Fluorescence Detection Limit Research Articles

Rationally designed imidazole derivative as colorimetric and fluorometric sensor for selective, qualitative and quantitative cyanide ion detection in real time samples.

A new imidazole derivative of 1,2-diaminoanthraquinone and fluorene-2-carboxaldehyde was designed as a sensor B2 to selectively detect the cyanide (CN-) ion through colorimetric and/or fluorometric methods. The photochemical characterizations of sensor B2 were tested using absorption and emission spectral studies in CH3CN-H2O (8:2) semi-aqueous medium. An excited state proton transfer process (ESIPT) was proved by theoretical and spectral studies. The colorimetric and fluorescence detection limit of CN- ion was found to be 5.3×10-6M and 4.11×10-8M, respectively. 1H NMR titration, electrochemical and DFT studies were supported the removal of -NH proton from B2. In order to utilize this sensor in real-time applications, we developed a test cassette which is coated with sensor B2 detected the presence of CN- ion in the food sample with endogenous cyanide ion.

A Turn-on Fluorescent Sensor For Cadmium Ion Detection In Aqueous Solutions

Fluorescent sensors have attracted an important interest due to their advantages such as high selectivity, rapid response, easy to use etc. In this study, a rhodamine based fluorescent sensor, RhDP, was synthesized, and used for selective detection of Cd2+ ions. The sensor responds to Cd2+ via the coordination induced fluorescence activation (CIFA) mechanism. RhDP gives a very fast and reversible fluorescence response to Cd2+ in the presence of the metal ions tested. The complex stoichiometry between RhDP and Cd2+ was found to be 1:1 and the binding constant was calculated as 2.70 × 107 M-1in ACN/HEPES buffer (10 mM, pH: 7.05, v/v 1:1). The fluorescent detection limit of RhDP for Cd2+ was found to be 0.218 µM, which gave a marked sensitivity towards Cd2+.

Layer-by-layer assembly of magnetic-core dual quantum dot-shell nanocomposites for fluorescence lateral flow detection of bacteria.

Lateral flow immunoassay (LFA) strips are extensively used for rapid tests of various biochemical molecules, but these strips still have some limitations in bacterial detection due to their low sensitivity and poor stability in complex samples. In this study, we reported a highly sensitive and quantitative fluorescent LFA strip for bacterial detection by using novel magnetic-core@dual quantum dot (QD)-shell nanoparticles (Fe3O4@DQDs) as multifunctional fluorescent labels. The Fe3O4@DQDs were prepared through a polyethyleneimine (PEI)-mediated layer-by-layer (LBL) assembly method, and they possess monodispersity, high magnetic responsiveness, good stability, and superior fluorescence properties. Based on these merits, the Fe3O4@DQDs were used to capture and enrich bacteria from complex samples and then used as advanced fluorescent labels of LFA strips for the quantitative detection of bacteria. Under optimal conditions, the assay ultra-sensitively detected Streptococcus pneumoniae with a low limit of detection of 8 cells per mL and a wide dynamic linear range of 10 cells per mL to 107 cells per mL. Systematic comparison revealed that the fluorescence detection limit of the Fe3O4@DQD-based strip was 55 and 1000 times higher than those of Fe3O4-core@QD-shell nanocomposite (Fe3O4-QD)-based and conventional QD microsphere-based strips, respectively. The proposed method also exhibited high specificity and selectivity for biological samples (human whole blood and sputum) and is thus a promising tool for real bacterial sample testing.

A pillar[5]arene-based and OH− dependent dual-channel supramolecular chemosensor for recyclable CO2 gas detection: High sensitive and selective off-on-off response

A novel supramolecular chemosensor (PNG) was successfully constructed by 5-(3-nitrophenyl)-furfural-functionalized Pillar[5]arene(PN) and bipyridine salt(G) via exo-wall π…π interactions. Interestingly, the chemosensor PNG could detect OH− and CO2 with high selectivity, sensitivity and excellent recyclable properties. The fluorescent detection limits of PNG for OH− and CO2 are 2.03 × 10−8 M and 9.1 × 10−8 M (2.22 ppm), respectively. The colorimetric detection limits for OH− and CO2 are 3.78 × 10−8 M and 1.13 × 10−7 M (2.76 ppm), respectively. This study is simple and effective for OH− and CO2 detection, and provides supramolecular fields with potential practical application in anion and gas detection.

