Sensitive Fluorescent Sensor Research Articles

A highly sensitive and selective “off-on” porphyrin-based fluorescent sensor for detection of thiophenol

Thiophenol and its derivatives easily cause damage to aquatic bioorganisms, animals and even human being, therefore, fluorescent probes for detecting thiophenol with sensitive and selective characters are highly popular. In this study, a highly sensitive and selective porphyrin-based fluorescent sensor (M1) was reported for detection of thiophenol based on the steric hindrance effect, where the recognition unit, 7-nitrobenzo[c][1,2,5]oxadiazolyl group is linked to aromatic ortho-position in the porphyrin, and correspondingly the fluorescence of fluorescein is efficiently quenched. Its time of fluorescence response for thiophenol was only 60s, and its fluorescence responses for the other anions/molecules were all far lower than the relative fluorescence ratio values for thiophenol, which means that the porphyrin-based fluorescent sensor is rapid, sensitive and selective to detection of thiophenol. This approach offers some useful insights for designing sensitive and selective fluorescent turn-on sensors in the detection assays for other analytes.

Highly sensitive ratiometric fluorescent paper sensor for the urine assay of cancer

Telomerase, as a valuable biomarker, is an important target in cancer diagnosis. Here, we report a ratiometric fluorescent probe for telomerase activity assay in urine and bladder cancer diagnoses based on the color change of Rox-DNA functionalized quantum dots (QDs). The green fluorescence of the QDs was sensitive to H2O2, but the red fluorescence of Rox showed no change. An HRP-mimicking hemin/G-quadruplex, which was formed with the help of telomerase activity, catalyzed H2O2 into H2O and O2. This quadruplex effectively avoided H2O2 interference with green fluorescence. In the presence of H2O2, the detected color changed from red to yellow-green by increasing the telomerase concentration. The detection limit (LOD) was 10 cells, and response time was within 60 min. More importantly, a paper sensor was developed based on this probe and used for the assay of telomerase activity in urine samples. The results were highly sensitive and reproducible, and visual semi-quantitative detection was realized using the naked eye.

Exciton energy transfer-based fluorescent sensor for the detection of Hg2+ through aptamer-programmed self-assembly of QDs

Herein, an original exciton energy transfer-based sensitive fluorescence sensor for the determination of Hg2+ has been designed through DNA aptamer-programmed self-assembly of CdTe quantum dots (QDs). In this work, CdTe QDs were applied as fluorescence signal source. The two pieces of T-rich aptamer played a role as molecular recognition probes which could bind to the target Hg2+ specifically. The extent of Hg2+-triggered self-assembly of QDs depended on the concentration of Hg2+, which resulted in an exciton energy transfer effect between QDs, giving an obvious fluorescence signal decrease and red-shift of the fluorescent peak. Based on this principle, we could detect the Hg2+ in two different signal modes. The limit of detection (LOD) was 3.33 nM. The proposed sensing method exhibited its application in detecting Hg2+ in real water samples with satisfactory performance. The results indicated that this proposed sensor will be of great potential in biological and analytical fields.

Molecularly imprinted polymer coated quantum dots for fluorescence sensing of acetaminophen

A molecularly imprinted coating with acetaminophen (AC) as template molecule was grafted onto L-cys-CdSe/ZnS quantum dots (QDs) using 3-aminopropyltriethoxysilane as the functional monomer and tetraethyl orthosilicate as the cross-linker via an adapted Stöber method, in order to develop a selective and sensitive fluorescence sensor for the determination of AC in water samples. The resulting MIP@QDs were characterized by Fourier-transform infrared spectroscopy, high resolution transmission electron microscopy, energy dispersive X-ray spectroscopy, thermogravimetric analysis and fluorescence spectrophotometry which confirmed the polymer coating. The fluorescence quenching of the sensor provided good linearity over the AC concentration range of 1.0–300 nmol L−1 with a detection limit of 0.34 nmol L−1 and the sensor showed good photostability over 5 days. The recoveries of AC in water samples at various spiking levels varied from 95% to 114%.

