Sensitive Fluorescent Sensor Research Articles

A facile method for the sensing of antioxidants based on the redox transformation of polyaniline

Polyaniline (PANI) is one of the most studied conducting polymers. It could adopt a number of chemical forms depending on the redox states of the assay solution. It was observed that the emeraldine base form of PANI could be reduced by common antioxidants (such as glutathione and ascorbic acid), which resulted in clear changes of the solution color and the UV–vis absorption spectra. In addition, it was observed that the fluorescence of CdTe quantum dots could be efficiently quenched by PANI, and the fluorescence quenching could not take place by the addition of antioxidants. The intensity of the quantum dots fluorescence could be directly related to the amount of antioxidant added to the assay solution, thus a sensitive fluorescent turn-on sensor for antioxidant was established. The detection limits for glutathione and ascorbic acid were estimated to be 50nM and 100nM, respectively. Our assay is simple, sensitive, and label-free, we envision it could facilitate the antioxidant sensing related applications.

Aminoquinoline based highly sensitive fluorescent sensor for lead(II) and aluminum(III) and its application in live cell imaging

We have synthesized a new probe 5-((anthracen-9-ylmethylene) amino)quinolin-10-ol (ANQ) based on anthracene platform. The probe was tested for its sensing behavior toward heavy metal ions Hg2+, Pb2+, light metal Al3+ ion, alkali, alkaline earth, and transition metal ions by UV–visible and fluorescent techniques in ACN/H2O mixture buffered with HEPES (pH 7.4). It shows high selectivity toward sensing Pb2+/Al3+ metal ions. Importantly, 10-fold and 5- fold fluorescence enhancement at 429nm was observed for probe upon complexation with Pb2+ and Al3+ ions, respectively. This fluorescence enhancement is attributable to the prevention of photoinduced electron transfer. The photonic studies indicate that the probe can be adopted as a sensitive fluorescent chemosensor for Pb2+ and Al3+ ions.

A sensitive and quantitative fluorescent multi-component immuno-chromatographic sensor for β-agonist residues

A sensitive and quantitative fluorescent multi-component immuno-chromatographic sensor was developed for detection of three β-agonizts: clenbuterol, ractopamine and salbuterol. A competitive immune strategy between antibody conjugated fluorescent beads and β-agonist or their antigens was employed. Each monoclonal antibody specifically recognizes it is corresponding β-agonist in the conjugating zone. The unreacted antibodies were captured by β-agonist antigens immobilized at three test lines in nitrocellulose membrane reaction zone. This enables simultaneous detection of 3 β-agonizts in one single test without any further sample preparation. The test results can be obtained within 10min. Limit of detections for clenbuterol, ractopamine and salbuterol were 0.10ng/mL, 0.10ng/mL and 0.09ng/mL, respectively. Recoveries ranged from 70.0% to 100.5% and relative standard deviations were below 15%. The assay was evaluated using spiked and real samples and the results were compared with LC–MS/MS. The developed novel assay method provides a low cost, sensitive and rapid approach for on site detection of β-agonizts.

4-(8′-Hydroxyquinolin-7′-yl)methyleneimino-1-phenyl-2,3-dimethyl-5-pyzole as a fluorescent chemosensor for aluminum ion in acid aqueous medium

A new fluorescent Al3+-sensor (L) was designed and synthesized from 8-hydroxyquinoline-7-carbaldehyde (HQ7A) and 4-aminopyrine. The sensor exhibited high selectivity and sensitivity “off-on” fluorescent responses toward Al3+ in methanol/water (1:9, v/v, acetate buffer, pH 4.5), with about 26-fold enhancement in fluorescence intensity and high sensitivity with the detection limit for Al3+ as low as 10−7M level. The sensor showed a significant fluorescent enhancement for Al3+ over a wide range of tested metal ions. These suggested that L could be served as a highly selective and sensitive fluorescence sensor for aluminum ion in acid medium, indicating the potential application in acid aqueous environment.

A label-free fluorescent sensor for Pb2+based on G-quadruplex and graphene oxide

A label-free sensitive and selective fluorescent sensor for Pb2+ was developed based on target-induced conformational change of an oligonucleotide and the difference in affinity of graphene oxide for unstructured and G-quadruplex DNA.