Synthesis of a novel hyperbranched polymer and its application in multi-channel sensing Fe3+

A novel hyperbranched polymer was designed and synthesized as a spectral probe for Fe3+. The polymer showed high selectivity and sensitivity to Fe3+ in CH3CN/H2O (75/25, v/v). Fe3+ caused a new peak at 560 nm in UV–Vis absorption, a 31 nm fluorescence redshift, a 35-fold enhancement in fluorescence intensity at 575 nm and an 8.3-fold enhancement in fluorescence quantum yield, accompanied by a visual color change from colorless to pink and a fluorescence from dark to bright orange. The colorimetric and fluorescent detection limits were 1.29 and 1.88 µM, respectively. The detection was almost not interfered by other common metal cations. The polymer could be applied in assaying Fe3+ in real sample with similar precision to that of atomic absorption spectroscopy.

A multifunctional perylenediimide-based dual-analyte chemodosimeter for specific and rapid detection of H2S and Pd0 in water, biofluids, live cells and solid state

We report design and synthesis of heterogeneously bay functionalized perylenedimide PN-PDI, endowed with two differentialy reacting functional groups –NO2 and propargyloxy, as dual analyte chemodosimeter for differential and instantaneous colorimetric (NIR) and fluorescence responses towards H2S and Pd0 with vivid color changes. The respective colorimetric and fluorescent detection limits for H2S (1.21 nM and 6.6 nM) and Pd0 (3.05 nM and 3.3 nM) are based on S/N = 3. Furthermore, the practical utility of PN-PDI for the detection of H2S and Pd0 has been demonstrated in blood serum, urine and live A549 cells. PN-PDI based test strips can be used to detect H2S 2.8 pg/cm2 and Pd0 11.5 pg/cm2 by the naked eye. The results of UV–vis, fluorescence spectroscopic and 1H NMR titration studies confirm that mechanism of H2S sensing is through both reduction of –NO2 group to –NH2 and thiolysis reactions, whereas mechanism of Pd0 sensing is through depropargylation reaction of propargyloxy group in PN-PDI. The multiple outputs have been further utilized to construct NOR and INH logic functions.

A simple pyrazine based ratiometric fluorescent sensor for Ni2+ ion detection

Herein, we checked if the existing mercury sensor (R) could be applied for the detection of Ni2+ ion in both colorimetrically as well as fluorimetrically. The fluorescent detection limit for Ni2+ ion is as low as 8.62 × 10−7 M, which is lower than the guideline for drinking water (1.2 × 10−6 M) by American Environmental Protection Agency (EPA). All the findings were theoretically supported using Density Functional Theory (DFT) studies. The sensing ability of R for Ni2+ was effectively applied to real water samples. Based on the color changing and spectral response in this method, we investigated molecular logic gates with single and dual input signal amplification by employing chemical input (Ni2+) and light input (UV). Furthermore, test kits containing R were constructed, which could perform as a suitable and competent analysis for “in-the-field” measurement of Ni2+.

Hg2+ -selective ratiometric and colorimetric probe based on dansyl-rhodamine and its staining function in cell imaging.

A new ratiometric probe composed of a dansyl-rhodamine dyad for the detection of Hg2+ via fluorescence resonance energy transfer was designed and synthesized. Rhodamine, dansyl chloride, and hydrazide were selected as the acceptor, donor, and reaction site, respectively. It displayed high selectivity and sensitivity to Hg2+ with obvious colour change and fluorescence change due to Hg2+ -assisted hydrolysis of rhodamine hydrazide. A good linear relationship ranging from 0 to 16μM and 0-28μM for the Hg2+ concentration was found based on absorbance and fluorescence assay, respectively. Detection limits of absorbance and fluorescence for Hg2+ were calculated to be 1.22μM and 9.10μM, respectively.

