been examined in the presence of different ketones viz. cyclohexanone, 4-heptanone, and 5-nonanone, to assess the interaction between the C=O group of the ketones and the molecular framework of 1. Moreover, 1 displays a selective recognition of Ag+ in the aqueous medium by an enhancement in its fluorescence intensity, representing its high sensitivity for the detection of Ag+ ions in a water sample. Additionally, 1 displays the selective adsorption of cationic dyes (methylene blue and rhodamine B). Hence, 1 showcases its potential as an excellent luminescent probe to detect acetone, other ketones, and Ag+ with an exceptional selectivity, and displaying a selective adsorption of cationic dye molecules.

Confined construction of CDs@MIL-101 as reusable and turn-on fluorescence sensor for highly sensitive water detection based on adsorption-solvent synergistic mechanism

Fabrication a reusable and highly sensitive fluorescence sensor in a controllable manner for water detection in solvents and humidity remains a top priority target yet a challenging task. In this work, carbon dots (CDs) are successfully implanted into confined metal–organic framework MIL-101(Cr) cages via “ship in the bottle” strategy and the confined CDs are firstly observed in MIL-101(Cr) cage showing high dispersion and high N content by advanced iDPC STEM technique. The highly selective water capture and sensitive changes of the fluorescence property with solution polarity and hydrogen-bonding donor acidity efficiently enhance the detection sensitivity and realize reusable turn-on detection based on the adsorption-solvent synergistic mechanism. Consequently, CDs@MIL-101 exhibits high sensitivity (detection limit: 0.036% and 0.028% v/v), wide response range (0.04–100% and 0.03–45%) and reusable stability for liquid water detection in acetone and tetrahydrofuran, respectively. Meanwhile, it can also detect gaseous water and the detection range is 23% to 85%. The analysis of real samples confirms the proposed method. Such construction strategy and detection mechanism will offer guidance for optimizing and expanding the detection performance of CDs, which is of great significance in the design and construction of novel multiphase sensors.

Highly efficient ferric ion sensing and high resolution latent fingerprint imaging based on fluorescent silicon quantum dots

Expanding the application of silicon based luminescent materials is a fast-growing interdisciplinary field. Herein, a novel fluorescent bifunctional probe based on silicon quantum dots (SiQDs) for highly sensitive Fe3+ sensing and high-resolution latent fingerprint (LFP) imaging was subtly devised. The SiQD solution was mildly prepared using 3-aminopropyl trimethoxysilane as the silicon source and sodium ascorbate as the reductant, showing green emission at 515 nm under UV irradiation with a quantum yield of 19.8%. As a highly sensitive fluorescent sensor, the SiQD was demonstrated to have a highly selective quenching with Fe3+ in the concentration range of 2–1000 μM with the LOD of 0.086 μM in water. The quenching rate constant and association constant of the SiQDs-Fe3+ complex was calculated to be 1.05 × 1012 mol/s and 6.8 × 103 L/mol, respectively, suggesting a static quenching effect between them. Moreover, to achieve high-resolution LFP imaging, a novel SiO2@SiQDs composite powder was further fabricated. The SiQDs were covalently anchored on the surface of silica nanospheres to conquer aggregation-caused quenching for the high-solid fluorescence. In the demonstration of LFP imaging, this silicon based luminescent composite exhibited high developing sensitivity, high selectivity and high contrast, indicating its practical value as a fingerprint developer at crime scenes.

Fluorescence sensor array of a multiplexing probe with three/four excitations/emissions for rapid and highly sensitive discrimination of foodborne pathogenic bacteria

Development of sensitive, accurate yet simplified fluorescence sensor array is crucial for rapid, multi-bacterial, on-site sensing applications. A fluorescence sensor array based on a multiplexing fluorescence probe (MFP, excitations/emissions with 278 nm/558 nm, 290 nm/364 nm, 362 nm/592 and 616 nm) was constructed. The positive MFP equipped with rich quinoline and pyridine groups can combine with the negative charge groups and electron-rich groups of bacterial surfaces, which causes the symbolic signal response in the sensing channels (four emissions and three excitations). The sensor array displayed sensitive response to bacteria even at a lower level (102 cfu mL−1) and high identification accuracy (100%) for drug-resistant bacteria, inactivated bacteria, and blends of bacteria. Furthermore, the developed sensor array demonstrated a high-throughput bacterial identification (92.1% accuracy) in real samples (pork and milk) with high sensitivity, rapid response, easy-to-operate, and independence of specific recognition elements, which would brighten the development of fluorescence sensor array.