Simple and sensitive fluorescence sensor for methotrexate detection based on the inner filter effect of N, S co-doped carbon quantum dots

Reliable and simple detection methods for chemotherapeutic agent contaminants, such as methotrexate, are required to minimize their possible toxic threat. However, detecting them remains a challenging in environmental and biological analysis. Here, we developed a fluorescent N, S co-doped carbon quantum dots (N, S co-doped CQDs) probe to detect methotrexate on the basis of the inner filter effect of fluorescence. Under optimized conditions, the fluorescent probe exhibits high sensitivity and specific selectivity with a linear detection range from 0.4 μg/mL to 41.3 μg/mL and a low detection limit of 12 ng/mL (S/N = 3). Further, this N, S co-doped CQDs fluorescent probe can be used to analyze extracellular fluids and wastewater samples satisfactorily, thereby showing a remarkable potential for broad applications in biological molecule determination and environmental analysis.

UV photocrosslinked polymeric fluorescent sensor for bisphenol A

Bisphenol A (BPA) is known as endocrine disrupting compound and it is widely used as an intermediate in manufacturing of polycarbonate and epoxy resins. These resins are used to manufacture inner surface of food cans or directly contact with food and can release BPA into food. It is known that BPA poses health risk, but how risky is a matter of debate. In this study, selective and sensitive fluorescent polymeric membrane sensor for detection of BPA was developed based on fluorescence quenching (λex/λem = 272/295 nm). Working concentration range was linear between 4.4 × 10−9 mol L−1 and 1.1 × 10−7 mol L−1 with a detection limit of 1.58 × 10−9 mol L−1. Optimization of sensor was done and the sensor exhibited satisfactory results for being used as a fluorescent sensor for determination of BPA. Additionally, the proposed method was successfully applied to plastic food containers real samples. The developed sensor was shown to be more sensitive than other methods currently in use, and was able to provide results in a matter of seconds, opening up the possibility of a rapid tool for BPA detection.

A highly selective and sensitive fluorescent sensor for relay recognition of Zn2+ and HSO4−/H2PO4− with “on-off” fluorescent responses

A simple and effective fluorescent sensor bearing pyridine units was designed and synthesized. The sensor can detect Zn2+ with high selectivity accompanied by a distinct fluorescence turn-on response, inducing the fluorescent color markedly changed from darkness to bright green. The limit of detection (LOD) was calculated as 8.56 × 10−9 M with a good linearity (R = 0.95943). In addition, the chelate of sensor with Zn2+ can further recognize H2PO4−/HSO4− with notable fluorescence quenching behaviors over other anions and the LODs were as low as 3.44 × 10−6 M (R = 0.99762) and 3.84 × 10−6 M (R = 0.99315), respectively.

Application of coated green source carbon dots with silica molecularly imprinted polymers as a fluorescence probe for selective and sensitive determination of phenobarbital

Herein, a selective and sensitive fluorescence sensor was developed for the detection of phenobarbital, an epilepsy drug, using molecularly imprinted polymers (MIPs) coated on the surface of green source carbon dots (GSCDs). First, GSCDs were synthesized through a hydrothermal method using Cedrus as a carbon source. Then, a MIPs-GSCDs as a fluorescence probe was obtained by coating a thin film of silica on the surface of the GSCDs using a reverse micro emulsion method. In this step, phenobarbital, 3-aminopropyltriethoxysilane (APTES) and tetraethoxysilane (TEOS) were applied as a template, a functional monomer, and cross linker, respectively. The fluorescence signal of MIPs-GSCDs was selectively quenched by phenobarbital rebinding with MIP cavities. The fluorescence quenching signal was applied for phenobarbital sensing at the pH = 8 without the interference of other materials. After optimizing the factors affecting the sensor's response, a linear range between 0.4 and 34.5 nmol L−1 with a detection limit of 0.1 nmol L−1 was obtained. The sensor's capability in the real sample analysis was investigated by phenobarbital determination in a human blood plasma samples.

Nitrogen-doped graphene quantum dots as highly sensitive and selective fluorescence sensor detection of iodide ions in milk powder

In this work, we have successfully designed an “off-on” fluorescent sensor based on nitrogen-doped graphene quantum dots (N-GQDs) system to detect iodide ions in milk powder. The fluorescence intensity of N-GQDs was significantly quenched by Ag+ through forming N-GQDs/Ag+ complexes due to the binding between Ag+ and functional groups on the surface of N-GQDs. However, with the addition of I− to the N-GQDs/Ag+ system, the fluorescence intensity was significantly restored because of the formation of AgI complexes by "hard and soft acids and bases principle"(HSAB) between Ag+ and I−. Under the optimal conditions, Ag+ had a good linear relationship in the range of 0.01–0.6 μM. The fluorescence intensity of N-GQDs/ Ag+ linearly increased with the increasing of I− concentrations in the range of 0.0125–4.0 μM, and the detection limit (LOD) was 5.6 nM. The proposed method has been successfully applied to the detection of milk powder, which is a detection system with good development prospects owing to convenience, rapidity and low toxicity.