Novel multi-responsive fluorescence switch for Hg2+ and UV/vis lights based on diarylethene-rhodamine derivative

A new multi-responsive fluorescent switch DTE-Pip-Rho 1O has been designed and synthesized in this study. For this molecule, the reactive site of spirolactam ring is far away from the diarylethene unit through the intramolecular piperazine. It exhibited high selectivity and sensitivity to Hg2+ in addition to obvious color change (colorless-pink) and fluorescence “off-on” (dark-orange) during this process. It is believed that the color change is due to Hg2+-assisted hydrolysis of rhodamine hydrazide. Therefore, the new molecule can be used as colorimentric and fluorescent chemosensor for Hg2+ with high selectivity. The detection limits of absorbance and fluorescence for Hg2+ were calculated to be 1.15 μM and 1.16 μM, respectively. The resulting DTE-Pip-Rho 1O-Hg2+ could also function as a reversible fluorescence photo-switch in response to UV/vis light owing to FRET mechanism. Moreover, it has been demonstrated that the photo-switchable system displayed excellent fatigue resistance and remarkable anti-photobleaching capability.

Biocatalyst and Colorimetric/Fluorescent Dual Biosensors of H2O2 Constructed via Hemoglobin-Cu3(PO4)2 Organic/Inorganic Hybrid Nanoflowers.

In this article, the three-dimensional hemoglobin (Hb)-Cu3(PO4)2 organic/inorganic hybrid nanoflowers (Hb-Cu3(PO4)2 HNFs) self-assembled by nanopetals were synthesized via a facile one-pot green synthetic method. The compositions and microstructure of the Hb-Cu3(PO4)2 HNFs were well-characterized with X-ray diffraction, scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, and UV-vis spectrometry, respectively. The as-prepared Hb-Cu3(PO4)2 HNFs were to be used as a biocatalyst to construct colorimetric/fluorescent dual biosensors. The experimental results show that the colorimetric/fluorescent dual biosensors exhibited two linear responses in the range of 2-10 ppb and 20-100 ppb for H2O2. The colorimetric and fluorescent detection limits were 0.1 and 0.01 ppb, respectively. Compared with the free Hb, the biocatalytic activity of the Hb-Cu3(PO4)2 HNFs can be improved for 3-4 times under optimal conditions. The sensing performance of these Hb-Cu3(PO4)2 HNF-based dual biosensors can be contributed such that the active sites of Hb molecules were more exposed on the surface of the Cu3(PO4)2 nanopetals. Second, the unique nanopetal-assembled hybrid flowerlike structure was favorable to contact the detected substance with the biosensors. The dual biosensors were successfully applied for the determination of H2O2 in rainwater, tap water, and waste water samples. These results show that the dual biosensors had a potential application in the field of medical analysis, environmental monitoring, and food engineering.

A triphenylamine-functionalized fluorescent organic polymer as a turn-on fluorescent sensor for Fe3+ ion with high sensitivity and selectivity

A triphenylamine-functionalized A3B2-type covalent organic polymer (TPA-COP) was synthesized by the palladium-catalyzed Sonogashira polycondensation reaction from tris(4-ethynylphenyl)amine and 4-bromo-N-(4-bromo-2-methoxybenzylidene)-2-methoxyaniline. The obtained polymer possessing amorphous structure and good thermal stability exhibited strong yellow–green luminescence with an emission band at 498 nm. It is worth noting that the polymer also shows selective turn-on fluorescence response to Fe3+ ion over a variety of other competing metal ions such as Na+, K+, Ca2+, Mg2+, Ba2+, Mn2+, Cr3+, Cu2+, Ni2+, Zn2+, Co2+, Al3+. The fluorescent detection limit of TPA-COP sensor for Fe3+ in solution was 4.3 × 10−7 M. Furthermore, the proposed sensing mechanism should result from complexation between tridentate-coordinated Schiff base sites and Fe3+ ion, which was further investigated by fluorescence titration, 1H NMR and IR measures, together with fluorescence lifetime analysis.

