Search

Inspired by the special reducing capability of ascorbic acid (AA), ascorbic acid 2-phosphate (AA2P) has been extensively utilized as a substrate in current alkaline phosphatase (ALP) activity assays owing to the ALP-triggered transformation of AA2P into AA. However, such assays usually require AA-related complicated and laborious synthesis and/or signal generation procedures. Herein, we report an interesting in situ fluorogenic interaction between o-phenylenediamine (OPD) and AA, which inspires us to put forward a novel and simple AA2P/OPD-participated fluorescence turn-on ALP activity assay for the first time, and then the corresponding ALP-based fluorescence enzyme-linked immunosorbent assay (ELISA) has also been developed by means of the conventional ELISA platforms. According to the convenient and facile detection process with clear response mechanism, our fluorogenic reaction-based assay exhibits good sensitivity, selectivity, and excellent sensing performance, which ensures fluorescence ELISA to potentially be applied in clinical diagnosis by employing a well-studied biomarker of hepatocellular carcinoma, α-fetoprotein (AFP) as the model analyte. Such original ELISA via in situ formation of fluorophore from scratch gives a new sight to develop other potential immunoassay platforms in early clinical diagnosis by controlling the target antigens in the near future.

Using sterculia lychnophora seeds as precursors for the first time, fluorescent carbon dots (CDs) were synthesized by simple hydrothermal treatment. The quantum yield of as-synthesized CDs was 6.9% by using quinine sulfate as the reference. The fluorescence of CDs could be effectively quenched by a MnO 2 nanosheet based on fluorescence resonance energy transfer (FRET). Ascorbic acid (AA) could reduce MnO 2 to Mn 2+ and result in the destruction of the MnO 2 nanosheets, which could induce the fluorescence recovery of the CDs. In particular, alkaline phosphatase (ALP) could bio-catalyze acid 2-phosphate (AAP) hydrolysis to AA. Here, an efficient fluorescence probe based on a CDs-MnO 2 nanosheet for rapid and selective detection of ALP was reported for the first time. Excellent performance for the detection of ALP was observed with high sensitivity and a detection limit of 0.4U/L owing to the low background. The detection of ALP in human serum was conducted with satisfactory results, demonstrating its potential applications in clinical diagnosis., (Copyright © 2016 Elsevier B.V. All rights reserved.)

A new fluorescence strategy was described for ratiometric sensing of formaldehyde (FA) with bifunctional MOF, which acted as a fluorescence reporter as well as biomimetic peroxidase. With the assistance of H2O2, NH2-MIL-101 (Fe) catalyzes the oxidation of non-luminescent substrate o-phenylenediamine (OPD) to produce fluorescent product (oxOPD) with the maximum emission at 570 nm. Besides, intrinsic fluorescence of MOF (λem = 445 nm) was quenched by oxOPD through inner filter effect (IFE). However, FA and OPD reacted to generate Schiff bases, which competitively consumed OPD inhibiting the generation of oxOPD. Under the excitation wavelength of 375 nm, a ratiometric strategy was designed to detect FA with the fluorescence intensity ratio at 445 nm and 570 nm (F445/F570) as readout signal. This strategy exhibited a wide linear range (0.1–50 μM) and low detection limit of 0.03 μM. This method was confirmed for FA detection in food samples. In addition to establishing a new method to detect FA, this work will open new applications of MOF in food safety. [ABSTRACT FROM AUTHOR]