Fluorescent Sensor Based on Magnetic Separation and Strand Displacement Amplification for the Sensitive Detection of Ochratoxin A.

Ochratoxin A (OTA) is a common mycotoxin, and it is a significant threat to human health throughout the food chain. In this study, a sensitive and specific fluorescent sensor based on magnetic separation technology combined with chain displacement amplification was developed for fast and easy detection of OTA in food. The designed strand displacement amplification can improve the sensitivity for the detection, and the magnetic nanomaterials can provide a large surface area, thus enhancing the capture efficiency of the target from the sample. Based on those designs, the experimental results showed that the proposed method displayed excellent performance. The linearity range was 0.5-128.0 ng/mL. The detection limit was 0.125 ng/mL; the relative standard deviations were 3.92-7.71%. Additionally, the developed method was satisfactorily applied to determine OTA in wheat, corn, and red wine samples at three spiked levels (1.0, 8.0, and 64.0 ng/mL). The recoveries ranged from 85.45 to 107.8% for wheat flour, 101.34 to 108.35% for corn flour, and 91.15 to 93.80% for red wine, respectively. Compared with high-performance liquid chromatography, the proposed method showed a lower limit of detection and equal recovery. Hence, the designed method is a potential and good detecting tool for OTA residue analysis in complex matrix samples.

Highly sensitive and selective fluorescence sensor based on zirconia nanotube array films for Cu2+ detection

ZrO2 nanotube array films (ZNA) were prepared by anodisation method, and ZNA was modified with γ-aminopropyltriethoxysilane (APTES) to prepare amino-functionalized ZNA (ZNA-NH2). Through immobilizing Cu2+ ions and RB on ZNA and ZNA-NH2, the detection of Cu2+ ions could be realized by measuring the change of fluorescence intensity of RB, and the effects of APTES and RB concentrations on the detection performances were studied. The results show that the fluorescence detection performances of ZNA-NH2 carrier are significantly better than those of ZNA. The best detection performances for Cu2+ ions are achieved with the RB concentration of 10 mg/L and the APTES concentration of 0.4 M. The minimum detection limit is 0.68 nM (S/N = 3), and the linear range is from 1 × 10−3 to 3 × 102 μM under the optimal experimental conditions. The carriers can be regenerated and reused after being soaked in acetic acid solution. This work can be applied to the detection of Cu2+ ions in real seawater.

Click chemistry in the design of AIEgens for biosensing and bioimaging

AbstractThe development of rapid, selective, and sensitive fluorescent sensors is essential for visualizing and quantifying biological molecules and processes in vitro, ex vitro, and in vivo, which is important for not only fundamental biological studies but the accurate diagnosis of diseases. The emerging field of activity‐based sensing (ABS), a sensing method that utilizes molecular reactivity for analyte detection possesses many advantages including high specificity, sensitivity and accuracy. The aggregation caused quenching phenomenon which occurs in most conventional fluorophores results in reduced labeling efficiency of the target analytes and low photobleaching resistance, therefore limiting the applications of the ABS strategy. In contrast, aggregation induced emission (AIE) active luminogens (AIEgens) provide exceptional molecular frameworks for ABS. Of the many reaction classes utilized in the AIEgen ABS approach, click chemistry has become increasing popular. In this review, the sensing concepts of the ABS approach with AIEgens and the principles of click chemistry are discussed, followed by a systematic summary of the application of specific click chemistry reactions in AIEgen ABS protocols for the detection of an array of target analytes. Furthermore, the utility of click chemistry in the construction of AIEgens for bioimaging will also be showcased throughout the review.