A highly selective and sensitive fluorescent chemosensor for mercury ions based on the mechanism of supramolecular self-assembly

In this work, a highly sensitive and selective mercury fluorescent sensor (E)-1-((5-(4-nitrophenyl)furan-2-yl)methylene) semicarbazone (BI) based on the 5-(4-nitrophenyl)-2-furan and semicarbazide groups was designed, prepared and utilized to monitor mercury ions in aqueous solution. Upon addition of mercury to BI in DMSO/H2O (8:2, v/v) HEPES buffer (pH=7.2) solution, an observable decrease of fluorescent to dim red change occurs that can be monitored by using fluorescence spectroscopy at room temperature. Concomitantly, a remarkably reducing in the emission maximum of BI takes place from 580 (a.u.) to 300 (a.u.). The observations indicate that association of the chemosensor with mercury ions leads to the supramolecular self-assembly breaking and the cooperation reaction occurrence, intra molecular charge density decreased in the chemosensor, the phenomenon likely responsible for the large decrease observed in emission spectra. And the detection limit of BI for the determination of mercury was estimated to be 2.084×10−9M. Notably, this sensor serves as a recyclable component in sensing materials. The experiment proved that this sensor can be repeated use above 10 times. Therefore, the chemosensor has good application prospect for recognizing and detecting Hg2+ in the environment.

Photoinduced electron transfer (PET) based label-free aptasensor for platelet-derived growth factor-BB and its logic gate application

Platelet-derived growth factor-BB (PDGF-BB) is often overexpressed in human malignant tumors as an indicator for tumor angiogenesis. Here by the photoinduced electron transfer (PET) between DNA-Ag fluorescent nanoclusters (NCs) and G-quadruplex/hemin complexes, we present a sensitive label-free fluorescent sensor for PDGF-BB. In the presence of PDGF-BB, the specific conjugation with its aptamer induced the conformational change of the duplex-like DNA sequence, releasing the G-quadruplex sequence part. Then in the presence of hemin and K+, the horseradish peroxidase mimicking DNAzyme (HRP-DNAzyme) was formed. With the electron transfer between the DNA-Ag NCs to the hemin Fe (III) center of HRP-DNAzyme, the PET occurred with a decrease in the fluorescence intensity of the DNA-Ag NCs. The detection performance such as selectivity, linear dynamic range, sensitivity, and the quenching capability of HRP-DNAzyme were estimated. The detection range for PDGF-BB is from 5×10−13 to 1×10−8M and the detection limit is 1×10−13M. The experimental results confirmed that the novel fluorescent aptasensor possessed a good sensitivity and high selectivity for PDGF-BB. In addition, the developed probe is nontoxic, label-free only involving one-step hybridization without sophisticated fabrication process. Furthermore, based on this quenching mode occurred by PDGF-BB and hemin, using PDGF-BB and hemin as inputs and the fluorescence signal as an output, a logic gate has been fabricated.

A novel highly sensitive and selective fluorescent sensor for imaging mercury(ii) in living cells

A novel phenothiazine-based derivative was designed and synthesized in this work, this molecule exhibited an obvious fluorescence quenching upon addition of Hg2+ due to the formation of a 1 : 1 metal–ligand complex. In addition to the high sensitivity toward Hg(II), it also displayed a high selectivity for Hg2+ over other transition metal ions in a rapid response time (<10 s). Simultaneously, the cell imaging experiment demonstrated the value of the sensor in fluorescent visualization of Hg2+ in biological systems.

Discriminating Cr(iii) and Cr(vi) using aqueous CdTe quantum dots with various surface ligands

The discrimination of Cr(III) and Cr(VI) is considered as one of the important analytical issues for environmental protection and disease prevention, because Cr(III) and Cr(VI) have different physiological effects and toxicities. Low cost, highly sensitive fluorescent sensors are highly demanded. Herein we report a facile and feasible method for discriminating Cr(III) and Cr(VI) by employing the aqueous CdTe quantum dots (QDs) with different surface ligands by virtue of their difference in quenching QD fluorescence. The QD fluorescence quenching by Cr(III)/Cr(VI) is mainly affected by electrostatic interaction, which is greatly determined by the surface functionalities of QDs. Thus, by combining the different fluorescence quenching behavior of carboxyl-, hydroxyl-, and/or amino-functionalized QDs, Cr(III) and Cr(VI) are discriminated. In comparison to the discrimination using the QDs with single surface functionality, the current method indicates improved reliability and accuracy.