A simple strategy has been designed for ratiometric fluorescence sensing of BLM on the basis of Cu2+-triggered fluorogenic reactions coupled with nanoparticle-mediated autocatalytic reactions. On one hand, Cu2+ can oxidize ascorbic acid (AA) to produce dehydroascorbic acid (DHAA), which condensates with o-phenylenediamine (OPD) to form fluorescent 3-(dihydroxyethyl) furo[3,4-b]quinoxaline-1-one (DFQ) with strong emission at 436 nm. On the other hand, Cu2+ and OPD undergo a redox reaction to form fluorescent 2,3-diaminophenazine (DAP) showing strong emission at 565 nm and copper nanoparticles (CuNPs) that further catalyze this redox reaction. A ratiometric fluorescence system comes into being due to these two well-resolved emission peaks. Ascribed to the complexation of BLM with Cu2+, larger CuNPs are obtained which weaken the autocatalytic reaction between Cu2+ and OPD. Thus, the fluorescence intensities at 565 nm belonging to DAP decrease while those at 436 nm corresponding to DFQ change slightly. With the fluorescence intensity ratio (F436/F565) as a readout, BLM can be detected selectively and sensitively with a detection limit of 50 pM. [ABSTRACT FROM AUTHOR]

Highlights: [•] DNA-Ag nanocluster-based glutathione reductase sensor is reported for the first time. [•] It is based on fluorescence enhancement in the presence of glutathione reductase. [•] The present sensor exhibits good selectivity toward glutathione reductase. [ABSTRACT FROM AUTHOR]

Proteases play a central role in several widespread diseases. Thus, there is a great need for the fast and sensitive detection of various proteolytic enzymes. Herein, we have developed a carbon nanotube (CNT)-based protease biosensing platform that uses peptides as a fluorescence probe for the first time. Single-walled carbon nanohorns (SWCNHs) and thrombin were used to demonstrate this detection strategy. SWCNHs can adsorb a fluorescein-based dye (FAM)-labeled peptide (FAM-pep) and quench the fluorescence of FAM. In contrast, thrombin can cleave FAM-pep on SWCNHs and recover the fluorescence of FAM, which allows the sensitive detection of thrombin. This biosensor has a high sensitivity and selectivity toward thrombin, with a detection limit of 100 p M. [ABSTRACT FROM AUTHOR]

Abstract: Fluorescence nanoclusters have been used for the determination of melamine for the first time. The method is based on the fluorescence turn-on of oligonucleotide-stabilized silver nanoclusters (DNA–Ag NCs) by melamine. The enhancement factors (I−I 0)/I 0 increase linearly with melamine concentrations over the range 5.0×10−8–7.0×10−6 M (R 2=0.998). The detection limit is 1.0×10−8 M, which is approximately 2000 times lower than the US Food and Drug Administration estimated melamine safety limit of 20.0μM. Furthermore, the milk samples spiked with melamine are analyzed with excellent recoveries. [Copyright &y& Elsevier]

A ratiometric fluorescence sensing platform for BLM has been designed based on chameleon DNA-AgNCs with dual fluorescence for the first time. [Display omitted] • Chameleon DNA-AgNCs were designed and applied for ratiometric fluorescence detection of BLM for the first time. • The presence of BLM-Fe(II) complex induces the fluorescence discoloration of DNA-AgNCs from orange to yellow. • This ratiometric assay exhibits a high sensitivity towards BLM with a detection limit of 67 pM. • The ratiometric nanoprobe is one single fluorophore with dual fluorescence and thus is simpler and cost-effective. The authors design dual-emissive DNA-templated silver nanoclusters (DNA-AgNCs) for ratiometric fluorescence sensing bleomycin (BLM) for the first time. A hairpin probe containing two different C-rich DNA templates at two terminals is used to synthesize chameleon DNA-AgNCs, which possess two emission peaks when they are in close proximity. A strong emission is founded at 622 nm (λex = 570 nm) while a weak one is located at 572 nm (λex = 504 nm). Meanwhile, the loop of this probe contains the scission site (5′-GC-3′) of BLM. The loop can be cleaved into two parts by BLM-Fe(II) complex, inducing the two DNA-AgNCs away from each other. The fluorescence intensity at 572 nm and 622 nm increases and decreases, respectively. Such chameleon DNA-AgNCs exhibit an obvious fluorescence discoloration from orange to yellow. Therefore, a sensitive ratiometric fluorescent strategy for BLM detection has been proposed with the detection limit of 67 pM. Finally, this ratiometric method is used to detect BLM in serum samples. [ABSTRACT FROM AUTHOR]