A reliable ratiometric fluorescence sensing of heparin and its antidote based on cationic carbon quantum dots and acid red 87

A reliable, selective, and sensitive ratiometric fluorescence sensor was fabricated for the detection of protamine (PROT) and heparin (HEPR). It is based on a rational combination of Acid Red 87 (AR 87) as an anionic dye and polyethyleneimine modified carbon quantum dots (PEI@CQDs) as cationic fluorescent nanoparticles via electrostatic interaction. Addition of positively charged PROT quenched the negatively charged AR 87 via static quenching; while, the addition of HEPR restored the fluorescence of AR 87 via the formation of PROT-HEPR complex. Simultaneously, the fluorescence emission of PEI@CQDs remained constant. Thus, a ratiometric response (FAR 87/FPEI@CQDs) was linear with the concentration of PROT and HEPR in the range of 0.006–20 µg mL−1 and 0.018–22 µg mL−1 with detection limits (S/N) of 1.7 ng mL−1 and 6.0 ng mL−1, respectively. The analytical sensing platform offers several advantages including good selectivity, low LOD values, low-cost, and fast-response. Importantly, the sensing platform was used to detect PROT and HEPR in human serum and urine samples with satisfactorily recoveries % and RSDs %.

Application of Monoferrocenylsumanenes Derived from Sonogashira Cross-Coupling or Click Chemistry Reactions in Highly Sensitive and Selective Cesium Cation Electrochemical Sensors.

This paper reports the synthesis and characterization of novel monoferrocenylsumanenes obtained by means of the Sonogashira cross-coupling or click chemistry reaction as well as their application in cesium cation electrochemical sensors. A new synthetic protocol based on Sonogashira cross-coupling was developed for the synthesis of monoferrocenylsumanene or ethynylsumanene. The click chemistry reaction was introduced to the sumanene chemistry through the synthesis of 1,2,3-triazole containing monoferrocenylsumanene. The designed synthetic methods for the modification of sumanene at the aromatic position proved to be efficient and proceeded under mild conditions. The synthesized sumanene derivatives were characterized by detailed spectroscopic analyses of the synthesized sumanene derivatives. The supramolecular interactions between cesium cations and the synthesized monoferrocenylsumanenes were spectroscopically and electrochemically investigated. Furthermore, the design of the highly selective and sensitive cesium cation fluorescence and electrochemical sensors comprising the synthesized monoferrocenylsumanenes as receptor compounds was analyzed. The tested cesium cation electrochemical sensors showed excellent limit of detection values in the range of 6.0-9.0 nM. In addition, the interactions between the synthesized monoferrocenylsumanenes and cesium cations were highly selective, which was confirmed by emission spectroscopy, laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS), and cyclic voltammetry.

Highly sensitive colorimetric and fluorescent pH sensor of physiological interest

Highly sensitive colorimetric and fluorescent pH sensor of physiological interest

Fluorescence sensing platform for Cronobacter sakazakii based on the cationic metal-organic frameworks modified upconversion nanoparticles

Cronobacter sakazakii ( C. sakazakii ) is a serious threat to human health. Efficient detection of C. sakazakii is crucial for food safety and the control of foodborne diseases. Here, a fluorescence sensing platform for C. sakazakii was constructed with α-glucosidase and cationic metal-organic framework-functionalized upconversion nanoparticles (UCNPs@MOFs). The anionic α-glucosidase was inhibited by binding to cationic UCNPs@MOFs. The presence of C. sakazakii competitively combined with cationic UCNPs@MOFs and released α-glucosidase into the enzyme substrate solution (para-nitrophenyl-α- d -glucopyranoside) to recover activity, thus triggering fluorescence quenching of cationic UCNPs@MOFs through the product of 4-nitrophenol. In addition, α-glucosidase from C. sakazakii accelerated the formation of 4-nitrophenol, thus improving the fluorescence response of cationic UCNPs@MOFs. This strategy illustrates high sensitivity of the designed platform for C. sakazakii with a wide linear range (1.1×10 2 –1.1 × 10 8 cfu mL −1 ), a low limit of detection (3.2 × 10 1 cfu mL −1 ), and an acceptable recovery value (85.2–111.5%) in real samples (tap water, infant formula powder, and goat milk powder). These results confirm that the proposed fluorescence platform is an ideal candidate tool for the detection of C. sakazakii in microbiological diagnostics. • A highly sensitive and rapid fluorescence sensor for Cronobacter sakazakii was developed. • The advantage of sensor based on the excellent fluorescence of functionalized upconversion nanoparticles probes. • The quenching was mainly arising from the competitive combination of UCNPs probes and the anionic enzyme. • A broad linear range (1.1×10 2 -1.1 × 10 8 cfu mL −1 ) and a high sensitivity (3.2 × 10 1 cfu mL −1 ). • Cronobacter sakazakii in real samples (tap water, infant formula powder and goat milk powder) were successfully detected.