A dual-mode probe for colorimetric and fluorometric detection of cysteine based on phosphorus/nitrogen co-doped CQDs and gold nanorods

In this study a novel method was developed for the fluorescent and colorimetric determination of cysteine (Cys). The fluorescent determination was designed based on surface plasmon-enhanced energy transfer (SPEET), and phosphorus/nitrogen co-doped CQDs (PNCQDs) were employed as the donor, of which the fluorescence was quenched by gold nanorods (AuNRs) (acceptor). For the colorimetric assay, under the catalytic effect of Fe3+, AuNRs were effectively etched by OH· that was generated by the Fenton reaction. The etch of the AuNRs lead to the decrease in the absorbance intensity, the blue shift of longitudinal surface plasmon resonance (LSPR) absorption peak of AuNRs as well as the fluorescence of PNCQDs recovery. However, Cys can suppress this etching reaction by coordination effect between hydrosulfide group (SH) in Cys and Fe3+, leading to red shift of the LSPR absorption peak. Similarly, the fluorescence will change with the absorbance. The peak shift and the fluorescence change can be applied to monitor of Cys. Under the optimal operation conditions, highly sensitive determination of Cys was achieved, with the fluorescent detection limit of 1.2 nM and the colorimetric detection limit of 0.9 nM. The linearity of the system towards Cys was in the range of 0.005–25 μM. The highly sensitive determination of Cys in urine samples demonstrates that this method possesses high potential for on-site and visual detection of urine Cys.

Novel PSMA-Coated On-Off-On Fluorescent Chemosensor Based on Organic Dots with AIEgens for Detection of Copper (II), Iron (III) and Cysteine.

Herein, a novel on-off-on fluorescent chemosensor for copper (II) ion (Cu2+), iron (III) ion (Fe3+) and cysteine is developed simply by the nano-precipitation method. The prepared organic dots with AIEgens (AIE dots) are advantageous over other metal ions in detecting Cu2+, Fe3+ with high selectivity and sensitivity by forming agglomerations (on-off). The agglomerations formed by AIE dots and Cu2+ redistributed and the fluorescence was obviously recovered in the presence of cysteine (off-on). This sensor has a wide linear range for Cu2+, Fe3+ and cysteine. The fluorescent detection limits of AIE dots are calculated to be 107 nM for Cu2+, 120 nM for Fe3+ and 78 nM for cysteine, respectively. These results indicate that the AIE dots can be used as a potential probe for Cu2+, Fe3+ and cysteine detection.

Assessing fluorescence detection and effective photothermal therapy of near-infrared polymer nanoparticles using alginate tissue phantoms.