Highly sensitive fluorescent sensor based on electrosynthesized poly(Fmoc-l-serine) enables ultra-trace analysis of Cr2O72− in water and agro-product samples

A fluorescent sensor based on the electrosynthesized conjugated polymer poly(Fmoc-l-serine) (PFOLS) for highly sensitive analysis of Cr2O72− at ultra-trace levels in water and agro-product samples was reported. PFOLS was obtained by potentiostatical electropolymerization of corresponding monomer Fmoc-l-serine in CH2Cl2-boron trifluoride diethyl etherate system. The introduction of serine group in PFOLS efficiently avoided the interference of anions and other acid substances in agro-products. Although metal ion Fe3+ could also quench the fluorescence of PFOLS, EDTA could recover the fluorescence of PFOLS-Fe3+ system. So in the presence of EDTA, PFOLS had a high-selectivity to Cr2O72− and it could detect Cr2O72− in linear ranges of 80 pM to 1.95 mM with a low detection limit of 72 pM. Then PFOLS was used to detect Cr2O72− in water samples (tap water, lake water, and wastewater) and agro-product samples (white rice, red rice, and black rice) with satisfactory results, revealing that PFOLS could be as a practical sensing platform for ultra-trace analysis of Cr2O72− in environment and agro-product samples.

A novel fluorescence “turn off−on” nanosensor for sensitivity detection acid phosphatase and inhibitor based on glutathione-functionalized graphene quantum dots

In this paper, we developed a label-free and sensitive fluorescence sensor for acid phosphatase (ACP) and its inhibitor parathion-methyl (PM) detection based on glutathione-functionalized graphene quantum dots (GQDs@GSH). Upon addition of MnO2 nanosheets, the fluorescence of GQDs@GSH could be efficiently quenched via a fluorescence resonance energy transfer. ACP could easily catalyze the hydrolysis of L-Ascorbic acid-2-phosphate (AAP) to ascorbic acid (AA), which could reduce MnO2 nanosheets to Mn2+ in acidic environment, leading to dramatically increase of the fluorescence intensity of GQDs@GSH. Quantitative detection of ACP in a broad range from 0.1 to 9 mU mL−1 with a detection limit of 0.027 mU mL−1 could be achieved. The feasibility of the proposed sensor in real samples analysis was also studied and satisfactory results were obtained. Furthermore, the fluorescence assay strategy could also be used for the detection of parathion-methyl (PM) as ACP inhibitor.

Luminescent, low-toxic and stable gradient-alloyed Fe:ZnSe(S)@ZnSe(S) core:shell quantum dots as a sensitive fluorescent sensor for lead ions

In this paper, an aqueous-based approach is introduced for facile, fast, and green synthesis of gradient-alloyed Fe-doped ZnSe(S)@ZnSe(S) core:shell quantum dots (QDs) with intense and stable emission. Co-utilization of co-nucleation and growth doping strategies, along with systematic optimization of emission intensity, provide a well-controllable/general method to achieve internally doped QDs (d-dots) with intense emission. Results indicate that the alloyed ZnSe(S)@ZnSe(S) core:shell QDs have a gradient structure that consists of a Se-rich core and a S-rich shell. This gradient structure cannot only passivate the core d-dots by means of the wider band gap S-rich shell, but also minimizes the lattice mismatch between alloyed core–shell structures. Using this novel strategy and utilizing the wider band gap S-rich shell can obviously increase the cyan emission intensity and also drastically improve the emission stability against chemical and optical corrosion. Furthermore, the cytotoxicity experiments indicate that the obtained d-dots are nontoxic nanomaterials, and thus they can be considered as a promising alternative to conventional Cd-based QDs for fluorescent probes in biological fields. Finally, it is demonstrated that the present low-toxicity and gradient-alloyed core:shell d-dots can be used as sensitive chemical detectors for Pb2+ ions with excellent selectivity, small detection limit, and rapid response time.