A New Sensitive Fluorescence Sensor and Photocatalyst for Determination and Degradation of Sodium Valproate Using g-C3N4@Fe3O4@CuWO4 Nanocomposite and FCCD Optimization.

In this research, carbon nitride nanocomposite coupled with Fe3O4 and CuWO4 was thermally synthesized and characterized by different techniques, including SEM, TEM, XRD, EDX, and FTIR. Due to sodium valproate's luminescence quenching of this nanocomposite, a reliable, accurate, sensitive, selective, and fast-acting sodium valproate assay was proposed. Optimization of this fluorescent sensor was carried out by the FCCD approach. In the optimum conditions, the plot of sodium valproate concentration versus nanocomposite fluorescence emission showed a linear response (R2 = 0.9918), with a range of 0-0.55µM, the limit of detection (S/N = 3) equal to 0.85nM and limit of qualification equal to 2.82nM. Photocatalytic activity of g-C3N4@Fe3O4@CuWO4 (40%) nanocomposite exhibited a good potency to sodium valproate degradation. Active species of degradation including superoxide radicals, holes, and hydroxyl radicals were investigated using ammonium oxalate, benzoquinone, and 2-propanol to identify the mechanism of photodegradation action. The activity of benzoquinone in the photocatalytic process led to a reduction in the rate of analyte degradation, which indicates the prominent role of superoxide radicals compared to other species in the degradation process. The degradation rate of the analyte using the Fenton reagent was found to be around two times more than in the Fenton reagent-free process. The possible mechanism for the fluorescence sensor and photocatalytic degradation reaction was also discussed.

Fluorimetric Reusable Polymeric Sensor for Hydrogen Sulfide Detection.

In this study, with the help of reactive monomers, crosslinkers, and photoinitiator that detect H2S in various matrices, an H2S sensitive fluorescence sensor polymerizes under ultraviolet (UV) light was developed. To this goal, a polymeric membrane was prepared, and the characterization of the membrane was carried out with Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM) methods. Afterward, appropriate conditions were identified, the excitation wavelength was determined as 370nm, and the emission wavelength was determined as 425nm. It was established that the fluorescence intensity of the prepared polymeric membrane decreased in the presence of H2S. A detailed analysis was executed to determine the sensor's most suitable pH value and time. It was found that the optimum pH was 8.0, and the optimal duration was 15s. It has been calculated that the linear range of the developed method is 2.19 × 10-8- 6.25 × 10-7M, and the detection limit (LOD) is 7.37 × 10-9M. The effect of some possible interfering ions was investigated, and it determined that the sensor had excellent selectivity. In addition, the sensor used to determine H2S can be used at least 100 times. The recovery percentages were 102.1%-103.2%, and 104.6%, using tap water samples. In terms of providing reliable, fast results, high sensitivity, reusable, low cost, and ease of use, the developed fluorimetric sensor, compared to standard methods, has become more advantageous.

Acylhydrazones as sensitive fluorescent sensors for discriminative detection of thorium (IV) from uranyl and lanthanide ions

Thorium, as a radioactive element, is always associated with rare earth in nature. So it is an exacting challenge to recognize thorium ion (Th4+) in the presence of lanthanide ions because of their overlapping ionic radii. Here three simple acylhydrazones (AF, AH and ABr, with the functional group fluorine, hydrogen and bromine, respectively) are explored for Th4+ detection. They all exhibit excellent “turn-on” fluorescence selectivity toward Th4+ among f-block ions in aqueous medium with outstanding anti-interference abilities, where the coexistence of lanthanide and uranyl ions in addition with other ordinary metal ions have negligible effects during Th4+ detection. Interestingly, pH variation from 2 to 11 has no significant influence on the detection. Among the three sensors, AF displays the highest sensitivity to Th4+ and ABr the lowest with the emission wavelengths in the order of λAF-Th < λAH-Th < λABr-Th. The detection limit of AF to Th4+ can reach 29 nM (pH = 2) with a binding constant of 6.64 × 109 M−2. Response mechanism for AF toward Th4+ is proposed based on the results of HR-MS, 1H NMR and FT-IR spectroscopies together with DFT calculations. This work provides important implications on the development of related series of ligands in nuclide ions detection and future separation from lanthanide ions.