Photothermal therapy (PTT) uses light absorbing materials to generate heat for treatment of diseases, like cancer. The advantages of using PTT components that absorb in the near-infrared (NIR) include reduced tissue auto-fluorescence and higher penetration depths. However, NIR laser light can still be scattered and absorbed by biological tissues, thus decreasing the amount of the energy reaching the PTT agents. We have developed two distinct formulations of NIR-absorbing nanoparticles, one which can be utilized for PTT only, and another for both PTT and fluorescence imaging of colorectal cancer. In this work, the fluorescence detection limit and the PTT heating potential of the two nanoparticle types were determined using alginate tissue phantoms. The objective of this study was to determine the PTT efficiency and theranostic potential of the nanoparticles by irradiating 3D collagen tumor spheroids, containing nanoparticles and CT26 mouse colorectal cancer cells, through increasing tissue phantom thicknesses and then quantifying cell death. Materials and Methods Our lab has previously developed nanoparticles based on the semiconducting, conjugated polymer poly[4,4-bis(2-ethylhexyl)-cyclopenta[2,1-b;3,4-b']dithiophene-2,6-diyl-alt-2,1,3-benzoselenadiazole-4,7-diyl] (PCPDTBSe). We have also made a hybrid nanoparticle that heats and fluoresces by combining PCPDTBSe polymer with the fluorescent poly[(9,9-dihexylfluorene)-co-2,1,3-benzothiadiazole-co-4,7-di(thiophen-2-yl)-2,1,3-benzothiadiazole] (PFBTDBT10) polymer to yield nanoparticles termed Hybrid Donor-Acceptor Polymer Particles (H-DAPPs). H-DAPPs and PCPDTBSe nanoparticles were added to three-dimensional collagen gel tumor spheroids in order to represent nanoparticles in a tumor. Alginate tissue phantoms, comprised of an optical scattering agent (Intralipid) and an optical absorbing material (hemoglobin) in order to mirror biological tissue scattering effects, were used to simulate increasing tissue thickness between the nanoparticles and the PTT energy source. Fluorescence from the H-DAPPs was detectable through 6 mm of tissue phantoms. It was found that less than 10% of the laser energy could penetrate through 9 mm of tissue phantoms and only 60% of the laser energy passed through the 1.5 mm phantoms, regardless of laser power. PTT experiments, using 800 nm light at 2.2 W/cm2 for 60 s through tissue phantoms to stimulate nanoparticle-doped tumor spheroids, showed 55% cell death through 3 mm of tissue phantoms using H-DAPPs. Results from using the PCPDTBSe nanoparticles showed 72% cell death through 3 mm and over 50% cell death through 6 mm of tissue phantoms. The results of this work validated the heating potential and fluorescence detection limitations of two theranostic polymer nanoparticles by utilizing alginate tissue phantoms and 3D tumor spheroids. H-DAPPs and PCPDTBSe polymer nanoparticles can be utilized as effective PTT agents by exploiting their absorption of NIR light and H-DAPPs have advantageous fluorescence for imaging colorectal cancer. The data generated from this study design can allow for other NIR absorbing and fluorescing nanoparticle formulations to be evaluated prior to in vivo experimentation. Lasers Surg. Med. 50:1040-1049, 2018. © 2018 Wiley Periodicals, Inc.

A new “on-off-on” fluorescent sensor for cascade recognition of Hg2+ and S2− ion in aqueous medium

A novel Hg2+ ion fluorescent sensor 1 has been synthesized based on amide group, sensor 1 showed a highly sensitive and selective response towards Hg2+ over other metal ions by reversibly forming a [1-Hg2+] complex in 100% aqueous solution. The fluorescence detection limits was 0.41 nM. The Job's plots, the MS analysis and 1H NMR titration experiments implied that there was only the formation of a 1/Hg2+ complex with 1:1 stoichiometry. Moreover, S2− ion can remove Hg2+ from the complex and restore the spectral signal of 1. This research may enrich the field of multi-functional chemosensors in natural products.

Electrokinetic stacking of electrically neutral analytes with paper-based analytical device

Electrokinetic stacking (ES) is effective for improving sensitivity of paper-based analytical device (PAD) for charged analytes. In this paper, we successfully demonstrated ES of electrically neutral analytes on PAD, and the performance was characterized by smartphone-based colorimetry and fluorescence. Firstly, SDS from cathode reservoir stacked as a micelle band on an open paper fluidic channel by ES, and the target analyte was swept by the micelle. Meanwhile, the probes at the other side were carried by electroosmotic flow (EOF). Eventually, neutral components preloaded on the channel were concentrated as the narrow stacking band. Taking the rhodamine B as a probe, the effects of EOF, background electrolyte concentration and anionic surfactant concentration were investigated. Fluorescence detection of rhodamine B and colorimetric analysis of Sudan III demonstrated the sensitivity enhanced and its potential for the semi-quantitative test. Under the optimized conditions, fluorescence detection limit of 50 nM of rhodamine B was achieved with a linear range of 1.0–10 μM (R2 = 0.99). The colorimetric detection limit for Sudan III was 5.2 μM and the linear range was 5–40 μM (R2= 0.99). Compared with direct analysis without stacking, the signal levels of rhodamine B and Sudan III were increased by 30-fold and 6-fold, respectively. This study showed that with ES, sensitive and rapid PAD detection of electrically neutral analytes could be achieved.