A sensitive and selective fluorescent sensor for Zinc(II) and its application to living cell imaging

A new dipyrromethene derivative (DP1) exhibits an enhanced fluorescence in the presence of Zn2+ ions and a high selectivity for Zn2+ ions over competing metal ions in methanol; Ag+, Ca2+, Co2+, Cr3+, Fe2+, Fe3+, Hg2+, K+, Mg2+, Mn2+, Ni2+, and Pb2+ produced only minor changes in the fluorescence of DP1. The binding ratio of the DP1–Zn2+ complexes was determined from a Job plot to be 1:1. The binding constant (Ka) of Zn2+ binding to DP1 was found to be 6.12×104M−1, with a detection limit of 0.236μM. Fluorescence microscopy imaging using RAW264.7 cells showed that DP1 could be used as an effective fluorescent probe for detecting Zn2+ in living cells.

A new colorimetric and fluorescent chemodosimeter for fast detection of cyanide

A new high selective and sensitive fluorescent sensor for the detection of cyanide was developed based on the conjugated of anthracene and hemicyanine. By the nucleophilic attacking of CN− to the indolenium C-2 atom of the sensor, the ICT progress (Intramolecular Charge Transfer) was blocked with color changed and fluorescence enhanced. The live cell fluorescent experiments demonstrated the value of the sensor in tracing the CN− in biological systems. Short responding time (less than 1s) and excellent water-soluble ability (only 20% organic solvents needed in the detection) provided a broader application prospect in the practical application. The sensing mechanism was well rationalized with the aid of TD-DFT (time-dependent density functional theory) calculations.

A highly selective and sensitive perylenebisimide-based fluorescent PET sensor for Al3+ determination in MeCN

A novel ‘turn-on’ fluorescent probe with perylene tetracarboxylic bisimide (PBI) as the fluorophore and di(2-(salicylideneamino))ethylamine (DSEA) as the metal ion receptor was designed. The capability of the prepared probe to detect metal ions was evaluated by the changes in its emission intensity. The probe demonstrated a considerable emission enhancement (ca. 110-fold) in the presence of Al3+ in MeCN with high selectivity and sensitivity. Furthermore, the considerably ‘off–on’ fluorescence response concomitantly led to the apparent color change from colorless to brilliant yellow, which could also be identified by naked eye easily under UV lamp.

Copper nanoclusters as a highly sensitive and selective fluorescence sensor for ferric ions in serum and living cells by imaging

A simple, one-step facile route for preparation of water soluble and fluorescent Cu nanoclusters (NCs) stabilized by tannic acid (TA) is described. The as-prepared TA capped Cu NCs (TA-Cu NCs) are characterized by UV–vis spectroscopy, Fourier transform infrared (FT-IR) spectroscopy, luminescence, transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). The TA-Cu NCs show luminescence properties having excitation and emission maxima at 360nm and 430nm, respectively, with a quantum yield of about 14%. The TA-Cu NCs are very stable even in 0.3M NaCl, and their luminescent properties show pH independent. The fluorescence (FL) of Cu NCs is strongly quenched by Fe3+ through an electron transfer mechanism, but not by other metal ions. Furthermore, the FL of the TA-Cu NCs shows no changes with the addition of Fe2+ or H2O2 individually. On this basis, a facile chemosensor was developed for rapid, reliable, sensitive, and selective sensing of Fe3+ ions with detection limit as low as 10nM and a dynamic range from 10nM to 10μM. The proposed sensor was successfully used for the determination of iron contents in serum samples. Importantly, the Cu NCs-based FL probe showed long-term stability, good biocompatibility and very low cytotoxicity. It was successfully used for imaging ferric ions in living cells, suggesting the potential application of Cu NCs fluorescent probe in clinical analysis and cell imaging.

A highly sensitive and selective fluorescent sensor for detection of Al(3+) using a europium(III) quinolinecarboxylate.