In this communication, we demonstrate for the first time the proof of concept that single-walled carbon nanohorns can be used as an effective fluorescent sensing platform for nucleic acid detection with a high selectivity down to single-base mismatch. [ABSTRACT FROM AUTHOR]

Herein, utilizing fluorescent Ag nanoclusters (Ag NCs) capped by polyethyleneimine (PEI) with different molecular weights, we constructed a novel Ag NCs-Cu 2+ sensing system based on fluorescence turn-on strategy for trace detection of quinolones, including nalidixic acid, cinoxacin, ciprofloxacin/ofloxacin, and moxifloxacin; these were the representatives of four generations of quinolone antibacterial drugs. The fluorescence of Ag NCs could be efficiently quenched by Cu 2+ , while with the addition of quinolones, the fluorescence of this system recovered rapidly. This protocol exhibited excellent sensitivities to these five quinolones. For instance, the linear ranges were from 1 to 100 nM for nalidixic acid with limit of detection (LOD) 0.47 nM, from 1 to 80 nM for cinoxacin with LOD 0.43 nM, from 0.1 to 120 nM for ciprofloxacin with LOD 38 pM, from 0.1 to 80 nM for ofloxacin with LOD 49 pM, and from 0.1 to 120 nM for moxifloxacin with LOD 48 pM, respectively, revealing that this approach showed low detection limits and wide linear ranges. Benefiting from the high sensitivity, the satisfactory recoveries were obtained for trace detection of quinolones in real samples, such as tablets, human urine and serum. [ABSTRACT FROM AUTHOR]

As the main existing form of copper, Cu+ plays vital roles in human health. It is highly significant to detect Cu+ selectively in biological matrixes especially in the coexistence of Cu2+. Herein, a ratiometric fluorescence sensor has been fabricated to discriminate Cu+ from Cu2+ and realize ratiometric detection of Cu+ by using Tb-MOFs and bathocuproine disulfonate (BCS). The sensor exhibits two fluorescence emissions at 400 nm from BCS as the response signal and 548 nm from Tb-MOFs as the reference signal. BCS can chelate with Cu+ selectively to form a stable adduct, inducing the fluorescence quenching of BCS through static quenching. When Cu+ is added, the intensity at 400 nm decreases significantly while that at 548 nm changes negligibly. Notably, the presence of Cu2+ exhibits no effect on the emissions both at 400 nm and 548 nm. Thus, Tb-MOFs-BCS system enable discrimination of Cu+ from Cu2+ and fast ratiometric detection of Cu+ within 1 min. The fluorescence ratio (F 548 / F 400) shows a good linear relationship in Cu+ concentrations ranging from 1 nM to 200 nM with a low detection limit of 0.3 nM, which is 1–3 orders magnitude lower than those of other methods. The high selectivity and sensitivity of this method enables the detection of Cu+ in human serum successfully. • Ratiometric probe assembled by Tb-MOFs and BCS was used for distinguishing Cu+ from Cu2+ for the first time. • The assembled probe exhibits high sensitivity towards Cu+ with a low detection limit of 0.3 nM. • This fluorescence probe exhibits fast response towards Cu+ within 1 min • Specific complex between BCS and Cu+ endows this nanoplatform high selectivity. [ABSTRACT FROM AUTHOR]