Rapid Screening of Cadmium in Rice and Identification of Geographical Origins by Spectral Method.

The accuracy, repeatability and detection limits of the energy-dispersive X-ray fluorescence (XRF) spectrometer used in this study were tested to verify its suitability for rapid screening of cadmium in samples. Concentrations of cadmium in rice grain samples were tested by the XRF spectrometer. The results showed that the apparatus had good precision around the national limit value (0.2 mg/kg). Raman spectroscopy has been analyzed in the discrimination of rice grain samples from different geographical origins within China. Scanning time has been discussed in order to obtain better Raman features of rice samples. A total of 31 rice samples were analyzed. After spectral data pre-treatment, principal component analysis (PCA), K-means clustering (KMC), hierarchical clustering (HC) and support vector machine (SVM) were performed to discriminate origins of rice samples. The results showed that the geographical origins of rice could be classified using Raman spectroscopy combined with multivariate analysis.

Silica Nanoparticle-Enhanced Fluorescent Sensor Array for Heavy Metal Ions Detection in Colloid Solution.

Sensitivity and detection limit are two vital factors that affect fluorophores-based sensing and imaging system. However, it remains a challenge to improve the sensitivity and detection limit of fluorophores, largely due to their limited response and photophysical properties. In this study, we report for the first time, a novel approach to enhance the sensitivity and detection limit of probes using silica nanoparticles, also known as silica nanoparticles-enhanced fluorescence (SiEF). SiEF can drastically improve the fluorescence intensities and detection limit of fluorophores. A SiEF-improved fluorescent sensor array for rapid and sensitive identification of different heavy metal ions is achieved, and a 3D spatial dispersion graph is obtained based on the SiEF-improved fluorescent sensor array, which provides a lower concentration dependent pattern than fluorophores alone, allowing qualitative, quantitative, and sensitive detection of heavy metal ions. Furthermore, with UV lamp irradiation of the sensor-metal ion mixtures, the output signals enable direct visual of heavy metal ions with low concentration. Thus, the SiEF approach provides a simple and practical strategy for fluorescent probes to improve their sensitivity and detection limit in analytes sensing.

An “off-on” fluorescein-based colormetric and fluorescent probe for the detection of glutathione and cysteine over homocysteine and its application for cell imaging

A new fluorescein-based probe (Py-F) was designed and synthesized to develop an optical and fluorescent sensor for biological thiols. Py-F possessed the thiol-responsed disulfide group and displayed selectivity and sensitivity for glutathione (GSH) and cysteine (Cys) over homocysteine (Hcy) in the CH3CN/PBS buffer solution, and the fluorescence detection limit was calculated to be 0.12 μM and 0.13 μM, respectively. Besides, the recognition mechanism was explained by density functional theory (DFT) calculation, and confirmed by mass spectroscope measurement. Furthermore, the thiols detection application in cellular imaging assays indicated that the probe has appreciable cell permeability and can serve as a fluorescent probe for detecting biothiols in living cells.

Design and synthesis of a fluorescent probe based on naphthalene anhydride and its detection of copper ions.

Copper, as the third most abundant transition metal ions of human, plays an essential role in the redox reaction, signal transduction, hematopoiesis, and other physiological processes. Abnormal content of copper ions in the body will cause some diseases such as anemia, coronary heart disease, Menkes’ syndrome. In this article, a new fluorescence probe L for Cu2+ was designed and synthetized by using 4-bromo-1,8 naphthalene anhydride and 2-thiophene formaldehyde as raw materials. Fluorescent probe L itself exhibited strong fluorescence, upon the addition of Cu2+ ions, the fluorescence was quenched. The fluorescent detection limit for Cu2+ ions was determined to be 1.8 μM based on a 3δ/S method. UV-vis absorption and fluorescence spectra indicated that probe L showed good selectivity and sensitivity for Cu2+, and this selectivity was not interfered by other metal ions and anions. Further cell fluorescence imaging experiments indicated that the probe L had potential to be used to examine copper ions in vivo.