Eu2PQC6 has been developed to detect Al(3+) by monitoring the quenching of the europium-based emission, with the lowest detection limit of ∼32 pM and the quantitative detection range to 150 μM. Eu2PQC6 is the first ever example that the europium(III) complex serves as an Al(3+) fluorescent sensor based on "competition-displacement" mode.

A label-free fluorescent probe for Hg²⁺ and biothiols based on graphene oxide and Ru-complex.

A novel, selective and sensitive switch-on fluorescent sensor for Hg2+ and switch-off fluorescent probe for biothiols was developed by using [Ru(bpy)2(pip)]2+ as the signal reporter and graphene oxide (GO) as the quencher. Due to the affinity of GO towards single-stranded DNA (ss-DNA) and [Ru(bpy)2(pip)]2+, the three components assembled, resulting in fluorescence quenching. Upon addition of Hg2+, a double-stranded DNA (ds-DNA) via T–Hg2+–T base pairs was formed, and [Ru(bpy)2(pip)]2+ intercalated into the newly formed ds-DNA. Then, [Ru(bpy)2(pip)]2+ and ds-DNA were removed from the surface of GO, resulting in the restoration of fluorescence. Subsequently, upon addition of biothiols, Hg2+ was released from ds-DNA, due to the higher affinity of Hg2+ to the sulfur atoms of biothiols, which could induce ds-DNA unwinding to form ss-DNA. Then ss-DNA and [Ru(bpy)2(pip)]2+ were adsorbed on the surface of GO, the fluorescence of [Ru(bpy)2(pip)]2+ was quenched again. Therefore, the changes in emission intensity of [Ru(bpy)2(pip)]2+ directly correlated to the amount of detection target (Hg2+ or biothiols) in solution. The assay exhibited high sensitivity and selectivity, with the limits of detection for Hg2+, cysteine (Cys) and glutathione (GSH) to be 2.34 nM, 6.20 nM and 4.60 nM, respectively.

A novel highly sensitive and selective fluorescent sensor for imaging copper (II) in living cells.

In this work, we designed and synthesized a novel quinolin-based derivative which exhibited signaling behaviors for Cu(2+). Upon the addition of Cu(2+) to the solution of the molecule, it displayed an obvious fluorescence quenching in a linear fashion due to the formation of a 1:1 metal-ligand complex. This fluorescent sensor exhibited a rare sensitivity toward Cu(II) (the level of magnitude could be 6 × 10(-8)), a rapid response (<10s) and also high selectivity toward Cu(2+) over other metal ions such as Na(+), K(+), Ca(2+), Mg(2+), Ba(2+), Fe(3+), Mn(2+), Hg(2+), Pb(2+), Cd(2+), Cr(3+), Co(2+), Zn(2+) and Al(3+). Simultaneously, the cell imaging experiments and filter paper test demonstrated its extensive applicability.

Gold and Silver Nanomaterial‐Based Optical Sensing Systems

Gold and silver nanomaterials (NMs) such as nanoparticles (NPs) and nanoclusters (NCs) possessing interesting optical properties have become popular sensing materials. With strong surface plasmon resonance (SPR) absorption, extraordinary stability, ease in preparation, conjugation, and biocompatibility, Au NPs are employed to develop sensitive and selective sensing systems for a variety of analytes. However, small sizes of Au and Ag NCs with interesting photoluminescence (PL) properties are used in many PL‐based sensing systems for the detection of important analytes. In addition, many bimetallic AuM NMs possessing strong catalytic activity are used to develop highly sensitive fluorescent sensors. This review article is categorized in four sections based on the NMs used in the sensing systems, including Au NPs, bimetallic AuM NMs, Au NCs, and DNA–Ag NCs. In each section, synthetic strategies and optical properties of the NMs are provided briefly, followed by emphasis on their analytical applications in the detection of small molecules, metal ions, DNA, proteins, and cells. Current challenges and future prospects of these NMs‐based sensing systems will be addressed.