A ratiometric fluorescence strategy has been designed for the detection of sulfide ions with fluorescent MOF-based nanozyme, which acts as fluorescence reporter as well as biomimetic oxidase. [Display omitted] • A ratiometric nanosensor for S2- based on multifunctional MOF was established for the first time. • NH 2 -Cu-MOF exhibits biomimetic oxidase activity besides its intrinsic fluorescence. • The presence of S2- inhibits the oxidase-like activity of MOF due to the formation of CuS. • The in situ-formed fluorophore can avoid additional synthesis of another probe. A novel ratiometric fluorescence strategy for sulfide ions (S2-) analysis has been developed using metal–organic framework (MOF)-based nanozyme. NH 2 -Cu-MOF displays blue fluorescence (λem = 435 nm) originating from 2-amino-1,4-benzenedicarboxylic acid ligand. Besides, it possesses oxidase-like activity due to Cu2+ node, which can trigger chromogenic reaction. o -Phenylenediamine (OPD), as a common enzyme substrate, can be oxidized by NH 2 -Cu-MOF to form luminescent products (oxOPD) (λem = 570 nm). Inner filter effect occurs between oxOPD and MOF. Upon exposure to S2-, oxidase-like activity of MOF is depressed significantly because of the generation of CuS. On one hand, the amount of free Cu2+ decreases, affecting the yielding of oxOPD. On the other hand, CuNPs with larger size are obtained during the oxidation–reduction reaction between Cu2+ and OPD, which show weaker autocatalytic ability for OPD oxidation. These result in the decrease and increase of intensities at 570 and 435 nm, respectively. This method exhibits sensitive and selective responses towards S2- with LOD of 0.1 μM. Furthermore, such ratiometric strategy has been applied to detect S2- in food samples. [ABSTRACT FROM AUTHOR]

A ratiometric fluorescence strategy has been designed for the first time to detect artemisinin by employing photoluminescent Zn-MOF as reference combined with the catalyzation reaction of hemin towards artemisinin. [Display omitted] • A ratiometric fluorescence method for the detection of artemisinin has been developed for the first time. • Zn-MOF was firstly used to construct sensing platform for artemisinin. • Hemin can catalyze artemisinin to generate oxygen species, which induces chromogenic reaction. • The in situ-formed fluorophore can avoid additional synthesis of another probe. Artemisinin (ART) is a type of frontline drug to treat drug-resistant falciparum malaria. Simple, accurate and selective determination of ART is significant to monitor its clinical pharmaceutical efficacy. Herein, a new ratiometric fluorescence method has been designed for the determination of ART with Zn-MOF as fluorescence reference and hemin as catalyst, respectively. Zn-MOF possesses intrinsic fluorescence at 443 nm owing to 2-aminoterephthalic acid ligand. When o -phenylenediamine (OPD) is mixed with hemin, a weak fluorescent signal at 570 nm ascribed to oxidized product of OPD (oxOPD) is observed. In the presence of ART, hemin can catalyze ART to break its peroxide bridge and release a large number of reactive oxygen species, which effectively oxidize OPD into luminescent oxOPD. Therefore, the fluorescence at 570 nm is enhanced significantly while the fluorescence of Zn-MOF remains basically unchanged. Thus, a ratiometric fluorescence sensing platform has been constructed for the detection of ART. This method exhibits wider linear range (0.15 μM-150 μM) with detection limit of 50 nM. This novel and selective method has been used to detect ART in compound naphthoquinone phosphate tablets. [ABSTRACT FROM AUTHOR]

Although fluorescent nanozymes exhibit great potential in sensing fields, few current nanozyme-based sensors are designed to discriminate catechol (CC) from its two isomers. Herein, fluorescent metal-organic framework (MOF)-based nanozyme is utilized for ratiometric and selective detection of CC without the interferences of hydroquinone (HQ) and resorcinol (RC). NH 2 -Cu-MOF plays multiple roles: (1) it exhibits excellent photoluminescence at 435 nm owing to the 2-amino-1,4-benzenedicarboxylic acid ligand; (2) Cu2+ imparts MOF oxidase activity to trigger the oxidation of o -phenylenediamine (OPD) into luminescent products (oxOPD) with emissive peak at 571 nm, which quenches the intrinsic fluorescence of NH 2 -Cu-MOF (435 nm) through inner filter effect (IFE); (3) Cu2+ can complex with CC specifically to produce complex containing o -semiquinone, which not only inhibits MOF's oxidase-like activity but also quenches the fluorescence of MOF. Therefore, the presence of CC induces the decrease of fluorescence at 571 nm followed by the slight recovery of fluorescence at 435 nm. Notably, HQ and RC have negligible influences on the fluorescence of NH 2 -Cu-MOFs/OPD system. Based on these facts, a ratiometric fluorescence platform for CC has been constructed. It exhibits high sensitivity towards CC with LOD of 0.1 μM. • A ratiometric nanosensor for catechol based on multifunctional MOF was established for the first time. • NH 2 -Cu-MOF acts as not only fluorescence reporter but also biomimetic oxidase. • Specific complex reaction between Cu2+ and catechol endows this nanoplatform high selectivity. • Ratiometric fluorescence probe based on in situ-formed oxOPD avoids additional preparation of another probe. [ABSTRACT FROM AUTHOR]