Highly sensitive and selective fluorescent sensor for tetrabromobisphenol-A in electronic waste samples using molecularly imprinted polymer coated quantum dots

In this study, an optosensing composite was fabricated by coating a molecularly imprinted polymer (MIP) layer onto CdTe quantum dots (MIP-QDs) to develop a fluorescent sensor for the determination of tetrabromobisphenol-A (TBBPA). The resulting MIP-QDs composite was well characterized and had ideal properties of morphology and photoluminescence. Under the optimized experiment conditions, this fluorescent sensor exhibited a good linearity with TBBPA covering the concentration range of 1.0–60.0 ng/mL and the detection limit was as low as 3.6 ng/g. This developed MIP-QDs sensor was successfully employed to detect TBBPA in electronic waste (e-waste) samples for the first time. The mean recoveries were in the range from 89.6% to 107.9% with the relative standard deviation below 6.2%, which were in accordance with the results of HPLC-UV method. The average concentration of TBBPA in electric fan and circuit board samples were 260.20 and 707.30 mg/kg, respectively. This study provided a simple, rapid, highly sensitive and selective method to detect TBBPA in e-waste samples.

A Salen-based covalent organic polymer as highly selective and sensitive fluorescent sensor for detection of Al3+, Fe3+ and Cu2+ ions

A novel covalent organic polymer (Salen-COP) based on Salen-type Schiff base was synthesized by one-pot protocol involving the self-condensation of 3-formyl-4-hydroxyphenylboronic acid and the subsequent aldehyde–amine condensation with benzene-1,2-diamine. The Salen-COP was characterized by 13C CP/MAS NMR, Fourier transform infrared spectroscopy, thermogravimetric analysis, X-ray photoelectron spectroscopy and X-ray powder diffraction spectrometry analysis. The morphological features of Salen-COP were also analyzed using scanning electron microscopy. The Salen-COP exhibited the significant fluorescence enhancing for the sensing of Al3+, while the obtained polymer also exhibited the dramatic fluorescence quenching for the sensing of Fe3+ and Cu2+. The detection limits were calculated to be 0.248 µM for Salen-COP@Al3+, 0.545 µM for Salen-COP@Fe3+ and 0.140 µM for Salen-COP@Cu2+, respectively. Furthermore, the Salen-COP was founded to be a reversible chemosensor for Al3+, Fe3+ and Cu2+ ions, which provided a unique opportunity in the development of multi-response polymer-based sensors.

Highly sensitive and selective fluorescence sensor based on nanoporous silicon-quinoline composite for trace detection of hydrogen peroxide vapors

We report the highly sensitive and selective detection of hydrogen peroxide vapors via fluorescence enhancement (turn-on mechanism) for boronate quinoline chromophore deposited on a flat substrate and entrapped in a nanoporous silicon multi-layered structure. The detection limit was determined to be 150 ppt with a negligible response to major volatile organic compounds and water. A distinctive feature is extraordinary sensitivity which critically depends on amount of the sensory material infiltrated inside nanoporous silicon.

A luminescent Cd(II)-MOF as recyclable bi-responsive sensor for detecting TNP and iron(III)/silver(I) with high selectivity and sensitivity

A new three dimensional framework {[Cd2(BPDPE)2(chdc)2(H2O)2]·4H2O}n (1) (BPDPE = 4,4′-bis(pyridyl)diphenyl ether H2chdc = 1,4-cyclohexanedicarboxylic acid) has been successfully synthesized and characterized. In this complex, the chdc2− adopts tran- configuration, was linked by three types of Cd ions to form wave-like 2D layer with hexagonal grids. The 2D layers are linked by meso-helical chains Cdn(BPDPE)n to form a 3D framework. It is surprised find that complex 1 can highly sensitive sense 2, 4, 6-trinitrophenol (TNP) through luminescence quenching effect, the quenching constant is up to 2.794 × 105M−1. In addition, complex 1 also presents highly sensitive fluorescent sensor for detecting Fe3+ and Ag+ ions. The quenching constants are 2.893 × 104M−1 and 1.483 × 104M−1. Furthermore, the quenching mechanisms of complex 1 as multifunctional sensor have been studied.