Determination of flumioxazin residue in food samples through a sensitive fluorescent sensor based on click chemistry

A sensitive and selective fluorescent sensor for flumioxazin was designed based on the formation of strong fluorescence compound (1,2,3-triazole compounds) via the reaction of the alkynyl group in flumioxazin with 3-azido-7-hydroxycoumarin, a weak-fluorescent compound, through the Cu+-catalysed azide–alkyne cycloaddition (CuAAC) reaction. The fluorescence increase factor (represented by F/F0) of the system exhibited a good linear relationship with the concentrations of flumioxazin in the range of 0.25–6.0μg/L with a detection limit of 0.18μg/L (S/N=3). Also, the proposed fluorescent sensor demonstrated good selectivity for flumioxazin assay even in the presence of high concentration of other pesticides. Based on such high sensitivity and selectivity, the proposed fluorescent sensor has been applied to test the flumioxazin residue in some vegetable and water samples with satisfied results.

A highly sensitive and selective turn-on fluorescence sensor for iodide detection based on newly synthesized oligopyrrole derivative and application to real samples

In this study, we have synthesized and characterized a novel oligopyrrole derivative (5-[1-(4-nitrophenyl)-1H-2-pyrrolyloxyl]-1-phenyl-1H-2-pyrrolol, NPPP) based iodide ion selective fluorescent turn-on sensor. The fluorescent iodide sensor NPPP was synthesized by oxidation reaction of N-phenyl pyrrole with Cu(II) nitrate in acetonitrile. Elemental analysis, MS-spectrometry, 1H NMR, 13C NMR, FT-IR, UV–vis and fluorescence spectrum of NPPP were carried out. A characteristic NPPP fluorescence emission was observed in acetonitrile and water solutions, indicating that the probe is stable in solution and the emission of NPPP was not influenced by the water molecules. NPPP displayed extremely high sensitivity to I− with 3.5-fold fluorescence enhancement by intramolecular charge transfer (ICT) process in the water media. Responses to other anions present in the solution, such as F−, Cl−, Br−, AcO−, NO3−, NO2−, SO42−, S2O52−, ClO4−, IO4−, IO3−, OH− and the effect of pH value on the efficiency of the sensor molecule have also been investigated. NPPP exhibits very good selectivity to iodide ions over various anions interference. Under optimal conditions, its response was linearly proportional to the concentration of I− ions in a range from 1.0×10−7 to 6.0×10−6molL−1 with a detection limit of 9.0×10−8molL−1. The proposed method was successfully applied to the direct determination of I− in real samples such as iodine-fortified salts.

A sensitive quantum dots-based “OFF-ON” fluorescent sensor for ruthenium anticancer drugs and ctDNA

In this contribution, a simple and sensitive fluorescent sensor for the determination of both the three ruthenium anticancer drugs (1 to 3) and calf thymus DNA (ctDNA) was established based on the CdTe quantum dots (QDs) fluorescence “OFF-ON” mode. Under the experimental conditions, the fluorescence of CdTe QDs can be effectively quenched by ruthenium anticancer drugs because of the surface binding of these drugs on CdTe QDs and the subsequent photoinduced electron transfer (PET) process from CdTe QDs to ruthenium anticancer drugs, which render the system into fluorescence “OFF” status. The system can then be “ON” after the addition of ctDNA which brought the restoration of CdTe QDs fluorescence intensity, since ruthenium anticancer drugs broke away from the surface of CdTe QDs and inserted into double helix structure of ctDNA. The fluorescence quenching effect of the CdTe QDs-ruthenium anticancer drugs systems was mainly concentration dependent, which could be used to detect three ruthenium anticancer drugs. The limits of detection were 5.5 × 10−8 M for ruthenium anticancer drug 1, 7.0 × 10−8 M for ruthenium anticancer drug 2, and 7.9× 10−8 M for ruthenium anticancer drug 3, respectively. The relative restored fluorescence intensity was directly proportional to the concentration of ctDNA in the range of 1.0 × 10−8 M ∼ 3.0 × 10−7 M, with a correlation coefficient (R) of 0.9983 and a limit of detection of 1.1 × 10−9 M. The relative standard deviation (RSD) for 1.5 × 10−7 M ctDNA was 1.5% (n = 5). There was almost no interference to some common chemical compounds, nucleotides, amino acids, and proteins. The proposed method was applied to the determination of ctDNA in three synthetic samples with satisfactory results. The possible reaction mechanism of CdTe QDs fluorescence “OFF-ON” was further investigated. This simple and sensitive approach possessed some potential applications in the investigation of interaction between drug molecules and DNA.