A novel and sensitive IFE-based fluorescence assay for isoniazid has been developed with manganese dioxide nanosheets (MnO 2) and gold nanoparticles (AuNPs) as dual nanoquenchers in combination of analyte-triggered cascade reactions for the first time. [Display omitted] A sensitive fluorescence sensing platform consisting of manganese dioxide nanosheets (MnO 2) and gold nanoparticles (AuNPs) as dual nanoquenchers has been constructed to detect isoniazid combined with analyte-triggered cascade reactions. The fluorescence of 2,3-diaminophenazine (DAP) is quenched simultaneously by MnO 2 and AuNPs via inner filter effect. MnO 2 is decomposed by isoniazid to generate Mn2+, which makes AuNPs aggregated. The quenching abilities of both the decomposed MnO 2 and aggregated AuNPs are inhibited, causing remarkable fluorescence recovery. The usage of dual nanoquenchers enhances the quenching efficiency and reduces the fluorescence background. Moreover, the isoniazid-triggered cascade reaction further amplifies the readout signal. Thus, this strategy exhibits higher sensitivity towards the detection of isoniazid. Compared with MnO 2 -based fluorescence assay, this strategy possesses lower limit of detection. This strategy has been successfully used to detect isoniazid in pharmaceutical preparations, which is of great significance for drug analysis. [ABSTRACT FROM AUTHOR]

Highlights: [•] A supersandwich fluorescent platform has been reported for the first time. [•] The supersandwich structure is formed through T-Hg2+-T coordination. [•] The label-free platform can detect Hg2+ with a detection limit of 2.5nM. [•] It is a signal-on sensing platform with fast response and good selectivity. [•] It is based on fluorescence enhancement of Genefinder by intercalation with dsDNA. [ABSTRACT FROM AUTHOR]

A ratiometric fluorescence assay for alendronate has been developed with Ce4+-triggered cascade chromogenic reaction in combination of the oxidase-like activity of Ce4+ for the first time. • Ce4+ oxidizes AA into DHAA, which condenses with OPD to generate fluorescent DFQ. • Ce4+ mimicked the function of oxidase to catalyze the oxidation of OPD to DAP. • A ratiometric assay for ALDS is developed based on DFQ and DAP for the first time. • This approach offers a convenient and effective "mix-then-test" way for detection. A ratiometric fluorescence assay for alendronate (ALDS) has been designed with Ce4+-triggered cascade chromogenic reaction. This strategy involves three processes: (1) Ce4+ oxidizes ascorbic acid (AA) into dehydroascorbic acid (DHAA), which then condenses with o -phenlenediamine (OPD) to generate fluorescent 3-(dihydroxyethyl)furo[3,4- b quinoxaline-1-one (DFQ), presenting the maximum emission at 434 nm; (2) As oxidase-mimics, Ce4+ can oxidize OPD into fluorescent 2,3-diaminophenazine (DAP) which shows a strong emission at 568 nm; (3) ALDS inhibits the oxidation ability of Ce4+ towards OPD, thus inhibiting the generation of DAP. Accordingly, a homogeneous ratiometric fluorescence system with dual emission comes into being and the presence of ALDS can change the fluorescence intensity ratio obviously. With F 434 / F 568 as readout, ALDS can be detected sensitively with the detection limit of 30 nM. Moreover, this ratiometric method was used to analyze ALDS in both human serum and pharmaceutical samples. [ABSTRACT FROM AUTHOR]