Pyranine functionalized Fe3O4 nanoparticles for the sensitive fluorescence detection of Cu2+ ions

In this study, a sensitive fluorescence sensor was synthesized for the detection of Cu2+ ions based on the quenching of fluorophore. The sensor is composed of pyranine functionalized amino silane shell modified magnetite (Fe3O4) core nanostructures. The synthesized nanomaterials were characterized by Fourier Transform Infrared Spectroscopy (FTIR), X-Ray Powder Diffraction (XRD), Vibrating Sample Magnetometer (VSM) and Transmission Electron Microscopy (TEM). The fluorescent magnetic nanoparticles were analyzed by fluorescence spectroscopy. The characterization data showed that the magnetic core was highly superparamagnetic with an average particles diameter up to 10 nm. The fluorescence response of Fe3O4@-SiO2-NH2-Pyr nanosensor towards Cu2+ ions showed an enhanced and selective fluorescence quenching. Pyranine functionalized magnetic nanoparticles were found to be highly selective for Cu2+ ions without giving any response to other interfering cations and biomolecules. The nanosensor not only provided a sensitive (LOD = 6 nM), fast and selective detection of Cu2+ ions but a new fluorescent and biocompatible material with potential uses in biological and environmental fields.

A highly sensitive fluorescent sensor for Zn2+ based on diarylethene with an imidazole unit

A new sensitive sensor for Zn2+ based on diarylethene with an imidazole unit has been synthesized. Its photochromic and fluorescent behaviors have been systematically investigated by the stimulation of UV/vis lights and Zn2+ ion in THF solution. It displayed a dual-mode with a “turn on” fluorescence and color response to Zn2+. With the addition of Zn2+, the emission intensity enhanced 26-fold, accompanied by the fluorescent color changed from dark red to bright yellow. The 1:1 stoichiometry between the sensor and Zn2+ was verified by Job's plot and MS. The LOD for Zn2+ was determined to be 6.12 × 10−9 mol L−1. Furthermore, a logic circuit was designed by using the fluorescence at 578 nm as output and the combinational stimuli of UV/vis and Zn2+/EDTA as inputs.

Highly sensitive fluorescent detection of p53 protein based on DNA functionalized Fe3O4 nanoparticles

The accurate quantification of p53 protein expression level is of great importance for cancer diagnosis. Here, a highly sensitive fluorescent sensor based on DNA functionalized magnetic nanoparticles was developed for the detection of p53 protein expression. Instead of a monoclonal antibody, a consensus DNA was employed to capture p53 protein. Meanwhile the fluorescent dye tethered DNA was used as the signal output instead of enzyme tagged nanoparticle or antibody. Consequently, our developed method is cost-effective for both the p53 capture and detection by compared with the conventional immunoassay. The biosensor developed by the above strategy was used to quantitatively detect p53, which yields a detection limit of 8 p.M. with the linear range of 50 p.M. to 2 nM. The sensitive for specific p53 detection was achieved due to the facile magnetic separation from the complex condition, and the reduced non-specific absorption effect by dextran. Moreover, the method is able to measure p53 from real cell lysate without extensive sample pretreatment/separation. The developed p53 biosensor has high sensitivity, good selectivity and reliable accuracy. It demonstrates great potential in clinical cancer diagnosis and early detection of cancer.

Selective and sensitive fluorescent sensor for Pd2+ using coumarin 460 for real-time and biological applications

The efficient fluorescent property of coumarin 460 (C460) is utilized to sense the Pd2+ selectively and sensitively. Fabrication of a sensor strip using commercial adhesive tape is achieved and the detection of Pd2+ is attempted using a handy UV torch. The naked eye detection in solution state using UV chamber is also attempted. The calculated high binding constant values support the strong stable complex formation of Pd2+ with C460. The detection limit up to 2.5 × 10−7 M is achieved using fluorescence spectrometer, which is considerably low from the WHO's recommendation. The response of coumarin 460 with various cations also studied. The quenching is further studied by the lifetime measurements. The binding mechanism is clearly explained by the 1H NMR titration. The sensing mechanism is established as ICT. C460 strip's Pd2+ quenching detection is further confirmed by solid-state PL study. The in-vitro response of Pd2+ in a living cell is also studied using fluorescent imaging studies by means of HeLa cell lines and this probe is very compatible with biological environments. It could be applicable to sense trace amounts of a Pd2+ ion from various industries. Compared with previous reports, this one is very cheap, sensitive, selective and suitable for biological systems.